For the first time, astronomers have spotted a critical moment in the life of galaxies: high-speed eruptions of gas that may halt the birth of stars.

Galaxies, such as our own Milky Way, are vast islands of stars littering space. How galaxies' star populations grow, and how they stop growing, could be explained by eruption observations in the journal Nature.

The international team of astronomers led by astronomer James Geach from the University of Hertfordshire discovered that dense, cold clouds of gas are ejected out of a compact galaxy, dubbed SDSS J0905+57, at a speed of a whopping two million miles (3.2 million kilometers) an hour.

The hydrogen gas clouds—some weighing more than a billion suns—traveled tens of thousands of light-years into space, far from star-forming regions of the galaxy. Radar telescope measurements revealed that intense radiation pressure from stars forming in large numbers inside the compact galaxy hurled the clouds away.

The presence of hydrogen gas is pivotal to successful star birth, and so astronomers suggest that by its removal, stellar factories within the galaxy are effectively shut down. The same mechanism may have halted an era of massive star formation in galaxies such as our own.

"What we found was something surprising—a large fraction of the gas is being blasted out of the galaxy by the concentration of stars forming at the galaxy's center," says Geach.

"We are witnessing the aggressive termination of star formation, and the mechanism by which this is happening is an important new clue in our understanding of the evolution of galaxies."

View Images A sky chart shows galaxy M82 in the northeast evening sky, just above the Big Dipper. Skychart by Andrew Fazekas

See for Yourself

Want to see what a galaxy undergoing "starburst" looks like? Sky-watchers can find just such an island of stars relatively nearby, in the constellation Ursa Major, and now visible throughout the Northern Hemisphere.

Messier 82, also known as Bode's Nebula, resides some 12 million light-years from Earth and hangs just above the bowl of the Big Dipper, late in the evening in the northeastern sky.

Shining at magnitude 8.2, binoculars offer a good glimpse of M82, even from suburbs. Backyard telescopes, however, will reveal its distinctive cigar shape, which stretches across some 130,000 light-years.

Recent encounters with neighboring spiral galaxy M81 (visible by backyard telescope) have caused strong tidal forces to build up within M82's core. That has led to extreme numbers of star births-estimated at ten times the rate seen within our own Milky Way galaxy.

Happy hunting!