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Category: cosmology

Self-interacting dark matter may solve three cosmic puzzles

A study led by UC Riverside physicist Hai-Bo Yu suggests that a new type of dark matter could explain three astrophysical puzzles across vastly different environments. Published in Physical Review Letters, the study proposes that dense clumps of self-interacting dark matter (SIDM)—each about a million times the mass of the sun—can account for unusual gravitational effects observed in gravitational lenses, stellar streams, and satellite galaxies.

Dark matter, which makes up about 85% of the universe’s matter, cannot be seen directly. The standard model assumes it is “cold” and collisionless, meaning that particles pass through one another without interacting. This model struggles, however, to explain certain high-density structures observed in the universe.

Yu’s work instead focuses on SIDM, in which dark matter particles collide and exchange energy. These interactions can trigger “gravothermal collapse,” forming extremely dense, compact cores.

After Decades of Searching, Astronomers Finally Track Down the Universe’s Missing Hydrogen

A vast new survey of the early universe has dramatically expanded the known population of hydrogen gas halos surrounding young galaxies, revealing that these structures are far more common and diverse than previously thought. Astronomers analyzing data from the Hobby–Eberly Telescope Dark Energy

Peculiar core-collapse supernova breaks the mold with a long, dim plateau

Astronomers from the Chinese Academy of Sciences (CAS) have employed the Lijiang 2.4-m telescope to perform optical photometric and spectroscopic observations of a core-collapse Type IIP supernova designated SN 2024abfl. Results of the observational campaign, published April 2 on the arXiv, preprint server, deliver essential information regarding the origin of this peculiar supernova.

Search for dark matter intensifies as leading detector reaches milestone

Deep underground in a Canadian mine, a refrigerator nearly 1,000 times colder than outer space has just reached its target temperature—a milestone that brings scientists one step closer to potentially detecting dark matter, the invisible material thought to make up most of the mass in the universe.

For researchers at Texas A&M University, the moment is especially meaningful. Their custom-designed detectors sit at the heart of the Super Cryogenic Dark Matter Search (SuperCDMS), and they only become sensitive enough to detect possible dark-matter interactions at these extreme temperatures. SuperCDMS is in SNOLAB, an underground research facility in a nickel mine near Sudbury, Ontario.

Scientists there are targeting “light dark matter,” a much lower-mass form of dark matter that’s even harder to detect.

What if dark matter came in two states?

The absence of a signal could itself be a signal. This is the idea behind a new study published in the Journal of Cosmology and Astroparticle Physics, which aims to redefine how we search for dark matter, showing that it may not be necessary to find the same “clues” everywhere in order to interpret it.

In particular, the study suggests that even if we observe a certain type of signal at the center of our galaxy—an excess of gamma radiation that could result from the annihilation of dark matter particles—failing to detect the same signal in other systems, such as dwarf galaxies, is not enough to rule out this explanation.

Dark matter, in fact, may not consist of a single particle, but of multiple slightly different components, whose behavior varies depending on the cosmic environment.

How young galaxies grew magnetic fields faster than expected

How fast can a galaxy build ordered magnetic fields spanning thousands of light-years? Existing theories say several billion years, but observations of galaxies in our universe imply shorter timescales. In a study published in the Physical Review Letters and highlighted in the Physics magazine, scientists propose an explanation that resolves this contradiction. They say that the collapse of plasma clouds during the formation of galaxies could significantly accelerate the growth of these magnetic fields.

Almost all visible matter in our universe is in the form of plasma, which can be stirred by forces related to gravity, temperature gradients and rotation. If these lead to turbulent flow, the dynamo theory predicts that the existing magnetic fields in the plasma are amplified. The dynamo theory is our primary framework for understanding the origin of cosmic magnetic fields.

“However, dynamo theory has its limitations,” says Pallavi, an assistant professor at the International Centre for Theoretical Sciences (ICTS) and an author of the study. “In particular, it struggles to explain observations of young galaxies with robust magnetic fields across thousands of light-years.”

First close pair of supermassive black holes detected

Supermassive black holes at the centers of galaxies are one of the most active fields of research in astronomy. In order to accumulate their enormous masses, they must merge with each other. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn has found direct evidence of two supermassive black holes in the galaxy Markarian 501, which orbit each other very closely. This could be the first time that a pair has been detected that is about to merge. This provides a unique opportunity to better understand a central process in galaxy evolution.

The findings suggest that there is a supermassive black hole at the center of almost every large galaxy, with a mass millions or even billions of times greater than that of our sun. It is still unclear exactly how they can reach such enormous masses. Collecting (accreting) gas from the surrounding area alone would take too long, so it is likely that they have to merge with other massive black holes. Galaxy collisions have been observed throughout our universe. It is thus very likely that the supermassive black holes at the centers of these colliding galaxies also merge, first orbiting each other ever closer and ultimately coalescing into one.

Astronomers discover Andromeda XXXVI, an ultra-faint dwarf satellite galaxy

By analyzing the data from the Pan-Andromeda Archaeological Survey (PandAS), European astronomers have discovered a new satellite of the Andromeda galaxy. The newfound object, which received the designation Andromeda XXXVI, appears to be an ultra-faint dwarf galaxy. The finding is reported in a paper published March 30 on the arXiv preprint server.

The so-called ultra-faint dwarf galaxies (UFDs) are the least luminous, most dark matter-dominated, and least chemically evolved galaxies known. Therefore, they are perceived by astronomers as the best candidate fossils from the universe at its early stages.

Now, a team of astronomers, led by Joanna D. Sakowska of the Institute of Astrophysics of Andalusia in Spain, reports the finding of a new UFD. Andromeda XXXVI was first spotted and classified as a candidate UFD by amateur astronomer Giuseppe Donatiello during a systematic, visual inspection search of public images from the full PAndAS footprint. Sakowska and her colleagues recently performed follow-up deep imaging of Andromeda XXXVI with the Roque de los Muchachos Observatory, which confirmed the UFD nature of this galaxy.

Astronomers thought the early universe was full of hydrogen: Now they’ve found it

The Eberly Telescope Dark Energy Experiment (HETDEX) has discovered tens of thousands of gigantic hydrogen gas halos, called “Lyman-alpha nebulae,” surrounding galaxies 10 billion to 12 billion years ago. Known as Cosmic Noon, this is an epoch in the early universe when galaxies were growing their fastest. To spur this growth, they would have needed access to vast reservoirs of hydrogen gas, a key building block for stars. However, until recently, astronomers had only found a handful of these essential structures.

A new study published in The Astrophysical Journal has now increased the known number of hydrogen gas halos by a factor of 10: from roughly 3,000 to over 33,000. This confirms suspicions that they are not rare curiosities. The study also increases the range of known sizes, providing a more representative sample for astronomers to study as they continue to tease out the origin and evolution of the first galaxies.

“We’ve been analyzing the same handful of objects for the past 20 or so years,” said Erin Mentuch Cooper, HETDEX data manager and lead author on the study. “HETDEX is letting us find many more of these halos and measure their shapes and sizes. It has really allowed us to create an amazing statistical catalog.”

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