Astronomers Find Strong Evidence There is a Supermassive Black Hole at the Center of Our Galaxy

Astronomers watched as gas approached 30 percent the speed of light during the most detailed observation ever made of material orbiting so close to a black hole.

by Daniel Oberhaus
Oct 31 2018, 5:22pm

There is something huge lurking at the center of the Milky Way. For years, astronomers have presumed that this object, known as Sagittarius A*, was a supermassive black hole, which are known to be at the center of most spiral and elliptical galaxies. Now they have strong confirmation that this assumption was correct.

An international team of astronomers used a special instrument on the European Space Observatory’s Very Large Telescope to observe infrared flares coming from the gas ring orbiting the black hole at the center of our galaxy. It’s the most detailed observation ever made of material orbiting so close to a black hole.

These flares are produced by matter orbiting extremely close to the black hole’s event horizon, the point at which no matter or light can escape the black hole’s gravity. Just beyond the event horizon is the black hole’s accretion disc, a belt of gas that is rapidly orbiting the black hole. Only about 1 percent of material is estimated to cross the event horizon and get pulled into the black hole. Most of the material orbiting Sagittarius A* is ejected and produces the flares seen by the ESO astronomers.

“It’s mind-boggling to actually witness material orbiting a massive black hole at 30 percent the speed of light,” Oliver Pfuhl, an astronomer at the Max Planck Institute for Extraterrestrial Physics, said in a statement. “GRAVITY’s tremendous sensitivity allowed us to observe the accretion process in real time in unprecedented detail.”

GRAVITY is an instrument added to the Very Large Telescope in 2015, which is able to look at galactic centers in unprecedented detail. The instrument is an interferometer, which combines the light measurements from four different telescopes to achieve image resolutions far higher than is possible with a single telescope. GRAVITY also has a novel stabilization mechanism that allows the long exposures that reveal the faint objects around our galactic center.

In the case of Sagittarius A*, a black hole with a mass 4 million times greater than the sun, the 26,000 light years between its center and Earth is filled with gas that makes observations difficult. GRAVITY’s extreme sensitivity, however, allows astronomers to watch as stars, gas, and planets orbit the black hole. If astronomers were using a stethoscope to observe the Milky Way’s heart before, GRAVITY was like introducing them surgery.

Read More: Astronomers Confirm Einstein’s Theory of Relativity By Watching a Star Orbit a Black Hole

Earlier this year, GRAVITY allowed researchers to confirm a critical feature of Einstein’s theory of relativity when a star passed within 12 billion miles of the black hole and was accelerated to approximately 3 percent the speed of light. During those observations, researchers observed the infrared flares that were used to confirm the existence of a supermassive black hole in the center of the Milky Way.