A Star just Survived Getting Eaten by a Black Hole!

Who would have thought that a burst of x-rays could tell such a rare and fascinating story!

GSN 069 is a supermassive black hole, located in the constellation Sculptor in an active Seyfert galaxy over 250 million light years away, and has been the talk of the town since 2010.

gsn069_525
X-ray emission of GSN 069, sped up. Credit: CHANDRA.

In 2018, Giovanni Miniutti and a team of astrophysicists observed GSN 069 using the XMM-Newton Observatory and then later using NASA’s CHANDRA. It was found that the X-ray emissions from the black hole were periodic, having a period of about 9 hours, with each emission itself lasting over an hour.

In case you’re not familiar with X-ray emission

Matter that’s falling into a black hole gets evenly spread around in a disk shape, called the accretion disk. The matter orbits around within this disk at a really high speed, and friction against the rest of the matter in the disk is so large that the disk itself heats up.

This heat is emitted as electromagnetic radiation, in this case X-rays!

GSN069
Credit: NASA/CXC/M. Weiss

 

Why is GSN 069 special?

While doctors do recommend 3 meals a day for us humans, black holes don’t need to eat so frequently. An article published by NASA in 2019 states that “instead of erupting every nine hours they should erupt every few months or years.” This thing is on a binge!

Miniutti and his team called these events X-ray Quasi-periodic Eruptions, but only just now are we beginning to understand what’s driving this black hole to eat so much.

Initially one theory for the irregularities was that GSN 069 is a very young and unstable black hole. GSN 069 is about 400’000 solar masses, making it a very small and perhaps young supermassive black hole. To simply put it, mealtime etiquette has not been learnt yet!

Recently, a far better theory has been proposed: A red giant narrowly escaped the wrath of the black hole!

gsn069_illus_orbit
Hypothesised orbit of the white dwarf. Credit: NASA/CXC/M. Weiss

Well, the story’s not quite that dramatic, according to Andrew King of the University of Leicester. King was part of Miniutti’s team of researchers and works at the university I’ll be going to!

The red giant was captured into a 9 hour orbit around the black hole and had its outer layers stripped off, leaving the core of the star. A white dwarf.

More outer layers are shed as the star reaches its perihelion (closest approach), which is every 9 hours. To compensate for the loss of mass, the radius of the orbit will increase to conserve angular momentum.

The star is trying to make a very slow getaway, but King states that there is no escape.

 

 

Read more:

https://chandra.harvard.edu/photo/2019/gsn069/

https://arxiv.org/abs/1909.04693

https://www.nasa.gov/mission_pages/chandra/images/scientists-discover-black-hole-has-three-hot-meals-a-day.html

https://phys.org/news/2020-04-star-survives-black-hole.html

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