Repeating outbursts of 40,000-degree wind discovered near black hole

About 25,000 light-years from Earth, astronomers have discovered intensely hot, screaming winds near a black hole. And those outbursts repeat every eight minutes. It’s the first time researchers have observed this around a black hole, according to a new study.

The study was published this week in the Monthly Notices of the Royal Astronomical Society.

The same system showed signs of a violent outburst in 2011. Then, it happened again in 2017. But this time, scientists noticed the repetitive behavior and took a look with the largest telescope in the Southern Hemisphere, the South African Large Telescope.

In the system, there’s a low-mass star like our sun and a black hole compact object that’s six times the mass of the sun.

The black hole compact object is pulling material from the star into a disk that separates the two of them. When the star’s material grows hot, it becomes unstable. This is the cause of the energetic outbursts, the researchers said.

In 2011, the researchers noticed dips in the system’s brightness, which shifted as the outburst evolved — not something they had observed before.

“The cause of these remarkable, fast dips has been a hot topic of scientific debate ever since their discovery,” said study author and lead researcher Phil Charles of the University of Southampton. “So it was with great excitement that astronomers greeted the second outburst of this object in mid-2017, presenting an opportunity to study this strange behaviour in greater detail.”

The telescope enabled the researchers to capture the different wavelengths of light associated with the dips in its brightness — even though the black hole compact object is 10,000 times dimmer than the faintest stars visible to the human eye.

Within the spectrum gathered by the telescope, the researchers were able to spot energized helium in the system that had been heated to 40,000 degrees and reached speeds of 600 kilometers per second.

“But what really astonished us was the discovery that these spectral features were visible only during the optical dips in the light-curve,” Charles said. “We have interpreted this quite unique property as due to a warp or ripple in the inner accretion disc that orbits the black hole on the dipping timescale. This warp is very close to the black hole at just 1/10 the radius of the disc.”

The wind is moving toward Earth rather than the black hole, and the researchers believe this is due to the pressure of the radiation being generated by X-rays so close to the black hole.

Such intense radiation should appear brighter than it does in the spectral data, but the black hole is pulling in material that probably obscures the light from our view. We’re also looking at the system’s edge, rather than head-on, because of its orientation.

Studying this intriguing system will allow astronomers to learn more about the end of star evolution and the formation of compact objects, like neutron stars, white dwarfs and black holes.

“These short-period binary versions are a perfect way to study this physics in action,” Charles said.

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