September 18, 2021

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Gravitational waves can reveal black holes in dark dresses

Gravitational waves can reveal black holes in dark dresses

Perplexing clouds of dark matter can hang like a garment around some black holes. The presence of such a garment may be visible in gravitational waves that arise when a black hole merges with another object. This is written by a group of Amsterdam and Spanish astrophysicists in Article on the pre-publishing site ArXiv.

About 85 percent of the matter in the universe is made up of something we don’t yet know about. We know that this “dark matter” is necessary to explain the movements of stars and galaxies. But no one knows what kind of things this is. Searches have been done in vain for years, including in particle physics experiments.

A few years ago, physicists developed a new way to study the universe: via gravitational waves. These waves originate in spacetime, for example, at two black holes or neutron neutrons Move towards each other, collide and merge.

dark dresses

A group of astrophysicists among them Gianfranco Burton employment Adam Cogan From the University of Amsterdam, he now proposes a way to search for dark matter using gravitational waves. These are clouds of dark matter that could be suspended around a black hole.

These dark dresses do not directly affect gravitational waves, but they do affect the way black holes move. Bradley Kavanagh From the Instituto Física de Cantabria in Spain. This is mainly caused by an effect called dynamic friction. A heavy object, such as a black hole, experiences some kind of friction as it moves through a cloud of particles. This friction is caused by the effects of gravity.

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This friction affects the movement of black holes or neutron stars that curl towards each other. This is also when gravitational waves are emitted. The gravitational waves that we can measure show the last few orbits in which two black holes or two neutron stars orbited each other before the merger.

If one of them is wearing a dark dress, they will wrap around each other less before merging. So if you measure gravitational waves with fewer cycles than you expect, it could be a sign of dark matter’s mantle.

Primordial black holes

It is not yet certain whether dark dresses exist. But astrophysicists believe there are two ways a black hole could fit into such a dress.

One possibility is that they formed around the so-called Primordial black holesEmail Cogan. These black holes may have formed shortly after the Big Bang, when dark matter was (most likely) evenly distributed throughout the universe.

The existence of primordial black holes is still uncertain. If present, the dark matter near the primordial black hole could become gravitationally bound to it during its formation, forming a dark mantle. This would be similar to the Moon gravitationally bound to the Earth.

know more? Read an interview with Gianfranco Bertone here, one of the authors of this study.

In the second scenario, the universe is somewhat older. “These are black holes that form in a cloud of dark matter,” Kavanagh says. A black hole, with an already high density of dark matter, can form a dark mantle around itself.

So you don’t get a dark dress like a black hole. And if you have one, it’s hard to keep. The dress can be easily ripped off due to environmental disturbances. Kavanagh: “One of the questions we hope to answer soon is: How many black holes can fit into a dark dress?”

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waiting for lisa

So the existence of dark dresses is still speculative. If they exist, the researchers wrote, it is likely that current gravitational wave detectors cannot detect them yet. “To detect a dark dress, we need a specific system,” Kavanagh says. “This is a black hole with a mass of one hundred to one hundred thousand times the mass of the Sun, surrounded by a much lighter black hole or spiral neutron star.” The heaviest black hole is wearing the dress.

“The frequency of the gravitational waves that these specific systems emit is too low for current gravitational wave detectors,” Kogan adds. The Detector Lisa in the future, which should be in space, will be able to measure it. We’ll have to wait at least another ten years to get a LISA. This gives us time to refine our theoretical models, so that we are ready when the measurements begin.

Reading tip: Astroparticle physicist Gianfranco Berton (one of the authors of the publication) explains how astronomy, thanks to the discovery of gravitational waves, is on the verge of a revolution. Available in our online store