BLOGS

Source: Same source for the Dark Matter definition below.

Topics: Astronomy, Astrophysics, Cosmology, Dark Matter, Einstein, General Relativity

Note: Your "secret decoder ring" for reading the Abstract.

Dark matter: It makes up about 85% of the universe, is invisible, and doesn't interact with matter except for gravitational effects. See: Center for Astrophysics, Harvard

"Tachyonic": Of, or referring to tachyons, (Greek for swift) theoretical particles that already travel faster-than-light and backward in time. Their rest mass, m₀ⁱ, is assumed to be imaginary. As it loses energy, it's assumed to become infinitely fast, so you can see why it's a favorite science fiction trope, along with dark matter, literally tableau rasas.

ΛCDM assumes that the universe is composed of photons, neutrinos, ordinary matter (baryons, electrons), and cold (non-relativistic) dark matter, which only interacts gravitationally, plus "dark energy," which is responsible for the observed acceleration in the Hubble expansion. Source: Goddard Spaceflight Center: Lambda

H₀ defines the Hubble constant, or, the rate at which the universe is expanding, determined by Hubble in the way back year of 1929 to be 500 km/s/Mpc. I'm going to defer to Wikipedia for this one.

km/s/Mpc = kilometers/second/megaparsec. Megaparsec is 1 million parsecs = 3,260,000 light years, or 3.26 x 10⁶ light years.

t₀ = the present age of the universe, t₀ = 2tH/3, where "tH" is the Hubble time. t₀ is roughly 13.7 × 10⁹ years, or 4.32 × 10¹⁷ seconds.

Gyr = giga years, or 1 billion years = 1 x 10⁹ years (a lot).

Abstract

An open or hyperbolic Friedmann-Robertson-Walker spacetime dominated by tachyonic dark matter can exhibit an “inflected” expansion—initially decelerating, later accelerating—similar but not identical to that of now-standard ΛCDM models dominated by dark energy. The features of the tachyonic model can be extracted by fitting the redshift-distance relation of the model to data obtained by treating Type Ia supernovae as standard candles. Here such a model is fitted to samples of 186 and 1048 Type Ia supernovae from the literature. The fits yield values of H₀ = (66.6±1.5) km/s/Mpc and H₀ = (69.6±0.4) km/s/Mpc, respectively, for the current-time Hubble parameter, and t₀ = (8.35 ± 0.68) Gyr and t₀ = (8.15 ± 0.36) Gyr, respectively, for the comoving-time age of the Universe. Tests of the model against other observations will be undertaken in subsequent works.

Subject headings: cosmology, dark matter, tachyons, distance-redshift relation, supernovae

Testing Tachyon-Dominated Cosmology with Type Ia Supernovae, Samuel H. Kramer, Ian H. Redmount, Physics arXiv

Credit: Menno Schaefer/Adobe

Starlings flock in a so-called murmuration, a collective behavior of interest in biological physics — one of many subfields that did not always “belong” in physics.

Topics: Applied Physics, Cosmology, Einstein, History, Physics, Research, Science

"To be rather than to seem." Translated from the Latin Esse Quam Videri, which also happens to be the state motto of North Carolina. It is from the treatise on Friendship by the Roman statesman Cicero, a reminder of the beauty and power of being true to oneself. Source: National Library of Medicine: Neurosurgery

If you’ve been in physics long enough, you’ve probably left a colloquium or seminar and thought to yourself, “That talk was interesting, but it wasn’t physics.”

If so, you’re one of many physicists who muse about the boundaries of their field, perhaps with colleagues over lunch. Usually, it’s all in good fun.

But what if the issue comes up when a physics faculty makes decisions about hiring or promoting individuals to build, expand, or even dismantle a research effort? The boundaries of a discipline bear directly on the opportunities departments can offer students. They also influence those students’ evolving identities as physicists, and on how they think about their own professional futures and the future of physics.

So, these debates — over physics and “not physics” — are important. But they are also not new. For more than a century, physicists have been drawing and redrawing the borders around the field, embracing and rejecting subfields along the way.

A key moment for “not physics” occurred in 1899 at the second-ever meeting of the American Physical Society. In his keynote address, the APS president Henry Rowland exhorted his colleagues to “cultivate the idea of the dignity” of physics.

“Much of the intellect of the country is still wasted in the pursuit of so-called practical science which ministers to our physical needs,” he scolded, “[and] not to investigations in the pure ethereal physics which our Society is formed to cultivate.”

Rowland’s elitism was not unique — a fact that first-rate physicists working at industrial laboratories discovered at APS meetings, when no one showed interest in the results of their research on optics, acoustics, and polymer science. It should come as no surprise that, between 1915 and 1930, physicists were among the leading organizers of the Optical Society of America (now Optica), the Acoustical Society of America, and the Society of Rheology.

That acousticians were given a cold shoulder at early APS meetings is particularly odd. At the time, acoustics research was not uncommon in American physics departments. Harvard University, for example, employed five professors who worked extensively in acoustics between 1919 and 1950. World War II motivated the U.S. Navy to sponsor a great deal of acoustics research, and many physics departments responded quickly. In 1948, the University of Texas hired three acousticians as assistant professors of physics. Brown University hired six physicists between 1942 and 1952, creating an acoustics powerhouse that ultimately trained 62 physics doctoral students.

The acoustics landscape at Harvard changed abruptly in 1946, when all teaching and research in the subject moved from the physics department to the newly created department of engineering sciences and applied physics. In the years after, almost all Ph.D. acoustics programs in the country migrated from physics departments to “not physics” departments.

The reason for this was explained by Cornell University professor Robert Fehr at a 1964 conference on acoustics education. Fehr pointed out that engineers like himself exploited the fundamental knowledge of acoustics learned from physicists to alter the environment for specific applications. Consequently, it made sense that research and teaching in acoustics passed from physics to engineering.

It took less than two decades for acoustics to go from being physics to “not physics.” But other fields have gone the opposite direction — a prime example being cosmology.

Albert Einstein applied his theory of general relativity to the cosmos in 1917. However, his work generated little interest because there was no empirical data to which it applied. Edwin Hubble’s work on extragalactic nebulae appeared in 1929, but for decades, there was little else to constrain mathematical speculations about the physical nature of the universe. The theoretical physicists Freeman Dyson and Steven Weinberg have both used the phrase “not respectable” to describe how cosmology was seen by physicists around 1960. The subject was simply “not physics.”

This began to change in 1965 with the discovery of thermal microwave radiation throughout the cosmos — empirical evidence of the nearly 20-year-old Big Bang model. Physicists began to engage with cosmology, and the percentage of U.S. physics departments with at least one professor who published in the field rose from 4% in 1964 to 15% in 1980. In the 1980s, physicists led the satellite mission to study the cosmic microwave radiation, and particle physicists — realizing that the hot early universe was an ideal laboratory to test their theories — became part-time cosmologists. Today, it’s hard to find a medium-to-large sized physics department that does not list cosmology as a research specialty.

Opinion: That's Not Physics, Andrew Zangwill, APS

A new image from the Event Horizon Telescope has revealed powerful magnetic fields spiraling from the edge of a supermassive black hole at the center of the Milky Way, Sagittarius A*.

Topics: Astrophysics, Black Holes, Cosmology, Einstein, General Relativity

Physicists have been confident since the 1980s that there is a supermassive black hole at the center of the Milky Way galaxy, similar to those thought to be at the center of most spiral and elliptical galaxies. It has since been dubbed Sagittarius A* (pronounced A-star), or SgrA* for short. The Event Horizon Telescope (EHT) captured the first image of SgrA* two years ago. Now the collaboration has revealed a new polarized image (above) showcasing the black hole's swirling magnetic fields. The technical details appear in two new papers published in The Astrophysical Journal Letters.

"The new picture of Sgr A* compared to the old one shows the advantages of using a paintbrush rather than a crayon," Maynooth University cosmologist Peter Coles said on BlueSky. The new image is also strikingly similar to another EHT polarized image of a larger supermassive black hole, M87*, so this might be something that all such black holes share.

The only way to "see" a black hole is to image the shadow created by light as it bends in response to the object's powerful gravitational field. As Ars Science Editor John Timmer reported in 2019, the EHT isn't a telescope in the traditional sense. Instead, it's a collection of telescopes scattered around the globe. The EHT is created by interferometry, which uses light in the microwave regime of the electromagnetic spectrum captured at different locations. These recorded images are combined and processed to build an image with a resolution similar to that of a telescope the size of the most distant locations. Interferometry has been used at facilities like ALMA (the Atacama Large Millimeter/submillimeter Array) in northern Chile, where telescopes can be spread across 16 km of desert.

Event Horizon Telescope captures stunning new image of Milky Way’s black hole, Jennifer Ouellette, Ars Technica.

A University of Minnesota Twin Cities-led team used a first-of-its-kind technique to measure the Universe's expansion rate, providing insight that could help more accurately determine the Universe’s age and help physicists and astronomers better understand the cosmos. Credit: NASA, ESA, and S. Rodney (JHU) and the FrontierSN team; T. Treu (UCLA), P. Kelly (UC Berkeley), and the GLASS team; J. Lotz (STScI) and the Frontier Fields team; M. Postman (STScI) and the CLASH team; and Z. Levay (STScI)

Topics: Astronomy, Astrophysics, Cosmology, General Relativity

Thanks to data from a magnified, multiply-imaged supernova, a team led by University of Minnesota Twin Cities researchers have successfully used a first-of-its-kind technique to measure the universe's expansion rate. Their data provide insight into a longstanding debate in the field and could help scientists more accurately determine the universe's age and better understand the cosmos.

The work is divided into two papers published in Science and The Astrophysical Journal.

In astronomy, there are two precise measurements of the expansion of the universe, also called the "Hubble constant." One is calculated from nearby observations of supernovae, and the second uses the "cosmic microwave background," or radiation that began to stream freely through the universe shortly after the Big Bang.

However, these two measurements differ by about 10 percent, which has caused widespread debate among physicists and astronomers. If both measurements are accurate, that means scientists' current theory about the makeup of the universe is incomplete.

"If new, independent measurements confirm this disagreement between the two measurements of the Hubble constant, it would become a chink in the armor of our understanding of the cosmos," said Patrick Kelly, lead author of both papers and an assistant professor in the University of Minnesota School of Physics and Astronomy.

First-of-its-kind measurement of the universe's expansion rate weighs in on a longstanding debate. University of Minnesota, Phys.org.

Images of six candidate massive galaxies, seen 500-800 million years after the Big Bang. One of the sources (bottom left) could contain as many stars as our present-day Milky Way but is 30 times more compact. Credit: NASA, ESA, CSA, I. Labbe (Swinburne University of Technology); Image processing: G. Brammer (Niels Bohr Institute’s Cosmic Dawn Center at the University of Copenhagen)

Topics: Astronomy, Astrophysics, Cosmology, Research

Nobody expected them. They were not supposed to be there. And now, nobody can explain how they had formed. 

Galaxies nearly as massive as the Milky Way and full of mature red stars seem to be dispersed in deep-field images obtained by the James Webb Space Telescope (Webb or JWST) during its early observation campaign. They are giving astronomers a headache. 

These galaxies, described in a new study based on Webb's first data release, are so far away that they appear only as tiny reddish dots to the powerful telescope. By analyzing the light emitted by these galaxies, astronomers established that they were viewing them in our universe's infancy, only 500 million to 700 million years after the Big Bang.

Such early galaxies are not in themselves surprising. Astronomers expected that the first star clusters sprung up shortly after the universe moved out of the so-called dark ages — the first 400 million years of its existence when only a thick fog of hydrogen atoms permeated space. 

But the galaxies found in the Webb images appeared shockingly big, and the stars in them were too old. The new findings are in conflict with existing ideas of how the universe looked and evolved in its early years and don't match earlier observations made by Webb's less powerful predecessor, the Hubble Space Telescope.

JWST Discovers Enormous Distant Galaxies That Should Not Exist, Tereza Pultarova, Scientific American/Space.com.

Numerical simulation of the neutron stars merging to form a black hole, with their accretion disks interacting to produce electromagnetic waves. Credit: L. Rezolla (AEI) & M. Koppitz (AEI & Zuse-Institut Berlin)

Topics: Black Holes, Cosmology, General Relativity, Gravity, Research

Scientists have advanced in discovering how to use ripples in space-time known as gravitational waves to peer back to the beginning of everything we know. The researchers say they can better understand the state of the cosmos shortly after the Big Bang by learning how these ripples in the fabric of the universe flow through planets and the gas between the galaxies.

"We can't see the early universe directly, but maybe we can see it indirectly if we look at how gravitational waves from that time have affected matter and radiation that we can observe today," said Deepen Garg, lead author of a paper reporting the results in the Journal of Cosmology and Astroparticle Physics. Garg is a graduate student in the Princeton Program in Plasma Physics, which is based at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL).

Garg and his advisor Ilya Dodin, who is affiliated with both Princeton University and PPPL, adapted this technique from their research into fusion energy, the process powering the sun and stars that scientists are developing to create electricity on Earth without emitting greenhouse gases or producing long-lived radioactive waste. Fusion scientists calculate how electromagnetic waves move through plasma, the soup of electrons and atomic nuclei that fuels fusion facilities known as tokamaks and stellarators.

Ripples in the fabric of the universe may reveal the start of time, Raphael Rosen, Princeton Plasma Physics Laboratory, Phys.org.

Rotation curve of the typical spiral galaxy M 33 (yellow and blue points with error bars) and the predicted one from the distribution of the visible matter (white line). The discrepancy between the two curves is accounted for by adding a dark matter halo surrounding the galaxy. Credit: Wikipedia

Topics: Astronomy, Astrophysics, Cosmology, Dark Matter

Although dark matter is central to the standard cosmological model, it's not without issues. There continue to be nagging mysteries about the stuff, not the least of which is the fact that scientists have found no direct particle evidence of it.

Despite numerous searches, we have yet to detect dark matter particles. Some astronomers favor an alternative, such as modified Newtonian dynamics (MoND) or the modified gravity model. And a new study of galactic rotation seems to support them.

The idea of MoND was inspired by galactic rotation. Most of the visible matter in a galaxy is clustered in the middle, so you'd expect that stars closer to the center would have faster orbital speeds than stars farther away, similar to the planets of our solar system. We observe that stars in a galaxy all rotate at about the same speed. The rotation curve is essentially flat rather than dropping off. The dark matter solution is that a halo of invisible matter surrounds galaxies, but in 1983 Mordehai Milgrom argued that our gravitational model must be wrong.

At interstellar distances, the gravitational attraction between stars is essentially Newtonian. So rather than modifying general relativity, Milgrom proposed modifying Newton's universal law of gravity. He argued that rather than the force of attraction as a pure inverse square relation, gravity has a small remnant pull regardless of distance. This remnant is only about ten trillionths of a G, but it's enough to explain galactic rotation curves.

New measurements of galaxy rotation lean toward modified gravity as an explanation for dark matter, Brian Koberlein, Universe Today/Phys.org.

The first direct image of the Milky Way's supermassive black hole shows an orange glowing ring — gas heated as it falls into the singularity — with the shadow of the black hole at the center. EHT Collaboration

Topics: Astrophysics, Black Holes, Cosmology, Einstein, General Relativity

In a triumph of observation and data processing, astronomers at the Event Horizon Telescope have captured the first-ever picture of the supermassive black hole at the center of the Milky Way Galaxy.

The black hole is named Sagittarius A* (pronounced “A-star”), and the reveal of its image received an international rollout this morning in simultaneous press conferences held by the National Science Foundation (NSF) at the National Press Club in Washington, D.C., and the European Southern Observatory headquarters in Garching, Germany.

The image represents 3.5 million gigabytes of data taken at millimeter wavelengths by eight radio telescopes around the world. “It took several years to refine our image and confirm what we had,” said Feryal Özel, an astronomer at the University of Arizona in Tucson, at the NSF press conference. “But we prevailed.”

Blackhole at the center of Milky Way imaged for the first time, Mark Zastrow, Astronomy

Figure 1: A cartoon showing the “self-lensing” of light by a supermassive black hole binary system. Jordy Davelaar and Zoltán Haiman of Columbia University predict that this effect could be used to study black hole binaries that are too far from Earth to probe with other techniques

Topics: Black Holes, Cosmology, Einstein, General Relativity

When galaxies collide, the central supermassive black holes that they contain begin to orbit each other. This supermassive black hole binary attracts gas, which flows through the system to form two disk-shaped structures, one around each of the supermassive black holes. The gas in these “minidisks” heats as it falls toward the holes and begins to radiate light. Astronomers have detected around 150 galaxies with candidate supermassive black hole binaries. And, as observations become more detailed, they expect the light from the minidisks in those systems to bear recognizable, time-dependent signatures from black hole distortions [1]. Now, Jordy Davelaar and Zoltán Haiman of Columbia University have theoretically tested how one such distortion—the “shadow” of the black hole—affects this light signature, finding that it causes a dip in the signal that should be observable in about 1% of candidate systems [2, 3]. The technique could allow astronomers to study black holes that are currently beyond the reach of conventional imaging methods (Fig. 1).

From gravitational-wave measurements of merging black holes to direct imaging of the plasma circling a black hole, the last decade has seen an explosion of observational evidence for black holes (see Viewpoint: The First Sounds of Merging Black Holes and News Feature: Black Hole Imaging Tests Einstein’s Limits) [4–6]. Yet despite these achievements, many questions remain about black holes, including a critical one: How do black holes grow to supermassive scales—millions to billions of times the mass of the Sun?

A black hole is a simple object, described by its mass, angular momentum, and electrical charge. Supermassive black holes are typically electrically neutral, so their mass and angular momentum parameters determine their gravitational fields. The gravitational field determines how the black holes bend light and thus how they appear to an observer on Earth. Light passing near the black hole is deflected by the gravitational field, producing a black hole shadow—a dark region that is often encircled by a bright light ring—whose size and shape come directly from the black hole’s mass and angular momentum.

Measuring a Black Hole Shadow, George N. Wong, APS Physics

A lone black hole gives off no light - but its gravity does distort the path of light traveling around it. Ute Kraus (background Milky Way panorama: Axel Mellinger), Institute of Physics, Universität Hildesheim

Topics: Astrophysics, Black Holes, Cosmology, Einstein, General Relativity

Each second, a brand new baby black hole is born somewhere in the cosmos as a massive star collapses under its own weight.

But black holes themselves are invisible. Historically, astronomers have only been able to detect these stellar-mass black holes when they are acting on a companion.

Now, a team of scientists has made the first-ever confirmed detection of a stellar-mass black hole that’s completely alone. The discovery opens up the possibility of finding even more — an exciting prospect, considering there should be around 100 million such “rogue” black holes drifting through our galaxy unseen.

Relying on the neighbors

Black holes are difficult to find because they don’t shine like stars. Anything with mass warps the fabric of space-time, and the greater the mass, the more extreme the warp. Black holes pack so much mass into such a tiny area that space folds back in on itself. That means that if anything, even light, gets too close, its path will always bend back toward the center of the black hole.

Astronomers have found a couple hundred of these ghostly goliaths indirectly, by seeing how they influence their surroundings. They’ve identified around 20 black holes of the small, stellar-mass variety in our galaxy by watching as stars are devoured by invisible companions. As the black hole pulls matter from its neighbor, the material forms a swirling, glowing accretion disk that signals the black hole’s presence.

Astronomers detect the first potential 'rogue' black hole, Ashley Balzer, Astronomy Magazine

An illustration of a black hole and its event horizon. (Image credit: Nicholas Forder/Future Publishing)

Topics: Astronomy, Astrophysics, Black Holes, Cosmology, Einstein, General Relativity

"Small" black holes are estimated to make up 1% of the universe's matter.

Scientists have estimated the number of "small" black holes in the universe. And no surprise: It's a lot.

This number might seem impossible to calculate; after all, spotting black holes is not exactly the simplest task. Because there are as pitch-black as the space they lurk in, the light swallowing cosmic goliaths can be detected only under the most extraordinary circumstances — like when they're bending the light around them, snacking on the unfortunate gases and stars that stray too close, or spiraling toward enormous collisions that unleash gravitational waves.

But that hasn't stopped scientists from finding some ingenious ways to guess the number. Using a new method, outlined Jan. 12 in The Astrophysical Journal, a team of astrophysicists has produced a fresh estimate for the number of stellar-mass black holes — those with masses 5 to 10 times that of the sun — in the universe.

And it's astonishing: 40,000,000,000,000,000,000, or 40 quintillions, stellar-mass black holes populate the observable universe, making up approximately 1% of all normal matter, according to the new estimate.

So how did the scientists arrive at that number? By tracking the evolution of stars in our universe they estimated how often the stars — either on their own or paired into binary systems — would transform into black holes, said first author Alex Sicilia, an astrophysicist at the International School of Advanced Studies (SISSA) in Trieste, Italy.

40 quintillion stellar-mass black holes are lurking in the universe, a new study finds, Ben Turner, Space.com

Topics: Astrobiology, Biology, Chemistry, Cosmology

The origin of life is one of the great unanswered questions in science. One piece of this puzzle is that life started on Earth 4.5 billion years ago, just a few hundred million years after the formation of the Solar System, and involved numerous critical molecular components. How did all these components come to be available so quickly?

One potential explanation is that the Earth was seeded from space with the building blocks for life. The idea is that space is filled with clouds of gas and dust that contain all the organic molecules necessary for life.

Indeed, astronomers have observed these buildings blocks in interstellar gas clouds. They can see amino acids, the precursors of proteins, and the machinery of life. They can also see the precursors of ribonucleotides, molecules that can store information in the form of DNA.

But there is another crucial component for life – molecules that can form membranes capable of encapsulating and protecting the molecules of life in compartments called protocells. On Earth, the membranes of all cells are made of molecules called phospholipids. But these have never been observed in space. Until now.

First evidence of cell membrane molecules in space, Physics arXiv blog, Astronomy

Image source: Link below

Topics: Astrophysics, Cosmology, Einstein, General Relativity, Star Trek

Note: One of the things you find out about sophomore, or junior year in physics is faster-than-light travel violates causality: the arrow of time points forward, not in "loop-de-loop." Thus, we can suspend belief as every version of Trek did time travel episodes, because superluminal speeds would allow grandfather paradoxes, so why not?

As a lifelong Trekkie, it pains me to critique genuine attempts at warp field mechanics. Just note the five stages of grief I have traveled often as I read such articles: "denial, anger, bargaining, depression and acceptance" (Elisabeth Kubler-Ross, and David Kessler), but based on the post that will appear in the morning, a little diversion might be a good thing.

For Erik Lentz, it all started with Star Trek. Every few episodes of Star Trek: The Next Generation, Captain Jean-Luc Picard would raise his hand and order, “Warp one, engage!” Then stars became dashes, and light-years flashed by at impossible speed. And Lentz, still in elementary school, wondered whether warp drive might also work in real life.

“At some point, I realized that the technology didn’t exist,” Lentz says. He studied physics at the University of Washington, wrote his Ph.D. dissertation on dark matter, and generally became far too busy to be concerned with science fiction. But then, at the start of the coronavirus pandemic, Lentz found himself alone in Göttingen, Germany, where he was doing postdoctoral work. He suddenly had plenty of free time on his hands—and childhood fancies in his head.

Lentz read everything he could find on warp drives in the scientific literature, which was not very much. Then he began to think about it for himself. After a few weeks, something occurred to him that everyone else seemed to have overlooked. Lentz put his idea on paper and discussed it with more experienced colleagues. A year later it was published in a physics journal.

It quickly became clear that Lentz was not the only person dreaming about warp drives. Media outlets all over the world picked up the story, and a dozen journalists asked for interviews. A discussion on the online forum Reddit attracted 2,700 comments and 33,000 likes. One Internet user wrote, “Anyone else feels like they were born 300 years too soon?”

Star Trek’s Warp Drive Leads to New Physics, Robert Gast, Scientific American

Topics: Astrophysics, Black Holes, Cosmology, Einstein, General Relativity

Note: From comments on a previous post, maybe science writers need to work on their chosen list of metaphors?

In the far reaches of the Universe, a supermassive black hole is throwing a tantrum.

It's blowing a tremendous wind into intergalactic space, and we're seeing the storm light from 13.1 billion years ago when the Universe was less than 10 percent of its current age. It's the most distant such tempest we've ever identified, and its discovery is a clue that could help astronomers unravel the history of galaxy formation.

"The question is when did galactic winds come into existence in the Universe?" said astronomer Takuma Izumi of the National Astronomical Observatory of Japan (NAOJ).

"This is an important question because it is related to an important problem in astronomy: How did galaxies and supermassive black holes coevolve?"

A Colossal Black Hole Storm Has Been Detected Raging in The Early Universe, Michelle Starr, Science Alert

Topics: Astronomy, Astrophysics, Cosmology

Physicists have spent centuries grappling with an inconvenient truth about nature: Faced with three stars on a collision course, astronomers could measure their locations and velocities in nanometers and milliseconds and it wouldn’t be enough to predict the stars’ fates. 

But the cosmos frequently brings together trios of stars and black holes. If astrophysicists hope to fully understand regions where heavenly bodies mingle in throngs, they must confront the “three-body problem.” 

While the result of a single three-body event is unknowable, researchers are discovering how to predict the range of outcomes of large groups of three-body interactions. In recent years, various groups have figured out how to make statistical forecasts of hypothetical three-body matchups: For instance, if Earth tangled with Mars and Mercury thousands of times, how often would Mars get ejected? Now, a fresh perspective developed by physicist Barak Kol simplifies the probabilistic “three-body problem,” by looking at it from an abstract new perspective. The result achieves some of the most accurate predictions yet. 

Physicists Edge Closer to Taming the Three-Body Problem, Charlie Wood, Scientific American

The mysterious object ‘Oumuamua passed through our solar system in 2017. Loeb has suggested it could have been sent by extraterrestrials. (Credit: European Southern Observatory/Kornmesser)

Topics: Astrobiology, Biology, Cosmology, SETI

Life, for all its complexities, has a simple commonality: It spreads. Plants, animals, and bacteria have colonized almost every nook and cranny of our world.

But why stop there? Some scientists speculate that biological matter may have proliferated across the cosmos itself, transported from planet to planet on wayward lumps of rock and ice. This idea is known as panspermia, and it carries a profound implication: Life on Earth may not have originated on our planet.

In theory, panspermia is fairly simple. Astronomers know that impacts from comets or asteroids on planets will sometimes eject debris with enough force to catapult rocks into space. Some of those space rocks will, in turn, crash into other worlds. A few rare meteorites on Earth are known to have come from Mars, likely in this fashion.

“You can imagine small astronauts sitting inside this rock, surviving the journey,” says Avi Loeb, an astrophysicist at Harvard University and director of the school’s Institute for Theory and Computation. “Microbes could potentially move from one planet to another, from Mars to Earth, from Earth to Venus.” (You may recognize Loeb’s name from his recent book Extraterrestrial: The First Sign of Intelligent Life Beyond Earth, which garnered headlines and criticism from astronomers for its claim that our solar system was recently visited by extraterrestrials.)</p>

Loeb has authored a number of papers probing the mechanics of panspermia, looking at, among other things, how the size and speed of space objects might affect their likelihood of transferring life. While Loeb still thinks it’s more likely that life originated on Earth, he says his work has failed to rule out the possibility that it came from somewhere else in space.

Did Life On Earth Come From Outer Space? Nathaniel Scharping, Discover Magazine

Astronomers searched for candidate antimatter stars among nearly 6000 gamma-ray sources. After eliminating known objects and sources that lacked the spectral signature of an antistar, 14 possibles remained. (Courtesy: Simon Dupourqué/IRAP)

Topics: Astronomy, Astrophysics, Cosmology, High Energy Physics

Fourteen possible antimatter stars (“antistars”) have been flagged up by astronomers searching for the origin of puzzling amounts of antihelium nuclei detected coming from deep space by the Alpha Magnetic Spectrometer (AMS-02) on the International Space Station.

Three astronomers at the University of Toulouse – Simon Dupourqué, Luigi Tibaldo, and Peter von Ballmoos – found the possible antistars in archive gamma-ray data from NASA’s Fermi Gamma-ray Space Telescope. While antistars are highly speculative, if they are real, then they may be revealed by their production of weak gamma-ray emission peaking at 70 MeV, when particles of normal matter from the interstellar medium fall onto them and are annihilated.

Antihelium-4 was created for the first time in 2011, in particle collisions at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory. At the time, scientists stated that if antihelium-4 were detected coming from space, then it would definitely have to come from the fusion process inside an antistar.

However, when it was announced in 2018 that AMS-02 had tentatively detected eight antihelium nuclei in cosmic rays – six of antihelium-3 and two of antihelium-4 – those unconfirmed detections were initially attributed to cosmic rays colliding with molecules in the interstellar medium and producing the antimatter in the process.

Subsequent analysis by scientists including Vivian Poulin, now at the University of Montpellier, cast doubt on the cosmic-ray origin since the greater the number of nucleons (protons and neutrons) that an antimatter nucleus has, the more difficult it is to form from cosmic ray collisions. Poulin’s group calculated that antihelium-3 is created by cosmic rays at a rate 50 times less than that detected by the AMS, while antihelium-4 is formed at a rate 10⁵ times less.

The mystery of matter and antimatter

The focus has therefore turned back to what at first may seem an improbable explanation – stars made purely from antimatter. According to theory, matter and antimatter should have been created in equal amounts in the Big Bang, and subsequently, all annihilated leaving a universe full of radiation and no matter. Yet since we live in a matter-dominated universe, more matter than antimatter must have been created in the Big Bang – a mystery that physicists have grappled with for decades.

“Most scientists have been persuaded for decades now that the universe is essentially free of antimatter apart from small traces produced in collisions of normal matter,” says Tibaldo.

The possible existence of antistars threatens to turn this on its head. “The definitive discovery of antihelium would be absolutely fundamental,” says Dupourqué.

Are antimatter stars firing bullets of antihelium at Earth? Physics World, published in Physical Review D

Topics: Astrobiology, Astronomy, Cosmology, SETI

I would extend his theme to cover something that comes naturally to us all, which I’ll call Pseudo-exceptionalism—the unearned conviction that we are exceptional, superior to others because we were born...us.

We simply assume that we’re kinder, more honest, more realistic, more wholesome than those around us. After all, we’re married to ourselves for life, so we make accommodations: We cut ourselves slack. We’re fast to forgive ourselves. When challenged, we’re much better at making our case than our opponent’s. We spot injustices to ourselves far faster than we spot our injustices to others.</em>

Why Some People (Maybe Even Us) Think They're So Special
… and what to do about it. Jeremy E. Sherman Ph.D., MPP, Psychology Today

It is presumptuous to assume that we are worthy of special attention from advanced species in the Milky Way. We may be a phenomenon as uninteresting to them as ants are to us; after all, when we’re walking down the sidewalk we rarely if ever examine every ant along our path.

Our sun formed at the tail end of the star formation history of the universe. Most stars are billions of years older than ours. So much older, in fact, that many sunlike stars have already consumed their nuclear fuel and cooled off to a compact Earth-size remnant known as a white dwarf. We also learned recently that of order half of all sunlike stars host an Earth-size planet in their habitable zone, allowing for liquid water and for the chemistry of life.

Since the dice of life were rolled in billions of other locations within the Milky Way under similar conditions to those on Earth, life as we know it is likely common. If that is indeed the case, some intelligent species may well be billions of years ahead of us in their technological development. When weighing the risks involved in interactions with less-developed cultures such as ours, these advanced civilizations may choose to refrain from contact. The silence implied by Fermi's paradox (“Where is everybody?”) may mean that we are not the most attention-worthy cookies in the jar.

Why Do We Assume Extraterrestrials Might Want to Visit Us? Avi Loeb, Scientific American

This artist’s concept shows a hypothetical planet covered in water around the binary star system of Kepler-35A and B. The composition of such water worlds has fascinated astronomers and astrophysicists for years. (Image by NASA/JPL-Caltech.)

Topics: Astronomy, Astrobiology, Astrophysics, Cosmology, Exoplanets

Out beyond our solar system, visible only as the smallest dot in space with even the most powerful telescopes, other worlds exist. Many of these worlds, astronomers have discovered, may be much larger than Earth and completely covered in water — basically ocean planets with no protruding land masses. What kind of life could develop on such a world? Could a habitat like this even support life?

A team of researchers led by Arizona State University (ASU) recently set out to investigate those questions. And since they couldn’t travel to distant exoplanets to take samples, they decided to recreate the conditions of those water worlds in the laboratory. In this case, that laboratory was the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility at the DOE’s Argonne National Laboratory.

What they found — recently published in Proceedings of the National Academy of Sciences — was a new transitional phase between silica and water, indicating that the boundary between water and rock on these exoplanets is not as solid as it is here on Earth. This pivotal discovery could change the way astronomers and astrophysicists have been modeling these exoplanets, and inform the way we think about life evolving on them.

Dan Shim, associate professor at ASU, led this new research. Shim leads ASU’s Lab for Earth and Planetary Materials and has long been fascinated by the geological and ecological makeup of these distant worlds. That composition, he said, is nothing like any planet in our solar system — these planets may have more than 50% water or ice atop their rock layers, and those rock layers would have to exist at very high temperatures and under crushing pressure.

Beneath the surface of our galaxy’s water worlds, Andre Salles, Argonne National Laboratory

Image Source: Axion particle spotted in solid-state crystal, Max Planck Society, Phys.org

Topics: Cosmology, Dark Matter, Particle Physics, Quantum Mechanics, Standard Model

A team of physicists has made what might be the first-ever detection of an axion.

Axions are unconfirmed, hypothetical ultralight particles from beyond the Standard Model of particle physics, which describes the behavior of subatomic particles. Theoretical physicists first proposed the existence of axions in the 1970s in order to resolve problems in the math governing the strong force, which binds particles called quarks together. But axions have since become a popular explanation for dark matter, the mysterious substance that makes up 85% of the mass of the universe, yet emits no light.

If confirmed, it’s not yet certain whether these axions would, in fact, fix the asymmetries in the strong force. And they wouldn’t explain most of the missing mass in the universe, said Kai Martens, a physicist at the University of Tokyo who worked on the experiment. These axions, which appear to be streaming out of the sun, don’t act like the “cold dark matter” that physicists believe fills halos around galaxies. And they would be particles newly brought into being inside the sun, while the bulk of the cold dark matter out there appears to have existed unchanged for billions of years since the early universe.*

Still, it sure seems like there was a signal. It turned up in a dark underground tank of 3.5 tons (3.2 metric tons) of liquid xenon—the XENON1T experiment based at the Gran Sasso National Laboratory in Italy. At least two other physical effects could explain the XENON1T data. However, the researchers tested several theories and found that axions streaming out of our sun were the likeliest explanation for their results.

Physicists who weren’t involved in the experiment have not reviewed the data as of the announcement at 10 a.m. ET today (June 17). Reporters were briefed on the finding before the announcement, but data and paper on the find were not made available.

Live Science shared the XENON collaboration’s press release with two axion experts.

Physicists Announce Potential Dark Matter Breakthrough, Rafi Letzter, Live Science/Scientific American