Black Holes Evolve As They Devour Stellar Matter

Black Holes Evolve As They Devour Stellar Matter

The star had been torn apart by the strong tidal forces of the Black hole, Whose gravity pulls on the near side of the star stronger than the distant and rips apart the star. According to scientists, this black hole sits at the heart of a galaxy about 300 million light-years away from Earth.

The TDE the team used in the study, ASASSN-14li, was discovered in November 2014.

"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.

Kavli Institute research scientist Jack Steiner, however, believes the cloud of high-energy electrons is being squeezed by an overwhelming pressure-generated by a swirling vortex of material accumulating around the black hole, known as an accretion disk.

Researchers from the US and the Netherlands were looking at a "tidal disruption event" or TDE (the name for a star being destroyed by a black hole) that was detected in 2014.

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. Even so, the researchers plan to search for more flare events around both younger and older black holes.

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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.

Scientists used these x-ray emissions to infer the black hole's mass and spin. That data, along with the black hole's mass, suggests the supermassive black hole at the centre of the event labelled ASASSN-14li is spinning at 50 percent the speed of light. 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.

Kara's team discovered that J1820's stretched iron K line remained constant, which means the inner edge of the disk remained close to the black hole - similar to a supermassive black hole. Pasham's team made a decision to look for a similar quasi-periodic oscillation in the X-rays coming from ASASSN-14li. They followed the signal that they said pulsed every 131 seconds and persisted for at least 450 days. With only a couple dozen examples it would be premature to make big-picture conclusions (especially if we're not interpreting the data correctly), but the pattern might indicate that supermassive black holes grow primarily by prolonged feeding from accretion disks, which would spin the black holes up like water from a hose hitting a basketball. "Stellar black holes like J1820 have much lower masses and evolve much faster, so we can see changes play out on human time scales". Alone, it would not have been enough to emit any sort of detectable radiation.

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. For all intents and purposes, the white dwarf would have been invisible to telescopes as it circled the relatively inactive, spinning black hole. It turns out that, in order for the gas to get as close as the pulse's frequency implies, the black hole has to be spinning rapidly, dragging the gas tightly around itself.

To endure for more than a year, the pulse is likely related to material orbiting the black hole, both Pasham and Levan say. "But at least in terms of the properties of the system, this scenario seems to work". The victory here is the ability to use tidal disruption flares to constrain the spin. The team now hopes to find more stable signals from TDEs to estimate the properties of other black holes.

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