Around revolving black holes, clouds of lightweight particles can form. These clouds would leave a distinctive mark on the gravitational waves emitted by binary black holes, according to scientists from the University of Amsterdam and Harvard University.
Black holes are supposed to absorb all matter and energy in their immediate vicinity. They can, however, lose some of their mass through a process called super-radiance, which has been recognized for a long time. While this phenomenon is well-known, it can only work if new, previously undetected particles with extremely low masses exist in nature, as predicted by various hypotheses outside the Standard Model of particle physics.
When mass is removed from a black hole through superradiance, a huge cloud grows around the black hole, forming a gravitational atom. Despite the gravitational atom’s enormous scale, the analogy with sub-microscopic atoms is accurate due to the black hole’s cloud’s resemblance to the familiar structure of conventional atoms, in which clouds of electrons surround a core of protons and neutrons.
A team of UvA physicists Daniel Baumann, Gianfranco Bertone, and Giovanni Maria Tomaselli, as well as Harvard University scientist John Stout, published a paper in Physical Review Letters this week that suggests the connection between conventional and gravitational atoms is more than simply structural. They claim that gravitational wave interferometers will be able to use the similarities to discover new particles.
The gravitational equivalent of the so-called “photoelectric effect” was investigated in the current study. Ordinary electrons absorb the energy of incident light particles and are ejected from a material in this well-known process, which is used to generate an electric current in solar cells, for example.
The presence of the large partner, which may be a second black hole or a neutron star, perturbs the gravitational atom when it is part of a binary system of two heavy objects in the gravitational analogue. In the same way that electrons absorb the energy of incident light in the photoelectric effect, the cloud of ultralight particles can absorb the orbital energy of the companion, causing some of the cloud to be ejected from the gravitational atom.
The researchers proved that this method can drastically alter the development of binary systems by drastically lowering the time it takes for the components to join. Furthermore, at extremely particular distances between binary black holes, the ionization of the gravitational atom is amplified, resulting in distinct characteristics in the gravitational waves that we detect from such mergers.
Future gravitational-wave interferometers, similar to the LIGO and Virgo detectors that have detected the first gravitational waves from black holes in recent years, may be able to detect these effects. The discovery of the expected properties in gravitational atoms would be compelling proof for the presence of new ultralight particles.