Finding new particles around black holes using gravitational waves

(ORDO NEWS) — Clouds of ultralight particles can form around rotating black holes. A team of physicists from the University of Amsterdam and Harvard University shows that these clouds leave a signature imprint on the gravitational waves emitted by binary black holes.

It is generally believed that black holes absorb all forms of matter and energy around them. However, it has long been known that they can also lose some of their mass through a process called superradiance.

Although this phenomenon does take place, it is effective only if there are new, yet unobservable particles with very low mass in nature.

When mass is extracted from a black hole via superradiance, it forms a large cloud around the black hole, creating what is known as a gravitational atom.

Despite the huge size of the gravitational atom, the comparison with submicroscopic atoms is accurate due to the similarity of a black hole and its cloud to the familiar structure of ordinary atoms, where clouds of electrons surround a core of protons and neutrons.

Scientists suggest that the analogy between ordinary and gravitational atoms goes deeper than just a similarity in structure. In their new work, they studied the gravitational equivalent of the so-called “photoelectric effect”.

In this well-known process, which is used, for example, in solar cells to generate electrical current, ordinary electrons absorb the energy of incident light particles and are thus ejected from the material – the atoms are “ionized”.

By analogy, when a gravitational atom is part of a binary system of two heavy objects, it is perturbed by the presence of a massive companion, which could be a second black hole or a neutron star.

Just as electrons in the photoelectric effect absorb the energy of incident light, a cloud of ultralight particles can absorb the orbital energy of a companion,

The team found that this process could drastically change the evolution of such binary systems, significantly reducing the time it takes for components to fuse with each other.

Moreover, the ionization of a gravitational atom is enhanced at very specific distances between binary black holes, resulting in the sharp features in the gravitational waves that we find in such mergers.

Future gravitational wave interferometers – machines like the LIGO and Virgo detectors that have shown us the first gravitational waves from black holes over the past few years – could observe these effects.

The detection of the predicted features of gravitational atoms will serve as convincing proof of the existence of new ultralight particles.

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