There were more black holes in the early universe than we thought, Hubble research reveals

Supermassive black holes are some of the most impressive (and scary) objects in the universe — with masses around one billion times more than that of the Sun. And we know they've been around for a long time.

In fact, astronomers have detected the extremely luminous compact sources that are located at the centres of galaxies, known as quasars (rapidly growing supermassive black holes), when the universe was less than 1 billion years old.

Now our new study, published in Astrophysical Journal Letters, has used observations from the Hubble Space Telescope to show that there were many more (much less luminous) black holes in the early universe than previous estimates had suggested. Excitingly, this can help us understand how they formed — and why many of them appear to be more massive than expected.

Black holes grow by swallowing up material that surrounds them, in a process known as accretion. This produces tremendous amounts of radiation. The pressure from this radiation places a fundamental limit on how quickly black holes can grow.

Scientists were therefore faced with a challenge in explaining these early, massive quasars: without much cosmic time in which to feed, they must have either grown quicker than physically possible, or been born surprisingly massive.

Related: A 'primordial' black hole may zoom through our solar system every decade

Light vs. heavy seeds

But how do black holes form at all? Several possibilities exist. The first is that so-called primordial black holes have been in existence since shortly after the big bang. While plausible for black holes with low masses, massive black holes cannot have formed in significant numbers according to the standard model of cosmology.