Observations of 11 galaxy clusters, such as MACSJ1206.2-0847 (shown), reveal that some globs of dark matter in these clusters are denser than expected. HUBBLE/ESA AND NASA

Not only is the mysterious substance invisible, but it’s also not all where we thought it was

By Maria Temming  September 10, 2020

Dark matter just got even more puzzling.

This unidentified stuff, which makes up most of the mass in the cosmos, is invisible but detectable by the way it gravitationally tugs on objects like stars. (SN: 11/25/19). Dark matter’s gravity can also bend light traveling from distant galaxies to Earth — but now some of this mysterious substance appears to be bending light more than it’s supposed to. A surprising number of dark matter clumps in distant clusters of galaxies severely warp background light from other objects, researchers report in the Sept. 11 Science.

This finding suggests that these clumps of dark matter, in which individual galaxies are embedded, are denser than expected. And that could mean one of two things: Either the computer simulations that researchers use to predict galaxy cluster behavior are wrong, or cosmologists’ understanding of dark matter is.

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NGC1052-DF2 is a large, but very diffuse galaxy located some 60 million light-years away. This image of the galaxy, which is thought to contain a negligible amount of dark matter, was captured by the Advanced Camera for Surveys on the Hubble Space Telescope. NASA/ESA/P. van Dokkum (Yale University

Ironically, by finding two galaxies severely lacking in dark matter, researchers have made a compelling case for the existence of the mysterious material.

By Jake Parks | Published: Friday, March 29, 2019

One year ago, astronomers were flabbergasted when they discovered a galaxy almost entirely devoid of dark matter. As the first galaxy ever found lacking the elusive substance — which is thought to account for 85 percent of the universe's mass — the news rippled through the astronomical community. This left some researchers delightfully intrigued, and others understandably skeptical.

"If there's [only] one object, you always have a little voice in the back of your mind saying, 'but what if you're wrong?'" astronomer Pieter van Dokkum of Yale University, who led last year's ground-breaking study, said in a press release. "Even though we did all the checks we could think of, we were worried that nature had thrown us for a loop and had conspired to make something look really special whereas it was really something more mundane."

Now, a new study published in The Astrophysical Journal Letters on March 27 shows van Dokkum and his team had it right all along.

According to the work, they've confirmed a ghostly galaxy located some 60 million light-years away named NGC 1052-DF2 (DF2 for short) has virtually no discernible dark matter. Furthermore, a second study published March 20 in the same journal announced the discovery of yet another dim and diffuse galaxy with a dearth of dark matter, nicknamed DF4.

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In the Bullet Cluster, light seems to bend in what should be empty space. Researchers now believe those areas contain dark matter. Image: X-ray: NASA/CXC/CfA/ M. Markevitch et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/ D.Clowe et al. Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.

Ryan F. Mandelbaum  7.6.2018

Five-sixths of the universe’s stuff seems to be missing, and we just can’t find it. It’s called “dark matter,” and scientists have gone looking for it with some of the world’s largest, most expensive experiments.

Time and time again, these experiments come up empty handed. Most recently, the scientists at the XENON1T experiment, a literal ton of super-sensitive liquid xenon, didn’t find the signal they were looking for after a nine-month search. Nor has the Large Hadron Collider, the world’s largest particle accelerator in Geneva, Switzerland, managed to turn up anything. So, you might wonder, what are we looking for and why? And why are the world’s physicists so deeply divided about what “dark matter” could be?

Big, strange somethings

As early as the late 19th century, scientific observations were telling us that the universe was more massive than it appeared. Scientists now consider Swiss physicist Fritz Zwicky to be the father of dark matter. Zwicky realized that galaxies in the Coma Cluster seemed to move much too quickly. He thought there should perhaps 400 times more mass in the cluster than he could see, a bit of an overshoot, and called the missing stuff dunkle Materie, or “dark matter.”

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X-ray image of the Perseus galaxy cluster, approximately 240 million light-years away from Earth. The x-ray radiation emitted by galaxies and galaxy clusters still poses numerous puzzles to astrophysicists. In particular, it may provide clues to the nature of the mysterious dark matter. Credit: Photo courtesy of NASA

February 8, 2018, Universitaet Mainz

Dark matter is increasingly puzzling. Around the world, physicists have been trying for decades to determine the nature of these matter particles, which do not emit light and are therefore invisible to the human eye. Their existence was postulated in the 1930s to explain certain astronomical observations. As visible matter, like the one that makes up the stars and the Earth, constitutes just 5 percent of the universe, it has been proposed that dark matter must represent 23 percent of what is out there. But to date and despite intensive research, it has proved impossible to actually identify the particles involved. Researchers at Johannes Gutenberg University Mainz (JGU) have now presented a novel theory of dark matter, which implies that dark matter particles may be very different from what is normally assumed. In particular, their theory involves dark matter particles which are extremely light—almost one hundred times lighter than electrons, in stark contrast to many conventional models that involve very heavy dark matter particles instead.

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May 24, 2016

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.

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By Nola Taylor Redd

Sometimes, a flaw in your magnifying glass can be a good thing; in the case of some new research, it can even reveal invisible dark matter galaxies.

Astronomers probing the sky used the gravity of a massive galaxy as a natural magnifying glass, and they found a strange distortion on its edge. That distortion proved to be a smaller, invisible galaxy composed of dark matter. The discovery, explained in a new video, could pave the way to finding more of these unusual objects, providing a better understanding of the mysterious material that makes up most of the matter in the universe.

"We can find these invisible objects in the same way that you can see rain droplets on a window," lead author Yashar Hezaveh said in a statement. Like raindrops, the massive clumps of matter warp objects seen through them. Hezaveh, an astronomer at Stanford University in California, worked with a team of scientists that used a massive radio telescope, the Atacama Large Millimeter/submillimeter Array (ALMA) inChile, to find a clump of missing matter in the outer rim of a larger galaxy that.

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Particle swarm. In Schnittman’s simulation, dark matter particles (shown with gray and pink trails) orbiting a rotating black hole (central sphere) could occasionally gain a large amount of energy and escape. The blue region (the ergosphere) is where the black hole’s rotation pulls spacetime along.

Particles orbiting near a spinning black hole might collide and get ejected with much more energy than previous calculations showed.

Black holes are mostly takers, not givers, but collisions among matter around a spinning black hole can result in high-energy particles that emerge with some of the black hole’s energy. Decades-old calculations showing only a modest energy gain for such particles are now contradicted by new results from two theoretical efforts showing that a particle can take away more than 10 times the energy that was put in. There are still questions about the feasibility of such collisions, but they might help astrophysicists understand some unexplained observations, such as an excess of gamma rays from the galactic center or ultrahigh-energy cosmic rays.

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