Some supermassive black holes announce their presence with screaming hot disks of orbiting gases. But the behemoth at the center of the Milky Way has been shy and demure. Now, astronomers have finally spotted the black holes faintly glowing accretion disk of infalling material, long suspected but never before seen.
“I was very surprised that we actually saw it,” says astrophysicist Elena Murchikova at the Institute for Advanced Study in Princeton, N.J. The disk was observed using the Atacama Large Millimeter/submillimeter Array, or ALMA, in northern Chile, the researchers report in the June 6 Nature.
The Milky Ways supermassive black hole, named Sagittarius A*, is a behemoth at 4 million solar masses. But while some black holes gobble the gas and dust around them, Sgr A* picks daintily. Such “underfed” black holes “dont have enough food supply” for their surrounding gases to glow brightly, Murchikova says.
The disks diminished glow helps explain why scientists with the Event Horizon Telescope were able to capture a picture of the central black hole in the more distant galaxy M87, but not yet Sgr A* (SN: 4/27/19, p. 6).
Previously, scientists had seen a cloud of hot gas (around 10 million kelvins) emitting high-energy X-rays around Sgr A*, as well as stars and gas clouds circling the black hole. But those gas sources didnt seem to be organized into a neat, orbiting disk. Murchikova and colleagues focused their search on cooler gases, about 10,000 kelvins, located within about 280 billion kilometers of Sgr A*. Looking at only the hot gas, she explains, is like trying to study Earths climate by focusing on summers in the desert. “Gas of both types should be falling into the black hole,” Murchikova says. “You need a full picture.”
ALMA measured the cooler gases by observing particles of light in a particular wavelength. Those photons are emitted when electrons and protons in the gases combine to form hydrogen atoms. When Murchikova and colleagues looked at the photon distribution around the black hole, they saw an oblong disk with a gap in the middle where the black hole sits.
On one side of the disk, the light wavelength was stretched, or redshifted. On the other side, the light was squished, or blueshifted. That finding means that one side of the disk is moving towardRead More – Source