NASA telescope spots black hole shrinking after devouring a star

NASA  Goddard Space Flight Center  CI Lab

NASA Goddard Space Flight Center CI Lab

They saw the galaxy's central, supermassive black hole lure in and rip apart a passing star.

About 10,000 light years away from Earth, a black hole is engaged in a stellar feast, devouring the gases of a nearby star - and we've been watching. The TDF that was spotted in November 2014 was called ASASSN-14li.

"Events where black holes shred stars that come too close to them could help us map out the spins of several supermassive black holes that are dormant and otherwise hidden at the centers of galaxies", said Dheeraj Pasham, the first author of the study. The team chose to assume that the glowing gas circles as close to the black hole as is physically possible; any stuff passing within this innermost stable orbit will instead plunge straight toward the event horizon.

Researchers from MIT analyzed all available data on the rare sight from multiple telescopes and found the intense and stable signal that appears to emanate from an area very close to the supermassive black hole's event horizon - the region in which the gravitational pull is so intense that nothing, not even light, can escape.

This method of studying black holes - by observing the dramatic shredding of stars - gives scientists improved insight into massive black holes that are actively ripping apart massive stars and creating disks of star matter.

Their observations are the first evidence that the corona becomes smaller in size as a black hole consumes material.

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.

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 star, under the influence of the black hole's enormous gravity, stopped being a star.

Pasham added that the supermassive black hole from their paper is exciting "because we think it's a poster child for tidal disruption flares".

The findings provide scientists with new evidence about a crucial phase in the black holes evolution, known as black-hole transient, the transition to a soft, low-energy state.

"NICER's observations of J1820 have taught us something new about stellar-mass black holes and about how we might use them as analogs for studying supermassive black holes and their effects on galaxy formation", said co-author Philip Uttley, an astrophysicist at the University of Amsterdam. Experts estimate that some black holes spin at up to 99 percent the speed of light, but this latest study offers a way of being able to know for sure. He chose to apply his code to the three datasets for ASASSN-14li, to see if any common periodic patterns would rise to the surface.

"At first I didn't believe it because the signal was so strong", Pasham says. The few supermassive black holes whose rotation rates have been clocked to date are in the same extreme neighborhood, generally whipping around between 33 percent and 84 percent the speed of light.

When the white dwarf comes into contact with this stellar material, it likely illuminates the white dwarf, emitting X-rays each time it circles the black hole, every 131 seconds.

"We would've been extremely lucky to find such a system", says Pasham. When a black hole begins to eat up a star, the star's gases swirl around its gravitational center in a ring known as an accretion disk. "But at least in terms of the properties of the system, this scenario seems to work".

"It's just a really rapidly spinning black hole", said Fryer. The victory here is the ability to use tidal disruption flares to constrain the spin.

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