Diagram of the orbit of a bubble of electrons around the Milky Way’s black hole
EHT Collaboration, ESO/M. Kornmesser
Astronomers have found what appears to be a bubble of hot electrons circling Sagittarius A*, the supermassive black hole at the centre of the Milky Way, at extraordinary speeds. This strange bubble could help us learn about how black holes devour the material around them.
Maciek Wielgus at the Max Planck Institute for Radio Astronomy in Germany and his colleagues used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe the area surrounding Sagittarius A* as the black hole was emitting a huge flare of X-rays. Minutes after the flare, they saw an enormous “hot spot” of radiation, most likely made up of electrons heated to billions of degrees, circling the black hole on an orbit about the distance that Mercury’s sits from the sun.
Mercury takes 88 days to orbit the sun, whereas it only took this bubble about 70 minutes to make a loop around Sagittarius A*, meaning that it was travelling at about 30 per cent the speed of light. The researchers were only able to see it for two orbits before it faded from view, either destroyed or no longer emitting light in wavelengths ALMA can see.
“The bubble cannot be too small, because a small bubble would not disappear that quickly,” says Wielgus. A small bubble would experience less shear force as it travelled around the black hole, so it would live longer. “It’s a huge bubble, it’s not a tiny little guy.”