ESA’s Herschel space telescope has completed its mission at the end of April, but the observations it made continue to be a source of discovery. A study of the supermassive black hole at the center of the Milky Way performed on observations conducted between 2011 and 2012 identified a significantly warmer than expected gas that may orbit around it or fall towards it.
The existence of a supermassive black hole at the center of the Milky Way has long been known. It’s located about 26,000 light years from the solar system and from the Earth it appears in the region known as Sagittarius A* or Sgr A* for short. Its mass is about four million times that of the Sun and yet it’s difficult to study it because of the huge amount of dust present between it and the Earth, which prevent us from observing the region around it at visible light.
The instruments PACS (Photodetecting Array Camera and Spectrometer) and SPIRE (Spectral and Photometric Imaging Receiver) of the Herschel Space Telescope have allowed us to perform infrared observations. Through them it was possible to see through the dust and study the central region of the Milky Way in great detail.
The spectrometric analyzes performed using Herschel allowed to find a great variety of molecules at the center of the Milky Way such as water and carbon monoxide. The biggest surprise came from the discovery that in the innermost region of the galaxy gases can reach a temperature of 1,000 degrees Celsius. Generally, clouds of interstellar gas have a temperature of a few tens of degrees above absolute zero.
A star cluster near the center of the Milky Way could be partly responsible for this heating but certainly not up to such a high temperature. According to Dr. Javier Goicoechea of the Centro de Astrobiología, Spain, collisions between gas clouds or in materials that move at high speeds from stars and protostars can cause a thermal shock which can contribute to the heating of the gas.
The observations are consistent with jets of hot gases that move towards Sgr A* falling towards the supermassive black hole at the center of the Milky Way. In the last stage of their journey they get heated a lot and emit X-ray and gamma rays. It’s as if the black hole was cooking a meal of gas.
By performing near-infrared observations, other astronomers have identified another cloud of gas that is approaching the supermassive black hole in a spiral path. This cloud is closer to the black hole than the gas observed by Herschel and could be swallowed up in the coming months.
Other space telescopes such as NASA’s NuSTAR and Chandra X-ray Observatory will be used to try to detect the X-rays that will be emitted when the first big gas cloud will be swallowed up. These study of the supermassive black hole also aim to improve our understanding of the evolution of galaxies, influenced by those huge gravity wells at their center.