Astronomers have discovered a diminutive supermassive black hole at the center of dwarf galaxy Mkr 462. It weighs 200,000 times the mass of our Sun. Certainly huge in human terms, but very much on the small side when we consider that supermassive black holes often weigh millions, if not billions, of solar masses.
This discovery was presented virtually at the 239th meeting of the American Astronomical Society.
The fact that it is so small could provide insights into how its heavier counterparts grew so much, and in some cases so fast. Supermassive black holes weighing over a billion solar masses were already in place just one billion years after the big bang. And we are not sure how. The observations that led to this new discovery might expand on that.
"We can't make strong conclusions from one example, but this result should encourage much more extensive searches for buried black holes in dwarf galaxies," Jack Parker of Dartmouth College in New Hampshire, who led the study, said in a statement. "We're excited about what we might learn."
The team of researchers focused on a set of eight dwarf galaxies that astronomers suspected could have a growing supermassive black hole at their center. This was based exclusively on observations conducted in visible light by the Sloan Digital Sky Survey.
But tell-tale signs of growing black holes can be more clearly seen beyond the visible spectrum. The reason is that black holes are messy eaters. When they actively feed, they release particles and high-energy light, and this process can be spotted using x-rays detectors.
NASA’s Chandra was tasked with this investigation. Among the eight galaxies with a suspected growing black hole, it only found convincing evidence of one – Mkr 462. And it was certainly a peculiar black hole.
"This black hole in Mrk 462 is among the smallest of the supermassive, or monster, black holes," explained Parker. "Black holes like this are notoriously hard to find."
There are a few theoretical scenarios that could explain the formation and rapid growth of these "monsters". The seeds of these supermassive black holes might have been planted by the first generation of stars, which are expected to be a lot more massive than the Sun. As they dramatically ended in supernovae, they would leave behind massive black holes that would merge with similar-sized objects, quickly growing to supermassive size.
Another possibility is the spontaneous formation of black holes in the chaotic aftermath of the big bang. These primordial black holes could be numerous and massive enough to lead to the formation of the supermassive type (and maybe explain dark matter).
Both scenarios will be tested out by the JWST, the most powerful space telescope ever launched, currently en route to its operational orbit.