Mystery of the Black Hole Cloud Solved

If you’re in Astronomy circles you may have heard about a big cloud of Hydrogen heading toward the supermassive black hole in the centre of our galaxy, Sagittarius A*.  The lead up to the cloud approaching the black hole had astronomers buzzing this year, as it would be a direct opportunity for us to see the black hole ‘devour’ the cloud.  The black hole would show us some celestial fireworks and give us a huge opportunity to study their behaviour.

Astronomers watched closely, and then the cloud passed right by….

This is what it was expected to look like.

We should have seen the cloud torn apart as matter spiralled into the central black hole of our Galaxy, but nothing happened.

Now the mystery has been solved by UCLA astronomer Andrea Ghez.  She and her colleagues used data from the 10-meter Keck telescopes in Hawaii to determine that the object, known as G2, is likely a pair of binary stars that had merged due to the black hole’s strong gravitational influence.  The massive resulting star was shrouded in a halo of hot gas and dust that obscured its true form.

When it passed by the black hole, instead of spiralling in, its own strong gravity kept it together and it simply kept going. “G2 survived and continued happily on its orbit; a simple gas cloud would not have done that,” said Ghez, whore research was published today in the journal Astrophysical Journal Letters. “G2 was basically unaffected by the black hole. There were no fireworks.”

But a black hole is not something you just pass by without incident.  Ghez says that G2 is now undergoing ‘spaghettification,’ where the object becomes elongated due to the incredible gravity of the black hole.

Stars in the galaxy don’t often merge, but in the close-quarters of the galactic centre, stars are packed in so tightly and moving so rapidly that collisions are common.  When two stars collide and merge into one, the resulting star expands for around a million years before finally settling down.  G2 may be in the inflated stage, and other stars near the Galactic Centre may be the result of past mergers that have now settled down.  The result is shedding new light on how stars behave around supermassive black holes.

The work would not have been possible without the new adaptive optics technology used by the Keck telescopes.

This allows the system to remove distortion effects of the atmosphere by making small adjustments in the composite pieces of the telescope’s main mirror.  This allows a ground based telescope to operate as if there is little to no atmosphere, along the lines of a space telescope, but since it is ground based, it can be much larger.

In the coming months we should get a better idea of what the fate of G2 is, and what it will teach us about black holes.

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