A Star Fell Into A Black Hole, Revealing Its Super-Fast Spin

Postado Janeiro 12, 2019

So when an unassuming star traversed near this black hole, it began to rip the star apart.

A black hole is all set in engaging in a stellar feast and its feeding like a monster on the gases of the nearby star as this black hole resides about 10,000 light years away from our Earth and eventually, we all have been watching this. That even created a burst of X-ray activity at the center of the galaxy and since the discovery, multiple observatories have had telescopes trained on the event to learn more about how precisely black holes consume stars. The scientists immediately searched for "quasi-periodic oscillations", regularly repeating but changing patterns of x-rays that vary in their power and are thought to originate from very close to the black hole.

Black holes are massive beasts that annihilate anything that dares to cross them. (The name is a reference to the survey project that found it, not a commentary on the black hole's destructive act.) It's one of the closest and best-studied TDEs astronomers have, confirming several phenomena predicted to come with these violent encounters - evidence of a jet, a hot accretion disk, and even material thrown out during the event, says Andrew Levan (University of Warwick, UK), who has studied ASASSN-14li but wasn't involved with the current work.

They noticed an intense, stable X-ray signal emanating from an area close to the black hole's event horizon - the point beyond which material is swallowed by the black hole.

From its stable proximity to the black hole and the black hole's mass, the team of researchers was able to calculate the speed in which the black hole is spinning: about 50 percent the speed of light.

From the rhythm of the x-ray pulses were derived by the researchers, how fast the Black hole.

The spin the team estimates - at least 70% of the black hole's theoretical maximum, or at least 50% the speed of light - continues the trend followed by other supermassive black holes we have spins for, nearly all of which spin at least 60% of their max.

The only problem might be the rarity of this sort of scenario: the researchers think a small white dwarf star was keeping its distance from the black hole undetected, until a second star arrived that was pulled into the black hole's clutches.

Most large galaxies have giant, sucking black holes at their centers. It's immensely hard to measure; we only have spin measurements for about 30 supermassive black holes, determined based on their X-ray spectra. The signal lasted a surprisingly long time - at least 450 days, a duration that Pasham says is "really weird". Waves of X-rays formed "light echoes" that reflected off the swirling gas near the black hole and revealed changes in the environment's size and shape.

Levan agrees. "I'm quite surprised that it seems to be so stable for so long", he says. Figuring out a black hole's mass is a little easier, by the way, because the pull it has on the galaxy around it can be measured to calculate an estimate. Alone, it would not have been enough to emit any sort of detectable radiation.

"The fact that we can track this region of bright X-ray emission as it circles the black hole lets us track just how quickly material in the disk is spinning", Pasham said in the same statement. A relatively low rotation rate would implicate mergers as the primary factor, because these random smashups likely wouldn't keep spinning the growing black hole up in the same direction. "But we now have evidence that the thing that's evolving in the system is the structure of the corona itself". "By finding instances where the mass from a shredded star glows especially brightly we can build a census of the black holes in the universe and probe how matter behaves in some of the most extreme areas and conditions in the cosmos". This dramatic moment is called a tidal disruption event, or flare.

"In the next decade, we hope to detect more of these events".