Flicker

A new breakthrough may reveal how black holes influenced the early universe

“We don't how they grew to be so supermassive so quickly in the universe.”

Colin Burke noticed something odd while observing a smaller-than-average supermassive black hole at the center of a nearby galaxy.

When he compared the flickering of light from the cosmic maw with the light coming from more massive black holes, there was a major difference. That variability in the flickering indicated that perhaps black holes of different sizes have different surrounding lights — bursts caused by matter sucked into the black hole itself.

Using that, Burke and his colleagues came up with a new way to measure the mass of black holes, by looking at the flickering light of their accretion discs.

In the process, they may have a game-changing new method for measuring the mass of black holes and other cosmic dense objects — and a tool that can eventually be used to understand how black holes influenced the early universe.

Their findings were detailed in a study published Thursday in the journal Science.

WHAT’S NEW — The study team focused on a small black hole at the center of the galaxy NGC 4395. The spiral galaxy has one of the smallest supermassive black holes scientists have observed. It is six times smaller than the one at the center of the Milky Way.

“... it’s kind of like a burning fire.”

Burke and colleagues measured the flickering timescale of the black hole’s accretion disc and compared it with the timescales of previous measurements of larger black holes. Accretion discs are discs of gas, plasma, dust, or particles that surround a black hole. As material from the accretion discs falls onto the black hole, it heats up and releases a massive amount of radiation, lighting up its surrounding space in the process.

“I saw there was a pretty big difference between them,” Burke tells Inverse. “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.”

Timescales are measured in the average time it takes for the disc to reach equilibrium.

In the paper, the authors suggest that the more massive a black hole is, the longer its flickering timescale. By measuring the timescale, scientists can figure out the mass of the black holes since supermassive black holes are scaled-up versions of their less massive counterparts.

This makes for a new and novel way to measure black hole masses rather than relying on interactions with nearby objects.

A simulation of what it’s like when supermassive black holes flicker. Mark A. Garlick / Simons Foundation

HERE’S THE BACKGROUND — A black hole is a region of space with a gravitational pull so strong that nothing can escape its influence, not even light itself. A black hole feeds on its surrounding material, gobbling up nearby stars and other objects in order to grow in size.

Black holes typically come in three sizes:

  • Stellar-mass black holes, which are five to 10 times the mass of the Sun
  • Intermediate black holes, the middleweight black holes 100 to 1 million times the mass of the Sun, which are poorly studied and whose formation isn’t well understood
  • Supermassive black holes, which are millions or billions of times the Sun’s mass

Why this matters — Astronomers aren’t exactly sure how intermediate and supermassive black holes grow to their enormous sizes.

“That's one of the major questions of and astronomy,” Burke says. “We don't how they grew to be so supermassive so quickly in the universe.”

This is why a new method for measuring mass is so important.

By figuring out the mass of the black holes, scientists can determine their influence on their surrounding environments, and maybe even how they influenced the early universe. It may also make it easier to measure intermediate-mass black holes, which power the centers of small dwarf galaxies and some globular clusters.

How they did it — After noticing the variability in flickering, Burke and colleagues took a sample of 67 well-studied active supermassive black holes. They examined their timescales to create a correlation between the observed light and the mass of the black holes.

They discovered that there was a correlation, meaning that it might be possible to measure black hole masses without using reference points around them. This could unlock our understandings of less-studied black holes and help classify them.

In addition, the method could be scaled down to other objects with similar accretion discs, whether its smaller black holes formed in the aftermath of supernovae or objects like white dwarfs, which form after the death of stars like the Sun.

WHAT’S NEXT — The scientists behind the new study are next taking aim at intermediate black holes. They may also examine the enigmatic black hole at the center of our galaxy.

That black hole, known as Sagittarius A*, also lacks visible jets of material usually shooting out from black holes of its size, and is unusually quiet with very little activity.

“The Milky Way’s black hole is a little weird, so we think the physics of its accretion disc might be a little different,” Burke says. By studying our own galaxy, we might, in turn, understand galaxies similar to our own spread through the universe.

Abstract — Accretion disks around supermassive black holes in active galactic nuclei produce continuum radiation at ultraviolet and optical wavelengths. Physical processes in the accretion flow lead to stochastic variability of this emission on a wide range of time scales. We measured the optical continuum variability observed in 67 active galactic nuclei and the characteristic time scale at which the variability power spectrum flattens. We found a correlation between this time scale and the black hole mass extending over the entire mass range of supermassive black holes. This time scale is consistent with the expected thermal time scale at the ultraviolet-emitting radius in standard accretion disk theory. Accreting white dwarfs lie close to this correlation, suggesting a common process for all accretion disks.
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