Most galaxies contain a supermassive black hole (SMBH) at their center, and the Milky Way is no exception. Sagittarius A* (Sgr A*, pronounced “A star”), the supermassive black hole at the center of our galaxy, sitting 26,000 light years from Earth, has a mass four million times greater than the Sun. However, clouds of dust between the Earth and the galactic center make viewing our neighborhood SMBH nearly impossible using visible light. Now, a new study of microwaves coming from the center of our galaxy has revealed a ring of cool gas encircling the supermassive black hole at the center of the Milky Way.
The Atacama Large Millimeter/submillimeter Array (ALMA), located in the Andes Mountains in Chile, was utilized to study this massive object. In doing so, astronomers at the observatory detected a previously unseen cool disk of gas hiding within the bright, heated sphere surrounding the black hole.
“We were the first to image this elusive disk and study its rotation. We are also probing accretion onto the black hole. This is important because this is our closest supermassive black hole. Even so, we still have no good understanding of how its accretion works. We hope these new ALMA observations will help the black hole give up some of its secrets,” stated Elena Murchikova, a member in astrophysics at the Institute for Advanced Study.
Hot and Cold Makes this the McDLT of the Milky Way
The region surrounding Sgr A* is replete with stars, swimming in clouds of interstellar gas and dust. The newly- discovered disk, containing one-tenth as much mass as the planet Jupiter, sits just 3.5 light days from the event horizon of its black hole. This distance is equivalent to 1,000 times the space separating the Earth from the Sun. Although this may sound far, material within the ring sits on the precipice of never being seen again by any observers outside the black hole. Once an object crosses past the border of the event horizon, not even light can escape the pull of gravity pulling it toward the object’s center.
Hans Reinhardt: Tonight, my friends, we stand on the brink of a feat unparalleled in space exploration. If the data on my returning probe ship matches my computerized calculations, I will travel where no man has dared to go.
Alex Durant: Into the black hole?
Reinhardt: In… through… and beyond.
Harry Booth: Why, that’s crazy! Impossible!
Reinhardt: The word “impossible”, Mr. Booth, is only found in a dictionary of fools.
— The Black Hole (1979), Walt Disney Productions
Although different regions within the disk are heated to varying degrees, this newly-discovered feature is still extremely cool compared to the sphere of gas and dust also surrounding the black hole. As the disk rotates around the center of gravity, the gas within it retains a temperature of just around 10,000 degrees Celsius (18,000 degrees Fahrenheit).
Temperatures within the nearly-spherical mass, however, reach 10 times greater than those found within the ring, making this structure two-thirds as hot as the center of the Sun. Although this sphere does not move with a regular rotation around Sgr A*, it does glow brightly in X-rays, making it an easy target for astronomers studying the structure.
Still, I’m Strangely Drawn to It
Black holes are, at their most basic, objects which have gathered so much mass for their size that not even light can escape their surface. Once an object becomes a black hole, it can grow further in mass by swallowing gas, dust, and larger materials which fall into its grasp.
“As the strong gravity of Sgr A* pulls clumps of material inwards, tidal forces stretch the clumps as they get closer to the black hole. Sgr A* also impacts its surroundings through occasional outbursts from its vicinity that result in the expulsion of material away from the giant black hole,” NASA reports.
Astronomers using ALMA were able to record the location and motion of the gas, as it follows a death spiral around our local galactic black hole.
The SMBH at the center of the Milky Way is fairly quiet, but radiation surrounding it is so enormous, the energy forces hydrogen atoms in the area to repeatedly lose and gain electrons. This phenomenon results in the emission of microwave radiation, with a wavelength of around 1 mm (1/25 inch). This energy easily passes through the distance between the galactic center and the Earth, before it is detected by ALMA.
The Joint was Jumpin’… Goin’ Round and Round…
This discovery could assist astronomers attempting to better understand the nature of accretion disks, the whirlpool-like spiral of matter often seen in science-fiction movies.
An international team of astronomers developed and released the first picture ever created of a black hole in April, 2019. That groundbreaking image focused on the supermassive black hole inside the M87 galaxy. This new study allows us a much more intimate look at the supermassive black hole right here at home.