Black holes as cosmic gas blowers
Gravity traps even sweep gas out of space between groups of galaxiesRead out
Many large galaxies harbor superheavy black holes in their centers. Because of their unimaginably great attraction they devour the surrounding matter. This cosmic meal releases large amounts of energy that are expelled in powerful jets. Now astronomers have shown in the journal "Astrophysical Journal" that not only matter is ejected from the galaxies themselves, but even a part of the gas between the members of a group of galaxies.
Astronomers have long been trying to understand how black holes interact with their environment - until today they have understood this so-called feedback only insufficiently. Observations and simulations, however, show that the jets in particularly active galaxies - they shine mainly in the radio range - transport large quantities of matter into space at near the speed of light. These plasma bubbles give off their energy to the gas that fills the space between each galaxy. The characteristic fingerprints for this radio feedback can be detected both in the radio and in the X-ray range.
Less gas than expected
Particularly interesting are galaxy groups in which several Milky Way systems are bound by gravity. Studies have recently shown that the amount of gas in such groups is lower than predicted in cosmological models. Astronomers explain this deficit by saying that large amounts of mechanical energy from the central black holes could blow away part of the intergalactic gas. However, this was only a hypothesis to date, and the research was limited to a handful of nearby objects populated by fewer (radio) luminous black holes.
Studies on galaxy groups and clusters
A team led by Stefania Giodini at the Max Planck Institute for Extraterrestrial Physics in Garching has now undertaken one of the largest studies of galaxy clusters and clusters detected in X-ray and identified with XMM-Newton. Galaxy clusters cover up to several thousand members, so they are much larger and more massive than galaxy clusters. The astronomers studied the radio-feedback energies in some of the nearly 300 galaxy groups located in a particular area of the sky - the large-area Cosmos field.
Puzzles solved by missing matter
The results show that the activity of the black holes in the centers of each galaxy actually has to have a dramatic effect on the environment: they emit so much energy that it blows the gas far out of the groups. Thus the riddle of the missing matter has been solved - and for the first time the significant influence of black holes in galaxy groups has been proven. display
Usually, the gas is bound by gravity. The black holes, however, can be so active that they break the gravity shackles. Thus, a significant portion of the gas is removed from the galaxy clusters, "explains Giodini. In the more massive clusters of galaxies, however, such an effect could not be detected. There evidently the enormous gravitational force prevents the gas from escaping the heap.
Radio galaxies as city peace
"It is impressive what can have a significant effect of the radioactivity of galaxies on their environment, " says Vernesa Smolčić of the California Institute of Technology, co-author of the study. "This is likely to happen not only on scale scales within the galaxies, but also on scales of a few million light-years." Radio galaxies, for example, seem to be veritable torrents of peace that surround the gas around the galaxy Unexpectedly high temperatures heat up and eject some of the matter from the galaxy groups.
Hans B hringer from the Research Group for Galaxy Clusters and Cosmology at the Max Planck Institute for Extraterrestrial Physics also participated in this study: In some nearby clusters of galaxies, we see the effect of energy bursts Black holes in their surroundings in the form of plasma bubbles that shine in the radio area. However, direct evidence of periodically recurring outbreaks can only be obtained by examining a large number of galaxy clusters.
The enormous influence of the individual galaxy cores astonishes even the astronomers. "I never imagined the extent to which black holes could displace gas into galaxy clusters, " says co-author Alexis Finoguenov of the Max Planck Institute for Extraterrestrial Physics and the University of Maryland, Baltimore. "They are the gasblazers of the universe."
(MPG, 03.05.2010 - DLO)