Axions...

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

There Be Monsters...

Two views of galaxy Markarian 1216. The red image on the left shows X-ray observations conducted by NASA's Chandra X-Ray Observatory, and the yellowish image on the right is composed of optical observations taken by the Hubble Space Telescope. The brighter colors at the center of the Chandra image represent the increased density of hot gas in the galaxy's core.

Topics: Astronomy, Astrophysics, Cosmology, Dark Matter

X-ray observations of a peculiar galaxy deep within the constellation Hydra (the Sea Serpent) have revealed more dark matter at its core than expected.

The galaxy is almost as old as the universe itself, representatives from NASA's Chandra X-Ray Observatory said in a statement published Monday (June 3). This celestial body, Markarian 1216, went through a different evolution than typical galaxies and is home to stars that are within 10% of the age of the universe.

To study the dark matter within this compact, elliptically shaped galaxy about 295 million light- years from Earth, researchers conducted new observations with the Chandra spacecraft. Markarian 1216 is packed with more dark matter in its core than researchers expected, according to their findings published June 1.

Ancient Galaxy in the 'Sea Serpent' Has More Dark Matter Than Expected, Doris Elin Salazar, Space,com

From Dark To Missing...

An artist's depiction of the filaments of gas that fill intergalactic space, with an inset chart of how those filaments interact with X-rays from a quasar.
Credit: Copyright Illustration: Springel et al. (2005); Spectrum: NASA/CXC/CfA/Kovács et al.

Topics: Astronomy, Astrophysics, Cosmology, Dark Matter, Women in Science

Astronomers think they've found a new clue in their continuing quest to solve one of the most substantial mysteries of the cosmos: where about a third of the universe's matter is hiding.

That missing matter isn't dark matter (a whole different head-scratcher), it's perfectly normal, run-of-the-mill matter that scientists simply can't find. And that makes it a massive cosmic annoyance for astronomers. But a team of researchers may have figured out a clue that will help them track down this missing matter, thanks to the NASA's Chandra X-ray Observatory.

"If we find this missing mass, we can solve one of the biggest conundrums in astrophysics," lead author Orsolya Kovács, a doctoral student at the Harvard Smithsonian Center for Astrophysics, said in a NASA statement. "Where did the universe stash so much of its matter that makes up stuff like stars and planets and us?"

Kovács and her research colleagues wanted to explore one popular theory: that the missing matter is hidden in the stringy filaments of warm gas that fill intergalactic space. Those filaments are typically hard to study, since telescopes tuned to the same light our eyes can see can't register these structures.

Astrophysicists Find New Clue in Search for Universe's Missing Matter
Meghan Bartels, Live Science

Doppelgänger...

(Courtesy: shutterstock/tomertu)

Topics: Antimatter, Astrophysics, Cosmology, Dark Matter, Star Trek, Theoretical Physics

Our universe could be the mirror image of an antimatter universe extending backwards in time before the Big Bang. So claim physicists in Canada, who have devised a new cosmological model positing the existence of an “antiuniverse” which, paired to our own, preserves a fundamental rule of physics called CPT symmetry. The researchers still need to work out many details of their theory, but they say it naturally explains the existence of dark matter.

Standard cosmological models tell us that the universe – space, time and mass/energy – exploded into existence some 14 billion years ago and has since expanded and cooled, leading to the progressive formation of subatomic particles, atoms, stars and planets.

However, Neil Turok of the Perimeter Institute for Theoretical Physics in Ontario reckons that these models’ reliance on ad-hoc parameters means they increasingly resemble Ptolemy’s description of the solar system. One such parameter, he says, is the brief period of rapid expansion known as inflation that can account for the universe’s large-scale uniformity. “There is this frame of mind that you explain a new phenomenon by inventing a new particle or field,” he says. “I think that may turn out to be misguided.”

Instead, Turok and his Perimeter Institute colleague Latham Boyle set out to develop a model of the universe that can explain all observable phenomena based only on the known particles and fields. They asked themselves whether there is a natural way to extend the universe beyond the Big Bang – a singularity where general relativity breaks down – and then out the other side. “We found that there was,” he says.

The answer was to assume that the universe as a whole obeys CPT symmetry. This fundamental principle requires that any physical process remains the same if time is reversed, space inverted and particles replaced by antiparticles. Turok says that this is not the case for the universe that we see around us, where time runs forward as space expands, and there’s more matter than antimatter.

Our universe has antimatter partner on the other side of the Big Bang, say physicists
Cosmology, Physics World

Accounting Dark Matter...

Fade to black: a type 1a supernova remnant as seen by the Hubble Space Telescope and the Chandra X-ray Observatory. (Courtesy: NASA)

Topics: Astrophysics, Black Holes, Cosmology, Dark Matter

Primordial black holes do not account for all dark matter, according to new research by Miguel Zumalacárregui and Uroš Seljak at the University of California, Berkeley. The duo has made the best measurement yet of the abundance of black holes in the cosmos by measuring the gravitational lensing of light from type 1a supernovae. Their study puts an upper limit of 40% on how much dark matter can be accounted for by primordial black holes.

For decades, physicists have grappled with growing evidence that the formation and dynamics of galaxies and larger structures in the universe are governed by gravitational forces from unseen dark matter. While the mysterious substance appears to account for about 85% of all matter in the universe, dark-matter particles have yet to detected directly.

Abstract

The nature of dark matter (DM) remains unknown despite very precise knowledge of its abundance in the Universe. An alternative to new elementary particles postulates DM as made of macroscopic compact halo objects (MACHO) such as black holes formed in the very early Universe. Stellar-mass primordial black holes (PBHs) are subject to less robust constraints than other mass ranges and might be connected to gravitational-wave signals detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO). New methods are therefore necessary to constrain the viability of compact objects as a DM candidate. Here we report bounds on the abundance of compact objects from gravitational lensing of type Ia supernovae (SNe). Current SNe data sets constrain compact objects to represent less than 35.2% (Joint Lightcurve Analysis) and 37.2% (Union 2.1) of the total matter content in the Universe, at 95% confidence level. The results are valid for masses larger than ∼ 0.01 M_⊙ (solar masses), limited by the size SNe relative to the lens Einstein radius. We demonstrate the mass range of the constraints by computing magnification probabilities for realistic SNe sizes and different values of the PBH mass. Our bounds are sensitive to the total abundance of compact objects with M ≳ 0.01 M_⊙ and complementary to other observational tests. These results are robust against cosmological parameters, outlier rejection, correlated noise, and selection bias. PBHs and other MACHOs are therefore ruled out as the dominant form of DM for objects associated to LIGO gravitational wave detections. These bounds constrain early-Universe models that predict stellar-mass PBH production and strengthen the case for lighter forms of DM, including new elementary particles.

Supernovae reveal that primordial black holes cannot account for all dark matter
Sam Jarman, Physics World

ADMX...

A cutaway rendering of the ADMX detector.
Image: ADMX collaboration

Topics: Dark Matter, Particle Physics, Theoretical Physics, Quantum Mechanics

Forty years ago, scientists theorized a new kind of low-mass particle that could solve one of the enduring mysteries of nature: what dark matter is made of. Now a new chapter in the search for that particle has begun.

This week, the Axion Dark Matter Experiment (ADMX) unveiled a new result, published in Physical Review Letters, that places it in a category of one: It is the world’s first and only experiment to have achieved the necessary sensitivity to “hear” the telltale signs of dark matter axions. This technological breakthrough is the result of more than 30 years of research and development, with the latest piece of the puzzle coming in the form of a quantum-enabled device that allows ADMX to listen for axions more closely than any experiment ever built.

ADMX is managed by the U.S. Department of Energy’s Fermi National Accelerator Laboratory and located at the University of Washington. This new result, the first from the second-generation run of ADMX, sets limits on a small range of frequencies where axions may be hiding and sets the stage for a wider search in the coming years.

“This result signals the start of the true hunt for axions,” said Fermilab scientist Andrew Sonnenschein, the operations manager for ADMX. “If dark matter axions exist within the frequency band we will be probing for the next few years, then it’s only a matter of time before we find them.”

ADMX announces breakthrough in axion dark matter detection technology, Fermilab

MOND on Maundy...

The image on the right shows the galaxy, full of "globular clusters." The image on the left shows the measurement the researchers used to track the speed of one such object.
Credit: Gemini Observatory / NSF / AURA / W.M. Keck Observatory / Jen Miller / Joy Pollard

Topics: Astronomy, Astrophysics, Cosmology, Dark Matter, Theoretical Physics

Note: I almost didn't blog about this, because the original links at Live Science and Cosmos Magazine lead to "page not found" errors. I was able to find the article on Nature's direct website and provide it here. It's strange both sites had the same bogus links.

Here's a problem: The universe acts like it's a lot more massive than it looks.

Take galaxies, those giant, spinning masses of stars. The laws of motion and gravity tell us how fast these objects should turn given their bulk. But observations through telescopes show them spinning way faster than we'd expect, as if they were actually much more massive than the stars we can see indicate.

Astrophysicists have come up with two main solutions to this problem. Either there's a lot of mass out there in the universe that we can't detect directly, mass scientists call dark matter, or there's no dark matter out there, but there is something missing from our laws of gravity and motion. Researchers call the second proposed solution modified Newtonian dynamics (MOND), which suggests that if the laws are properly tweaked, the universe would make sense without dark matter.

A new paper, published today (March 28) in the journal Nature, provides compelling evidence that there really is dark matter out there and that modifying the laws of physics wouldn't by itself solve the universe's weight problem.

In that study, the researchers found an object that could exist in a universe that has dark matter, but that would be nearly unimaginable in a MOND universe: a totally normal galaxy, one that seems to operate without any dark matter-type forces. [1]

*****

In a study published in the journal Nature, scientists have found a galaxy that appears to contain no dark matter — the unknown material thought to be common in the universe because of its gravitational effect on normal matter.

It was a startling discovery, because galaxies similar to our own Milky Way generally appear to contain 30 times more of the mysterious substance than normal matter, while smaller galaxies can contain up to 400 times as much.

The dark-matter-free galaxy, called NGC 1052-DF2, lies 65 million light years away in the constellation Cetus. It initially caught the attention of astronomers because, while it’s about the size of the Milky Way, it contains only 0.5% as many stars.

“That makes it very diffuse,” says the study’s lead author, Pieter van Dokkum of Yale University, in Connecticut, US. “You can look straight through it. You can see galaxies behind it.”

It was discovered by a special, low-tech telescope in New Mexico called the Dragonfly Telephoto Array, which consists of a bundle of 400-millimetre camera lenses of the same type used by sports photographers, and can scan the sky for large, dim objects. So far, it’s found 23 of them, but NGC 1052-DF2 (the DF is for “Dragonfly”) stood out because it wasn’t just a big, diffuse blob. [2]

1. Astrophysicists Claim They Found a 'Galaxy Without Dark Matter', Rafi Letzter, Live Science
2. Found: a galaxy devoid of dark matter, Richard A Lovett, Cosmos Magazine

Through a Glass, Darkly...

A simulation of the dark matter distribution in the universe 13.6 billion years ago.
ILLUSTRATION COURTESY VOLKER SPRINGEL, MAX PLANCK INSTITUTE FOR ASTROPHYSICS, ET AL, NatGeo

Topics: Astrophysics, Dark Matter, Neutrons, Research, Theoretical Physics

Alliteration source: "For now we see through a glass, darkly; but then face to face: now I know in part; but then shall I know even as also I am known." 1 Corinthians 13:12

Scientists at the University of Sussex have disproved the existence of a specific type of axion - an important candidate 'dark matter' particle - across a wide range of its possible masses.

The data were collected by an international consortium, the Neutron Electric Dipole Moment (nEDM) Collaboration, whose experiment is based at the Paul Scherrer Institut in Switzerland. Data were taken there and, earlier, at the Institut Laue-Langevin in Grenoble.

Professor Philip Harris, Head of Mathematical and Physical Sciences at the University of Sussex, and head of the nEDM group there, said:

"Experts largely agree that a major portion of the mass in the universe consists of 'dark matter'. Its nature, however, remains completely obscure. One kind of hypothetical elementary particle that might make up the dark matter is the so-called axion. If axions with the right properties exist it would be possible to detect their presence through this entirely novel analysis of our data.

"We've analyzed the measurements we took in France and Switzerland and they provide evidence that axions – at least the kind that would have been observable in the experiment – do not exist. These results are a thousand times more sensitive than previous ones and they are based on laboratory measurements rather than astronomical observations. This does not fundamentally rule out the existence of axions, but the scope of characteristics that these particles could have is now distinctly limited.

"The results essentially send physicists back to the drawing board in our hunt for dark matter."

Hunt for dark matter is narrowed by new research, Phys.org
More information: C. Abel et al. Search for Axionlike Dark Matter through Nuclear Spin Precession in Electric and Magnetic Fields, Physical Review X (2017). DOI: 10.1103/PhysRevX.7.041034

LIGO 2...

Artist’s rendition of colliding neutron stars creating gravitational waves and a kilonova. Image: Fermilab

Topics: Astrophysics, Black Holes, Dark Energy, Dark Matter, Nobel Prize, White Dwarfs

(Oct 16) A team of scientists using the Dark Energy Camera (DECam), the primary observing tool of the Dark Energy Survey, was among the first to observe the fiery aftermath of a recently detected burst of gravitational waves, recording images of the first confirmed explosion from two colliding neutron stars ever seen by astronomers.

Scientists on the Dark Energy Survey joined forces with a team of astronomers based at the Harvard-Smithsonian Center for Astrophysics (CfA) for this effort, working with observatories around the world to bolster the original data from DECam. Images taken with DECam captured the flaring-up and fading over time of a kilonova — an explosion similar to a supernova, but on a smaller scale — that occurs when collapsed stars (called neutron stars) crash into each other, creating heavy radioactive elements.

This particular violent merger, which occurred 130 million years ago in a galaxy near our own (NGC 4993), is the source of the gravitational waves detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo collaborations on Aug. 17. This is the fifth source of gravitational waves to be detected — the first one was discovered in September 2015, for which three founding members of the LIGO collaboration were awarded the Nobel Prize in physics two weeks ago.

Scientists spot explosive counterpart of LIGO/Virgo’s latest gravitational waves
Andre Salles, Fermilab Office of Communication, asalles@fnal.gov, 630-840-6733

Pushing the Quantum Limit...

A zoom in on the Josephson junctions. Two layers of niobium are visible in the image, with the upper film colored blue and the lower film colored red. Josephson junctions are formed in the circular pits (they look a bit like an element of a muffin tin) where the two layers overlap (green). Credit: K. Lehnert/NIST/JILA

Topics: Black Holes, Dark Matter, General Relativity

Here’s a surprising fact: We don’t know what makes up 80 percent of the matter in the universe. I don’t mean that the matter is made of atoms, and we just don’t know which kind of atoms. What I mean is that four-fifths of the universe appears to be made of something that isn’t atoms at all, or more to the point, it’s not made from any of the fundamental particles that we know of.

Why do we think that this mystery matter exists? The short answer is that Albert Einstein’s theory of gravity, general relativity, has painted us into a corner. When we look through telescopes at stars and galaxies moving through the universe, something we can’t see is causing their motion to bend in a particular way. Einstein’s theory of gravity tells how much of this invisible mass—physicists call it “dark matter”—there must be to bend the trajectory of things we can see.

Faced with a situation like this, we make guesses (hypotheses) that we hope explain our strange observations. A good hypothesis should both be consistent with every known fact and have other detectable consequences. If we look for these other consequences and don’t find them, we discard or revise our hypothesis.

Somewhat to my surprise, I find myself working on an experiment designed to look for the consequences of a hypothetical dark matter particle known as the axion. This was surprising because physicists, like those in all professions, divide themselves up into distinct sub-fields. Predictably there are rivalries between, and stereotypes associated with, different cultures that build up around the subfields—the rough equivalent of engineering versus sales in the corporate world.

NIST: Pushing the Quantum Limit in the Search for Dark Matter, Konrad Lehnert

Poquito...

A schematic illustration showing how differences in the distribution of dark matter (red) alter the spin rates of modern-day spiral galaxies (left) and spiral galaxies from the early universe (right). Modern spiral galaxies tend to spin faster than their counterparts in the distant, earlier universe due to greater concentrations of dark matter near their centers. Credit: ESO/L. Calçada

Topics: Astronomy, Astrophysics, Cosmology, Dark Matter

Although the invisible substance known as dark matter dominates galaxies nowadays, it was apparently only a minor ingredient of galaxies in the early universe, a new study finds.

This new finding sheds light on how galaxies and their mysterious "haloes" of dark matter have changed over time, researchers said.

Dark matter is thought to make up about 84 percent of the matter in the universe. Although dark matter is invisible, its presence can be inferred by its gravitational effects on visible matter. For instance, previous work discovered that the outer parts of galactic disks whirl faster than expected around the cores of those galaxies. These findings make sense if one assumes that "haloes" of dark matter envelop those galaxies and gravitationally pull at their outer regions. [The Search for Dark Matter in Pictures]

Now, the researchers unexpectedly find that in the early universe, dark matter played a much smaller role in galaxies than previously thought. The scientists detailed their findings in the March 16 issue of the journal Nature.

Using the European Southern Observatory's Very Large Telescope in Chile, the researchers examined six massive, star-forming galaxies from the early universe during the peak of galaxy formation 10 billion years ago. They analyzed the rotation of these galaxies to calculate how much dark matter they possessed.

Scientific American: Dark Matter Did Not Dominate Early Galaxies, Charles Q. Choi

Cosmic Mystery...

Figure 1: Both the LUX and PandaX-II experiments look for dark matter particles (χ𝜒) by sensing their interaction with xenon atoms. The detector in each experiment consists of a large tank of ultrapure liquid xenon (dark purple) topped with xenon gas (light purple). An interaction produces two light signals, one from photons, S1, and another, S2, from electrons when they drift into the gas. The signals are detected by photomultiplier tubes at the top and bottom of the tank (yellow cylinders). [Credit: APS/Carin Cain]

Topics: Astronomy, Astrophysics, Cosmology, Dark Matter

Over 80 years ago astronomers and astrophysicists began to inventory the amount of matter in the Universe. In doing so, they stumbled into an incredible discovery: the motion of stars within galaxies, and of galaxies within galaxy clusters, could not be explained by the gravitational tug of visible matter alone [1]. So to rectify the situation, they suggested the presence of a large amount of invisible, or “dark,” matter. We now know that dark matter makes up 84% of the matter in the Universe [2], but its composition—the type of particle or particles it’s made from—remains a mystery. Researchers have pursued a myriad of theoretical candidates, but none of these “suspects” have been apprehended. The lack of detection has helped better define the parameters, such as masses and interaction strengths, that could characterize the particles. For the most compelling dark matter candidate, WIMPs, the viable parameter space has recently become smaller with the announcement in September 2016 by the PandaX-II Collaboration [3] and now by the Large Underground Xenon (LUX) Collaboration [4] that a search for the particles has come up empty.

Since physicists don’t know what dark matter is, they need a diverse portfolio of instruments and approaches to detect it. One technique is to try to make dark matter in an accelerator, such as the Large Hadron Collider at CERN, and then to look for its decay products with a particle detector. A second technique is to use instruments such as the Fermi Gamma-ray Space Telescope to observe dark matter interactions in and beyond our Galaxy. This approach is called “indirect detection” because what the telescope actually observes is the particles produced by a collision between dark matter particles. In the same way that forensic scientists rely on physical evidence to reverse-engineer a crime with no witnesses, scientists use the aftermath of these collisions to reconstruct the identities of the initial dark matter particles.

The third technique, and the one used in both the LUX and PandaX-II experiments, is known as “direct detection.” Here, a detector is constructed on Earth with a massive target to increase the odds of an interaction with the dark matter that exists in our Galaxy. In the case of LUX and PandaX-II, the dark matter particles leave behind traces of light that can be detected with sophisticated sensors. This is akin to having placed cameras at the scene of a crime, capturing the culprit in the act.

The heart of both LUX, located in South Dakota in the US, and PandaX-II, situated in Sichuan, China, is a time-projection chamber. This consists of a large tank of ultrapure liquid xenon—250 kg at LUX and 500 kg at PandaX-II—topped with xenon gas (Fig. 1). A particle (dark matter or ordinary matter) that enters the chamber and interacts with a xenon atom in the liquid generates photons (by scintillation) and electrons (by ionization). The photons produce a signal, S1, which is read by photomultiplier tubes located at the top and bottom of the tank. The electrons are instead coaxed into the gaseous portion of the detector by an electric field where they induce a second round of scintillation and a signal S2. The pattern of S1 and S2 signals is different when the xenon interacts with a dark matter particle than with an ordinary particle, which is what allows scientists to distinguish between two such events. To reduce the background signal from ordinary particles, both LUX and PandaX-II are buried underground to provide protection from cosmic rays. In addition, the use of ultrapure materials in the construction of the experiment cuts the background contributed by radioactive emissions.

APS Viewpoint: Dark Matter Still at Large
Jodi A. Cooley, Department of Physics, Southern Methodist University, 3215 Daniel Ave., Dallas, TX 75205, USA
January 11, 2017• Physics 10, 3

Sino Science...

Phosphorene is a graphene-like material that is a hot research topic, according to a new study. (Courtesy: Robert Brook/Science Photo Library)

Topics: Dark Matter, Materials Science, Neutrinos, Research

China is performing "outstanding" research in a number of emerging scientific topics, putting the country's output on a par with the UK but still behind the US. That is the conclusion of a new study by the Chinese Academy of Sciences (CAS) and the scientific data company Clarivate Analytics. The Research Fronts 2016 annual report identifies 100 "hot" and 80 "emerging" research areas based on citation analysis of papers published in 2015.

The research areas – divided in various fields of science – reflect global interest in specific topics that have resulted in "core" journal articles. These articles are defined by an algorithm that takes into account, among other things, the time of publication and how frequently an article is cited by other papers in the same area. In physics, for instance, the hottest research pursuits last year included the detection of dark matter and experiments that measure neutrino oscillations. Research into properties and applications of black phosphorus – a 2D material also called phosphorene because of its similarity to graphene – was also identified. The study of topological materials called Weyl semimetals was also named as a hot topic in physics.

Six countries – China, France, Germany, Japan, UK and US – made the greatest contributions in the 180 research areas, according to the report. The US retained its leadership, with its researchers publishing core papers in 152 of the 180 areas, ranging from the hunt for dark matter to the health impact of electronic cigarettes. The UK, meanwhile, contributed core papers in 90 research topics, covering more areas than China's 68. However, China had top-cited papers among the core papers in 30 research areas, which is more than twice that of the UK. "China has a significant gap with the US, and fierce competition with the UK," the report says, adding it was likely that China would soon overtake the UK.

Physics World: China forges ahead in global research
Binglin Chen is a science writer based in Beijing

Slingshot...

Image Source: Physics Today

Topics: Astrophysics, Black Holes, Cosmology, Dark Matter, General Relativity

Shooting out of the galaxy at speeds greater than the escape velocity, hypervelocity stars provide a window on black holes and the distribution of dark matter surrounding the glowing Milky Way.

Because gravity keeps stars on their orbits, astronomers can use the motions of stars to infer the mass distribution of the visible and invisible constituents of the Milky Way. The Milky Way is the only galaxy whose visible mass distribution we can see in three dimensions and in which we can accurately measure the velocities of millions of individual stars. Gravitational accelerations in the galaxy are usually small, however. Our sun, for instance, experiences a gravitational acceleration of just 2 Å/s² as it orbits the Milky Way. That’s 10⁻¹¹ of what we experience on Earth’s surface. It’s also the gravitational- acceleration regime of dark matter—the unseen material inferred to exist in and around galaxies.

Some of the initial evidence for dark matter came in 1932 after Dutch astronomer Jan Oort developed the first modern theory of stellar motions.¹ Oort compared the velocity dispersion of stars near the Sun with their number density and inferred the existence of more mass than could be accounted for by the visible stars. In more recent times, radio astronomers have measured the rotation speeds of gas—specifically neutral hydrogen—in the outer parts of the Milky Way and other disk galaxies with much higher accuracy than could be done in Oort’s era. Intriguingly, they found that rotation speeds do not decline with increasing distance outward but stay constant. To keep galaxies like the Milky Way bound together requires the gravitational pull of dark matter, if not a modified theory of gravity.

The focus of this article is a new class of astronomical objects, known as hypervelocity stars, that uniquely connect the center of the galaxy to its outer halo. A decade ago I and my colleagues Margaret Geller, Scott Kenyon, and Michael Kurtz at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, unexpectedly discovered a star moving away from Earth at 850 km/s, roughly 2 million miles per hour.³ The speed is astonishing: The star is racing outward with at least twice the galactic escape velocity at its distance of 300 000 light-years from the galactic center.

Physics Today: Hypervelocity stars in the Milky Way, Warren R Brown

Black Holes and Dark Matter...

After masking out all known stars, galaxies and artifacts and enhancing what's left, an irregular background glow appears. This is the cosmic infrared background (CIB); lighter colors indicate brighter areas. The CIB glow is more irregular than can be explained by distant unresolved galaxies, and this excess structure is thought to be light emitted when the universe was less than a billion years old. Scientists say it likely originated from the first luminous objects to form in the universe, which includes both the first stars and black holes.
Credits: NASA/JPL-Caltech/A. Kashlinsky (Goddard)

Topics: Astrophysics, Black Holes, Dark Matter, Physics Humor

I'll admit to being a fan of The Flash, but an informed one. For instance, speed in physics - along with mass (that's "us") is associated with momentum; acceleration and mass is associated with force. Every time I hear "speed force," I cringe. There was the memorable episode where Barry "talked" to the speed force (who looked like Joe, Iris, his mom and dad; a wraith that looked like him), which the writers obligatorily associated with Dark Energy, Dark Matter and the Big Bang. Barry had one memorable line that sounded kinda "science-y" when conversing with said speed deities: "this is like talking to gravity, or light," which as a part of nature, are not typically conversant. This of course is the fanciful departure of Hollywood cartoon physics, and as I allude at the link provided: don't take me to your Sci-Fi movie night!

The following is rather exciting, a hypothesis that will have to stand up to relentless peer review. Even though I'm a fan of superhero comic shows, I look forward to the coming published scientific conversations that will eventually (hopefully) hash this out.

Dark matter is a mysterious substance composing most of the material universe, now widely thought to be some form of massive exotic particle. An intriguing alternative view is that dark matter is made of black holes formed during the first second of our universe's existence, known as primordial black holes. Now a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, suggests that this interpretation aligns with our knowledge of cosmic infrared and X-ray background glows and may explain the unexpectedly high masses of merging black holes detected last year.

"This study is an effort to bring together a broad set of ideas and observations to test how well they fit, and the fit is surprisingly good," said Alexander Kashlinsky, an astrophysicist at NASA Goddard. "If this is correct, then all galaxies, including our own, are embedded within a vast sphere of black holes each about 30 times the sun's mass."

In 2005, Kashlinsky led a team of astronomers using NASA's Spitzer Space Telescope to explore the background glow of infrared light in one part of the sky. The researchers reported excessive patchiness in the glow and concluded it was likely caused by the aggregate light of the first sources to illuminate the universe more than 13 billion years ago. Follow-up studies confirmed that this cosmic infrared background (CIB) showed similar unexpected structure in other parts of the sky.

NASA Scientist Suggests Possible Link Between Primordial Black Holes and Dark Matter
Francis Reddy

Dwarf Dark Galaxy...

Composite image of the gravitational lens SDP.81 showing the distorted ALMA image of the more distant galaxy (red arcs) and the Hubble optical image of the nearby lensing galaxy (blue center object). By analyzing the distortions in the ring, astronomers have determined that a dark dwarf galaxy (data indicated by white dot near left lower arc segment) is lurking nearly 4 billion light-years away. Credit: Y. Hezaveh, Stanford Univ.; ALMA (NRAO/ESO/NAOJ); NASA/ESA Hubble Space Telescope

Topics: Astronomy, Astrophysics, Dark Matter, Einstein, General Relativity, Gravitational Lensing, Radio Astronomy

Subtle distortions hidden in ALMA’s stunning image of the gravitational lens SDP.81 are telltale signs that a dwarf dark galaxy is lurking in the halo of a much larger galaxy nearly 4 billion light-years away. This discovery paves the way for ALMA to find many more such objects and could help astronomers address important questions on the nature of dark matter.

In 2014, as part of ALMA’s Long Baseline Campaign, astronomers studied a variety of astronomical objects to test the telescope's new, high-resolution capabilities. One of these experimental images was that of an Einstein ring, which was produced by the gravity of a massive foreground galaxy bending the light emitted by another galaxy nearly 12 billion light-years away.

This phenomenon, called gravitational lensing, was predicted by Einstein’s general theory of relativity and it offers a powerful tool for studying galaxies that are otherwise too distant to observe. It also sheds light on the properties of the nearby lensing galaxy because of the way its gravity distorts and focuses light from more distant objects.

National Radio Astronomy Observatory:
Dwarf Dark Galaxy Hidden in ALMA Gravitational Lens Image

Sterile Neutrinos...

A section of CERN's Super Proton Synchrotron, which could be home to the SHiP experiment by 2026.
(Courtesy: Piotr Traczyk)

Topics: CERN, Cosmology, Dark Matter, Neutrinos, Particle Physics, Theoretical Physics

This is very interesting. Sterile neutrinos are dark matter candidates. From APS Physics, April 24, 2014:

A hypothetical neutrino that does not interact through the weak force could be the source of a recently detected x-ray emission line coming from galaxy clusters. However, previous models using this so-called “sterile” neutrino as a form of dark matter were not able to satisfy constraints from cosmological observations. Now, writing in Physical Review Letters, Kevork Abazajian of the University of California, Irvine, shows that a sterile neutrino with a mass of 77 kilo-electron-volts (keV) could be a viable dark matter candidate that both explains the new x-ray data and solves some long-standing problems in galaxy structure formation.

* * * * *

A new experiment to search for hypothetical particles known as sterile neutrinos has been given the green light by scientists at the CERN particle-physics laboratory near Geneva. The SFr 200m (£140m) Search for Hidden Particles experiment (SHiP) would be built at CERN and start up a decade from now. The lab's member states will, however, need to approve the project before construction.

Predicted by certain extensions of the Standard Model, sterile neutrinos – if they exist – would interact extremely weakly, if at all, with ordinary matter. However, sterile neutrinos would transform into and out of standard neutrinos, revealing themselves via a greater- or lesser-than-expected rate of oscillation between the different types, or "flavors", of neutrinos. Physicists working on the Liquid Scintillator Neutrino Detector (LSND) at the Los Alamos National Laboratory in New Mexico between 1993 and 1998 saw some evidence for such a transformation, but other experiments have failed to see a similar signal.

There are other plans to look for these hypothetical particles, but these experiments would focus on light sterile neutrinos with masses of less than one electronvolt. SHiP, in contrast, would seek more massive sterile neutrinos known as heavy neutral leptons. Weighing a few gigaelectronvolts, such particles would, very occasionally, decay into ordinary matter. According to SHiP spokesman Andrey Golutvin of CERN, their existence, unlike that of their lighter counterparts, could explain the predominance of matter over antimatter in the universe and the nature of dark matter. "Finding a light sterile neutrino would be a Nobel prize discovery, but it wouldn't solve the problems of the Standard Model," he claims.

Physics World: CERN gives thumbs up to new sterile-neutrino detector
Edwin Cartlidge

The Q Continuum...

Image Source: Argonne National Laboratory

Topics: Dark Energy, Dark Matter, Physics Humor, Star Trek, Theoretical Physics, Quantum Cosmology

This is the title of the original post, I kid you not! There are apparently a few Trekkies at Argonne National Lab...\\//_

Researchers are sifting through an avalanche of data produced by one of the largest cosmological simulations ever performed, led by scientists at the U.S. Department of Energy’s (DOE's) Argonne National Laboratory.

The simulation, run on the Titan supercomputer at DOE's Oak Ridge National Laboratory, modeled the evolution of the universe from just 50 million years after the Big Bang to the present day — from its earliest infancy to its current adulthood. Over the course of 13.8 billion years, the matter in the universe clumped together to form galaxies, stars, and planets; but we’re not sure precisely how.

These kinds of simulations help scientists understand dark energy, a form of energy that affects the expansion rate of the universe, including the distribution of galaxies, composed of ordinary matter, as well as dark matter, a mysterious kind of matter that no instrument has directly measured so far.

Argonne National Laboratory:
Researchers model birth of universe in one of largest cosmological simulations ever run
Louise Lerner

Accretion of Dark Matter...

Image Source (and sound): Dark Matter Sound System - Band Camp

Topics: Black Holes, Dark Matter, General Relativity, Heliophysics, Humor, Quantum Cosmology

First of all, from the astrophysics classes I've taken, accretion is attributed to stars diffusing material around it, usually to create things like planets. This is a novel way to look at the pursuit of dark matter and I found the paper intriguing.

What teachers will hate me for: since everyone knows what a black hole looks like, and it really didn't coincide with the paper (abstract below), I did find a techno metal group that has a whole unique take on combining the two subjects (link below above image). As always, I get no gratuities for sharing this, but hopefully like me, it makes you grin for many of you, the first day of school (at least in Texas). Think of it as your "hook," but don't dwell on it very long...the students will catch on you're enjoying it too much.

Abstract

Searches for dark matter imprints are one of the most active areas of current research. We focus here on light fields with mass mB, such as axions and axion-like candidates. Using perturbative techniques and full-blown nonlinear Numerical Relativity methods, we show that (i) dark matter can pile up in the center of stars, leading to configurations and geometries oscillating with frequency which is a multiple of f=2.51014 m_Bc²/eV Hz. These configurations are stable throughout most of the parameter space, and arise out of credible mechanisms for dark-matter capture. Stars with bosonic cores may also develop in other theories with effective mass couplings, such as (massless) scalar-tensor theories. We also show that (ii) collapse of the host star to a black hole is avoided by efficient gravitational cooling mechanisms.

Physics arXiv: Accretion of dark matter by stars
Richard Brito, Vitor Cardoso, Hirotada Okawa

Dark Matter Shine...

An artist's concept shows a black hole eating material from a nearby star. Researchers say its possible dark matter swirling around a black hole could radiate gamma rays that could be seen by telescopes.
Credit: An artist's concept shows a black hole eating material from a nearby star. Researchers say its possible dark matter swirling around a black hole could radiate gamma rays that could be seen by telescopes.

Topics: Black Holes, Cosmology, Dark Matter, General Relativity

Dark matter circling the drain of a massive black hole could radiate gamma-rays that might be visible from Earth, according to new research.

Dark matter is five times more plentiful in the universe than regular matter, but it does not emit, reflect or absorb light, making it not just dark but entirely transparent. But if dark-matter particles around black holes can produce gamma-rays (high-energy light), such emissions would give scientists a new way to study this mysterious material.

The process responsible for creating the gamma-rays is somewhat counterintuitive, because it seems to defy two common assumptions: that nothing can escape from a black hole and that there's no such thing as a free lunch.

A 3D computer model of what the dark-matter gamma-ray signal might look like around a black hole. Because the particles are orbiting around the black hole (left to right) the signal is only visible on one side.
Credit: Jeremy Schnittman

Space.com: Black Holes Might Make Dark Matter Shine, Calla Cofield