An article published in “The Astrophysical Journal” describes a research on one of the giant gas bubbles regurgitated by the supermassive black hole at the center of the Milky Way. Called Fermi bubble, it’s a type of structure still not well understood and a team led by Rongmon Bordoloi of MIT used the Hubble Space Telescope to change that measuring various characteristics of the gas inside the bubble.
Fermi bubbles were discovered in 2010 using NASA’s Fermi Gamma-ray Space Telescope observing the center of the Milky Way. Two of these bubbles extend above and below the supermassive black hole occupying that area for approximately 25,000 light years. After that discovery, new observations began, also with the Hubble Space Telescope, with an initial estimated age of the bubbles of about 2 million years.
Astronomers have long known that supermassive black holes can be surrounded by large amounts of gas of which they can swallow a part. They also know that theyeject a part of that gas that escapes getting ejected along its polar regions, creating jets that extend above and below the galaxy plane. These materials can also form Fermi bubbles accumulating instead of being projected into intergalactic space.
This new research is an extension of an earlier one from 2015 in which astronomers in particular used the Hubble Space Telescope’s Hubble’s Cosmic Origins Spectrograph (COS) to analyze the ultraviolet light of a quasar, an active galactic nucleus that emits strong electromagnetic radiation, to examine Fermi bubbles.
The detections exploit the fact that the radiation coming from the quasar contain information on the bubbles because they crossed them, as illustrated in the image. This time, the astronomers analyzed the ultraviolet light from 47 quasars getting information about the Fermi bubble’s gas velocity and temperature and even its composition.
The temperature of the gas in the Milky Way’s north bubble turned out to be around 9,800° Celsius (17,700° Fahrenheit). It can seem very high but is low compared to that of most of the very hot gas in the outflow, which is about 10,000,000° Celsius (about 18,000,000° Fahrenheit). This very high temperature makes them visible at gamma rays.
The gas detected by the COS instrument could be interstellar gas coming from the galactic disk that was dragged into the hot flow. COS also identified the presence of silicon and carbon among the swept materials: they’re common in most galaxies since they’re elements produced by stars.
This research allowed to estimate that the supermassive black hole consumed a sort of giant cosmic meal between 6 and 9 million years ago. It’s a step forward in understanding Fermi bubbles, huge structures which luckily are far away from the solar system.