Two supermassive black holes have been found orbiting each other, forming a binary system in a galaxy about 9 billion light-years from Earth. This is the second pair of its kind found by astronomers and the objects are expected to merge in 10,000 years, a blink of an eye on the cosmic timescale.
Astronomers led by Caltech discovered evidence for this scenario, but it took data from more than 40 years of observation. The object of study was a quasar, a type of extremely energetic object, formed by a galaxy with an active nucleus. In these nuclei, there is a supermassive black hole that sucks matter from a disk that surrounds it.
In this process, the environment around the black hole generates tremendous energy, visible primarily in the radio and X-ray wavelengths of the electromagnetic spectrum, so quasars are among the most extreme and brightest objects in the world. ‘universe. In some of them, it creates a jet that shoots near the speed of light.
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When this jet is pointed at Earth, the quasar is classified into a subclass called the blazar. The quasar seen in the new study, PKS 2131-021, is one of them. Astronomers already knew that quasars could have two supermassive black holes orbiting each other, but finding direct evidence of this is difficult.
However, the authors of the new study claim that PKS 2131-021 is now the second candidate for a supermassive black hole binary system, detected moments before the merger. The first candidate pair is OJ 287, where two supermassive black holes orbit at greater distances, completing one revolution every nine years.
In turn, the PKS 2131-021 objects complete an orbit in just two years, suggesting that the collision will occur long before that of the first candidate. According to the team, black holes are only 2,000 astronomical units apart (about 50 times the distance between our Sun and Pluto). This means that they are 10 to 100 times closer to each other than the black holes in OJ 287.
How did supermassive black holes meet?
Scientists have good reason to say that at the heart of most, if not all, galaxies is a supermassive black hole. It is even possible that they play an important role in the formation of galaxies. But the presence of two could only be explained by a single event: the collision between two galaxies.
When two galaxies meet, they merge, just as they are. occurring with the Milky Way and Andromeda. When the merger is complete, the black holes from each “sink” towards the center of the new galaxy and begin to orbit each other, supposedly heading for a colossal collision that should generate intense waves. gravitational.
Despite expectations of a future collision between these outsized objects, some theoretical physicists suspect that it is impossible. Calculations show that black holes must be about 0.01 light-years away, which is equivalent to the distance between the Sun and trans-Neptunian objects – remembering that currently the two objects from PKS 2131- 021 are separated by about 50 times the distance between them. our Sun and Pluto.
These theorists also calculate that the mechanisms behind approaching black holes, such as dynamic friction and loss of orbital energy, thus bring black holes closer together. Therefore, it is possible that they will simply stop approaching after a certain minimum distance limit and not collide. This mathematical assumption is known as final parsec problem.
One of the ways to detect collisions like this is through gravitational waves, predicted by Albert Einstein over 100 years ago and confirmed by the first detection in 2016. As black holes spiral, they increasingly disrupt the fabric of space and time, sending these ripples through the universe , just like when we throw a stone into a lake.
Unfortunately, supermassive black holes at the center of galaxies emit gravitational wave frequencies lower than those detected by our current instruments. Therefore, scientists intend to put new instruments into action in the future. One of them is LISA, which would detect the merger of black holes whose masses are 1,000 to 10 million times greater than the mass of our Sun.
So far, no gravitational wave from a binary system of supermassive black holes has been recorded. So PKS 2131-021 is, for now, the most promising target to date. The article describing the discovery was published in The Astrophysical Journal Letters.