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Category: cosmology

Gravitational waves from colliding black holes may allow detection of dark matter

Dark matter is thought to make up most of the matter in the universe, but the only way it interacts with its surroundings is through gravity. If two colliding black holes spiral through a dense region of dark matter and merge, gravitational waves rippling across space and time could carry an imprint of that dark matter.

Now, physicists may be able to spot such imprints of dark matter in gravitational waves that are detected on Earth.

Researchers at MIT and in Europe have developed a method that makes predictions for what a gravitational wave should look like if it were produced by black holes that moved through dark matter, rather than empty space. They applied the technique to publicly available gravitational-wave data previously recorded by LIGO-Virgo-KAGRA (LVK), the global network of observatories that detect gravitational waves from black hole mergers and other far-off astrophysical sources.

Gravitational wave detectors can now ‘autotune’ signals to harmonize the heavens

Gravitational wave researchers working on the world’s most sensitive scientific instruments have found a way to tune their detectors using a process akin to the pitch-correction used in music production.

Scientists at the international LIGO, Virgo and KAGRA (LVK) gravitational wave observatory collaboration have employed the technique, which they call astrophysical calibration, to use gravitational-wave signals to measure the response of their incredibly sensitive instruments.

It enables them to ensure that they can clearly “hear” the sounds of colossal cosmic events like the collision of black holes, even when one gravitational wave detector is slightly out of tune. This is crucial to accurately interpret the signals and find their source location.

Largest-ever survey of physicists puts Standard Model of cosmology under scrutiny

The largest-ever survey of physicists from around the world—released today—shows a distinct lack of consensus across many of physics’s most important questions, from the nature of black holes and dark matter, to the still-incomplete unification of Einstein’s theory of gravity with quantum mechanics.

Even the best theory of the universe’s expansion, known as the standard model of cosmology or ΛCDM (Lambda Cold Dark Matter), did not attain majority support. This surprising outcome is perhaps due to results from the Dark Energy Spectroscopic Instrument (DESI) last year, which hinted that dark energy may change over time, in opposition to the standard model’s conviction that dark energy remains constant.

But that wasn’t the only surprising outcome. The survey doesn’t seem to find much agreement anywhere.

What If Dark Matter Is Just Black Holes?

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It may be that for every star in the universe there are billions of microscopic black holes streaming through the solar system, the planet, even our bodies every second. Sounds horrible — but hey, at least we’d have explained dark matter.

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In Quantum Gravity, the Cosmological Constant May Behave Similar To The Quantum Hall Effect

So why not do the same thing for a gravitational field? Well, it turns out that quantum renormalization only works for Euclidean space. In general relativity, the mass-energy of a system warps space and time. So all those quantum fluctuations curve spacetime, and curved spacetime induces even more virtual particles, which warp space even more… oh no! It all breaks down, and we can’t quantize gravitational fields the way we quantize the other fundamental forces.

Problems like these have led some researchers to develop a model known as loop quantum gravity. Rather than trying to calculate the behavior of quantum particles in a timey-wimey background, why not treat the entire mass-energy-spacetime structure as a single quantum system? It’s like imagining the Universe within an unseen background that is Euclidean. This way the problem of renormalization can be overcome in many cases. One case where it doesn’t work well is the cosmological constant. In most cosmological models, the cosmological constant is what drives cosmic expansion. Since it is a universal dark energy field, it amplifies the loop quantum gravity sums, and once again the whole thing diverges. You can handle this by fixing the cosmological constant to a specific value, but that isn’t really a solution to the problem. It’s the cosmology equivalent of ignoring the engine light in your car…

A new study finds this might not be too bad after all. In it, the authors demonstrate an interesting similarity between the cosmological constant in loop quantum gravity and the quantum Hall effect in standard quantum theory.

Physicists find evidence that the universe isn’t perfectly uniform — potentially unraveling a 100-year-old model of cosmology

The universe may not be perfectly uniform after all, a new series of papers hints. If confirmed, this could upend a nearly 100-year-old model of cosmology.

JWST spots two early black holes growing far faster than their galaxies

Astronomers have discovered two early-universe galaxies where the central black holes appear to have grown far faster than their host galaxies. Observations with the James Webb Space Telescope (JWST) reveal that the black holes in these galaxies, seen just 800 million years after the Big Bang, are significantly more massive relative to their host galaxies, as opposed to what astronomers see in the nearby universe. The study is published on the arXiv preprint server.

Astronomers have long discovered quasars—extraordinarily luminous galaxies powered by accreting black holes weighing billions of solar masses—in the first billion years of the universe. For these to exist so early, the black holes must have started as large as heavy seeds and grown at their maximum rate possible for most of their lives. These early black holes appear oversized compared to the galaxies they live in.

On the other hand, when JWST began its operation in 2022, it made a huge splash in astronomy with the discovery of an astonishingly large number of mature galaxies and black holes in the first billion years of the universe. Among them were some “overmassive” black holes weighing billions of times the mass of our sun, but rarely as massive as those found in luminous quasars.

How a single star can reshape an entire galaxy

Astronomers who simulate galaxies do not always get the same result, even when they start from identical conditions. New research from Leiden University shows that this is not a flaw, but a consequence of how galaxies behave—and how they are modeled.

The findings offer, for the first time, a way to address a long-standing question: how chaotic is a galaxy like the Milky Way really? The computer simulations by Tetsuro Asano and Simon Portegies Zwart (Leiden Observatory) will soon be published in Astronomy & Astrophysics and are available now on the arXiv preprint server.

The researchers created hundreds of models of Milky Way-like galaxies: flat disks of stars, embedded in a large, invisible cloud of dark matter that holds the system together. In each experiment, they ran two almost identical simulations, differing by just one tiny detail—for instance, a small shift in the position of a single star. Over time, that slight difference grows into visible structural changes: the spiral arms develop differently and the central bar rotates in another way.

Unexplored interactions between electrons and atomic nuclei shed light on dark matter

Dark matter particles could be mediators of the interaction between electrons and atomic nuclei, as shown by a study conducted by junior group leader, Dr. Konstantin Gaul, Dr. Lei Cong, and Professor Dr. Dmitry Budker, of Johannes Gutenberg University Mainz (JGU), Helmholtz Institute Mainz (HIM) and the PRISMA++ Cluster of Excellence. Their work, published last week in Physical Review Letters, presents new constraints on previously unexplored candidates for dark matter and, more generally, some hypothetical particles that are not included in the Standard Model of particle physics ℠.

Using results from precision measurements on barium monofluoride (BaF) molecules, the team constrained these interactions mediated by Z’ bosons for the first time. Z’ bosons are hypothetical mediators of the weak interaction and possible dark matter particles in several SM extensions. “These results address a significant blind spot in physics: a regime of forces between electrons and nuclei that had remained unexplored by both laboratory experiments and cosmological data,” explained Gaul.

Our universe is made up of about 4% of visible, or ordinary, matter. This includes planets, stars, and life on Earth. The remaining 96% of the universe is invisible and consists of dark matter and dark energy, with dark matter making up about 23%. Astrophysical observations confirm its presence throughout the cosmos, where it, for example, plays an important part in the structure of galaxies. However, we don’t know what particles make up dark matter. Many theories and ongoing experiments are looking for an answer to this open question.

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