Euclid space telescope blasts off to explore dark matter

SpaceX’s Falcon 9 rocket has launched the European Space Agency’s Euclid telescope from Florida. The extraordinary telescope is set to unravel the "dark" or unknown mysteries of the universe.

The Euclid's primary goal is to study dark matter and dark energy

Image: Malcolm Denemark/Florida Today/USA TODAY Network/IMAGO

The European Space Agency’s Euclid space telescope lifted off aboard a SpaceX rocket from Florida on Saturday.

The telescope, which successfully separated from the rocket about an hour after the launch, is set to explore the "dark" or unknown realms of the universe.

Flight controllers in Germany declared success less than an hour into the flight, applauding and shouting "Yes" after they received a signal from the telescope after it separated from the rocket.

"I'm so thrilled, I'm so excited to see now this mission up in space, knowing it is on its way," the European Space Agecy Director General Josef Aschbacher said from the launch site in Florida.

The Euclid telescope now sets off on a monthlong journey to its destination, known as the second Lagrange point (L2) of the solar orbit, where gravity from the sun and Earth balance the orbital motion of a satellite.



There are five so-called "Lagrange Points," according to NASA. L2 is nearly 1 million miles (1.6 million kilometers) away from Earth.

From L2, the telescope will survey galaxies as far away as 10 billion light years from Earth across an immense expanse of the sky beyond our own Milky Way galaxy.

EUCLID probe aims to discover secrets of universe  04:09

The spacecraft, which weighs 2 tons, is also equipped with instruments designed to measure the intensity and spectrums of infrared light from those galaxies in a way that will precisely determine their distances.

 
Why exploring the "dark" side of the universe matters

The telescope is set to produce the largest and the most accurate map of the universe so far, including the distribution of galaxies spanning the last 10 billion years of cosmic time, explained Elsa Montagnon, the head of Mission Operations Division at NASA.

That gives scientists the ability to comprehensively study the evolution and composition of the universe, Montagnon added during a live broadcast of the launch.

The Euclid mission is set to unravel the mysteries of the dark energy, which together with dark matter comprises 95% of the cosmos, Montagnon said.

Visible stars and galaxies make up less than 5% of the universe, and the Euclid will allow scientists to study the universe as it is.

What to know about dark energy and dark matter

There are two highly important instruments within the telescope that will take images to allow scientists to study the two foundational components of the universe.

One is dark matter, which is an invisible form of matter that makes up most of the universe's mass and creates its underlying structure. Dark matter's gravity drives normal matter (gas and dust) to collect and build up into stars and galaxies.

The other is dark energy, an equally enigmatic force believed to explain the universe's expansion.

Other than that, dark energy is a complete mystery to scientists.

Roughly 68% of the universe is dark energy, while dark matter makes up about 27%. The rest, or everything else ever observed on Earth, adds up to less than 5% of the universe.

rm/wd (AFP, Reuters)

SEE 

BEFORE DARK MATTER OR DARK ENERGY THERE WAS ETHER  

LA REVUE GAUCHE - Left Comment: Search results for AETHYR 

LA REVUE GAUCHE - Left Comment: Search results for DARK MATTER 

LA REVUE GAUCHE - Left Comment: Search results for DARK ENERGY

Europe’s space telescope to target universe’s dark mysteries

By AFP
Published July 1, 2023

The Euclid spacecraft, pictured before being sent to Florida, will blast off on a mission to find out more about the 'dark universe' - Copyright AFP/File Valery HACHE

Gianrigo Marletta, with Lucie Aubourg in Washington

Europe’s Euclid space telescope is scheduled to blast off Saturday on the first-ever mission aiming to shed light on two of the universe’s greatest mysteries: dark energy and dark matter.

The launch is planned from Cape Canaveral in Florida at 11:12 am local time (1512 GMT) on a Falcon 9 rocket of the US company SpaceX.

The European Space Agency was forced to turn to billionaire Elon Musk’s firm to launch the mission after Russia pulled its Soyuz rockets in response to sanctions over the war in Ukraine.

After a month-long journey through space, Euclid will join its fellow space telescope James Webb at a stable hovering spot around 1.5 million kilometers (more than 930,000 miles) from Earth called the second Lagrange Point.

From there, Euclid will chart the largest-ever map of the universe, encompassing up to two billion galaxies across more than a third of the sky.

By capturing light that has taken 10 billion years to reach Earth’s vicinity, the map will also offer a new view of the 13.8-billion-year-old universe’s history.

Scientists hope to use this information to address what the Euclid project manager Giuseppe Racca calls a “cosmic embarrassment”: that 95 percent of the universe remains unknown to humanity.

Around 70 percent is thought to be dark energy, the name given to the unknown force that is causing the universe to expand at an accelerated rate.

And 25 percent is dark matter, thought to bind the universe together and make up around 80 percent of its mass.

“Ever since we could see stars we’ve wondered, is the universe infinite? What is it made out of? How does it work?” NASA Euclid project scientist Michael Seiffert told AFP.

“It’s just absolutely amazing that we can take data and actually start to make even a little bit of progress on some of these questions.”

– ‘Dark detective’ –

Euclid consortium member Guadalupe Canas told a press conference that the two-tonne space telescope was a “dark detective” which can reveal more about both elements.

Euclid, which is 4.7 meters (15 feet) tall and 3.5 meters wide, will use two scientific instruments to map the sky.

Its visible light camera will let it measure the shape of galaxies, while its near infrared spectrometer and photometer will allow it to measure how far away they are.

So how will Euclid try to spot things that cannot be seen? By searching for their absence.

The light coming from billions of light years away is slightly distorted by the mass of visible and dark matter along the way, a phenomenon known as weak gravitational lensing.

“By subtracting the visible matter, we can calculate the presence of the dark matter which is in between,” Racca told AFP.

While this may not reveal the true nature of dark matter, scientists hope it will throw up new clues that will help track it down in the future.

For dark energy, French astrophysicist David Elbaz compared the expansion of the universe to blowing up a balloon with lines drawn on it.

By “seeing how fast it inflates,” scientists hope to measure the breath — or dark energy — making it expand.

– ‘Goldmine’ –

A major difference between Euclid and other space telescopes is its wide field of view, which takes in an area equivalent to two full moons.

Project scientist Rene Laureijs said that this wider view means Euclid will be able to “surf the sky and find exotic objects” like black holes that the Webb telescope can then investigate in greater detail.

Beyond dark energy and matter, Euclid’s map of the universe is expected to be a “goldmine for the whole field of astronomy,” said Yannick Mellier, head of the Euclid consortium.

Scientists hope Euclid’s data will help them learn more about the evolution of galaxies, black holes and more.

The first images are expected once scientific operations start in October, with major data releases planned for 2025, 2027 and 2030.

The 1.4 billion euro ($1.5 billion) mission is intended to run until 2029, but could last a little longer if all goes well.

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The Euclid telescope: On the trail of dark energy and matter

Esteban Pardo

DW
June 29, 2023

On July 1 a new telescope will begin mapping the distant universe in greater detail than ever seen before, improving our understanding of dark matter and dark energy.

The Euclid space telescope has optical and near-infrared detectors and will map the distribution and evolution of distant galaxies and dark matter.

You've probably heard of dark matter and dark energy, right? They sound like something straight out of a Star Wars movie. Terms like these can sound so foreign to us that we just don't bother thinking about them. That's what often happens in science. Getting our heads around some of its concepts can be very challenging — yes, I'm looking at you, quantum mechanics.

Unraveling these mysteries is one of the main goals of the new Euclid space telescope, which is set for launch on July 1 on a SpaceX Falcon 9 rocket in Cape Canaveral, Florida, USA. Its mission is to deepen our understanding of dark matter and dark energy. Euclid won't be able to answer the many questions that remain about the dark universe, but it will take a big step on the path to investigating two of its most intriguing components.

Ok, cool, but why should we care? Well, because ultimately Euclid's task is to explore some of the most profound and fundamental questions in cosmic history: How did the universe originate and what is it made of? What are the fundamental physical laws of the universe? Just take a second to pause, look up into the stars, and ask yourself these questions. Let the mind wander.
The building blocks of the universe

"Both dark matter in particular, but also dark energy, ultimately our existence traces back to those," Hans-Walter Rix, astronomer and director of the Max Planck Institute for Astronomy, in Heidelberg, Germany, told DW.

Dark matter and dark energy provided the right conditions for enough material to come together and form the stars, planets, galaxies, life, you and me. So understanding them is a step closer to understanding where we come from.

This is what makes the mission such an historic one. The Euclid telescope is led by the European Space Agency (ESA) with contributions from NASA. It took more than ten years of development, €1.4 billion and more than 3,500 scientists from 21 countries.

Euclid was originally planned to launch from a Russian Soyuz rocket in 2022, but Russia's invasion of Ukraine called for a change of plans.

This simulation from 2014 shows the distribution of galaxies in the universe and how a kind of web pattern emerges on a very large scale

.Image: Illustris Collaboration/AP Photo/picture alliance

The distant universe in unprecedented detail

Good news for the James Webb Space Telescope — it's getting company. Euclid, like the Webb, will also orbit the second Lagrange point (L2), 1.5 million kilometers (about 930,000 miles) from Earth. This point is a special place in space that moves in synchrony with the Earth around the sun.

The questions Euclid is tasked with addressing are pretty ambitious ones. The primary goal is to create a map. "It is the biggest and most accurate map of the universe, what we are basically aiming to do, that has never been done before," Guadalupe Cañas Herrera, a cosmologist working on the Euclid mission at ESA, told DW.

It takes its name from the Greek mathematician Euclid of Alexandria, who lived in the 3rd century BC and is known as the father of geometry — and the terror of high school students. The mission is named in his honor because better understanding of how everything is distributed in the universe tells us a lot about its geometry.

To make the map, Euclid is going to look at and measure billions of galaxies — yes, that's a thousand million — with extreme precision over a span of at least six years. Euclid is equipped with a visible light sensor and a near-infrared instrument capable of accurately measuring the distance of these galaxies.

"We are aiming to do something really challenging or something that is really ambitious, which is mapping a third of the full sky," said Cañas.
Euclid vs. the James Webb

One third of the sky is huge. Just take a look at the deep field image from the James Webb, down here.

This was the Webb's first picture. It pointed at a galaxy cluster in the center of the image that is so massive that it causes light from background objects to bend, like looking at space through a glass of water. That's why some objects appear distorted or stretched.

Image: NASA, ESA, CSA, STScI, Webb ERO Production Team

That was just a portion of the sky the size of a grain of sand on your fingertip on a stretched arm, so imagine how many stars and galaxies there are in a third of the whole sky, — and how many planets.

They are both space telescopes, but they have different purposes. Euclid's mirror is 1.2 m in diameter, compared to the Webb's huge 6.5 m. But the James Webb is like a precise pencil that sketches fine details, it looks at a very small portion of the sky with amazing detail. Euclid is more like a brush that can cover big patches of sky quickly.

But don't be fooled by Euclid's size, "Euclid will actually take a very high-resolution picture of the sky that will deliver gorgeous, gorgeous pictures," added Rix.

How the shape of the universe has changed over time

Euclid will be glimpsing into the past. That's because light takes a while to travel through the immensity of space. For example, it takes light eight minutes to travel from the sun to us. So, at larger distances, the farther we look, the earlier we see into our universe.

And these galaxies can be very far away, with their light taking up to 10 billion years to reach us. For reference, the age of the universe is around 13.8 billion years.

The goal here is to have the best understanding to date of where galaxies are in the distant universe up to 10 billion light-years away, but also how the shape of the distant universe has evolved over time.

But to better understand how this can help answer the previously mentioned questions and how all of these is related to dark matter and dark energy, we first need to talk about the dark universe.

The dark universe

Everything we know and see — bacteria, plants, animals, stars, planets, galaxies — is made of atoms that you can pinpoint in the periodic table. Astronomers refer to this as baryonic matter, in case you want to dazzle your cosmologist cousin.

But this visible matter is just a fraction of what the universe is made of — just 5%. The rest is dark matter and dark energy.

We might not know what they are, but there are many different lines of evidence that tell us that for sure they are there.

Dark matter seems to be keeping galaxies together, making the stars inside orbit faster than we would expect them to, and preventing galaxies from falling apart. It doesn't emit or absorb light, but we can also tell it's there by how seemingly empty regions of space bend the light of objects behind it — what's called gravitational lensing. And there's a lot of dark matter, around five times more than ordinary matter.

The idea of dark energy was first mooted in the 1990s, when scientists discovered that, contrary to what they thought, everything in the universe, on a larger scale, is moving apart from everything else at an accelerated rate. Just as your speed increases every second when you press down on the gas pedal, a very distant galaxy is moving away from us faster every second. Dark energy is what we call the unknown driving agent of this accelerating expansion.

A good analogy, and something you can try at home, is to grab a balloon that's just slightly inflated, draw a few dots with a marker on it and then start blowing it up. You'll see every dot getting further apart from all the other dots. That's exactly like what happens in our universe.

We don't experience this expansion in our daily life because our galaxy, for example, is tightly bound by gravity — mostly from dark matter.

This optical illusion happens due to gravitational lensing. There's so much mass on that bright red galaxy at the center that its gravity causes the light of a background blue galaxy to bend, what makes it appear distorted. It is possible to determine the amount of mass needed to have such a distortion and compare it with the mass we can see, if it doesn't add up, it's because there's dark matter too.

Image: ESA/Hubble & NASA

Euclid, dark matter and dark energy

"You are not just mapping where all the stuff you can see is, but we will also map where all the stuff we can't see is," Becky Smethurst, a Royal Astronomical Society Research Fellow at the University of Oxford, told DW.

Euclid will not only map the visible, "ordinary" matter, but also dark matter in the universe. A more detailed map of where dark matter is and how it is distributed can be a huge help in trying to better understand what dark matter is.

About that gravitational lensing mentioned earlier. This occurs when a gravitational field distorts light just like a lens, or a glass of water. The light of very far away galaxies gets distorted — often in a sausage shape. And depending on the level of distortion, gravitational lensing can indirectly tell us how much dark matter there is.

Well, Euclid is going to exploit the phenomenon to look into billions of distorted galaxies and infer the amount and distribution of dark matter there is, effectively creating a gigantic 3D map.

Mapping all these millions of galaxies requires very precise measurements of how distant they are. This is measured by the red shift. The expanding universe stretches light waves, and that can be measured. This way, Euclid is going to provide the most precise measurements ever taken of how the larger cosmic structures have changed over time, effectively tracing the effects of dark energy, which ultimately will tell us much more about what dark energy is and what it is not.

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.

Related Stories:

— Hundreds of supernova remnants remain hidden in our galaxy. These astronomers want to find them

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

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

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.

WHAT IS DARK ENERGY? PHYSICISTS AREN'T EVEN SURE

15-Minute Listen Download Transcript

MADDIE SOFIA, HOST:

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SOFIA: You're listening to SHORT WAVE...

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SOFIA: ...From NPR.

Going out into nature - hiking, paddling, looking up at the stars - has always helped me center myself. It reminds me that I'm just Madeline Kelly (ph) Sofia, one human among millions of critters and trees and galaxies that don't care about me or acknowledge me at all. I'm just a group of random atoms - matter taking up space. And it turns out that matter as we normally think of it is a tiny, tiny portion of the universe, meaning your genes, the ocean, trees, computers, all the stars and planets - all of that is only 5% of the universe.

SARAFINA NANCE: And the rest of the stuff is dark matter and dark energy.

SOFIA: Right, which is wild. That's so much. (Laughter) That's so much of it. That's too much of it. Honestly, it's too much.

NANCE: (Laughter) Yeah. It's like a very uncomfortable place to be in when you think about - oh, you know, we study the universe, and theoretically we understand, you know, on some scale, how the universe works. And then all of a sudden, you're like - oh, wait; we actually do not understand, like, over 95% of our universe. What?

SOFIA: The large majority of our universe is made up of this mysterious thing called - I kid you not - dark energy.

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SOFIA: And get this - it's how we know that our universe is expanding. I learned about dark energy, honestly, like, three weeks ago. And it blew my mind.

NANCE: Dark energy is intrinsic to the fabric of space-time that is somehow pushing galaxies apart.

SOFIA: This is Sarafina Nance's day job.

NANCE: I am a Ph.D. student at UC Berkeley studying supernova and cosmology.

SOFIA: Supernova, meaning an exploding star that can help us understand how our universe is changing. You know, no big deal.

NANCE: It's a really phenomenal thing in sort of the scale of the universe to see something change. And that's this class of astronomy called transience, where things change in the night sky and you can learn about them through their changes.

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SOFIA: So today we explore one of the universe's biggest mysteries - dark energy - from the days of Einstein to the exploding stars that help us understand the very fabric of our universe.

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SOFIA: So. OK, Sarafina, to really understand dark energy, we have to go back to Einstein. Right?

NANCE: Yeah. So Einstein came up with this theory of general relativity, which is basically his version of gravity, in the early 1900s. And the only way to make his equations work and satisfy what he thought was a static universe, he introduced this fudge factor - in his words - called the cosmological constant.

SOFIA: So Einstein actually thought that the universe was static, not that it was expanding.

NANCE: That's right. And over the next 10 years, people sort of manipulated these equations and tried to find solutions and started hinting at perhaps the universe wasn't static.

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SOFIA: Well, it's nice to see that, you know, Einstein can get things wrong. That's cool.

NANCE: (Laughter) So the funny thing is this cosmological constant, he called it his biggest blunder.

SOFIA: Honestly, it's just nice to hear Einstein say I messed up, you know what I mean?

NANCE: I know. Well, the fun fact...

SOFIA: We can all mess up.

NANCE: The fun fact is that he ended up actually being right.

SOFIA: Right (laughter). Dang it.

NANCE: So it turns out that that cosmological constant is exactly what we think dark energy is...

SOFIA: (Laughter).

NANCE: ...And is necessary to actually describe our universe.

SOFIA: I feel like that's classic Einstein. Him being wrong...

NANCE: Yep.

SOFIA: ...Is being more right than I've ever been in my entire life.

NANCE: Exactly. Yes (laughter).

SOFIA: OK. So after Einstein introduces this idea that the universe is static, we figure out, actually, that the universe is expanding. Right?

NANCE: Yeah. So in 1929, Edwin Hubble showed that the universe is not static; it's actually expanding. So what he did is he measured, basically, galaxies and how far away they are. And he found that galaxies are actually moving away from us. So that means that the universe is not static. It's, in fact, expanding.

SOFIA: And at this point, we think that the universe is expanding but that that expansion is slowing down. Is that correct?

NANCE: Exactly. So we think that the expansion comes from the Big Bang and it comes from inflation, which was right after the Big Bang, which is this rapid expansion of space. But because there's gravity in the universe and there's mass in the universe, we would think that gravity starts to take over and the expansion decelerates because gravity starts to pull things back in.

SOFIA: And then in the late '90s, we get turned on our head again, right? There's another big discovery. And we're like - oh, wait, wait wait...

NANCE: (Laughter).

SOFIA: ...Maybe she's not slowing down.

NANCE: That's right. So in 1998 and in 1999, there were two teams that were studying a specific type of supernova. And they found that these supernova that were super far away from us were fainter than what we would have expected if the universe was in fact expanding but decelerating that expansion. And the only way to explain away that faintness is if the universe was instead accelerating its expansion.

SOFIA: Wild. So we went from, the universe is static - OK, it's not static; it's expanding, but it's slowing down that expansion to - wait, wait, wait - not only is it expanding but it's expanding faster than we thought it was and it's speeding up. And what...

NANCE: That's right.

SOFIA: And the explanation for that is dark energy?

NANCE: You killed it. That's right.

SOFIA: I nailed it. OK. So yes, we have finally gotten to the point where I can ask you - Sarafina, what is dark energy? (Laughter).

NANCE: So I think the only answer to that question is we don't know.

SOFIA: Oh, come on, Sarafina. You brought me all the way here. You told me Einstein's story, and we don't know.

NANCE: I know. It's really uncomfortable to sit with.

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NANCE: We can see dark energy through its effects on the expansion of the universe, but we don't actually know what it is.

SOFIA: Wow. I don't even know - I don't even know what to say about that. That's - so - 'cause it's wild. We don't know what dark energy is, but we know it exists.

NANCE: Yes.

SOFIA: And - so what are you doing over there, astronomers?

NANCE: (Laughter).

SOFIA: This is what we've got - 4% to 5%? No, I'm just teasing you. So that - I mean, that's wild. And the amount of dark energy is staying the same, right?

NANCE: So that's an interesting question. So I like to kind of describe dark energy and the expansion of the universe in - the way that I think about it is sort of picture a loaf of bread and picture a bunch of raisins in the bread. And the raisins are like our universe's galaxies. And the bread itself is like space-time.

SOFIA: OK.

NANCE: And so as you bake the bread, the bread rises and the raisins get farther and farther apart. They're sort of carried along the fabric of space-time, which means that the distance between galaxies increases with time.

SOFIA: OK. I'm with you. I'm with you.

NANCE: And the introduction of dark energy is like - imagine you have this special type of yeast that you can put into a bread and the bread starts to rise with yeast. And then all of a sudden, it starts to rise a lot, and it gets bigger and bigger and bigger over time. And that's dark energy.

SOFIA: So dark energy is the weird yeast that causes...

NANCE: Exactly.

SOFIA: ...Our universe to grow and push our galaxies farther and farther apart from each other.

NANCE: Exactly. And it causes it to grow exponentially.

SOFIA: Well, I totally get it now.

NANCE: (Laughter) Great. We'll...

SOFIA: Now that we put...

NANCE: We'll publish a paper.

SOFIA: Now that we started talking about carbs, I'm starting to understand.

NANCE: (Laughter).

SOFIA: OK. OK. So we actually figured a lot of this out by studying a particular type of exploding star - a supernova.

NANCE: Right.

SOFIA: Tell me about that.

NANCE: So when dark energy was first basically discovered, it was discovered through a specific type of supernova that forms when you have a binary system of a really big star or a really small star and another small star, which is called a white dwarf. And basically, the white dwarf accretes matter from the companion star - the binary star - and ignites an explosion. And the really interesting thing about this particular type of supernova is that all of them blow up with the same brightness.

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NANCE: And that makes them what we call standard candles. So if you can imagine a lightbulb and you have a lightbulb right next to you and you have a lightbulb a hundred feet away from you, the one that's right next to you seems to be way brighter. And the one that's farther away from you is way fainter. And so by using the intrinsic brightness of the sort of lightbulb or, in the universe, of the supernova and comparing it to what is observed, we can determine the distance to the supernova and determine how fast that galaxy that hosts the supernova is expanding away from us.

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SOFIA: Wild. That's wild. That's your job.

NANCE: Yes, it's really cool.

SOFIA: I mean, it's very cool. That is very cool. OK. So basically studying these supernovae help us understand how fast the universe is expanding because we can kind of try to calculate how far those explode-y stars are away from us. Is that fair?

NANCE: Yeah, that's exactly right.

SOFIA: OK. And tell me if I'm overselling this, but all of this potentially gives us clues into how the universe could end.

NANCE: That's exactly right.

SOFIA: So what is our best guess as far as, like, how the universe could end?

NANCE: So right now, we think that dark energy stays constant with time, which means that the universe is going to continue to accelerate its expansion. Distances between galaxies are going to get further and further apart with time. And so it's going to accelerate forever, and it's going to be a cold, dark universe.

SOFIA: I mean, that sounds about right to me, you know?

NANCE: (Laughter) You know, it's kind of where we're at right now.

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SOFIA: So what's the coolest thing about all of this to you, Sarafina? Because this is objectively very cool.

NANCE: Well, thanks. I love it. I think it kind of goes back to what drew me to astronomy in the first place, which is we are trying to understand some of the most fundamental aspects of our universe and human existence. And we can derive some sort of meaning about, you know - how did we get here? what is the fate of the universe? how does that change with time? - and learn some really profound things about what it means to exist here.

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SOFIA: Sarafina Nance studies supernova and cosmology at UC Berkeley.

This episode was produced by Rebecca Ramirez, edited by Geoff Brumfiel and was fact-checked by Emily Vaughn I'm Maddie Sofia, and we are all in awe of our universe. Thanks for listening to SHORT WAVE from NPR. See you tomorrow.

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SEE 
https://plawiuk.blogspot.com/search?q=DARK+ENERGY
https://plawiuk.blogspot.com/search?q=ETHER
https://plawiuk.blogspot.com/search?q=DARK+MATTER