New study looks at giant galaxies near the Milky Way

Feb 26, 2014 10:03 GMT  ·  By
Herschel finds that black holes stop stellar formation in massive elliptical galaxies
   Herschel finds that black holes stop stellar formation in massive elliptical galaxies

Astronomers using data from the European Space Agency's (ESA) Herschel Space Observatory were recently able to discover the reason why massive elliptical galaxies near the Milky Way are not producing new stars, even though sufficient amounts of molecular gas are available.

Hydrogen gas clouds are the main source of material for new stars. These objects can appear when the gas cools down and begins clumping up around common centers of gravity. When a critical mass is reached, the entire cloud implodes. The friction that occurs at this stage heats up the gas to millions of degrees, setting it ablaze and igniting nuclear fusion.

This process should theoretically occur in any galaxy with sufficient gas reserves. Over the past few years, astronomers have detected a series of massive elliptical galaxies – significantly larger than the Milky Way – that contain enough cold molecular hydrogen gas but appear to be forming no stars.

These galaxies are currently getting redder, in tone with the average age of their stars. When new stars are formed, they shine blue due to the massive amount of ultraviolet radiations they release. As they age, their light shifts to longer wavelengths, appearing red to telescopes on Earth.

In the new study, researchers from the Stanford University in California have determined that radiation jets released by massive and supermassive black holes at the cores of these galaxies are responsible for dispersing the gas clouds so that no new stars can develop.

Interstellar gas is white hot near the central regions of these massive elliptical galaxies, and its natural tendency is to cool down and form stars. However, the black hole jets heat up the gas again, preventing it from imploding and forming blue stars.

“We looked at eight giant elliptical galaxies that nobody had looked at with Herschel before and we were delighted to find that, contrary to previous belief, six out of eight abound with cold gas,” says Stanford expert and study leader Norbert Werner.

Details of the new study appear in the latest issue of the esteemed journal Monthly Notices of the Royal Astronomical Society. Another thing that amazed researchers was that this study was the first to demonstrate the existence of hydrogen gas at the core of galaxies that did not lay inside massive clusters.

“While we see cold gas, there is no sign of ongoing star formation. This is bizarre: with plenty of cold gas at their disposal, why aren't these galaxies forming stars?” asks Raymond Oonk, an expert at the Netherlands Institute for Radio Astronomy (ASTRON) and a coauthor of the new investigation.

“The contrasting behavior of these galaxies may have a common explanation: the central supermassive black hole,” the investigators conclude.