As we wait for the Event Horizon Telescope team to assemble the first image of the supermassive black hole at the center of the Milky Way Galaxy, astronomers are pushing ever closer to the object’s fringes. A team of scientists with the European Southern Observatory has recently observed flares of infrared light coming from the spinning disk of gas around Sagittarius A*, the official name for the massive object at the heart of the galaxy. The flares provide crucial confirmation of the existence of the Milky Way’s monster black hole, an object with a mass of more than 4 million suns.
Artist impression of the star S2 passing close to the Milky Way’s supermassive black hole. Notice that the star doesn’t get sucked into the black hole directly, but only has its orbit changed by the gravitational pull of the hole. The star’s color also changes to red due to something called gravitational redshift. As the star’s light leaves for our eyes, its loses energy “fighting” against the hole’s powerful gravity. Since it can’t slow down — it is light after all — it changes color from more energetic blue to less energetic red. Once it leaves the gravity field of the hole, its normal color returns.
Because the flares originate from gas orbiting very close to the black hole’s event horizon, these are the most detailed observations yet of material orbiting this close to a black hole. And get this — the gas has been measured whirling around the hole at 30% the speed of light or more than 200 million miles an hour (322 million km/hour). The closest point that material can orbit without being drawn over the event horizon is known as the innermost stable orbit, and that’s where the flares originate. Step inward of this zone and not even light can travel fast enough to return.
Great graphics in this video about the flare discovery
Light or lack of it defines a black hole. A black hole is black, a mere silhouette in space, because the gravity of the hole is so powerful that not even light can escape.
The GRAVITY instrument works by combining light from four telescopes of the VLT to create a virtual super-telescope 427 feet (130-meters) in diameter. Astronomers saw three prominent, bright flares orbiting close to the black that exactly match theoretical predictions for where the hot spots should be.