What heats gas near supermassive black holes at the centre of galaxies?
Astronomers have looked at the centre of the Milky Way with ESA’s Herschel Space Observatory and discovered a rich variety of molecules at surprisingly high temperatures – up to 727 degrees Celsius.
The team of astronomers examined a number of possible heating mechanisms. They excluded a dominant role from ultraviolet radiation from nearby massive stars, X-rays emitted in the vicinity of Sagittarius A* (the region harbouring the supermassive black hole at the heart of the Milky Way), and interactions with cosmic rays – highly energetic particles present in the interstellar medium. None of these three mechanisms seemed efficient enough to explain the high temperature of carbon monoxide gas.
The new data suggest that the molecular gas is heated up by shocks. Shocks develop in the gas as the material surges towards Sagittarius A*.
Among the possible mechanisms producing the shocks are high-velocity clouds of gas that are surging towards the black hole, protostars being born close to the galactic centre and outflows blown by stellar winds.