How Black Holes Eat Reveals Their Mass

Black hole accretion disk
An artist’s impression of an accretion disk rotating round an unseen supermassive black hole. The accretion course of produces random fluctuations in luminosity from the disk over time, a sample discovered to be associated to the mass of the black hole.
Mark A. Garlick / Simons Foundation

No one is aware of why quasars flicker. Yet these wavering beacons of sunshine could be sending us a message in regards to the black hole programs that energy them.

Whirling plasma disks feed supermassive black holes in distant galaxies, and these disks produce a cascade of seen and ultraviolet gentle that may outshine all of the stars within the host. With a lot power packed into such a small space, although, the disks turn into unstable. As a outcome, their emissions change randomly, brightening and dimming with no recognizable sample attributable to any single characteristic, similar to, say, a scorching spot orbiting across the black hole.

Astronomers are actively working to know why black hole disks behave the way they do. But even when we don’t absolutely perceive the mechanism behind the flickering, we will nonetheless use it to know the programs themselves, assert Colin Burke and Yue Shen (University of Illinois, Urbana-Champaign) and their colleagues within the August thirteenth Science.

Mass from Flickers

Mass is one among solely two descriptors of black holes (the opposite being spin) — they’re in any other case the final word black field. Yet supermassive black holes are troublesome to heave onto a scale.

Astronomers can measure the whirling stars or gas within the galactic heart to immediately “weigh” the central black hole, however this technique solely works for close by specimens (most notably our personal 4 million-solar-mass behemoth, Sgr A*). Other extra oblique mass measures contain timing gentle coming from the disk because it “echoes” off close by clouds, or much more not directly, figuring out the mass based mostly on relationships with properties of the host galaxy.

Finding a brand new technique to find out black hole mass could be an enormous win, and former research hinted that variability could be the way to do it. So Burke’s crew analyzed 67 quasars to find out on what timescales — days, weeks, months, or years — their random brightness adjustments turn into noticeably smaller.

Black hole disk variability
As gas spirals right into a black hole, it heats up and emits gentle. Due to instabilities within the gas stream, that gentle glints. The common distinction in brightness between two random timestamps will increase because the hole between the 2 timestamps will increase. However, longer than a sure timescale, this sample adjustments; this “damping” timescale correlates tightly with mass.
Lucy Reading-Ikkanda / Simons Foundation

The researchers then in contrast that damping timescale to the black holes’ beforehand measured lots (utilizing a type of different means talked about above).

Lo and behold, they discovered that the damping timescale predicts the black hole mass over an enormous scale, from 10,000 to 10 billion solar lots. The improved information, particularly the big selection in mass, enabled the crew to clarify a relation that earlier research had solely hinted at.

It’s not an ideal 1:1 correlation, although; particular person predictions are nonetheless unsure by an element of two. It may very well be that completely different black hole spins or feeding charges throw the relation off a bit, or maybe the black hole lots themselves will not be precisely proper. But general, the relation is nearly as good as every other that astronomers at present use to acquire black hole mass.

This technique has a draw back, although, and that’s time. The crew wanted years of brightness information for every quasar of their pattern. What’s extra, the farther a black hole is, the extra its alerts are stretched out in time. More huge black holes even have longer damping timescales, and the distant black holes we see are usually extra huge.

While Burke and Shen’s crew pored by means of beforehand revealed information for his or her pattern, sooner or later information on extra distant quasars might come from giant all-sky surveys, such because the one astronomers intend to conduct with the Rubin Observatory when it comes on-line subsequent year.

Why Do Quasars Flicker?

The relation with damping timescale might have given astronomers a brand new way to measure mass. But it additionally provides them a brand new way to know variability.

“One of the most interesting aspects of the study of Burke et al. is that it extends its findings to much less massive objects, such as white dwarf stars,” Paulina Lira (University of Chile) and Patricia Arevalo (University of Valparaiso, Chile) write in an accompanying perspective piece. “That the same relation extends through many orders of magnitude suggests that the physics of accretion disks is, at least in some aspects, scalable.”


What a flickering black hole accretion disk really appears like stays consigned to artist’s interpretations. Is your complete disk crackling with magnetic fields, or do hotspots flare up and dissipate within the denser inside areas?

Shen means that the damping timescale his crew measured is definitely the thermal timescale, or how lengthy it takes for the disk to chill off after one thing has riled it up. Instabilities within the spiraling plasma are continuously agitating the disk, however any particular person temperature flare solely lasts on the order of 100 days. Whatever is inflicting the variability, it’s intrinsic to the seething plasma within the hottest and densest a part of the disk.

Without the flexibility to resolve a picture of those disks, astronomers will proceed to make use of completely different wavelengths and arrival instances of quasar gentle to higher perceive these black hole–powered programs.

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