Detecting Primordial Black Hole Mergers Might be Within Our Grasp

An artistic take on primordial black holes. Credit: NASA’s Goddard Space Flight Center

Imagine a black hole with the mass of the asteroid Ceres. It would be no larger than a bacterium and practically undetectable. But if such black holes are common in the Universe, they would affect the motions of stars and galaxies, just as we observe. Perhaps they are the source of dark matter.

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Neutron Stars May be Shrouded in Extremely Light Particles Called Axions

Image from a computer simulation of the distribution of matter in the universe. Orange regions host galaxies; blue structures are gas and dark matter. Credit: TNG Collaboration

Since the 1960s, astronomers have theorized that the Universe may be filled with a mysterious mass that only interacts with “normal matter” via gravity. This mass, nicknamed Dark Matter (DM), is essential to resolving issues between astronomical observations and General Relativity. In recent years, scientists have considered that DM may be composed of axions, a class of hypothetical elementary particles with low mass within a specific range. First proposed in the 1970s to resolve problems in the Standard Model of particle physics, these particles have emerged as a leading candidate for DM.

In addition to growing evidence that this could be the case, researchers at CERN are developing a new telescope that could help the scientific community look for axions – the CERN Axion Solar Telescope (CAST). According to new research conducted by an international team of physicists, these hypothetical particles may occur in large clouds around neutron stars. These axions could be the long-awaited explanation for Dark Matter that cosmologists have spent decades searching for. What’s more, their research indicates that these axions may not be very difficult to observe from Earth.

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Dark Matter Has a Firm Grip on These Galaxies

NGC 1270 is just one member of the Perseus Cluster, a group of thousands of galaxies that lies around 240 million light-years from Earth in the constellation Perseus. This image, taken with the Gemini Multi-Object Spectrograph (GMOS) on the Gemini North telescope, one half of the International Gemini Observatory, captures a dazzling collection of galaxies in the central region of this enormous cluster. Image Credit: International Gemini Observatory/NOIRLab/NSF/AURA/ Image Processing: J. Miller & M. Rodriguez (International Gemini Observatory/NSF NOIRLab), T.A. Rector (University of Alaska Anchorage/NSF NOIRLab), M. Zamani (NSF NOIRLab) Acknowledgements: PI: Jisu Kang (Seoul National University)

The elliptical galaxy NGC 1270 lies about 240 million light-years away. But it’s not alone. It’s part of the Perseus Cluster (Abell 426), the brightest X-ray object in the sky and one of the most massive objects in the Universe.

NGC 1270 plays a starring role in a new image from the Gemini North telescope. However, the image doesn’t show the dark matter that has a firm grip on the galaxy and the rest of the galaxies in the Perseus Cluster.

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Dark Matter Could a Have Slight Interaction With Regular Matter

A comparison of non-interacting and interacting dark matter. Credit: Gabriel Pérez

The reason we call dark matter dark isn’t because it’s some shadowy material. It’s because dark matter doesn’t interact with light. The difference is subtle, but important. Regular matter can be dark because it absorbs light. It’s why, for example, we can see the shadow of molecular clouds against the scattered stars of the Milky Way. This is possible because light and matter have a way to connect. Light is an electromagnetic wave, and atoms contain electrically charged electrons and protons, so matter can emit, absorb and scatter light. Dark matter isn’t electrically charged. It has no way to connect with light, and so when light and dark matter meet up they simply pass through each other.

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Could We Find Primordial Black Holes in the Solar System?

An artistic take on primordial black holes. Credit: NASA’s Goddard Space Flight Center

Astronomers have observed three types of black holes in the Universe. Stellar-mass black holes formed from the collapse of a massive star, intermediate mass black holes found in some star clusters, and supermassive black holes that lurk in the centers of galaxies. But there is a fourth type that remains hypothetical an unobserved. Known as primordial black holes, they are thought to have formed from tiny fluctuations in the hot and dense early cosmos. Since they wouldn’t have formed from stars or mergers, they could have a much smaller mass. And with small masses, primordial black holes would be tiny. Their event horizons would be smaller than an apple, perhaps as small as a grain of sand. You can see why they would be hard to find.

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Largest Dark Matter Detector is Narrowing Down Dark Matter Candidate

Technicians scanning for dust on the LUX-ZEPLIN (LZ) Dark Matter Detector. Credit: LZ Experiment

In 2012, two previous dark matter detection experiments—the Large Underground Xenon (LUX) and ZonEd Proportional scintillation in Liquid Noble gases (ZEPLIN)—came together to form the LUX-ZEPLIN (LZ) experiment. Since it commenced operations, this collaboration has conducted the most sensitive search ever mounted for Weakly Interacting Massive Particles (WIMPs) – one of the leading Dark Matter candidates. This collaboration includes around 250 scientists from 39 institutions in the U.S., U.K., Portugal, Switzerland, South Korea, and Australia.

On Monday, August 26th, the latest results from the LUX-ZEPLIN project were shared at two scientific conferences. These results were celebrated by scientists at the University of Albany‘s Department of Physics, including Associate Professors Cecilia Levy and Matthew Szydagis (two members of the experiment). This latest result is nearly five times more sensitive than the previous result and found no evidence of WIMPs above a mass of 9 GeV/c2. These are the best-ever limits on WIMPS and a crucial step toward finding the mysterious invisible mass that makes up 85% of the Universe.

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Dark Matter Could Have Driven the Growth of Early Supermassive Black Holes

An image from the Event Horizon Telescope shows lines of polarization, a signature of magnetic fields, around the shadow of the Milky Way's central supermassive black hole. Astronomers want to know how massive black holes like this one formed early in cosmic history. (Credit: EHT Collaboration)
An image from the Event Horizon Telescope shows lines of polarization, a signature of magnetic fields, around the shadow of the Milky Way's central supermassive black hole. Astronomers want to know how massive black holes like this one formed early in cosmic history. (Credit: EHT Collaboration)

The James Webb Space Telescope (JWST) keeps finding supermassive black holes (SMBH) in the early Universe. They’re in active galactic nuclei seen only 500,000 years after the Big Bang. This was long before astronomers thought they could exist. What’s going on?

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New Limits on Dark Matter

LZ’s central detector, the time projection chamber, in a surface lab clean room before delivery underground. Credit: Matthew Kapust/Sanford Underground Research Facility

As it’s name suggests, dark matter is dark! That means it’s largely invisible to us and only detectable through its interaction with gravity. One of the leading theories to explain the stuff that makes up the majority of the matter in the Universe are WIMPs, Weakly Interacting Massive Particles. They are just theories though and none have been detected. An exciting new experiment called LUX-ZEPLIN has just completed 280 days of collecting data but still, no WIMPs have been detected above 9 Gev/c2. There are plans though to narrow the search.

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Giant Collision Decouples Dark Matter from Regular Matter

This artist's concept shows what happened when two massive clusters of galaxies, collectively known as MACS J0018.5, collided: The dark matter in the galaxy clusters (blue) sailed ahead of the associated clouds of hot gas, or normal matter (orange). Both dark matter and normal matter feel the pull of gravity, but only the normal matter experiences additional effects like shocks and turbulence that slow it down during collisions. Credit: W.M. Keck Observatory/Adam Makarenko

Dark matter is a mysterious and captivating subject. It’s a strange concept and we don’t really have a handle on what it actually is. One of the strongest pieces of evidence that dark matter is a particle comes from cosmic collisions. These collisions chiefly occur when clusters of galaxies interact such as the famous Bullet Cluster. Gravitational lensing reveals how the dark matter component couples from gas and dust in the cluster but now, astronomers have found another galaxy cluster collision but it is different, showing the collision from a new angle. 

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A Solution to the “Final Parsec Problem?”

Simulation of merging supermassive black holes. Credit: NASA's Goddard Space Flight Center/Scott Noble
Simulation of merging supermassive black holes. New research shows how dark matter overcomes the Final Parsec Problem. Credit: NASA's Goddard Space Flight Center/Scott Noble

Supermassive Black Holes are Nature’s confounding behemoths. It’s difficult for Earth-bound minds to comprehend their magnitude and power. Astrophysicists have spent decades studying them, and they’ve made progress. But one problem still baffles even them: the Final Parsec Problem.

New research might have solved the problem, and dark matter plays a role in the solution.

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