Star formation in the largest elliptical galaxies may be halted by super-massive black holes, according to a new study.
Astronomers questioned why many large galaxies near our own Milky Way fail to produce large numbers of new stars. These are known as "red-and-dead" galaxies for their cool (red) color, and lack of stellar birth. Most believed the groups of stars contained only small quantities of the cool gas needed for star formation.
Norbert Werner collected data from the now-defunct Herschel Space Observatory, which observed the Universe in near infra-red wavelengths from 2009 to 2013.
Of the eight galaxies observed by Werner and his team, six were found to contain vast quantities of cold gas. In order to determine why so few stars were forming, researchers compared the infra-red data from the Herschel Observatory to optical images. These wavelengths show material that is slightly warmer than that shown by infra-red telescopes. The coolest material was seen in radio waves. Finally, data showing ultra-hot material, shining in x-ray light, was compared to the other data.
Hot gas within six of the galaxies is cooling, according to measurements from X-ray images. However, rather than cool enough to form stars, the process stops, leaving the gas too hot to coalesce into stars. In the pair of galaxies without cool gas, the hot material present does not appear to be cooling.
The team believes the cause of this warming lies with super-massive black holes at the cores of each of those galaxies. Medium-sized black holes lie at the center of the six galaxies containing moderate amounts of cool gas, while the two hot galaxies are home to super-massive examples. As these bodies rotate, they can produce jets, which heats gas and pushes it away from the center of the galaxy, limiting star formation. Radio observations show powerful jets of gas being ejected from their cores.
"Once again, Herschel has detected something that was never seen before: significant amounts of cold gas in nearby red-and-dead galaxies. [N]evertheless, these galaxies do not form stars, and the culprit seems to be the black hole," Göran Pilbratt, Herschel Project Scientist for the European Space Agency, said.
This study could completely change the way astronomers look at these galaxies.
"These galaxies are red, but with the giant black holes pumping in their hearts, they are definitely not dead," Werner said in a statement.
Details of the study into the effect of super-massive black holes on star formation was published in the Monthly Notices of the Royal Astronomical Society.
