The Most Massive Ancient Black Holes Might Not Be So Massive After All

Artist impression of a quasar. ESO/M. Kornmesser

An open question in astronomy is how some of the biggest black holes detected in the early universe got so big so quickly. Current theories have struggled to explain their hefty weight as there was not enough time for them to assemble, according to the current theories. A new study has a radical new suggestion: we might have been fooled by the universe into thinking that these objects are bigger than they actually are.

Astronomers can’t look at supermassive black holes directly, but if they are active their host galaxy may be in a quasar state, where the energy released around the black hole outshines all the stars in that galaxy.

There are about 200 known quasars from when the universe was less than 950 million years old. Of these, the one with the heaviest supermassive black hole is J0100+2802. Based on the energy it releases, the supermassive black hole weighs about 12 billion times our Sun – but a paper recently submitted in the Astrophysical Journal suggests that this incredible energy output, and consequently the black hole's mass, might be a trick of the light.

The study offers up evidence that the object might be being gravitationally lensed. Black holes, galaxies, and galaxy clusters can be dense enough to warp space-time in a way that makes them act as a lens, the gravitational field from the object bending the light from a source as it travels towards the observer. These lenses can magnify the light of background objects significantly. The researchers estimated that J0100+2802 is experiencing a magnification factor of about 450. That would mean that the actual black hole mass would be only 800 million times the mass of the Sun.

The new study, available as a pre-print on ArXiv, looked at the consequences of this. If J0100+2802 is indeed being lensed what does this mean for the population of quasars as a whole? According to the researchers, if J0100+2802 is being lensed, then it is likely that the other 50 quasars recorded in the Sloan Digital Sky Survey are also being subjected to some magnification. And if that were to be the case, then our expectations of quasars as a whole would have to change significantly. On the plus side, this would make these early black holes much smaller and easier to explain with current theories.

"It turns out that, if this quasar is indeed magnified by 450, it is extremely unlikely that the other sources in the sample are not magnified, because they share the same foreground of lensing galaxies. This is because a factor 450 is very large and unlikely to happen, especially in a relatively small sample of about 50 sources," lead author Dr Fabio Pacucci, from the Center for Astrophysics Harvard & Smithsonian, told IFLScience.

"So, if the population of lensing galaxies allowed for a magnification factor 450, it is overwhelmingly likely that it will allow for other sources to be magnified, even if by smaller factors."

It's important to note that this research is speculative and more observations are needed. The chance that this incredible quasar is experiencing such magnification is one-in-a-thousand, so it is unlikely, though not impossible. There is also the fact that the region around the quasar is ionized for tens of million light-years, something only an extremely powerful quasar could do.

The researchers are hoping other scientists will look into these claims and more observations will be made of these objects to check. Future space observatories such as WFIRST and the James Webb Space Telescope will be able to provide important new insights into these distant objects.


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