At the centers of galaxies, supermassive black holes are often found. However, some of these amazing cosmic objects may move about, wobbling from galaxy to galaxy as if they were cosmic nomads.
Black holes with wandering paths are known as wanderers, and, although they are very hard to observe (though not impossible), they are not quantifiable. A team of Scientists have been able to determine how many wanderers there should be, as well as whereabouts – which they hope will make it easier to find them.
Observing a supermassive black hole would allow us to understand how they form and grow, a mysterious process that could explain how supermassive black holes form and grow.
The nuclei of all galaxies in the universe are thought to have supermassive black holes (SMBHs). Black holes and the galaxy around them are typically about equal in mass, which implies that they have evolved parallel to one another.
However, supermassive black holes have unclear formation pathways. Black holes originating from massive stars are formed by their cores collapsing, but that mechanism does not apply to black holes with masses greater than 55 times the mass of the Sun.
Scientists believe that stellar merger black holes grow through the accretion of stars and gas, and mergers with other black holes (colossal ones that reside at the cores of other galaxies when they collide).
The process of two galaxies colliding is very long-term in nature, whereas human timescales are very short. In this situation, the possibility of disruption is quite wide, and therefore these ‘wanderers’ within a black hole can be affected to some degree.
According to the role of cosmological simulations in the calculation, worlds that have black holes still roam around in the present are most likely to have occurred in the past. The team was led by Angelo Ricarte of the Harvard & Smithsonian Center for Astrophysics.
The simulations self-consistently predict which supermassive black holes will reach their new galactic center and how long this will take. However, they cannot predict how many will never reach the center.
“Romulus predicts that many supermassive black hole binaries form after several billions of years of orbital evolution, while some SMBHs will never make it to the center,” researchers said in the paper.
“As a result, Milky Way-mass galaxies in Romulus are found to host an average of 12 supermassive black holes, which typically wander the halo far from the galactic center.”
A team of researchers found that wanderers outnumber and outshine supermassive black holes in galactic nuclei in the early Universe, before about 2 billion years after the Big Bang. As a result, they would be responsible for most of the light shined from the material surrounding active SMBHs, which glows brightly while orbiting and accreting onto black holes.
It is likely that they originate in smaller satellite galaxies orbiting larger ones and that they remain near their seed mass.
There are still some wanderers believed to exist today, based on simulations. There should actually be quite a few people hanging around the local Universe.
“We find that the number of wandering black holes scales roughly linearly with the halo mass, such that we expect thousands of wandering black holes in galaxy cluster halos,” the researchers wrote.
“When seed masses are taken into account, wanderers account for around 10 percent of the local black hole mass budget.”
It would be very difficult to detect black holes that are not necessarily active. Detailed investigations of the possible means by which we can observe lost wanderers will be presented in an upcoming paper.
After finding stellar-mass black holes, all that remains is to find intermediate-mass black holes.
Researchers have published their research in Monthly Notices of the Royal Astronomical Society.