Livescience | April 27, 2019 | By Rafi Letzter
DENVER — Astronomers watched a high-speed gas cloud slam into the matter getting sucked toward Sagittarius A* — the supermassive black hole at the center of the Milky Way — and then zip away into space. Now, careful observations have revealed just how much the gas cloud, which astronomers named G2, slowed after the collision.
That measurement tells scientists something important: the density of the hot matter surrounding Sagittarius A* , which is the nearest known supermassive black hole to Earth. SagittariusA* (SagA*) is quiescent, meaning it’s not gobbling up a huge disk of matter and firing off jets. But there’s still something hot and glowing surrounding it that physicists don’t understand very well. The collision with G2 is offering astronomers one of their best clues yet as to what that glowing ring is made of.
“There was this drag force. The thing [G2] became slower,” said Stefan Gillessen, an astronomer at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany.