For black holes, size matters. Or does it?
A team of researchers has uncovered a novel method of measuring the mass of black holes via observing the flickering light of their accretion discs, according to a recent study published in the journal Science.
This means we might have a new way of inferring the mass of any black hole, regardless of its mass.
A very tiny supermassive black hole yields a game-changing method
Colin Burke, a graduate student of astronomy at the University of Illinois, discovered something about an atypically small supermassive black hole that wasn't up to snuff. The flickering light flashing from the insatiable maw of the black hole broke with the norm of larger singularities of the same massive type, suggesting that the size of black holes has a direct bearing on the surrounding flickers that, while small from our Earth-bound distance, are actually terrifying bursts of energy generated as the monstrous phenomenon sucks in matter, like a last cosmic gasp before passing the event horizon.
Following up on this observation, Burke and his colleagues derived a novel method for measuring black hole masses that involves examining the flickering light of their accretion discs. And in so doing, the team of researchers may have invented an exciting new means of measuring not only black holes, but other dense objects in the universe. And this flicker-focused mass measuring tool could even reveal how black holes reshaped the salad days of the cosmos itself. The team focused their study on a specific black hole — a (comparatively) small one at the heart of a galaxy named NGC 4395. It's a spiral galaxy, and it's housing one of the tiniest supermassive black holes astronomers have ever spotted.
A new measuring tool for black holes could help unlock the mysteries of cosmic evolution
For reference, this galaxy's dark heart is only one-sixth the size of the supermassive black hole churning relentlessly at the center of our own Milky Way. Burke and colleagues then measured the timescale of the flickering accretion disc of the black hole, and compared it with those from earlier measurements of other, larger ones. Accretion discs are not your friend: They're unconscionably hot discs of plasma, gas, dust, and other particles swirling around the big angry maw in space. As matter composing accretion discs falls helplessly into the black hole, it warms to deadly temperatures, lashing out with colossal volumes of radiation, which lights up all surrounding space. And we can see it happen so far away that the entire universe had time to evolve before the light reached us.
"I saw there was a pretty big difference between them," said Burke in an Inverse report. "It's not a solid disc, it's kind of like a burning fire, but some parts are hotter, and some parts are cooler than the other side." The average time it takes for each accretion disc to achieve equilibrium defines the timescale that astronomers measure, and in the recent study, the researchers propose that black holes' masses are proportional to the duration of the flickering timescale. In other words, if it's massive, a black hole's accretion disc takes longer, on average to reach equilibrium. This means that, by measuring the flickering light, scientists may infer the real-world mass of black holes, since supermassive ones are just like ordinary-sized ones. But more massive.
We've learned a lot about black holes in the last several years, most notably perhaps how critical they might be to the most crucially formative years of our universe's evolution. But with this method, we might also be able to take a more accurate census of the masses of black holes throughout the universe, both from (comparatively) recent cosmic history, like the supermassive one at the center of our galaxy, and also the intermediate and smaller ones that litter the cosmos, marking the end of long-lost stars.