Among the black holes identified to date, they are either small or galaxy-eating monsters, roaring inside star clusters. “Between these two limits, we see nothing,” said astrophysicist James Paynter of the University of Melbourne. But behold, from the dawn of the cosmos, a black hole of intermediate size appears, one that may mean the key to understanding how singularities are born and, above all, grow.
“Although we know that supermassive black holes hide in the nuclei of galaxies, we do not understand how these giants are able to grow so much within the age of the Universe,” said Paynter, lead author of the study now published in the journal Nature Astronomy.
The importance of the discovery, considered the missing link in the study of black holes, is measured by an unusual fact: astronomers have never confirmed that it is a “medium” size black hole. The small black holes (or stellar masses) are what remains of supermassive stars. They are common in the Universe, as much as the stars that originate them.
Less common are those that inhabit the center of galaxies, with a hundred billion solar masses (the Milky Way has one, called Sagittarius A *). They are thought to originate from the first black holes, which arose when the cosmos was less than a billion years old. In common, the two have the way they grow: joining other black holes, feeding on anything that falls beyond their event horizon and, finally, becoming supermassive.
The problem is that, by equalizing the estimated age of the Universe and the size of the largest black holes in existence, the account does not match. According to black hole physics, there is a limit to the speed with which they devour matter, and how much a black hole can grow. In addition, merging with others assumes that there are black holes available to be absorbed.
For this reason, astronomers were looking for a black hole that was neither so small (with size ranging from 100 to 100,000 times the mass of the Sun) nor monstrously large, such as J2157-3602, the uniqueness of 34 billion solar masses that faster grows, swallowing the equivalent of one sun a day.
“This black hole could be a relic, a primordial black hole created at the beginning of the Universe even before the formation of the first stars and galaxies. These first singularities may be the seeds of the supermassive black holes that live in the heart of galaxies today,” said the astrophysicist Eric Thrane, from the Monash University School of Physics and co-author of the study.
Paynter reviewed the more than 2,700 records of explosions that BATSE (acronym for Burst And Transient Source Experiment, or Experiment in Blast and Transient Source) captured between 1990 and 1999, looking for one that would reveal, through gravitational lenses, the presence of a IMBH.
Gravitational lenses are an effect that astronomers use to locate celestial bodies and measure the Universe. It is caused by powerful gravity-generating objects, such as galaxies and black holes.