When galaxies collide, the supermassive black holes at their centers are thrown together. Sometimes the pair merge together gracefully. But if the two black holes come together with enough energy, the new black hole can be pushed away from the center of that galaxy, or even kicked out completely. Hunting for these off-center black holes can help scientists better understand how often galaxies merge as well as determine the frequency of the gravitational waves they generate.
Supermassive black holes absorb all light and cannot be directly seen. Instead, scientists presented them by hunting down gravitational effects on stars, gas and dust. But unlike the black holes that are small they generate by single stars and supermassive black holes have somewhere around 100 times the mass of the sun. Because they are huge mass, their mergers should produce gravitational waves that the European Space Agency’s Laser Interferometer Space Antenna (LISA) spacecraft will be able to detect after its launch.
Intrigued by the connection to gravitational waves, Yashashree Jadhav, a graduate student at Rochester Institute of Technology has searched for supermassive black holes that were offset from the center of their galaxy. Jadhav is combing through a hundred galaxies imaged by NASA’s Hubble Space Telescope to determine how many host off-center black holes. Jadhav presented her work in January at the annual winter meeting of the American Astronomical Society in Seattle, Washington.
The Laser Interferometer Gravitational-Wave Observatory (LIGO) has detected gravitational-wave signals. That produced by merging black holes, at least one came from the collision of a pair of neutron stars, the densest type of star in the universe. According to Jadhav, LIGO isn’t able to detect the type of supermassive black holes that are heavy enough to generate a kick. That’s because more massive objects, as well as those in wider orbits, release a longer wavelength than those LIGO is hunting.
Enter LISA, a space-based mission set to launch by 2034. LISA will operate in a lower frequency range than LIGO, allowing the spacecraft to probe a wider range of gravitational-wave sources. With her results, Jadhav hopes to estimate how many supermassive black holes LISA will be able to spot once it has been launched.