It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
The serendipitous detection of the cosmic microwave background radiation in 1964 changed cosmology forever, settling a long-running debate about the origin of the Universe. The radio hiss hinted that the Universe had arisen from an instantaneous fiery beginning, a theory championed by cosmologist George Gamow, who sought to account for the origin of the chemical elements. His rival, Fred Hoyle, who developed the alternative steady-state theory, which posited an infinite Universe, had long insisted that the chemical elements formed continuously in the cores of massive stars. Both cosmic models were falsifiable by solving a simple puzzle: Has the Universe evolved? The feeble whisper detected in 1964 was an undeniable “Yes!”
In Flashes of Creation, Paul Halpern presents a scintillating account of the intellectual travails of Gamow and Hoyle, two animated, curious, provocative, and controversial figures in 20th-century physics. In this joint biography, the reader is introduced to the two physicists' theories and their efforts to explain the origin of elements.
Gamow, we learn, first encountered cosmology in the early 1920s while studying at the University of Leningrad under Alexander Friedmann, the Russian mathematician who pioneered the idea that the Universe is expanding. In Göttingen and Copenhagen, while a doctoral student in physics, he mingled with pioneers who were working on the new quantum theory. These interactions enabled his breakthrough in 1928, when he showed how an alpha particle could escape from an atomic nucleus by quantum tunneling.
Gamow's subsequent realization that quantum tunneling is reversible spurred two colleagues, Robert Atkinson and Fritz Houtermans, to demonstrate that sufficiently energetic protons could penetrate the atomic nuclei often enough to account for the source of stellar energy. Physicist Hans Bethe made the next advance, finding that proton-proton collisions in the cores of stars like the Sun fuse hydrogen to helium. For more-massive stars, he suggested a cycle of nuclear reactions in which carbon, nitrogen, and oxygen catalyze hydrogen to helium. This scheme left open the question that Gamow and Hoyle would confront head on: How did the elements from carbon to uranium come into existence?
Hoyle entered the Cavendish Laboratory at the University of Cambridge in 1936 as a doctoral student supervised by Rudolf Peierls. As academics, including Peierls, later fled the Cavendish Laboratory to professorships elsewhere, Hoyle remained at Cambridge until the war years, working alone on extending Enrico Fermi's theory of beta decay. By peacetime, he had developed the steady-state theory and witheringly dismissed Gamow's cosmology as a mere “big bang.”
Fred Hoyle (left) and George Gamow disagreed about the origins of the Universe
.PHOTOS (LEFT TO RIGHT): A. BARRINGTON BROWN/SCIENCE SOURCE; GRANGER
Hoyle could perceive no merit in Gamow's notion that the elements were created in a flash by the eruption of a primeval atom—it violated the conservation laws of physics. His ageless steady-state approach envisaged that new matter trickled continuously into the empty space left by the expansion of the Universe. The buildup of chemical elements then arose as a consequence of the evolution of massive stars, he postulated. When the hydrogen fuel in a star's core became exhausted, it would implode gravitationally, thereby sparking the physical conditions conducive to the rapid assembly of heavier elements.
The Gamowian school had considered the role of neutrinos in core collapse, but Hoyle's powerful rebuttal of their model in 1946 was vastly more efficient at building heavy elements. By 1957, Hoyle's team had completed its brilliant synthesis of element building via neutron capture reactions. However, steady-state theory came under relentless attack as report after report by observational astronomers cemented Big Bang cosmology.
In 1964, Hoyle reluctantly conceded that “a small residue of Gamow's idea”—the synthesis of light elements in the Big Bang—had merit. Within months, news broke of the discovery of the cosmic microwave background. Hoyle never accepted this as evidence that “the entire cosmos had a start date.” By contrast, Gamow opportunistically seized the moment, claiming primary credit for a neglected prediction of the background temperature made in 1948 by his associates Ralph Alpher and Robert Herman.
In the book's closing pages, Halpern sensitively handles with commendable candor the tragic endgames of these two giants. Gamow's alcoholism, we learn, destroyed him and much of his reputation. And while Hoyle commanded great respect after resigning from Cambridge in 1972, his little tweaks to steady-state cosmology failed to find a following.
Gamow and Hoyle were friendly rivals who seldom interacted in person. Halpern nonetheless renders their contributions and clashes vividly in this expertly crafted biography of two contentious cosmologists who thrived on ingenious invention. http://www.sciencemag.org/about/science-licenses-journal-article-reuse
Tuesday, May 16, 2023
Simulation provides images from the carbon nucleus
International study with participation of the University of Bonn also provides new insights into the puzzling Hoyle state
IMAGE: ARE PRESENT IN THE CARBON NUCLEUS AS THREE CLUSTERS OF FOUR. DEPENDING ON THE ENERGY STATE OF THE NUCLEUS, THESE CAN BE ARRANGED INTO AN EQUILATERAL TRIANGLE (LEFT) OR LIKE A SLIGHTLY BENT ARM (RIGHT).view more
CREDIT: IMAGE: PROF. SERDAR ELHATISARI/UNIVERSITY OF BONN
What does the inside of a carbon atom’s nucleus look like? A new study by Forschungszentrum Jülich, Michigan State University (USA) and the University of Bonn provides the first comprehensive answer to this question. In the study, the researchers simulated all known energy states of the nucleus. These include the puzzling Hoyle state. If it did not exist, carbon and oxygen would only be present in the universe in tiny traces. Ultimately, we therefore also owe it our own existence. The study has now been published in the journal “Nature Communications.”
The nucleus of a carbon atom normally consists of six protons and six neutrons. But how exactly are they arranged? And how does their configuration change when the nucleus is bombarded with high-energy radiation? For decades, science has been searching for answers to these questions. Not least because they could provide the key to a mystery that has long puzzled physicists: Why is there a significant amount of carbon in space at all - an atom without which there would be no life on Earth?
After all, shortly after the Big Bang, there was only hydrogen and helium. The hydrogen nucleus consists of a single proton, that of helium of two protons and two neutrons. All heavier elements were only created many billions of years later by aging stars. In them, helium nuclei fused into carbon nuclei at immense pressure and extremely high temperatures. This requires three helium nuclei to fuse together. “But it's actually very unlikely for this to happen,” explains Prof. Dr. Ulf Meißner of the Helmholtz Institute of Radiation and Nuclear Physics at the University of Bonn and the Institute for Advanced Simulation at Forschungszentrum Jülich. The reason: The helium nuclei together have a much higher energy than a carbon nucleus. However, this does not mean that they fuse particularly readily - on the contrary: It is as if three people wanted to jump onto a merry-go-round. But since they run much faster than the merry-go-round turns, they do not succeed.
Simulation on the supercomputer
As early as the 1950s, the British astronomer Fred Hoyle therefore postulated that the three helium nuclei first come together to form a kind of transition state. This "Hoyle state" has a very similar energy to the helium nuclei. To stay in the picture: It is a faster-spinning version of the merry-go-round, which the three passengers can therefore easily jump onto. When that happens, the carousel slows down to its normal speed. “Only by taking a detour via the Hoyle state can stars create carbon at all in any appreciable quantity,” says Meißner, who is also a member of the Transdisciplinary Research Areas “Modeling” and “Matter” of the University of Bonn.
About ten years ago, together with colleagues from the USA, Forschungszentrum Jülich and Ruhr-Universität Bochum, he succeeded in simulating this Hoyle state for the first time. “We already had an idea then of how the protons and neutrons of the carbon nucleus are arranged in this state,” he explains. “However, we were not able to prove with certainty that this assumption was true.” With the help of an advanced method, the researchers have now succeeded. This is essentially based on confinement: In reality, the protons and neutrons - the nucleons - can be located anywhere in space. For their calculations, however, the team restricted this freedom: “We arranged our nuclear particles on the nodes of a three-dimensional lattice,” Meißner explains. “So we allowed them only certain strictly defined positions.”
Computing time: five million processor hours
Thanks to this restriction, it was possible to calculate the motion of nucleons. Since nuclear particles affect each other differently depending on their distance from each other, this task is very complex. The researchers also ran their simulation several million times with slightly different starting conditions. This allowed them to see where the protons and neutrons were most likely to be. “We performed these calculations for all known energy states of the carbon nucleus,” Meißner says. The calculations were performed on the JEWELS supercomputer at Forschungszentrum Jülich. They required a total of about five million processor hours, with many thousands of processors working simultaneously.
The results effectively provide images from the carbon nucleus. They prove that the nuclear particles do not exist independently of each other. “Instead, they are clustered into groups of two neutrons and two protons each,” the physicist explains. This means that the three helium nuclei can still be detected after they have fused to form the carbon nucleus. Depending on the energy state, they are present in different spatial formations - either arranged into an isosceles triangle or like a slightly bent arm, with the shoulder, elbow joint and wrist each occupied by a cluster.
The study not only allows researchers to better understand the physics of the carbon nucleus. Meißner: “The methods we have developed can easily be used to simulate other nuclei and will certainly lead to entirely new insights.”
Participating institutions and funding:
Forschungszentrum Jülich, Michigan State University (USA), the China Academy of Engineering Physics and the University of Bonn were involved in the study. The work was made possible by funding from the German Research Foundation, the National Natural Science Foundation of China, the Chinese Academy of Sciences (CAS), the Volkswagen Foundation, the European Research Council (ERC), the U.S. Department of Energy, the Nuclear Computational Low-Energy Initiative (NUCLEI), and the Gauss Center for Supercomputing e.V.
Publication: Shihang Shen, Serdar Elhatisari, Timo A. Lähde, Dean Lee, Bing-Nan Lu & Ulf-G. Meißner: Emergent geometry and duality in the carbon nucleus; Nature Communications; https://www.nature.com/articles/s41467-023-38391-y
Emergent geometry and duality in the carbon nucleus
ARTICLE PUBLICATION DATE
15-May-2023
Monday, August 23, 2021
PAPER: CULTURE, COMPUTING SHOULD BE CONSIDERED “LIFE FORMS”
The idea of broadening the definition of life isn’t wholly new. Astronomer Fred Hoyle wrote a sci-fi novel about intelligent gaseous clouds
NEWS AUGUST 21, 2021
Some researchers are urging us to broaden our definition of life, which may have an impact on the search for life on exoplanets.
In a new paper, published in the Journal of Molecular Evolution, Santa Fe Institute researchers Chris Kempes and David Krakauer argue that in order to recognize life’s full range of forms, we must develop a new theoretical frame.
Although there are many definitions of life, they all assume a strict separation between life and non-life — and that is what the researchers challenge:
Culture, computation, and forests are all forms of life in this frame. As Kempes explains, “human culture lives on the material of minds, much like multicellular organisms live on the material of single-celled organisms.”
Their broader definition of life includes the idea that life has multiple origins; all life did not begin with a single cell; it may not even require cells. Viruses would certainly be considered alive in their scheme.
When researchers focus on the life traits of single organisms, they often neglect the extent to which organisms’ lives depend upon entire ecosystems as their fundamental material, and also ignore the ways that a life system may be more or less living. Within the Kempes-Krakauer framework, by contrast, another implication appears: life becomes a continuum rather than a binary phenomenon. In this vein, the authors point to a variety of recent efforts that quantitatively place life on a spectrum.
On one hand, this broader approach might make it easier to envision, thus look for, extraterrestrial life. We would not insist that it be like life on Earth.
The idea is not entirely new. Astronomer Fred Hoyle (1915–2001) wrote a science fiction novel, The Black Cloud (1957) in which the extraterrestrials turn out to be a dark, gaseous cloud, much more intelligent than humans. The cloud is creating havoc by accidentally blocking the sun but, being so informed, it expresses surprise that there are life forms that are actually solids.
On the other hand, there is a danger is losing a grip on what makes life on Earth unique. Culture, for example, originates as ideas, which are immaterial in character. That makes culture quite different from cells. And, while forests are full of life forms, the concept of a “forest” is an idea in the human mind.
Similarly, however powerful computers may become, insisting that they are “life” could only have the effect of diminishing the importance of biological life. If all computers “went extinct,” the effect on the environment would be negligible compared to what would happen if most pollinators did.
Kempes and Krakauer’s approach sounds like one of those ideas that is better explored in a conference workshop than used for definitions or enacted into law. The paper is open access.
You may also wish to read: Scientists try to understand how one-celled life forms learn. Artificial intelligence may offer a model for learning without a brain.
MIND MATTERS NEWS
Breaking and noteworthy news from the exciting world of natural and artificial intelligence at MindMatters.ai.
Tuesday, December 28, 2021
CTHULHU STUDIES
A Weird Paper Tests The Limits of Science by Claiming Octopuses Came From Space
A summary of decades of research on a rather 'out-there' idea involving viruses from space raises questions on just how scientific we can be when it comes to speculating on the history of life on Earth.
It's easy to throw around words like crackpot, rogue, and maverick in describing the scientific fringe, but then papers like this one, from 2018, come along and leave us blinking owlishly, unsure of where to even begin.
A total of 33 names were listed as authors on this review, which was published by Progress in Biophysics and Molecular Biology back in August 2018. The journal is peer reviewed and fairly well cited. So it's not exactly small, or a niche pay-for-publish source.
Science writer Stephen Fleischfresser goes into depth on the background of two of the better known scientists involved: Edward Steele and Chandra Wickramasinghe. It's well worth a read.
For a tl;dr version, Steele is an immunologist who has a fringe reputation for his views on evolution that relies on acquiring gene changes determined by the influence of the environment rather than random mutations, in what he calls meta-Lamarckism.
Wickramasinghe, on the other hand, has had a somewhat less controversial career, recognized for empirically confirming Sir Fred Hoyle's hypothesis describing the production of complex carbon molecules on interstellar dust.
Wickramasinghe and Hoyle also happened to be responsible for another space biology thesis. Only this one is based on more than just the origins of organic chemistry.
The Hoyle Wickramasinghe (H-W) thesis of Cometary (Cosmic) Biology makes the rather simple claim that the direction of evolution has been significantly affected by biochemistry that didn't start on our planet.
In Wickramasinghe's own words, "Comets are the carriers and distributors of life in the cosmos, and life on Earth arose and developed as a result of cometary inputs."
Those inputs, Wickramasinghe argued, aren't limited to a generous sprinkling of space-baked amino acids, either.
Rather, they include viruses that insert themselves into organisms, pushing their evolution into whole new directions.
The report, titled "Cause of Cambrian Explosion – Terrestrial or Cosmic?", pulls on existing research to conclude that a rain of extra-terrestrial retroviruses played a key role in the diversification of life in our oceans roughly half a billion years ago.
"Thus retroviruses and other viruses hypothesized to be liberated in cometary debris trails both can potentially add new DNA sequences to terrestrial genomes and drive further mutagenic change within somatic and germline genomes," the authors wrote.
Let that sink in for a moment. And take a deep breath before continuing, because that was the tame part.
It was during this period that a group of mollusks known as cephalopods first stretched out their tentacles from beneath their shells, branching into a stunning array of sizes and shapes in what seemed like a remarkably short time frame.
The genetics of these organisms, which today include octopuses, squid, and cuttlefish, are as weird as the animals themselves, due in part to their ability to edit their DNA on the fly.
The authors of the paper make the rather audacious claim that these genetic oddities might be a sign of life from space.
Not of space viruses this time, but the arrival of whole genomes frozen in stasis before thawing out in our tepid waters.
"Thus the possibility that cryopreserved squid and/or octopus eggs, arrived in icy bolides several hundred million years ago should not be discounted," they wrote.
In his review of the paper, medical researcher Keith Baverstock from the University of Eastern Finland conceded that there's a lot of evidence that plausibly aligns with the H-W thesis, such as the curious timeline of the appearance of viruses.
But that's just not how science advances.
"I believe this paper justifies skepticism of the scientific value of stand alone theories of the origin of life," Baverstock argued at the time.
"The weight of plausible, but non-definitive, evidence, great though that might be, is not the point."
While the idea is as novel and exciting as it is provocative, nothing in the summary helps us better understand the history of life on Earth any better than existing conjectures, adding little of value to our model of evolution.
Still, with solid caveats in place, maybe science can cope with a generous dose of crazy every now and then.
Journal editor Denis Noble concedes that 'further research is needed', which is a bit of an understatement.
But given the developments regarding space-based organic chemistry in recent years, there's room for discussion.
"As space chemistry and biology grows in importance it is appropriate for a journal devoted to the interface between physics and biology to encourage the debates," said Noble.
"In the future, the ideas will surely become testable."
Just in case those tests confirm speculations, we recommend being well prepared for the return of our cephalopod overlords. Who knows when they'll want those eggs back?
A version of this article was first published in August 2018.
Thursday, November 18, 2021
Why is there something not nothing? The big bang isn’t the only answer
News Post || Tech News The idea that the universe started in the big bang revolutionised 20th-century cosmology. But it seems increasingly unlikely it was a case of something from nothing
17 November 2021 By Joshua Howgego Louis Koo/Getty Images
“NO QUESTION is more sublime than why there is a Universe: why there is anything rather than nothing,” philosopher Derek Parfit once wrote. Ads
Sublime it might be, but the question has traditionally exercised philosophers and theologians. Creation myths, a feature of many cultures, satisfied a deep-seated need for meaning and narrative drive in our existence (see “Why do we exist?”). Scientific thought, insofar as it paid attention to such matters, assumed the cosmos had always been there in an eternal, unchanging state.
Then came the greatest scientific revelation of the past century, arguably of all time: what came to be known as the big bang.
Its seeds were sown by Albert Einstein with general relativity, his theory of gravity, back in 1915, and by Edwin Hubble and others in the 1920s. Their astronomical measurements showed that far-off galaxies were receding from us, as if the universe were expanding.
As late as the 1940s, physicists including Hermann Bondi, Thomas Gold and Fred Hoyle were explaining these observations in terms of an eternal, steady state universe that expanded through the continuous creation of matter. Today, we can cross this possibility off the list.
That is partly because it is hard to square with the way gravity works, only pulling inwards, not pushing outwards. But it is mainly down to the discovery of the cosmic microwave background radiation in the 1960s. This all-pervasive radiation was exactly what you would expect to see …
Why Johannes Kepler is a scientist’s best role model
When people pick the greatest scientist of all-time, Newton and Einstein always come up. Perhaps they should name Johannes Kepler, instead.
Johannes Kepler, whose life spanned from the late 1500s to the early 1600s, was perhaps most remarkable as a scientist for his discovery that planets moved in ellipses around the Sun. Without the ability to throw out his own brilliant idea, he never could've gotten there. (Credits: August Köhler/public domain (L); Datumizer/Wikimedia Commons (R)
KEY TAKEAWAYS
The annals of history are filled with scientists who had incredible, revolutionary ideas, sought out and found the evidence to support them, and initiated a scientific revolution.
But much rarer is someone who has a brilliant idea, discovers that the evidence doesn't quite fit, and instead of doggedly pursuing it, tosses it aside in favor of a newer, better, more successful idea.
That's exactly what separates Johannes Kepler from all of the other great scientists throughout history, and why, if we have to choose a scientific role model, we should admire him so thoroughly.
For a great many people in the world, the three hardest words to say are simply, “I was wrong.” Even if the evidence is overwhelmingly decisive that your idea or conception is unsupported, most people will instead find a way to discount or ignore that evidence and stick to their guns. People’s minds are notoriously resistant to change, and the greater their own personal stake in the outcome of the issue under debate, the less open they are to even the possibility that they might be mistaken.
Although it’s often asserted that science is the exception to this general rule, that’s only true of science as a collective enterprise. On an individual basis, scientists are just as susceptible to confirmation bias — overweighting the supporting evidence and discounting the evidence to the contrary — as anyone in any other walk of life. In particular, the greatest difficulties await those who themselves have formulated ideas and invested tremendous efforts, often amounting to years or even decades of time, in hypotheses that simply cannot explain the full suite of data that humanity has amassed. This applies even to the greatest minds in all of history.Albert Einstein could never accept quantum indeterminism as a fundamental property of nature.
Arthur Eddington could never accept quantum degeneracy as a source for holding white dwarfs up against gravitational collapse.
Newton could never accept the experiments that demonstrated the wave nature of light, including interference and diffraction.
And Fred Hoyle could never accept the Big Bang as the correct story of our cosmic origins, even nearly 40 years after the critical evidence, in the form of the Cosmic Microwave Background, was discovered.
But one person stands above the rest as an exemplar for how to behave when the evidence comes in against your brilliant idea: Johannes Kepler, who showed us the way more than 400 years ago. Here’s the story of his scientific evolution, an example we should all strive to emulate.
This chart, from around 1660, shows the signs of the zodiac and a model of the solar system with Earth at the centre. For decades or even centuries after Kepler clearly demonstrated that not only is the heliocentric model valid, but that planets move in ellipses around the Sun, many refused to accept it, instead hearkening back to the ancient idea of Ptolemy and geocentrism.
(Credit: Johannes Van Loon, Andreas Cellarius Harmonia Macrocosmica, 1660/61)
For thousands of years, humans assumed that the Earth was a static, stable, and unchanging point in the Universe, and that all the heavens literally moved around us. Observations seemed to support this: there was no detectable motion occurring on our surface that supported an Earth that either rotated on its axis or revolved around the Sun through space. Instead, there were three key observations that had been made that helped people determine what our best model of the Universe would be.
The entire sky appeared to rotate a full 360 degrees over the course of 24 hours, most evident at night, as the stars rotated about either the northern or southern celestial pole.
The stars themselves appeared to remain fixed in their relative position to one another from night-to-night and even over much longer timescales.
However, there were a few objects that did move relative to one another from night-to-night or day-to-day: the planets, or “wanderers” of the sky.
Additionally, the Sun and Moon shifted in the night as well, as did the entire canopy of stars over longer periods of time. However, it was the first observation that led to the static, stable, unchanging conception of the Universe.
This timelapse view of the night sky from Hyatt Lake shows the sky as it appeared just after the summer solstice on June 21, 2020. The apparent motion of the objects in Earth’s sky could either be explained by the Earth rotating beneath our feet or by the heavens above rotating about a fixed Earth. Simply by watching the skies, we cannot tell these two explanations apart.
(Credit: Bureau of Land Management OR & WA/Kyle Sullivan)
Think about the above observation: that everything in the sky appears to rotate a full 360 degrees over the span of a full day. This could be caused by one of two potential explanations. Either the Earth itself was rotating about some axis, and that our world completed a full rotation once per 24 hours, or the Earth was stationary and everything in the heavens was rotating around it, also once per 24 hours.
How, physically, could we tell these two situations apart? The answers were twofold.
First, it should be possible, if the Earth were rotating, to note a curved trajectory to falling objects. The higher they fell from, the greater the curve would be. Yet no curve was ever observed; in fact this effect wouldn’t be measured until the demonstration of the Foucault pendulum in the 19th century.
Second, a rotating Earth would lead to a difference in the relative positions of the stars from dusk until dawn. The Earth was big, and its diameter had been measured precisely by Eratosthenes in the 3rd century B.C.E., so if any of the stars were closer than most of them, a parallax would appear: similar to holding your thumb out and watching it shift relative to the background as you alternated which eye you used to view it. But no parallax could be seen; in fact this wouldn’t be observed until the 19th century as well!
The stars that are closest to Earth will appear to shift periodically with respect to the more distant stars as the Earth moves through space in orbit around the Sun. Before the heliocentric model was established, we weren’t looking for “shifts” with a ~300,000,000 kilometer baseline over the span of ~6 months, but rather a ~12,000 kilometer baseline over the span of one night: Earth’s diameter as it rotated on its axis.(Credit: ESA/ATG medialab)
It’s easy to see, based on what we knew and could observe at the time, how we’d conclude that the Earth was static and fixed, while the heavenly bodies all moved around us.
Then, there were those additional observations that required an explanation: why did the stars remain fixed relative to one another while the planets appeared to “wander” through the sky?
It was quickly modeled that the planets, as well as the Sun and the Moon, must be closer to Earth than the stars were, and that these bodies must be in motion relative to one another.
With a fixed, static Earth, that meant that it must be the planets themselves that were in motion. The motion must have been incredibly complex, however. While the planets overwhelmingly appeared to move in one direction relative to the backdrop of stars on a night-to-night basis, every once in a while, the planets would:slow down in their usual motion, come to a complete stop, reverse their motion to move opposite their original direction (a phenomenon known as retrograde motion), would then slow and stop again, and finally would continue on in their normal (prograde) direction of motion.
This phenomenon was the most challenging aspect of planetary motion to model and understand.
Mars, like most planets, normally migrates very slowly across the sky in one predominant direction. However, a little less than once a year, Mars will appear to slow down in its migration across the sky, stop, reverse directions, speed up and slow down, and then stop again, resuming its original motion. This retrograde (west-to-east) period stands in contrast to Mars’s normal prograde (east-to-west) motion.(Credit: E. Siegel/Stellarium)
The prevailing assumption, since the Earth had already been deemed to be static, was that the planets themselves each typically moved in circular paths around the Earth, but atop those circles were smaller circles known as “epicycles” that they moved about as well. When the motion through the smaller circle proceeded in the opposite direction from the main motion through the larger circle, the planet would appear to reverse course for a brief while: a period of retrograde motion. Once the two motions lined up in the same direction again, prograde motion would resume.
Although epicycles did not start with Ptolemy — with whose name they are now synonymous — Ptolemy did make the best, most successful model of the Solar System that incorporated epicycles. In his model, the following occurred.Each planet’s orbit was dominated by a “great circle” that it moved along, moving around the Earth. Atop each great circle, a smaller circle (an epicycle) existed, with the planet moving along the outskirts of that small circle, with the center of the small circle always moving along the larger one. And the Earth, rather than being at the center of the great circle, was offset from that center by a particular amount, with the specific amount differing for each planet.
That was the Ptolemaic theory of epicyclic motion, leading to a geocentric model of the Solar System.
One of the great puzzles of the 1500s was how planets moved in an apparently retrograde fashion. This could either be explained through Ptolemy’s geocentric model (L), or Copernicus’ heliocentric one (R). However, getting the details right to arbitrary precision was something that would require theoretical advances in our understanding of the rules underlying the observed phenomena, which led to Kepler’s laws and eventually Newton’s theory of universal gravitation.(Credit: E. Siegel/Beyond the Galaxy)
Going all the way back to ancient times, there was some evidence — from Archimedes and Aristarchus, among others — that a Sun-centered model for planetary motion was considered. But once again, the lack of any detectable motion for the Earth or of any detectable parallax for the stars failed to provide the corroborating evidence. The idea languished in obscurity for centuries, but was finally revived in the 16th century by Nicolaus Copernicus.
The great idea of Copernicus was that if the planets moved in circles around the Sun, then during most times, the inner planets would orbit more quickly than the outer ones. From the perspective of any one planet, the others would appear to migrate relative to the fixed stars. But whenever an inner planet passed by and overtook an outer planet, then retrograde motion would occur, as the normal apparent direction-of-motion would appear to reverse.
Copernicus realized this and put forth his theory of a Sun-centered Solar System, or a heliocentric (rather than geocentric) one, offering it up as an exciting and possibly superior alternative to Ptolemy’s older Earth-centered model
. This simulation of the Solar System over the duration of one Earth-year shows the innermost planet, Mercury, “overtaking” the Earth from an interior orbit three independent times during the year. With Mercury’s orbital period of just 88 days, three or four retrograde periods exist every year for Mercury: the only planet annually with more than one. The outer planets, by contrast, experience retrograde only when Earth overtakes them: roughly once per year for all planets except Mars, which experiences them less frequently.(Credit: dynamicdiagrams.com, 2011, now defunct)
But in science, we always have to follow the evidence, even if we loathe the path it leads us down. It’s not aesthetics, elegance, naturalness, or personal preference that decides the issue, but rather the success of the model in predicting what can be observed. Leveraging circular orbits for both the Ptolemaic and the Copernican models, Copernicus was frustrated to discover that his model gave less successful predictions when compared against Ptolemy’s. The only way Copernicus could devise to equal Ptolemy’s successes, in fact, relied on employing the same ad hoc fix: by adding epicycles, or small circles, atop his planetary orbits!
In the decades following Copernicus, others took interest in the Solar System. Tycho Brahe, for example, constructed the best naked eye astronomy setup in history, measuring the planets as precisely as human vision allows: to within one arc-minute (1/60th of a degree) during every night that planets were visible towards the end of the 1500s. His assistant, Johannes Kepler, attempted to make a glorious, beautiful model that fit the data precisely.
Given that there were six known planets (if you included the Earth as one of them), and exactly five (and only five) perfect polyhedral solids — the tetrahedron, cube, octahedron, icosahedron, and dodecahedron — Kepler constructed a system of nested spheres called the Mysterium Cosmographicum
. Kepler’s original model of the Solar System, the Mysterium Cosmographicum, consisted of the 5 Platonic solids defining the relative radii of 6 spheres, with the planets orbiting around the circumferences of those spheres. As beautiful as this is, it couldn’t describe the Solar System as well as ellipses could, or even as well as Ptolemy’s model could.(Credit: Johannes Kepler, 1597)
In this model, each planet orbited along a circle defined by the circumference of one of the spheres. Outside of it, one of the five Platonic solids was circumscribed, with the sphere touching each of the faces in one spot. Outside of that solid, another sphere was circumscribed, with the sphere touching each of the solid’s vertices, with the circumference of that sphere defining the orbit of the next planet out. With six spheres, six planets, and five solids, Kepler made this model where “invisible spheres” held up the Solar System, accounting for the orbits of each of Mercury, Venus, Earth, Mars, Jupiter, and Saturn.
Kepler formulated this model in the 1590s, and Brahe boasted that only his observations could put such a model to the test. But no matter how Kepler did his calculations, not only did disagreements with observation remain, but Ptolemy’s geocentric model still made superior predictions.
In the face of this, what do you think Kepler did?Did he tweak his model, attempting to save it? Did he distrust the critical observations, demanding new, superior ones? Did he make additional postulates that could explain what was truly occurring, even if it was unseen, in the context of his model?
No. Kepler did none of these. Instead, he did something revolutionary: he put his own ideas and his own favored model aside, and looked at the data to see if there was a better explanation that could be derived from demanding that any model needed to agree with the full suite of observational data. Kepler’s second law states that planets sweep out equal areas, using the Sun as one focus, in equal times, regardless of other parameters. The same (blue) area is swept out in a fixed time period. The green arrow is velocity. The purple arrow directed towards the Sun is the acceleration. Planets move in ellipses around the Sun (Kepler’s first law), sweep out equal areas in equal times (his second law), and have periods proportional to their semimajor axis raised to the 3/2 power (his 3rd law).
(Credit: Gonfer/Wikimedia Commons, using Mathematica)
If only we could all be so brave, so brilliant, and at the same time, so humble before the Universe itself! Kepler calculated that ellipses, not circles, would better fit the data that Brahe had so painstakingly acquired. Although it defied his intuition, his common sense, and even his personal preferences for how he felt the Universe ought to have behaved — indeed, he thought that the Mysterium Cosmographicum was a divine epiphany that had revealed God’s geometrical plan for the Universe to him — Kepler was successfully able to abandon his notion of “circles and spheres” and instead used what seemed to him to be an imperfect solution: ellipses.
It cannot be emphasized enough what an achievement this is for science. Yes, there are many reasons to be critical of Kepler. He continued to promote his Mysterium Cosmographicum even though it was clear ellipses fit the data better. He continued to mix astronomy with astrology, becoming the most famous astrologer of his time. And he continued the long tradition of apologetics: claiming that ancient texts meant the opposite of what they said in order to reconcile the acceptability of the new knowledge that had emerged.
But it was through this revolutionary action, of abandoning his model for a new one that he himself devised to explain the observations more successfully than ever before, that Kepler’s laws of motion became elevated to scientific canon.
Tycho Brahe conducted some of the best observations of Mars prior to the invention of the telescope, and Kepler’s work largely leveraged that data. Here, Brahe’s observations of Mars’s orbit, particularly during retrograde episodes, provided an exquisite confirmation of Kepler’s elliptical orbit theory.(Credit: Wayne Pafko)
Even today, more than four full centuries after Kepler, we all learn his three laws of planetary motion in schools.Planets move in ellipses around the Sun, with the Sun at one of the ellipse’s two focal points. Planets sweep out equal areas, with the Sun at once focus, in equal amounts of time. And planets orbit in time periods proportional to their semimajor axes (half of the longest-axis of the ellipse) to the 3/2 power.
These were the first calculations that advanced the science of astronomy beyond the stagnated realm of Ptolemy, and they paved the way for Newton’s theory of universal gravitation, which transformed these laws from simple descriptions of how motion occurred to one that was physically motivated. By the end of the 17th century, all of Kepler’s laws could be derived simply from the laws of Newtonian gravity.
But the greatest achievement of all was the day Kepler put his own idea of a Mysterium Cosmographicum — an idea that he was arguably more emotionally attached to than any other — in order to follow the data, wherever it led him. That brought him to elliptical orbits for the planets, which kicked off the revolution in our understanding the physical universe around us, i.e., the modern sciences of physics and astronomy, that continues to the present day. Like all scientific heroes, Kepler certainly had his faults, but the ability to admit when you’re wrong, to reject your insufficient ideas, and to follow the data wherever it leads are traits we should all aspire to. Not only in science, of course, but in all aspects of our lives.
Monday, September 06, 2021
AFTER ALL THEY ORIGINATED IN SPACE
Viruses may exist ‘elsewhere in the universe’, warns scientist
The Covid pandemic has already turned life as we know it upside down – and no doubt prompted some people to want to leave the planet.
Now a leading scientist has warned that viruses may not only be found on Earth, but might occur – should life exist – elsewhere in the universe.
Prof Paul Davies, an astrobiologist, cosmologist and director of the Beyond Center for Fundamental Concepts in Science at Arizona State University, said that the idea of aliens ranges from microbial life to super advanced civilisations that might be signalling to us.
But Davies backed the idea that a wide range of microbes and other microscopic agents would probably be needed to support life as a whole, whatever form it takes. And it seems viruses – or something that performs a similar role – could be part of the equation.
“Viruses actually form part of the web of life,” said Davies. “I would expect that if you’ve got microbial life on another planet, you’re bound to have – if it’s going to be sustainable and sustained – the full complexity and robustness that will go with being able to exchange genetic information.”
Viruses, said Davies, can be thought of as mobile, genetic elements. Indeed, a number of studies have suggested genetic material from viruses has been incorporated into the genomes of humans and other animals by a process known as horizontal gene transfer.
“A friend of mine thinks most, but certainly a significant fraction, of the human genome is actually of viral origin,” said Davies, whose new book, What’s Eating the Universe?, was published last week.
According to Davies, while the importance of microbes to life is well known, the role of viruses is less widely appreciated. But he said if there is cellular life on other worlds, viruses or something similar, would probably exist to transfer genetic information between them.
What’s more, he said, it is unlikely alien life would be homogenous.
“I don’t think it’s a matter that you go to some other planet, and there will just be you one type of microbe and it’s perfectly happy. I think it’s got to be a whole ecosystem,” he added.
While the thought of extraterrestrial viruses may seem alarming, Davies suggests there is no need for humans to panic.
“The dangerous viruses are those that are very closely adapted to their hosts,” he said. “If there is a truly alien virus, then chances are it wouldn’t be remotely dangerous.”
Davies’ comments come after a study, published in late August, suggested that signs of life may be detected beyond our solar system within two to three years.
But the need to consider entire ecosystems does not only apply when considering alien life.
Davies – whose conversation is peppered with nods to former colleagues and associates from Stephen Hawking to Fred Hoyle, the great if unconventional former director of the Institute of Astronomy at Cambridge University – said it is also important should humans attempt to colonise another planet.
“Most people think about, well, we would need to have very large spacecraft, and then sort of recycle things for the very long journey, and then all the technology you’d need to take,” he said.
“Actually, the toughest part of this problem is what would be the microbiology that you’d have to take – it’s no good just taking a few pigs and potatoes and things like that and hoping when you get to the other end it’ll all be wonderful and self sustainable.” Safe space: the cosmic importance of planetary quarantine – podcast
While Covid has left most of us with a dim view of viruses, Davies said they are not all bad. “In fact, mostly, they’re good,” he said.
“We hear about the microbiome inside us, and there’s a planetary microbiome,” said Davies. But, he argues there is also a human and planetaryvirome, with viruses playing a fundamental role in nature.
“I think without viruses, there may be no sustained life on planet Earth,” he said.
Does human consciousness exist separate from matter, or is it embodied in the body –a critical player in anything that has to do with mind? “We are not thinking machines that feel; rather, we are feeling machines that think.” answers neuroscientist Antonio Damasio, who pioneered the field of embodied consciousness –the bodily origins of our sense of self. “We may smile and the dog may wag the tail, but in essence,” he says. “we have a set program and those programs are similar across individuals in the species. There is no such thing as a disembodied mind.”
Consciousness is considered by leading scientists as the central unsolved mystery of the 21st Century: “I have a much easier time imagining how we understand the Big Bang than I have imagining how we can understand consciousness,” says Edward Witten, theoretical physicist at the Institute for Advanced Study in Princeton, New Jersey who has been compared to Isaac Newton and Einstein about the phenomena that has been described as assuming the role spacetime did before Einstein invented his theory of relativity.
Some scientists have asked how can we be sure that the source of consciousness lies within our bodies at all? One popular, if mystical, idea, writes astrophysicist Paul Davies in The Demon in the Machine, “is that flashes of mathematical inspiration can occur by the mathematician’s mind somehow ‘breaking through’ into a Platonic realm of mathematical forms and relationships that not only lies beyond the brain but beyond space and time altogether.”
The English astronomer, Fred Hoyle, infamous for his rejection of the Big Bang theory, suggested an even more radical hypothesis: that quantum effects in the human brain leave open the possibility of a “superintelligence in the cosmic future using a subtle but well-known backwards-in-time property of quantum mechanics in order to steer scientific progress.” Four billion years ago, writes Damasio, in The Strange Order of Things: Life, Feeling, and the Making of the Cultural Mind, “the first primitive organisms monitored changes in their bodily state – equivalent to hunger, thirst, pain and so on – and had feedback mechanisms to maintain equilibrium. The relic of those primitive mechanisms is our autonomic nervous system, which controls bodily functions such as heartbeat and digestion, and of which we are largely unconscious.
Then, about half a billion years ago, the central nervous system, featuring a brain, evolved an afterthought of nature,” says Damasio who a proposes three layered theory of consciousness based on a hierarchy of stages, with each stage building upon the last. The most basic representation of the organism is referred to as the Protoself, next is Core Consciousness, and finally, Extended Consciousness.
Damasio, who is an internationally recognized leader in neuroscience, was educated at the University of Lisbon and currently directs the University of Southern California Brain and Creativity Institute. The human brain, he argues, became the “anchor” of what had once been a more distributed mind. Changes in bodily state were projected onto the brain and experienced as emotions or drives – the emotion of fear, say, or the drive to eat. Subjectivity evolved later again, he argues. “It was imposed by the musculoskeletal system, which evolved as a physical framework for the central nervous system and, in so doing, also provided a stable frame of reference: the unified ‘I’ of conscious experience.”
Life was regulated at first without feelings of any sort; here was no mind and no consciousness.
“There was,” Damasio writes, “a set of homeostatic mechanisms blindly making the choices that would turn out to be more conducive to survival. The arrival of nervous systems, capable of mapping and image making, opened the way for simple minds to enter the scene. During the Cambrian explosion, after numerous mutations, certain creatures with nervous systems would have generated not just images of the world around them but also an imagetic counterpart to the busy process of life regulation that was going on underneath. This would have been the ground for a corresponding mental state, the thematic content of which would have been valenced in tune with the condition of life, at that moment, in that body. The quality of the ongoing life state would have been felt.”
Enter Sarah Garfinkel, at the University of Sussex, UK, who joins Damasio in arguing that our thoughts, feelings and behaviors are shaped in part by the internal signals that arise from our body. But, she reports in New Scientist: “it goes beyond that. It is leading her and others to a surprising conclusion: that the body helps to generate our sense of self and is a key part of consciousness. This idea has practical implications in assessing people who show little sign of consciousness. It may also force us to reconsider where we draw the line between life and death, and provide a new insight into how consciousness evolved.”
Since 2000, concludes Damasio, “I have been defending the idea that the body is a critical player in anything that has to do with mind.”
The Daily Galaxy, Max Goldberg, via New Scientist and Antonio R. Damasio, Descartes Error and the Strange Order of Things: Life, Feeling, and the Making of the Cultural Mind and Paul Davies, The Demon in the Machine –All Kindle editions
Image credit: Shutterstock License
Friday, July 25, 2025
SPACE/COSMOS
The evolution of life may have its origins in outer space
Astronomers find signs of complex organic molecules – precursors to sugars and amino acids – in a planet-forming disc.
This artist’s impression shows the planet-forming disc around the star V883 Orionis. In the outermost part of the disc, volatile gases are frozen out as ice, which contains complex organic molecules. An outburst of energy from the star heats the inner disc to a temperature that evaporates the ice and releases the complex molecules, enabling astronomers to detect it.
The inset image shows the chemical structure of complex organic molecules detected and presumed in the protoplanetary disc (from left to right): propionitrile (ethyl cyanide), glycolonitrile, alanine, glycine, ethylene glycol, and acetonitrile (methyl cyanide).
Using the Atacama Large Millimeter/submillimeter Array (ALMA), a team of astronomers led by Abubakar Fadul from the Max Planck Institute for Astronomy (MPIA) has discovered complex organic molecules – including the first tentative detection of ethylene glycol and glycolonitrile – in the protoplanetary disc of the outbursting protostar V883 Orionis. These compounds are considered precursors to the building blocks of life. Comparing different cosmic environments reveals that the abundance and complexity of such molecules increase from star-forming regions to fully evolved planetary systems. This suggests that the seeds of life are assembled in space and are widespread. The findings were published in the Astrophysical Journal Letters today.
Astronomers have discovered complex organic molecules (COMs) in various locations associated with planet and star formation before. COMs are molecules with more than five atoms, at least one of which is carbon. Many of them are considered building blocks of life, such as amino acids and nucleic acids or their precursors. The discovery of 17 COMs in the protoplanetary disc of V883 Orionis, including ethylene glycol and glycolonitrile, provides a long-sought puzzle piece in the evolution of such molecules between the stages preceding and following the formation of stars and their planet-forming discs. Glycolonitrile is a precursor of the amino acids glycine and alanine, as well as the nucleobase adenine.
The assembly of prebiotic molecules begins in interstellar space
“Our finding points to a straight line of chemical enrichment and increasing complexity between interstellar clouds and fully evolved planetary systems.” – Abubakar Fadul, MPIA
The transition from a cold protostar to a young star surrounded by a disc of dust and gas is accompanied by a violent phase of shocked gas, intense radiation and rapid gas ejection.
Such energetic processes might destroy most of the complex chemistry assembled during the previous stages. Therefore, scientists had laid out a so-called ‘reset’ scenario, in which most of the chemical compounds required to evolve into life would have to be reproduced in circumstellar discs while forming comets, asteroids, and planets.
“Now it appears the opposite is true,” MPIA scientist and co-author Kamber Schwarz points out. “Our results suggest that protoplanetary discs inherit complex molecules from earlier stages, and the formation of complex molecules can continue during the protoplanetary disc stage.” Indeed, the period between the energetic protostellar phase and the establishment of a protoplanetary disk would, on its own, be too short for COMs to form in detectable amounts.
As a result, the conditions that predefine biological processes may be widespread rather than being restricted to individual planetary systems.
Astronomers have found the simplest organic molecules, such as methanol, in dense regions of dust and gas that predate the formation of stars. Under favourable conditions, they may even contain complex compounds comprising ethylene glycol, one of the species now discovered in V883 Orionis. “We recently found ethylene glycol could form by UV irradiation of ethanolamine, a molecule that was recently discovered in space,” adds Tushar Suhasaria, a co-author and the head of MPIA’s Origins of Life Lab. “This finding supports the idea that ethylene glycol could form in those environments but also in later stages of molecular evolution, where UV irradiation is dominant.”
More evolved agents crucial to biology, such as amino acids, sugars, and nucleobases that make up DNA and RNA, are present in asteroids, meteorites, and comets within the Solar System.
Buried in ice – resurfaced by stars
The chemical reactions that synthesize those COMs occur under cold conditions, preferably on icy dust grains that later coagulate to form larger objects. Hidden in those mixtures of rock, dust, and ice, they usually remain undetected. Accessing those molecules is only possible either by digging for them with space probes or by external heating, which evaporates the ice.
In the Solar System, the Sun heats comets, resulting in impressive tails of gas and dust, or comas, essentially gaseous envelopes that surround the cometary nuclei. This way, spectroscopy – the rainbow-like dissection of light – may pick up the emissions of freed molecules. Those spectral fingerprints help astronomers to identify the molecules previously buried in ice.
A similar heating process is occurring in the V883 Orionis system. The central star is still growing by accumulating gas from the surrounding disc until it eventually ignites the fusion fire in its core. During those growth periods, the infalling gas heats up and produces intense outbursts of radiation. “These outbursts are strong enough to heat the surrounding disc as far as otherwise icy environments, releasing the chemicals we have detected,” explains Fadul.
“Complex molecules, including ethylene glycol and glycolonitrile, radiate at radio frequencies. ALMA is perfectly suited to detect those signals,” says Schwarz. The MPIA astronomers were awarded access to this radio interferometer through the European Southern Observatory (ESO), which operates it in the Chilean Atacama Desert at an altitude of 5,000 metres. ALMA enabled the astronomers to pinpoint the V883 Orionis system and search for faint spectral signatures, which ultimately led to the detections.
Further challenges ahead
“While this result is exciting, we still haven't disentangled all the signatures we found in our spectra,” says Schwarz. “Higher resolution data will confirm the detections of ethylene glycol and glycolonitril and maybe even reveal more complex chemicals we simply haven't identified yet.”
“Perhaps we also need to look at other regions of the electromagnetic spectrum to find even more evolved molecules,” Fadul points out. “Who knows what else we might discover?”
Additional information
The MPIA team involved in this study comprised Abubakar Fadul, Kamber Schwarz, and Tushar Suhasaria.
Other researchers were Jenny K. Calahan (Center for Astrophysics — Harvard & Smithsonian, Cambridge, USA), Jane Huang (Department of Astronomy, Columbia University, New York, USA), and Merel L. R. van ’t Hoff (Department of Physics and Astronomy, Purdue University, West Lafayette, USA).
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning, and operation of ALMA.
Astronomers at MIT, Columbia University, and elsewhere have used NASA’s James Webb Space Telescope to peer through the dust of nearby galaxies and into the aftermath of a black hole’s stellar feast.
Astronomers at MIT, Columbia University, and elsewhere have used NASA’s James Webb Space Telescope (JWST) to peer through the dust of nearby galaxies and into the aftermath of a black hole’s stellar feast.
In a study appearing today in Astrophysical Journal Letters, the researchers report that for the first time, JWST has observed several tidal disruption events — instances when a galaxy’s central black hole draws in a nearby star and whips up tidal forces that tear the star to shreds, giving off an enormous burst of energy in the process.
Scientists have observed about 100 tidal disruption events (TDEs) since the 1990s, mostly as X-ray or optical light that flashes across relatively dust-free galaxies. But as MIT researchers recently reported, there may be many more star-shredding events in the universe that are “hiding” in dustier, gas-veiled galaxies.
In their previous work, the team found that most of the X-ray and optical light that a TDE gives off can be obscured by a galaxy’s dust, and therefore can go unseen by traditional X-ray and optical telescopes. But that same burst of light can heat up the surrounding dust and generate a new signal, in the form of infrared light.
Now, the same researchers have used JWST — the world’s most powerful infrared detector — to study signals from four dusty galaxies where they suspect tidal disruption events have occurred. Within the dust, JWST detected clear fingerprints of black hole accretion, a process by which material, such as stellar debris, circles and eventually falls into a black hole. The telescope also detected patterns that are strikingly different from the dust that surrounds active galaxies, where the central black hole is constantly pulling in surrounding material.
Together, the observations confirm that a tidal disruption event did indeed occur in each of the four galaxies. What’s more, the researchers conclude that the four events were products of not active black holes but rather dormant ones, which experienced little to no activity until a star happened to pass by.
The new results highlight JWST’s potential to study in detail otherwise hidden tidal disruption events. They are also helping scientists to reveal key differences in the environments around active versus dormant black holes.
“These are the first JWST observations of tidal disruption events, and they look nothing like what we’ve ever seen before,” says lead author Megan Masterson, a graduate student in MIT’s Kavli Institute for Astrophysics and Space Research. “We’ve learned these are indeed powered by black hole accretion, and they don’t look like environments around normal active black holes. The fact that we’re now able to study what that dormant black hole environment actually looks like is an exciting aspect.”
The study’s MIT authors include Christos Panagiotou, Erin Kara, Anna-Christina Eilers, along with Kishalay De of Columbia University and collaborators from multiple other institutions.
Seeing the light
The new study expands on the team’s previous work using another infrared detector — NASA’s Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) mission. Using an algorithm developed by co-author Kishalay De of Columbia University, the team searched through a decade’s worth of data from the telescope, looking for infrared “transients,” or short peaks of infrared activity from otherwise quiet galaxies that could be signals of a black hole briefly waking up and feasting on a passing star. That search unearthed about a dozen signals that the group determined were likely produced by a tidal disruption event.
“With that study, we found these 12 sources that look just like TDEs,” Masterson says. “We made a lot of arguments about how the signals were very energetic, and the galaxies didn’t look like they were active before, so the signals must have been from a sudden TDE. But except for these little pieces, there was no direct evidence.”
With the much more sensitive capabilities of JWST, the researchers hoped to discern key “spectral lines,” or infrared light at specific wavelengths, that would be clear fingerprints of conditions associated with a tidal disruption event.
“With NEOWISE, it’s as if our eyes could only see red light or blue light, whereas with JWST, we’re seeing the full rainbow,” Masterson says.
A Bonafide signal
In their new work, the group looked specifically for a peak in infrared, that could only be produced by black hole accretion — a process by which material is drawn toward a black hole in a circulating disk of gas. This disk produces an enormous amount of radiation that is so intense that it can kick out electrons from individual atoms. In particular, such accretion processes can blast several electrons out from atoms of neon, and the resulting ion can transition, releasing infrared radiation at a very specific wavelength that JWST can detect.
“There’s nothing else in the universe that can excite this gas to these energies, except for black hole accretion,” Masterson says.
The researchers searched for this smoking-gun signal in four of the 12 TDE candidates they previously identified. The four signals include: the closest tidal disruption event detected to date, located in a galaxy some 130 million light years away; a TDE that also exhibits a burst of X-ray light; a signal that may have been produced by gas circulating at incredibly high speeds around a central black hole; and a signal that also included an optical flash, which scientists had previously suspected to be a supernova, or the collapse of a dying star, rather than tidal disruption event.
“These four signals were as close as we could get to a sure thing,” Masterson says. “But the JWST data helped us say definitively these are bonafide TDEs.”
When the team pointed JWST toward the galaxies of each of the four signals, in a program designed by De, they observed that the telltale spectral lines showed up in all four sources. These measurements confirmed that black hole accretion occurred in all four galaxies. But the question remained: Was this accretion a temporary feature, triggered by a tidal disruption and a black hole that briefly woke up to feast on a passing star? Or was this accretion a more permanent trait of “active” black holes that are always on? In the case of the latter, it would be less likely that a tidal disruption event had occurred.
To differentiate between the two possibilities, the team used the JWST data to detect another wavelength of infrared light, which indicates the presence of silicates, or dust in the galaxy. They then mapped this dust in each of the four galaxies and compared the patterns to those of active galaxies, which are known to harbor clumpy, donut-shaped dust clouds around the central black hole. Masterson observed that all four sources showed very different patterns compared to typical active galaxies, suggesting that the black hole at the center of each of the galaxies is not normally active, but dormant. If an accretion disk formed around such a black hole, the researchers conclude that it must have been a result of a tidal disruption event.
“Together, these observations say the only thing these flares could be are TDEs,” Masterson says.
She and her collaborators plan to uncover many more previously hidden tidal disruption events, with NEOWISE, JWST, and other infrared telescopes. With enough detections, they say TDEs can serve as effective probes of black hole properties. For instance, how much of a star is shredded, and how fast its debris is accreted and consumed, can reveal fundamental properties of a black hole, such as how massive it is and how fast it spins.
“The actual process of a black hole gobbling down all that stellar material takes a long time,” Masterson says. “It’s not an instantaneous process. And hopefully we can start to probe how long that process takes and what that environment looks like. No one knows because we just started discovering and studying these events.”
This research was supported, in part, by NASA.
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Written by Jennifer Chu, MIT News
Paper: “JWST’s First View of Tidal Disruption Events: Compact, Accretion-Driven Emission Lines & Strong Silicate Emission in an Infrared-selected Sample”
