If the prediction is correct, the titanic encounter will take place between the next hundred and three hundred days.
At the center of a distant galaxy, 1.2 billion light-years away, something extraordinary is about to happen: two enormous black holes, with a combined mass of hundreds of millions of suns, appear to be taking the final steps of a merger. a cataclysmic event that will hammer the space-time fabric of the Universe, sending powerful gravitational waves through space. And this time, when scientists announce that the event is ‘about to happen, they are not saying that it will take place in thousands or millions of years, but in a period of between one hundred and three hundred days.
As soon as the study appeared on the arXiv pre-publication server a few days ago, other astronomers did not hesitate to tune up their telescopes so as not to miss a show that, in addition to gravitational waves, could produce a burst of light across the entire electromagnetic spectrum. and send out massive amounts of neutrinos that would reveal valuable details of the collision.
Nobody, in short, wants to miss the show when it happens. In the words of Huan Yang, of the Perimeter Institute in Waterloo, Canada, and a co-author of the work, “we have seen people reacting quite quickly.”
Could be a mirage
Of course, it could also be that absolutely nothing happens and the prediction turns out to be a mere mirage. For example, it is not entirely clear that this galaxy has two black holes, and according to some, all the evidence presented by the researchers “is quite circumstantial.”
We know that virtually all galaxies harbor supermassive black holes at their centers, although theorists disagree on how they can grow so large (several have been found to have tens of billions of times the mass of the galaxy). Sun). Some of these ‘beasts feed sporadically on the surrounding material, heating it to such an extent that it begins to glow with enormous intensity. But that might not be enough to explain its sheer size.
Others think that they could grow by merging with other black holes, something they would do during the many collisions that occur between galaxies. Each one would contribute a black hole and both would gravitationally attract each other until they merge into a single much larger one.
But those pairs of black holes are not easy to detect. So far, large X-ray telescopes have only managed to discover a handful of active galactic nuclei (AGN) with two separate central sources. ‘ be brief. In fact, and although it is certain that they will end up merging, the process can even take billions of years. Too long for any astronomer.
However, some active galaxy nuclei dim and then re-brighten regularly, and astronomers think this is because there are two black holes revolving around each other before merging, regularly reheating material with each orbit. a galactic environment that surrounds them, giving rise to cycles of brightening and dimming. They are known as periodic AGN.
A very particular case
Under the direction of Ning Jiang of the University of Science and Technology of China, the study authors stumbled upon one such periodic AGN, called SDSSJ1430+2303. “And my first instinct,” says Jiang, “was that it must be related to a pair of supermassive black holes.”
But the researchers saw something else, something that makes them think of a pair of black holes very close to merging: the cycles of brightening and dimming is rapidly shortening. So much so that in just three years of observation they went from lasting a year to lasting only a month. That implies that their orbits around each other were getting closer and closer, heralding a very close encounter in time. If this downward trend continues, the black holes, which Jiang says are already as close as the Sun is to Pluto, will merge over the next 100 to 300 days.
A burst of light
If the team is correct and the merger does happen, there will most likely be “a big bang across the entire electromagnetic spectrum, from gamma rays to radio.” A true avalanche of neutrinos could also take place, easily detectable by the Ice Cube, the neutrino detector installed at the South Pole. Although none of this is certain.
The only certain thing is that if the fusion takes place it will generate powerful gravitational waves, although there is also a problem with them. The enormous mass of the two colliding objects will, in effect, emit them at a frequency too low to be picked up by current detectors, which are ‘tuned’ to the waves generated by the merger of much smaller objects (and with higher frequencies). higher). Although even so, according to the researchers, it would be possible to detect the trace they leave in space-time itself, a kind of relaxation of distance and time called ‘gravitational wave memory and that it could be visible for many years by monitoring the activity of pulsars. Complicated, yes, but possible. And if it is achieved, it would be irrefutable proof of the merger of two supermassive black holes.
For now, all that can be done is to keep watching and see if the cycle lengths continue to shorten over the next few weeks, which would reveal that the black holes are getting closer to each other. If everything turns out as the study predicts, it would be the first time this type of merger has been observed between such huge objects. And perhaps an answer will finally be found to the question of the excessive growth of these dark space giants.
