Watch a 180-year-old star eruption unfold in new time-lapse movie (video)

Samantha Mathewson
Wed, September 27, 2023 

Watch a 180-year-old star eruption unfold in new time-lapse movie (video)

Using over two decades of data from NASA’s Chandra X-ray Observatory, astronomers have crafted a stunning new video of a stellar eruption that took place some 180 years ago.

The time-lapse video uses Chandra observations from 1999, 2003, 2009, 2014 and 2020 — along with data from ESA’s XMM-Newton spacecraft — and retraces the history of the stellar explosion known as Eta Carinae. This famous star system contains two massive stars. One of those stars is about 90 times more massive than the sun, scientists say, while the other is  about 30 times more massive than the sun.

The massive explosion, dubbed the "Great Eruption, came from Eta Carinae. It is believed to be the result of a merger between two stars that originally belonged to a triple star system. The aftermath of the collision was witnessed on Earth in the mid-19th century, and the new video shows how the stellar eruption has since continued to rapidly expand into space at speeds reaching up to 4.5 million miles per hour , according to a statement from NASA.

Related: Eta Carinae's epic supernova explosion comes to life in new visualization

"During this event, Eta Carinae ejected between 10 and 45 times the mass of the sun,” NASA officials said in the statement. "This material became a dense pair of spherical clouds of gas, now called the Homunculus Nebula, on opposite sides of the two stars."

The Homunculus Nebula is the bright blue cloud at the center of the image, fueled by high-energy X-rays produced by the two massive stars, which are too close to be observed individually. They are surrounded by a bright orange ring of X-ray emissions that appear to grow and expand rapidly over time.

"The new movie of Chandra, plus a deep, summed image generated by adding the data together, reveal important hints about Eta Carinae’s volatile history," NASA officials said in the statement. "This includes the rapid expansion of the ring, and a previously-unknown faint shell of X-rays outside it.

The faint X-ray shell is outlined in the image above, showing that it has a similar shape and orientation to the Homunculus nebula, which suggests both structures have a common origin, according to the statement.

Based on the motion of clumps of gas, astronomers believe  the stellar material was blasted away from Eta Carinae sometime between the years 1200 and 1800 — well before the Great Eruption was observed in 1843. As the blast extended into space, it collided with interstellar material in its path. The collision then heated the material, creating the bright X-ray ring observed. However, the blast wave has now traveled beyond the ring, given the X-ray brightness of Eta Carinae has faded with time, scientists said.

Their findings on Eta Carinae’s expansion were published in a 2022 study in the Astrophysical Journal.

"We’ve interpreted this faint X-ray shell as the blast wave from the Great Eruption in the 1840s," Michael Corcoran at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who led the study, said in a statement from the Chandra X-ray Observatory. "It tells an important part of Eta Carinae’s backstory that we wouldn’t otherwise have known."

Scientists confirm that the first black hole ever imaged is actually spinning

The researchers analyzed 22 years' worth of observations of the galaxy M87.

Mariella Moon
·Contributing Reporter
Thu, September 28, 2023 

Elen11 via Getty Images


The first black hole humanity has ever imaged has also provided us with what researchers are calling "unequivocal evidence" that black holes spin. An international team of scientists headed by Chinese researcher Dr. Cui Yuzhu analyzed 22 years of observational data gathered by more than 20 telescopes around the world. What they found was that the black hole at the center of galaxy M87, which is 6.5 billion times more massive than our sun, exhibits an oscillating jet that swings up and down every 11 years. This phenomenon confirms that the black hole is indeed spinning.

Black holes gobble up huge amounts of gas and dust, which they attract with their massive gravitational pull. A small fraction of those particles that don't fall into the black hole get spewn out and travel close to the speed of light, showing up as narrow beams along the axis. These beams are called "jets." The telescopes' observations show that M87's jet oscillates by 10 degrees in a recurring 11-year cycle, just as predicted by Einstein's General Theory of Relativity.

So, what causes the M87's jet to swing back and forth? The researchers' analysis indicates that the black hole's spin axis doesn't perfectly align with the rotational axis of its accretion disk. This disk-like structure is typically found surrounding a black hole, because it's made of materials that gradually spiral into the void to be consumed. That misalignment between the rotating mass and the matter that swirls around it causes "a significant impact on surrounding spacetime," which affects the movement of nearby objects in what the General Theory of Relativity calls "frame-dragging."

This is a significant discovery that massively improves our understanding of the mysterious region of spacetime — aside from proving Einstein right, of course. Scientists have yet to find out the size of M87's accretion disk and how fast its black hole is spinning, though, and that entails further observation and analysis.

Scientists just proved that 'monster' black hole M87 is spinning — confirming Einstein’s relativity yet again

Ben Turner
Thu, September 28, 2023 

An artist's illustration of the black hole M87* wobbling on its axis.

Astronomers have found the first direct evidence of a black hole spinning, and it's confirmed Einstein's theory of relativity yet again.

The discovery was made by studying powerful jets of energy beamed from the solar system-size black hole at the center of the neighboring Messier 87 galaxy. The black hole, called M87, is the best studied black hole to date and the first to ever be directly imaged in 2019, with its "donut hole" shadow crowned by a fuzzy halo of light.

Astrophysicists have long predicted that black holes spun, but the challenge of imaging the cosmic monstrosities has, until now, made evidence hard to come by. The researchers published their findings Sept. 27 in the journal Nature.

Related: The closest black holes to Earth may be 10 times closer than we thought

"After the success of black hole imaging in this galaxy with the [Event Horizon Telescope (EHT)], whether this black hole is spinning or not has been a central concern among scientists," Kazuhiro Hada, an astronomer at the National Astronomical Observatory of Japan, said in a statement. "Now anticipation has turned into certainty. This monster black hole is indeed spinning."

Black holes have such a powerful gravitational pull that nothing (not even light) can escape their maws, but this doesn't mean they can't be seen. This is because active black holes are surrounded by accretion disks — vast plumes of material stripped from gas clouds and stars, heated to red-hot temperatures by friction as it spirals into the black holes' mouths.



Some of this material is spat out, forming two jets of hot material that, in roughly a tenth of cases, travels at 99.9% the speed of light. How black hole jets acquire the enormous energy needed to do this has been a mystery, but physicists used Einstein's general theory of relativity to suggest the material could get it from the cosmic monsters' magnetic fields, if they were spinning rapidly on their axes.

Black holes likely acquired some of their spin from their early days as stars that, as they suddenly collapsed inward, became like figure skaters pulling in their arms to rotate faster. Over time, this spin probably grew faster due to the effect of infalling matter from stars ripped apart by the black holes, or from catastrophic collisions with other massive objects.

To search for clues of this elusive spin, astronomers turned to the M87 supermassive black hole, an enormous space-time tear that uses its mass (6.5 billion times that of the sun) to anchor an entire galaxy.

By studying M87* using a global network of radio telescopes from 2000 to 2022, the astronomers found that the black hole's jets were ticking back and forth like metronomes marking out an 11-year cycle. This showed that the black hole was precessing or wobbling on its axis as it rotated, just like a spinning top.

"We are thrilled by this significant finding," lead author Cui Yuzhu, an astronomer at Zhejiang Lab in Hangzhou, China, said in the statement. "Since the misalignment between the black hole and the disk is relatively small and the precession period is around 11 years, accumulating high-resolution data tracing M87's structure over two decades and thorough analysis are essential to obtain this achievement."

Beyond confirming Einstein's theory yet again, a number of exciting questions emerge from the discovery of black hole spin. Among them are ones relating to what catastrophic events could have caused the rapid rotation, as well as the possibility of discovering photon spheres — a faint ring of light surrounding the black hole that could give important hints into a theory of quantum gravity.

Scientists get closer to solving mystery of antimatter

Pallab Ghosh - BBC Science correspondent

Wed, September 27, 2023 

Scientists have made a key discovery about antimatter - a mysterious substance which was plentiful when the Universe began.

Antimatter is the opposite of matter, from which stars and planets are made.

Both were created in equal amounts in the Big Bang which formed our Universe. While matter is everywhere, though, its opposite is now fiendishly hard to find.

The latest study has discovered the two respond to gravity in the same way.

For years, physicists have been scrambling to discover their differences and similarities, to explain how the Universe arose.

Discovering that antimatter rose in response to gravity, instead of falling would have blown apart what we know about physics.

They've now confirmed for the first time that atoms of antimatter fall downwards. But far from being a scientific dead end this opens the doors to new experiments and theories. Does it fall at the same speed, for example?

During the Big Bang, matter and antimatter should have combined and cancelled each other, leaving nothing but light. Why they didn't is one of physics' great mysteries and uncovering differences between the two is the key to solving it.

Somehow matter overcame antimatter in those first moments of creation. How it responds to gravity, may hold the key, according to Dr Danielle Hodgkinson, a member of the research team at Cern in Switzerland, the world's largest particle physics laboratory.

"We don't understand how our Universe came to be matter-dominated and so this is what motivates our experiments," she told me.

Engineers adding liquid helium to the system to keep antimatter at minus 270 celcius, near to the lowest possible temperature, absolute zero

Most antimatter exists only fleetingly in the Universe, for fractions of seconds. So to carry out experiments, the Cern team needed to make it in a stable and long-lasting form.

Prof Jeffrey Hangst has spent thirty years building a facility to painstakingly construct thousands of atoms of antimatter from sub-atomic particles, trap them and then drop them.

"Antimatter is just the coolest, most mysterious stuff you can imagine," he told me.

"As far as we understand, you could build a universe just like ours with you and me made of just antimatter," Prof Hangst told me.

"That's just inspiring to address; it's one of the most fundamental open questions about what this stuff is and how it behaves."
What is antimatter?

Let's start with what matter is: Everything in our world is made from it, from tiny particles called atoms.

The simplest atom is hydrogen. It's what the Sun is mostly made from. A hydrogen atom is made up of a positively charged proton in the middle and negatively charged electron orbiting it.

With antimatter, the electric charges are the other way round.

Take antihydrogen, which is the antimatter version of hydrogen, used in the Cern experiments. It has a negatively charged proton (antiproton) in the middle and a positive version of the electron (positron) orbiting it.

These antiprotons are produced by colliding particles together in Cern's accelerators. They arrive at the antimatter lab along pipes at speeds that are close to the speed of light. This is much too fast for them to be controlled by the researchers.

The first step is to slow them down, which the researchers do by sending them around a ring. This draws out their energy, until they are moving at a more manageable pace.

The antiprotons and positrons are then sent into a giant magnet, where they mix to form thousands of atoms of antihydrogen.

The magnet creates a field, which traps the antihydrogen. If it were to touch the side of the container it would instantly be destroyed, because antimatter can't survive contact with our world.

When the field is turned off the antihydrogen atoms are released. Sensors then detect whether they have fallen up or down.

Some theorists have predicted that antimatter might fall up, though most, notably Albert Einstein in his General theory of Relativity more than a hundred years ago, say it should behave just like matter, and fall downwards.

The researchers at Cern have now confirmed, with the greatest degree of certainty yet, that Einstein was right.

But just because antimatter doesn't fall up, it doesn't mean that it falls down at exactly the same rate as matter.

For the next steps in the research, the team are upgrading their experiment to make it more sensitive, to see if there is a slight difference in the rate at which antimatter falls.

If so, it could answer one of the biggest questions of all, how the Universe came into existence.

The results have been published in the journal Nature.

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Mysterious antimatter observed falling down for first time

Daniel Lawler

AFP
Wed, September 27, 2023 

Physicists an CERN used a 25-centimetre-long cylinder, called ALPHA-g, to observe antimatter falling downwards due to gravity (Handout)


For the first time, scientists have observed antimatter particles -- the mysterious twins of the visible matter all around us -- falling downwards due to the effect of gravity, Europe's physics lab CERN announced on Wednesday.

The experiment was hailed as "huge milestone", though most physicists anticipated the result, and it had been predicted by Einstein's 1915 theory of relativity.

It definitively rules out that gravity repels antimatter upwards -- a finding that would have upended our fundamental understanding of the universe.

Around 13.8 billion years ago, the Big Bang is believed to have produced an equal amount of matter -- what everything you can see is made out of -- and antimatter, its equal yet opposite counterpart.

However there is virtually no antimatter in the universe, which prompted one of the greatest mysteries of physics: what happened to all the antimatter?

"Half the universe is missing," said Jeffrey Hangst, a member of CERN's ALPHA collaboration in Geneva which conducted the new experiment.

"In principle, we could build a universe -- everything that we know about -- with only antimatter, and it would work in exactly the same way," he told AFP.

Physicists believe that matter and antimatter did meet and almost entirely destroyed each other after the Big Bang.

Yet matter now makes up nearly five percent of the universe -- the rest is even less understood dark matter and dark energy -- while antimatter vanished.

- Newton's apple flying up? -

One of the key outstanding questions about antimatter was whether gravity caused it to fall in the same way as normal matter.

While most physicists believed that it did, a few had speculated otherwise.

A falling apple famously inspired Isaac Newton's work on gravity -- but if that apple was made of antimatter, would it have shot up into the sky?

And if gravity did in fact repel antimatter, it could have meant that impossibilities such as a perpetual motion machine were possible.

"So why not drop some and see what happens?" Hangst said.

He compared the experiment to Galileo's famous -- though likely apocryphal -- 16th-century demonstration that two balls of different mass dropped from the Leaning Tower of Pisa would fall at the same rate.

But this experiment -- the result of 30 years of work on antimatter at CERN -- was "a little bit more involved" than Galileo's, Hangst said.

One problem was that antimatter barely exists outside of rare, short-lived particles in outer space.

However in 1996, CERN scientists produced the first atoms of antimatter -- antihydrogen.

Another challenge was that, because matter and antimatter have an opposite electrical charge, the moment they meet they destroy each other in a violent flash of energy scientists call annihilation.

- A magnetic trap -

To study gravity's effect on antimatter, the ALPHA team constructed a 25-centimetre-long (10-inch) bottle placed on its end, with magnets at the top and bottom.

Late last year, the scientists placed around 100 very cold antihydrogen atoms into this "magnetic trap" called ALPHA-g.

As they turned down the strength of both magnets, the antihydrogen particles -- which were bouncing around at 100 metres a second -- were able to escape out either end of the bottle.

The scientists then simply counted how much antimatter was annihilated at each end of the bottle.

Around 80 percent of the antihydrogen went out of the bottom, which is a similar rate to how regular bouncing hydrogen atoms would behave if they were in the bottle.

This result, published in the journal Nature, shows that gravity causes antimatter to fall downwards, as predicted by Einstein's 1915 theory of relativity.

In more than a dozen experiments, the CERN scientists varied the strength of the magnets, observing gravity's effect on antimatter at different rates.

While the experiment rules out that gravity makes antihydrogen go upwards, Hangst emphasised it did not prove that antimatter behaves in exactly the same way as normal matter.

"That's our next task," he said.

Marco Gersabeck, a physicist who works at CERN but was not involved in the ALPHA research, said it was "a huge milestone".

But it marks "only the start of an era" of more precise measurements of gravity's effect on antimatter, he told AFP.

Other attempts to better understand antimatter include using CERN's Large Hadron Collider to investigate strange particles called beauty quarks.

And there is an experiment onboard the International Space Station trying to catch antimatter in cosmic rays.

But for now, exactly why the universe is awash with matter but devoid of antimatter "remains a mystery," said physicist Harry Cliff.

Since both should have annihilated each other completely in the early universe, "the fact that we exist suggests there is something we don't understand" going on, he added.

Antimatter isn't immune to gravity, landmark experiment confirms

Peter Weber
Thu, September 28, 2023 

Antihydrogen Laser Physics Apparatus (ALPHA) lab at CERN.


Antimatter — the mysterious substance that's the mirror opposite of matter in most ways — falls downward in gravity like everything else in the universe, a team of physicists reported Wednesday in the journal Nature. In a delicate, groundbreaking experiment conducted at the European Center for Nuclear Research (CERN), the scientists pretty conclusively proved that antiparticles are not governed by antigravity.

The results are a bit of a wet blanket for science fiction. "The bottom line is that there's no free lunch, and we're not going to be able to levitate using antimatter," study coauthor Joel Fajans of the University of California, Berkeley, told The New York Times. But they are kind of a relief for science. The tug of gravity on antimatter conforms with Albert Einstein's general theory of relativity. If the antiparticles had floated upward in the experiment, as some scientists had hypothesized, it would have turned the world of physics on its head.

"Antimatter is just the coolest, most mysterious stuff you can imagine," Jeffrey Hangst, the particle physicist whose 30 years of work trapping antiparticles led to the discovery, told BBC. "As far as we understand, you could build a universe just like ours with you and me made of just antimatter."

For this experiment, Fajans and his colleagues collected and suspended antihydrogen — the antimatter version of hydrogen, with one positively charged electron (positron) orbiting a negatively charged proton (antiproton) — in a magnetic field inside a specially designed tube. When the magnetic force was turned down on the top and bottom of the tube, some of the antiparticles rose but about 80% fell, roughly in line with hydrogen atoms.

The experiment left a bunch of huge questions about antimatter unanswered, however. The big one: Where is it?

When matter and antimatter meet, they annihilate each other in flashes of pure energy. Scientists believe that when the universe was born, the Big Bang created equal quantities of matter and antimatter. And they don't understand why matter won out while antimatter all but disappeared, only fleetingly observed in cosmic ray showers or created by colliding particles in labs like CERN.

One theory to explain what happened posited that all the antimatter was drawn away from the matter by antigravity and formed its own mirror antigravity universe. That hypothesis looks more implausible now.

One of world’s greatest physics mysteries finally decoded

Vishwam Sankaran
Thu, September 28, 2023

One of world’s greatest physics mysteries finally decoded


Physicists have answered the long-standing question of whether antimatter falls up or down under gravity, an advance that could help crack one of the biggest mysteries of why almost everything in the universe is only made of matter.

The new study, published in the journal Nature on Wednesday, found that antimatter falls downwards under gravity – as expected by much of the scientific community,

Antimatter is made of particles possessing the opposite electric charge as ordinary particles.

For instance, the antimatter equivalent of the negatively charged electron is the positron, and the two annihilate each other to produce gamma radiation if they collide.

One of the strangest mysteries of the universe, scientists have observed, is that almost all the visible matter in the universe is made of ordinary matter and not antimatter.

“Right now, we don’t have an explanation about where all the antimatter in the universe is. To find a solution for this conundrum, what we do is test the elements of the physics of antimatter to see if we can find an inconsistency,” study co-author Robert Thompson from the University of Calgary in Canada said.

In the new study, scientists assessed the gravitational characteristics of antihydrogen – the simplest atom in antimatter that mirrors hydrogen.

Matter dropped from any height on Earth accelerates towards the planet’s surface at the constant rate of about 9.8m/s each second – a mathematical constant used in physics calculations, known as acceleration due to gravity g.

Now, with the latest groundbreaking study, physicists say, this value for antihydrogen – accounting for errors in the experiment – “is consistent with a downward gravitational acceleration of 1g” or about“32 feet per second per second”.

Graphic shows antihydrogen atoms falling and annihilating inside a magnetic trap, part of the ALPHA-g experiment at CERN to measure the effect of gravity on antimatter.

 (U.S. National Science Foundation)

The experiment, which has never been done before, is a milestone in physics marking “a leap forward” in the world of antimatter research, they say.

Researchers used the new ALPHA-g apparatus in operation at CERN – Europe’s largest physics laboratory.

In the experiment, physicists created antimatter and trapped the neutral antihydrogen atoms in a magnetic bottle, making the environment as cold as possible.

They then released the antihydrogen within the vertical apparatus to witness and measure its gravitational behaviour under free-fall.

Scientists observed the physical properties of the antihydrogen by making precise measurements, including of its charge and colour spectrum.

The milestone study is the first step in taking precise measurements of the gravitational properties of antimatter to determine whether antimatter falls in the exact same way as matter.

“Here we show that antihydrogen atoms, released from magnetic confinement in the ALPHA-g apparatus, behave in a way consistent with gravitational attraction to the Earth,” scientists wrote in the study.

Researchers have also ruled out “repulsive ‘antigravity’” in this case – findings that can help better understand the lack of antimatter observed in the universe.

“We know there’s a problem somewhere in quantum mechanics and gravity. We just don’t know what it is. There has been a lot of speculation on what happens if you drop antimatter, though it’s never been tested before now because it’s so hard to produce and gravity is very weak,” Timothy Friesen, another author of the study, said.

The new finding, according to scientists, allows for more precise studies of the magnitude of the acceleration of anti-atoms under the influence of Earth’s gravitational force.

Antimatter Reacts to Gravity in the Same Way as Ordinary Matter, Physicists Find

Isaac Schultz
Wed, September 27, 2023 



In the 95 years we’ve known about antimatter, physicists have not tested how the elusive inverse of ordinary matter is affected by gravity, the force that pulls masses to Earth and seems to affect all things in the classical realm.

Now, a group of physicists have. Members of the Antihydrogen Laser Physics Apparatus (ALPHA) collaboration at CERN directly observed antihydrogen—hydrogen’s antimatter foil—free-falling in a container. The observations confirm the weak equivalence principle set forth by Einstein in his general theory of relativity, which holds that all masses react the same way to gravity, regardless of their composition. The team’s research was published today in Nature.

“In modern physics, inertial mass is encoded in the standard model of particle physics, whereas gravitational mass is dealt with in Einstein’s general theory of relativity,” wrote Anna Soter, a physicist at ETH Zürich, in an accompanying News & Views article. “The assumed equivalence of inertial mass and gravitational mass is incorporated in the weak equivalence principle, which is the cornerstone of general relativity—but no proposal has yet succeeded in unifying the theories.”

Plans to test gravity’s force on antimatter were first made by 2018, as Gizmodo reported at the time, when the ALPHA collaboration built ALPHA-g, a magnetic trap for antihydrogen atoms. The antimatter particles are suspended and then dropped inside the trap, in a 21st-century equivalent to the story of Galileo Galilei dropping objects off the Leaning Tower of Pisa.

The antimatter particles are cooled in order to slow their movement, giving the physicists precious time to observe and measure them. In 2021, the ALPHA collaboration announced that they managed to cool antihydrogen to near-absolute zero. “Slowing down the motion of antiatoms allows us to perform more precise measurements on its properties. In daily life, you can imagine things moving fast are harder to see than things moving slowly,” Makoto Fujiwara, a particle physicist with Canada’s TRIUMF particle accelerator team, told Gizmodo at the time. “The same thing happens in quantum physics…. The more time you have to observe a certain property, the more precise your measurement.”

As the cooled antihydrogen escaped the magnetic trap, the particles entered a vertical vacuum chamber; if the particles came in contact with the sides of the chamber or its ends (i.e., regular matter) they were annihilated. The researchers fiddled with the strength of the magnetic field, but found that when the fields were balanced on either side of the chamber, about 80% of the antimatter particles annihilated towards the bottom of the trap. Which is to say, gravity got them there.

It’s a good thing that gravity influences matter the same way it does the ordinary stuff—if it didn’t, it would mean that physicists were missing something pretty fundamental to the standard model. It’s not yet clear if antimatter was affected by gravity in the exact same way as ordinary matter, but the very fact that it’s affected affirms both Einstein and the standard model.

But mysteries remain. The magnitude of the gravitational acceleration on the antihydrogen was not precisely measured, but set the foundations for such future experiments. That can be done with even colder atoms—and better understand the weak equivalence principle. And beyond—which is to say below—the masses of the smallest particles, there is the quantum realm, which seems to be beyond the influence of gravity, at least as we know it.

Put in perspective, it seems that this confirmation of something long suspected is just a baby step in physicists’ understanding of the forces of nature and particle physics. But the baby steps are the most important ones to take.

More: Antimatter Could Travel Through Our Galaxy With Ease, Physicists Say

Gizmodo

 Astronomers discover thousands of active red galaxy hearts with powerful radio signals

Keith Cooper
Thu, September 28, 2023 at 9:00 AM MDT·4 min read

Astronomers discover thousands of active red galaxy hearts with powerful radio signals


Red quasars filled with cosmic dust produce stronger radio emissions than their bluer, dust-free counterparts — and these phenomena, scientists say, could represent a generation of younger active galaxies with supermassive black holes that only recently switched into overdrive.

"There are still many unanswered questions surrounding red quasars, such as whether black hole winds or radio jets are ultimately responsible for this enhanced radio emission," Victoria Fawcett, lead author of a new study on this finding and an astronomer at Newcastle University in the United Kingdom, said in a statement.

However, Fawcett believes we're getting close to the brink of fully understanding the nature of these incredible marvels.

Related: 1st black hole imaged by humanity is confirmed to be spinning, study finds

A quasar is the powerful central region of an active galaxy, and is driven by a supermassive black hole that is being fed huge amounts of matter. That matter forms a disk of gas around the black hole, known as an accretion disk, that reaches millions of degrees and releases fierce radiation winds. Meanwhile, magnetically collimated jets launch outwards from the disk.

Quasars are so bright that they vastly outshine the collective starlight of their host galaxies and can therefore be seen across the universe.

Most quasars appear blue, a hue caused by optical and ultraviolet emissions from the hot accretion disk. However, a fraction appears red instead. To reach their conclusions about those red quasars, Fawcett and fellow researchers sampled approximately 35,000 quasars observed by DESI, the Dark Energy Spectroscopic Instrument on the Mayall Telescope at Kitt Peak National Observatory in Arizona.

Of this collection, Fawcett’s group found 3,038 to be red quasars. Cross-referencing with radio astronomy data from the LOFAR (Low Frequency Array) Two-meter Sky Survey (LoTSS), they confirmed that most of these red ones are also emitting strongly in radio waves.

The redness comes from the presence of dust, which absorbs shorter, bluer wavelengths but allows longer, redder wavelengths to pass. The red quasars must therefore be smothered in cosmic dust, formed of tiny grains just microns in size.

"It was really exciting to see the amazing quality of the DESI data and to discover thousands of these previously rare red quasars," Fawcett said. "I think this is the strongest evidence so far that red quasars are a key element in how galaxies evolve."

The red quasars seem to be radiating more strongly in radio waves than the blue quasars because of interactions between outflows of radiation pouring from a quasar and the surrounding curtains of dust. As the outflows slam into the dust, they excite molecules within the dust to prompt the emission of radio waves. Over time, the outflows, driven by the energy of a supermassive black hole hungrily feeding on vast amounts of matter, will blow the dusty cloak away to leave a naked blue quasar with much weaker radio emission. Fawcett calls this the 'blow-out' phase.

Therefore, when astronomers see a red quasar, they are seeing a younger quasar than if they were to see a blue one.

Related Stories:

— Milky Way vs M87: Event Horizon Telescope photos show 2 very different monster black holes

— Astronomers may have discovered the closest black holes to Earth

— Black holes keep 'burping up' stars they destroyed years earlier, and astronomers don't know why

The realization that red quasars represent a younger type of quasar could prove to be an important missing piece in our understanding of how galaxies develop and evolve over time. It’s believed that most galaxies, at one time or another, undergo a quasar phase, and that there is an observed relationship between the mass of the supermassive black hole at the heart of a quasar and the mass of the galactic bulge belonging to the quasar's host galaxy. In other words, quasar activity seems to help grow the mass of a galaxy.

The origin of quasar dust may be a by-product of this. Cosmic dust is produced by stars when they die, either as explosive supernovas or in more sedate fashion by putting off their outer layers to form a planetary nebula. Either way, the presence of dust in a quasar suggests that it has undergone a starburst – an intense period of rapid star formation, with many of those stars having already expired. Starbursts are commonly found in active galaxies, particularly those that have endured a galactic merger that has forced massive molecular clouds to crash into one another and instigate the star formation process.

The research was published on Sept. 13 in the journal Monthly Notices of the Royal Astronomical Society.

SPACE RACE 2.0

Why astronomers want to put a telescope on the dark side of the moon

Andrew Paul
Wed, September 27, 2023 

LuSEE-Night will arrive aboard Firefly Aerospace's Blue Ghost lunar lander.


The dark side of the moon, despite its name, is a perfect vantage point for observing the universe. On Earth, radio signals from the furthest depths of space are obscured by the atmosphere, alongside humanity’s own electronic chatter, but the lunar far side has none of these issues. Because of this, establishing an observation point there could allow for unimpeded views of some of cosmic history’s earliest moments—particularly a 400 million year stretch known as the universe’s Dark Ages when early plasma cooled enough to begin forming the protons and electrons that eventually made hydrogen.

After years of development and testing, just such an observation station could come online as soon as 2026, in part thanks to researchers at the Lawrence Berkeley National Laboratory in California.

The team is currently working alongside NASA, the US Department of Energy, and the University of Minnesota on a pathfinder project called the Lunar Surface Electromagnetics Experiment-Night (LuSEE-Night). The radio telescope is on track to launch atop Blue Ghost, private space company Firefly Aerospace’s lunar lander, as part of the company’s second moon excursion. Once in position, Blue Ghost will detach from Firefly’s Elytra space vehicle, then travel down to the furthest site ever reached on the moon’s dark side.

“If you’re on the far side of the moon, you have a pristine, radio-quiet environment from which you can try to detect this signal from the Dark Ages,” Kaja Rotermund, a postdoctoral researcher at Berkeley Lab, said in a September 26 project update. “LuSEE-Night is a mission showing whether we can make these kinds of observations from a location that we’ve never been in, and also for a frequency range that we’ve never been able to observe.”

More specifically, LuSEE-Night will be equipped with specialized antennae designed by the Berkeley Lab team to listen between 0.5 and 50 megahertz. To accomplish this, both the antennae and its Blue Ghost transport will need to be able to withstand the extreme temperatures experienced on the moon’s far side, which can span between -280 and 250 degrees Fahrenheit. Because of its shielded lunar location, however, LuSEE-Night will also need to beam its findings up to an orbiting satellite that will then transfer the information back to Earth.

“The engineering to land a scientific instrument on the far side of the moon alone is a huge accomplishment,” explained Berkeley Lab’s antenna project lead, Aritoki Suzuki, in the recent update. “If we can demonstrate that this is possible—that we can get there, deploy, and survive the night—that can open up the field for the community and future experiments.”

If successful, LuSEE-Night could provide data from the little known Dark Ages, which breaks up other observable eras such as some of the universe's earliest moments, as well as more recent moments after stars began to form.

According to Berkeley Lab, the team recently completed a successful technical review, and is currently working on constructing the flight model meant for the moon. Once landed, LuSEE-Night will peer out into the Dark Age vastness for about 18 months beginning in 2026.


Radio telescope will launch to moon's far side in 2025 to hunt for the cosmic Dark Ages

Keith Cooper
Thu, September 28, 2023 

Radio telescope will launch to moon's far side in 2025 to hunt for the cosmic Dark Ages


A small mission to test technology to detect radio waves from the cosmic Dark Ages over 13.4 billion years ago will blast off for the far side of the moon in 2025.

The Lunar Surface Electromagnetic Experiment-Night mission, or LuSEE-Night for short, is a small radio telescope being funded by NASA and the U.S. Department of Energy with involvement from scientists at the Lawrence Berkeley National Laboratory, the Brookhaven National Laboratory, the University of California, Berkeley and the University of Minnesota. LuSEE-Night will blast off as part of NASA's Commercial Lunar Payloads program.

The Dark Ages are the evocative name given to the period of time after the Big Bang, when the first stars and galaxies were only just beginning to form and ionize the neutral hydrogen gas that filled the universe. Little is known about this period, despite efforts by the James Webb Space Telescope to begin probing into this era.

Related: The moon: Everything you need to know about Earth's companion

The neutral hydrogen present during the Dark Ages was able to absorb some of the radiation of the cosmic microwave background, creating a dip in the intensity of radio waves from that era at frequencies between 0.5 and 50 megaHertz.

"We're looking for this very tiny dip that is potentially the Dark Ages signal," said Kaja Rotermund of the Lawrence Berkeley National Laboratory in a statement.

Earth's atmosphere, in conjunction with terrestrial radio interference, obscures this faint signal. The solution is to go to the far side of the moon, where there is no atmosphere and Earth and all its radio noise is not visible.

"If you're on the far side of the moon, you have a pristine, radio-quiet environment from which you can try to detect this signal from the Dark Ages," said Rotermund. "LuSEE-Night is a mission showing whether we can make these kinds of observations from a location that we've never been in, and also for a frequency range that we've never been able to observe."


LuSEE-Night will be joined on the moon by LuSEE-Lite, which will blast off for Schrödinger Basin, which is located on the far side near the moon's south pole, in 2024. LuSEE-Lite will operate in daylight, but LuSEE-Night will test technologies such as antennas and batteries to see if they can function efficiently in the freezing-cold conditions of lunar night, where the temperature can reach as low as minus 280 degrees Fahrenheit (minus 170 degrees Celsius). While the lunar far side experiences daytime as well as night-time, night lasts for two weeks, so any long-duration mission to the moon has to deal with that. Because LuSEE-Night will not be able to see Earth from the lunar far side, a relay satellite will have to communicate with Earth on its behalf.

Rotermund and her colleagues at Berkeley Lab are building two pairs of antennas that will fly on LuSEE-Night to try and detect the hydrogen absorption in the radio waves from the cosmic Dark Ages. The antennas are 20 feet (6 meters) long from tip to tip, and are spring-loaded and designed to uncoil upon landing.

"The engineering to land a scientific instrument on the far side of the moon alone is a huge accomplishment," said Aritoki Suzuki of Berkeley Labs. "If we can demonstrate that this is possible — that we can get there, deploy and survive the night — that can open up the field for the community and future experiments."

The first-ever successful landing on the lunar far side was in 2019, when China's Chang'e 4 mission touched down and deployed a small rover named Yutu-2.

LuSEE-Night could be seen as a precursor for a much larger and more ambitious radio telescope. Scientists have long proposed the building of a radio telescope on the far side of the moon that could probe the entirety of the radio spectrum without radio frequency interference from Earth, and therefore spot frequencies undetectable from our planet. Such a telescope would pose intriguing engineering challenges, such as how to build a large telescope in the moon's low gravity and cold temperatures.

A larger, more sensitive telescope may well be needed, for LuSEE-Night is not necessarily expected to be able to detect the Dark Ages. First and foremost it is a technology demonstrator, and any scientific results that it can achieve will be a bonus.

LuSEE-Night will be flown to the moon in partnership with Firefly Aerospace, which is building the "Blue Ghost" lander that will carry it. The plan is for LuSEE-Night to function on the moon for 18 months, recharging its batteries using solar power during the two-week long lunar days.

Chinese Scientists Ponder Moon Base Inside Ancient Lunar Lava Tube

Victor Tangermann
Thu, September 28, 2023 


Dig Dug

Chinese researchers are investigating the feasibility of having astronauts construct a base inside lava tubes under the lunar surface, an exciting prospect that could one day allow astronauts to establish a more permanent presence on the Moon.

Scientists have long suspected that our natural satellite is riddled with intricate systems of hollow, tube-like tunnels, left behind by ancient lava currents.

Our evidence so far is still relatively limited, with NASA's Lunar Reconnaissance Orbiter picturing hundreds of "skylights," per Universe Today, which scientists suspect were left behind after tunnel ceilings collapsed. But we have yet to get a first-hand look at these structures — if they exist as we've been picturing them at all, that is.

But if they are there, international space agencies are intrigued. Once inside a lava tube, astronauts could be sheltered not only from showers of micrometeorites but also from the dangerous levels of radiation the atmosphere-less space rock is blasted with.
Lunar Skylight

During a recent conference, Zhang Chongfeng from the Shanghai Academy of Spaceflight Technology said that future spacecraft and lunar landers could explore these lava tubes, according to state-run news outlet Xinhua.

Zhang and his colleagues have been studying lava caves in China to get a better understanding of the structures. To explore the vertical "skylight" entrances to these caves, the researchers suggest that space travelers may have to fly inside with a spacecraft.

China isn't alone in investigating the idea. NASA scientists have also been exploring ways to do just that for well over a decade, with various teams coming up with a number of solutions over the years, from "hopping pit-bots" to rolling spacecraft.

To hone in on a destination, Chinese researchers have picked lava tubes at the Moon's Mare Tranquillitatis and Mare Fecunditatis as their primary targets, according to Xinhua.

They suggest we could probe the surrounding areas and openings with walking or wheeled robots capable of adapting to a range of different environments. Zhang suggests auxiliary spacecraft could fly into these caves to map the walls and ceilings with radars.

A lunar base could be composed of multiple residential and scientific research cabins inside the cave with a communication and energy hub at the entrance, Zhang proposed.

But getting to the point where Chinese taikonauts could set up shop inside one of these lava tubes could take many years.

At the same time, the country has made astonishing progress in terms of exploring the lunar surface — China has successfully sent several rovers to the lunar surface over the last decade — and its first crewed landing is tentatively scheduled for 2030.

More on China and the Moon: China Announces Plans to Build Moon Base Using Lunar Soil


Chinese researchers look to build underground moon base for future manned mission

Bryan Ke
Wed, September 27, 2023 at 12:11 PM MDT·2 min read



[Source]

A team of Chinese researchers is studying the possibility of building an underground lunar base through the moon’s lava tubes that would be used for China’s future manned moon missions.

Revealing the plan: Shanghai Academy of Spaceflight Technology’s Zhang Chongfeng, who was also credited as the vice chief designer of the Shenzhou series spacecraft and moon landers, unveiled the study at the 10th CSA-IAA Conference on Advanced Space Technology held in Shanghai from Sept. 13 to 16.

Their study: Zhang said he and his team and other planetary geology experts from China studied lava tubes found in the country, which they believed to have similarities to the ones on the moon, to understand the underground structures better for the mission.

Different kinds of lava tubes: During the presentation, Zhang reportedly noted that lava tubes have two types of entrances, one with a vertical opening and another with a sloping entrance.

He explained that the vertical type of lava tube entrance would require a lifting mechanism for humans to get in and outside, while the sloping entrance provides a more suitable path without the need for machinery. Zhang noted that they have now chosen the Mare Tranquillitatis and Mare Fecunditatis lava tubes as the primary exploration targets.

Establishing a lunar base: The Chinese scientist also proposed building a long-term underground lunar research base, which could be accomplished by setting up a support center for communication and energy by the entrance of the tubes.

The team would also have to landscape the terrain in the tubes to prepare for multiple cabins with different functionalities, which would be placed inside the tunnels, such as residential and research.

Future mission: The China Manned Space Agency (CMSA) announced its plans to conduct manned missions on the lunar surface before 2030 in May.

The CMSA is also asking the public to help them name the moon lander and the new generation crew spacecraft for the mission. The name, which can have a maximum of four Chinese characters, must highlight China’s intelligent manufacturing. The competition ends on Sept. 30.

The ‘least crazy’ idea: Early dark energy could solve a cosmological conundrum

Dan Falk
Thu, September 28, 2023 

CREDITS: NASA, ESA, CSA, AND STSCI

At the heart of the Big Bang model of cosmic origins is the observation that the universe is expanding, something astronomers have known for nearly a century. And yet, determining just how fast the universe is expanding has been frustratingly difficult to accomplish. In fact, it’s worse than that: Using one type of measurement, based on the cosmic microwave background — radiation left over from the Big Bang — astronomers find one value for the universe’s expansion rate. A different type of measurement, based on observations of light from exploding stars called supernovas, yields another value. And the two numbers disagree.

As those measurements get more and more precise, that disagreement becomes harder and harder to explain. In recent years, the discrepancy has even been given a name — the “Hubble tension” — after the astronomer Edwin Hubble, one of the first to propose that the universe is expanding.

The universe’s current expansion rate is called the “Hubble constant,” designated by the symbol H0. Put simply, the Hubble constant can predict how fast two celestial objects — say, two galaxies at a given distance apart — will appear to move away from each other. Technically, this speed is usually expressed in the not-very-intuitive units of “kilometers per second per megaparsec.” That means that for every megaparsec (a little more than 3 million light-years — nearly 20 million trillion miles) separating two distant celestial objects, they will appear to fly apart at a certain speed (typically measured in kilometers per second).

For decades, astronomers argued about whether that speed (per megaparsec of separation) was close to 50 or closer to 100 kilometers per second. Today the two methods appear to yield values for the Hubble constant of about 68 km/s/mpc on the one hand and about 73 or 74 km/s/mpc on the other.

That may seem like an insignificant difference, but for astronomers, the discrepancy is a big deal: The Hubble constant is perhaps the most important number in all of cosmology. It informs scientists’ understanding of the origins and future of the cosmos, and reflects their best physics — anything amiss suggests there may be missing pieces in that physics. Both of the measurements now come with fairly narrow margins of error, so the two figures, as close as they may seem, are a source of conflict.

Another source of consternation is the physics driving the cosmic expansion — especially following the 1998 discovery of a myserious entity dubbed “dark energy.”

In the Big Bang model, spacetime began expanding some 13.8 billion years ago. Later, galaxies formed, and the expansion carried those galaxies along with it, making them rush away from one another. But gravity causes matter to attract matter, which ought to slow that outward expansion, and eventually maybe even make those galaxies reverse course. In fact, the universe’s expansion did slow down for the first several billion years following the Big Bang. Then, strangely, it began to speed up again. Astronomers attribute that outward push to dark energy.

But no one knows what dark energy actually is. One suggestion is that it might be a kind of energy associated with empty space known as the “cosmological constant,” an idea first proposed by Albert Einstein in 1917. But it’s also possible that, rather than being constant, the strength of dark energy’s push may have varied over the eons.

For theoretical physicist Marc Kamionkowski, the Hubble tension is an urgent problem. But he and his colleagues may have found a way forward — an idea called “early dark energy.” He and Adam Riess, both of Johns Hopkins University, explore the nature of the tension and the prospects for eventually mediating it in the 2023 Annual Review of Nuclear and Particle Science.

In 2021, Kamionkowski was awarded the Gruber Cosmology Prize, one of the field’s top honors, together with Uroš Seljak and Matias Zaldarriaga, for developing techniques for studying the cosmic microwave background. Though Kamionkowski spends much of his time working on problems in theoretical astrophysics, cosmology and particle physics, his diverse interests make him hard to pigeonhole. “My interests are eclectic and change from year to year,” he says.

This conversation has been edited for length and clarity.

In your paper, you talk about this idea of “early dark energy.” What is that?

With the Hubble tension, we have an expansion rate for the universe that we infer from interpreting the cosmic microwave background measurements, and we have an expansion rate that we infer more directly from supernova data — and they disagree.

And most solutions or explanations for this Hubble tension involve changes to the mathematical description of the components and evolution of the universe — the standard cosmological model. Most of the early efforts to understand the discrepancy involved changes to the late-time behavior of the universe as described by the standard cosmological model. But nearly all of those ideas don’t work, because they postulate very strange, new physics. And even if you’re willing to stomach these very unusual, exotic physics scenarios, they’re inconsistent with the data, because we have constraints based on observational data on the late expansion history of the universe that don’t match these scenarios.

So the other possibility is to change something about the model of the early history of the universe. And early dark energy is our first effort to do that. So early dark energy is a class of models in which the early expansion history of the universe is altered through the introduction of some new exotic component of matter that we call early dark energy.

“A component of matter” — is dark energy a type of matter?

It is a type of “matter,” but unlike any we experience in our daily lives. You could also call it a “fluid,” but again, it’s not like any fluids we have on Earth or in the solar system.

Dark energy appears to be pushing galaxies away from one another at an accelerating rate — would “early dark energy” add a new kind of dark energy to the mix?

Well, we don’t really know what dark energy is, and we don’t know what early dark energy is, so it’s hard to say whether they’re the same or different. However, the family of ideas we’ve developed for early dark energy are pretty much the same as those we’ve developed for dark energy but they are active at a different point in time.

The cosmological constant is the simplest hypothesis for something more broadly referred to as dark energy, which is some component of matter that has a negative pressure and the correct energy density required to account for the observations. And early dark energy is a different type of dark energy, in that it would become important in the early universe rather than the later universe.

Turning back to the Hubble tension: You said one measurement comes from the cosmic microwave background, and the other from supernova data. Tell me more about these two measurements.

The cosmic microwave background is the gas of “relic radiation” left over from the Big Bang. We have measured the fluctuations in the intensity, or temperature, of that cosmic microwave background across the entire sky. And by modeling the physics that gives rise to those fluctuations, we can infer a number of cosmological parameters (the numerical values for terms in the math of the standard cosmological model).

So we have these images of the cosmic microwave background, which look like images of noise — but the noise has certain characteristics that we can quantify. And our physical models allow us to predict the statistical characteristics of those cosmic microwave background fluctuations. And by fitting the observations to the models, we can work out various cosmological parameters, and the Hubble constant is one of them.

And the second method?

The Hubble constant can also be inferred from supernovae, which gives you a larger value. That’s a little more straightforward.… We infer the distances to these objects by seeing how bright they appear on the sky. Something that is farther away will be fainter than something that’s close. And then we also measure the velocity at which it’s moving away from us by detecting Doppler shifts in the frequencies of certain atomic transition lines. That gives us around 73 or 74 kilometers per second per megaparsec. The cosmic microwave background gives a value of about 68.

What’s the margin of error between the two measurements?

The discrepancy between the two results is five sigma, so 100,000-to-one odds against it being just a statistical fluctuation.

The first question that comes to mind would be, maybe one of the two approaches had some systematic error, or something was overlooked. But I’m sure people have spent months or years trying to see if that was the case.

There’s no simple, obvious mistake, in either case. The cosmic microwave background analyses are complicated, but straightforward. And many different people in many different groups have done these analyses, with different tools on different datasets. And that is a robust measurement. And then there’s the supernova results. And those have been scrutinized by many, many people, and there’s nothing obvious that’s come up that’s wrong with the measurement.

So just to recap: Data gleaned from the cosmic microwave background (CMB) radiation yield one value for the cosmological constant, while data obtained from supernovae give you another, somewhat higher value. So what’s going on? Is it possible there’s something about the CMB that we don’t understand, or something about supernovae that we’re wrong about?

Well, honestly, we have no idea what’s going on. One possibility is that there’s something in our interpretation of the cosmic microwave background measurements — the way it’s analyzed — that is missing. But again, a lot of people have been looking at this for a long time, and nothing obvious has come up.

Another possibility is that there is something missing in the interpretation of the supernova data; but again, a lot of people look at that, and nothing has come up. And so a third possibility is that there’s some new physics beyond what’s in our standard cosmological model.

Can you explain what the standard cosmological model is?

We have a mathematical model for the origin and evolution of the whole universe that is fit by five parameters — or six, depending on how you count — that we need to specify or fit to the data to account for all of the cosmological observations. And it works.

Contrast that with the model for the origin of the Earth, or the solar system. The Earth is a lot closer; we see it every day. We have a huge amount of information about the Earth. But we don’t have a mathematical model for its origin that is anywhere close to as simple and successful as the standard cosmological model. It’s a remarkable thing that we can talk about a mathematical physical model for the origin and evolution of the universe.

Why is this standard cosmological model called the “lambda CDM” model?

It’s a ridiculous name. We call it “lambda CDM,” where CDM stands for “cold dark matter” and the Greek letter lambda stands for the cosmological constant. But it’s just a ridiculous name because lambda and CDM are just two of the ingredients, and they’re not even the most crucial ingredients. It’s like naming a salad “salt-and-pepper salad” because you put salt and pepper in it.

What are the other ingredients?

One of the other ingredients in the model is that, of the three possible cosmological geometries — open, closed or flat — the universe is flat; that is, the geometry of spacetime, on average, obeys the rules of Euclidean plane geometry. And the critical feature of the model is that the primordial universe is very, very smooth, but with very small-amplitude ripples in the density of the universe that are consistent with those that would be produced from a period of inflation in the early universe.

Inflation — that’s the idea of cosmic inflation, a very brief period in the early universe when the universe expanded very rapidly?

Inflation is in some sense an idea for what set the Big Bang in motion. In the early 1980s, particle theorists realized that theories of elementary-particle physics allowed for the existence of a substance that in the very early universe could temporarily behave like a cosmological constant of huge amplitude. This substance would allow a brief period of superaccelerated cosmological expansion and thereby blow a tiny, pre-inflationary patch of the universe into the huge universe we see today. The idea implies that our universe today is flat, as it appears now to be, and was initially very smooth — as consistent with the smoothness of the CMB — and has primordial density fluctuations like those in the CMB that would then provide the seeds for the later growth of galaxies and clusters of galaxies.

So if early dark energy is real, it would add one more ingredient to the universe?

It is more ingredients. It’s the last thing you want to resort to. New physics should always be the last thing that you ever resort to. But most people, I think, would agree that it’s the least ridiculous of all the explanations for the Hubble tension. That’s kind of the word on the street.

What would early dark energy’s role have been in the early universe?

Its only job is to increase the total energy density of the universe, and therefore increase the expansion rate of the universe for a brief period of time — within the first, say, 100,000 years after the Big Bang.

Why does a higher energy density lead to a greater expansion rate?

This is difficult to understand intuitively. A higher energy density implies a stronger gravitational field which, in the context of an expanding universe, is manifest as a faster expansion rate. This is sort of analogous to what might arise in planetary dynamics: According to Newton’s laws, if the mass of the sun were larger, the velocity of the Earth in its orbit would be larger (leading to a shorter year).

And just so I’m following this: You mentioned the two approaches to measuring the Hubble constant; one from supernovas and one from the CMB. And this idea of early dark energy allows you to interpret the CMB data in a slightly different manner, so that you come up with a slightly different value for the Hubble constant — one which more closely matches the supernova value. Right?

That is correct.

What kind of tests would have to be done to see if this approach is correct?

That’s pretty straightforward, and we’re making progress on it. The basic idea is that the early dark energy models are constructed to fit the data that we have. But the predictions that they make for data that we might not yet have can differ from lambda CDM. And in particular, we have measured the fluctuations of the cosmic microwave background. But we’ve imaged the cosmic microwave background with some finite angular resolution, which has been a fraction of a degree. With Planck, the satellite launched by the European Space Agency in 2009, it was about five arc-minute resolution — equivalent to one-sixth of the apparent width of a full moon.

Over the past decade, we’ve had experiments like ACT, which stands for Atacama Cosmology Telescope, and SPT, which stands for South Pole Telescope. These are two competing state-of-the-art cosmic microwave background experiments that have been ongoing for about the past decade, and keep improving. And they’re mapping the cosmic microwave background with better angular resolution, allowing us to see more features that we weren’t able to access with Planck. And the early dark energy models make predictions for these very small angular scale features that we’re now beginning to resolve and that differ from the predictions of lambda CDM. That suggests the possibility of new physics.

In the next few years, we expect to have data from the Simons Observatory, and on a decade timescale we expect to have new data from CMB-S4, this big US National Science Foundation and Department of Energy project. And so, if there’s a problem with lambda CDM, if there’s something different in the early expansion history of the universe beyond lambda CDM, the hope is that we’ll see it in there.

Is there evidence that could conceivably come from particle physics that would help you decide if early dark energy is on the right track?

In principle, someday we will have a theory for fundamental physics that unifies quantum gravity with this broad understanding of strong, weak and electromagnetic interactions. And so someday we might have a model that does that and says, look, there’s this additional new scalar field lying around that’s going to have exactly the properties that you need for early dark energy. So in principle, that could happen; in practice, we’re not getting a whole lot of guidance from that direction.

What’s next for you and your colleagues?

My personal interest in theoretical cosmology and astrophysics was really eclectic, and I kind of bounced around from one thing to another. My collaborators on the early dark energy paper, they’ve been very, very focused on continuing to construct and explore different types of early dark energy models. But it has become an endeavor of the community as a whole.

So there are lots of people, theorists, now all over the place, thinking about detailed models for early dark energy, following through with the detailed predictions of those models, and detailed comparisons of those predictions with measurements, as they become available. It’s not my personal top priority day-to-day in my research. But it is the top priority for many of the collaborators I had on the original work, and it’s definitely a top priority for many, many people in the community.

As I said, nobody thinks early dark energy is a great idea. But everybody agrees that it’s the least crazy idea — the most palatable of all the crazy models to explain the Hubble tension.

10.1146/knowable-092823-1

Dan Falk (@danfalk) is a science journalist based in Toronto. His books include The Science of Shakespeare: A New Look at the Playwright’s Universe and In Search of Time: The History, Physics, and Philosophy of Time.

This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews.

Right before exploding, this star puffed out a sun's worth of mass

Keith Cooper

SPACE.COM
Thu, September 28, 2023 

Right before exploding, this star puffed out a sun's worth of mass


A massive star that exploded in the Pinwheel Galaxy in May appears to have unexpectedly lost approximately one sun's worth of ejected mass during the final years of its life before going supernova, new observations have shown. This discovery reveals more about the enigmatic end days of massive stars.

On the night of May 19, Japanese amateur astronomer Kōichi Itagaki was conducting his regular supernova sweep using telescopes based in three remote observatories dotted around the country. They were located, for instance, in Yamagata, Okayama and on the island of Shikoku.

Amateur astronomers have a long history of discovering exploding stars before the professionals spot them: Itagaki has raked in over 170, just beating out UK amateur astronomer Tom Boles’ tally of more than 150. When Itagaki spotted the light of SN 2023ixf, however, he immediately knew he'd found something special. That’s because this star had exploded in the nearby Pinwheel Galaxy (Messier 101), which is just 20 million light-years away in the constellation of Ursa Major, the Great Bear. Cosmically speaking, that's pretty close.

Related: See new supernova shine bright in stunning Pinwheel Galaxy photo

Soon enough, amateur astronomers around the world started gazing at SN 2023ixf because the Pinwheel in general is a popular galaxy to observe. However, haste is key when it comes to supernova observations: Astronomers are keen to understand exactly what is happening in the moments immediately after a star goes supernova. Yet all too often, a supernova is spotted several days after the explosion took place, so they don’t get to see its earliest stages.

Considering how close, relatively speaking, SN 2023ixf was to us and how early it was identified, it was a prime candidate for close study.

Itagaki sprang into action.

"I received an urgent e-mail from Kōichi Itagaki as soon as he discovered SN 2023ixf," said postgraduate student Daichi Hiramatsu of the Harvard–Smithsonian Center for Astrophysics (CfA) in a statement.

The race to decode a supernova

Alerted to the supernova, Hiramatsu and colleagues immediately followed-up with several professional telescopes at their disposal including the 6.5-meter Multi Mirror Telescope (MMT) at the Fred Lawrence Whipple Observatory on Mount Hopkins in Arizona. They measured the supernova's light spectrum, and how that light changed over the coming days and weeks. When plotted on a graph, this kind of data forms a "light curve."

The spectrum from SN 2023ixf showed that it was a type II supernova — a category of supernova explosion involving a star with more than eight times the mass of the sun. In the case of SN 2023ixf, searches in archival images of the Pinwheel suggested the exploded star may have had a mass between 8 and 10 times that of our sun. The spectrum was also very red, indicating the presence of lots of dust near the supernova that absorbed bluer wavelengths but let redder wavelengths pass. This was all fairly typical, but what was especially extraordinary was the shape of the light curve.

Normally, a type II supernova experiences what astronomers call a 'shock breakout' very early in the supernova's evolution, as the blast wave expands outwards from the interior of the star and breaks through the star's surface. Yet a bump in the light curve from the usual flash of light stemming from this shock breakout was missing. It didn’t turn up for several days. Was this a supernova in slow motion, or was something else afoot?



"The delayed shock breakout is direct evidence for the presence of dense material from recent mass loss," said Hiramatsu. "Our new observations revealed a significant and unexpected amount of mass loss — close to the mass of the sun — in the final year prior to explosion."

Imagine, if you will, an unstable star puffing off huge amounts of material from its surface. This creates a dusty cloud of ejected stellar material all around the doomed star. The supernova shock wave therefore not only has to break out through the star, blowing it apart, but also has to pass through all this ejected material before it becomes visible. Seemingly, this took several days for the supernova in question.

Massive stars often shed mass — just look at Betelgeuse’s shenanigans over late 2019 and early 2020, when it belched out a cloud of matter with ten times the mass of Earth’s moon that blocked some of Betelgeuse’s light, causing it to appear dim. However, Betelgeuse isn’t ready to go supernova just yet, and by the time it does, the ejected cloud will have moved far enough away from the star for the shock breakout to be immediately visible. In the case of SN 2023ixf, the ejected material was still very close to the star, meaning that it had only recently been ejected, and astronomers were not expecting that.

Hiramatsu’s supervisor at the CfA, Edo Berger, was able to observe SN 2023ixf with the Submillimeter Array on Mauna Kea in Hawaii, which sees the universe at long wavelengths. He was able to see the collision between the supernova shockwave and the circumstellar cloud.

"The only way to understand how massive stars behave in the final years of their lives up to the point of explosion is to discover supernovae when they are very young, and preferably nearby, and then to study them across multiple wavelengths," said Berger. "Using both optical and millimeter telescopes we effectively turned SN 2023ixf into a time machine to reconstruct what its progenitor star was doing up to the moment of its death."

The question then becomes, what caused the instability?

Stars, they're just like onions

We can think of an evolved massive star as being like an onion, with different layers. Each layer is made from a different element, produced by sequential nuclear burning in the star's respective layers as the stellar object ages and its core contracts and grows hotter. The outermost layer is hydrogen, then you get to helium. Then, you go through carbon, oxygen, neon and magnesium in succession until you reach all the way to silicon in the core. That silicon is able to undergo nuclear fusion reactions to form iron, and this is where nuclear fusion in a massive star’s core stops — iron requires more energy to be put into the reaction than comes out of it, which is not efficient for the star.

Thus the core switches off, the star collapses onto it and then rebounds and explodes outwards.

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One possibility is that the final stages of burning high-mass elements inside the star, such as silicon (which is used up in the space of about a day), is disruptive, causing pulses of energy that shudder through the star and lift material off its surface. It's certainly something that astronomers will look for in the future, now that they’ve been able to see it in a relatively close supernova.

What the story of SN 2023ixf does tell us is, at the very least, that despite all the professional surveys hunting for transient objects like supernovas, amateur astronomers can still make a difference.

"Without … Itagaki’s work and dedication, we would have missed the opportunity to gain critical understanding of the evolution of massive stars and their supernova explosions," said Hiramatsu.

In recognition of his work Itagaki, who continued to make observations of the supernova that were of use to the CfA team, is listed as an author on the paper describing their results. That paper was published on Sept. 19 in The Astrophysical Journal Letters.