A bubble of hot electrons appears to be 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 occurred, the researchers 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 roughly the distance that Mercury’s sits from the sun in our solar system.
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 percent the speed of light. The researchers were only able to see it for two orbits before it faded from view, meaning it was either destroyed or was no longer emitting light in wavelengths ALMA can observe.
The bubble cannot be too small, because a small bubble would not disappear that quickly
“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.”
From observations of the two orbits, the researchers managed to determine that the magnetic fields affecting the bubble seem to be aligned as we would expect them to be based on a model of black holes called the magnetically arrested disc model.
“It tells us that maybe our models of these systems really have something to do with reality,” says Wielgus.
