Astronomers using the GRAVITY instrument on ESO’s Very Large Telescope Interferometer (VLTI) have detected flares of infrared radiation coming from the accretion disk around Sagittarius A*, the 4-million-solar-mass black hole at the heart of our Milky Way Galaxy.
This visualization uses data from simulations of orbital motions of gas swirling around at about 30% of the speed of light on a circular orbit around the supermassive black hole. Image credit: ESO / GRAVITY Collaboration / L. Calçada.
The flares the GRAVITY instrument detected provide long-awaited confirmation that the object in the center of our Galaxy is a supermassive black hole.
The flares originate from material orbiting very close to the black hole’s event horizon — making these the most detailed observations yet of material orbiting this close to a black hole.
While some matter in the accretion disk — the belt of gas orbiting Sagittarius A* at relativistic speeds — can orbit the black hole safely, anything that gets too close is doomed to be pulled beyond the event horizon.
The closest point to a black hole that material can orbit without being irresistibly drawn inwards by the immense mass is known as the innermost stable orbit, and it is from here that the observed flares originate.
“It’s mind-boggling to actually witness material orbiting a massive black hole at 30% of the speed of light,” said team member Dr. Oliver Pfuhl, a researcher at the Max Planck Institute for Extraterrestrial Physics, Germany.
“GRAVITY’s tremendous sensitivity has allowed us to observe the accretion processes in real time in unprecedented detail.”
Earlier this year, GRAVITY and SINFONI, an instrument on the Very Large Telescope, allowed the same team to accurately measure the close fly-by of the star S2 as it passed through the extreme gravitational field near Sagittarius A*, and for the first time revealed the effects predicted by Einstein’s general relativity in such an extreme environment.
During S2’s close fly-by, strong infrared emission was also observed.
“We were closely monitoring S2, and of course we always keep an eye on Sagittarius A*,” Dr. Pfuhl said.
“During our observations, we were lucky enough to notice three bright flares from around the black hole — it was a lucky coincidence.”
“This emission, from highly energetic electrons very close to the black hole, was visible as three prominent bright flares, and exactly matches theoretical predictions for hot spots orbiting close to a black hole of four million solar masses.”
“The flares are thought to originate from magnetic interactions in the very hot gas orbiting very close to Sagittarius A*.”
The results appear in the journal Astronomy & Astrophysics.
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R. Abuter et al (GRAVITY Collaboration). 2018. Detection of orbital motions near the last stable circular orbit of the massive black hole SgrA*. A&A 618, L10; doi: 10.1051/0004-6361/201834294
