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Jostling gas jets are found to curb growth of active ‘starburst’ galaxies

AFP-JIJI

Images from a nearby galaxy might explain how star factories can bizarrely slow down, astronomers reported Wednesday.

Astrophysicists have long puzzled why the universe has very few galaxies with high mass, even though there are many galaxies that create stars at a phenomenal rate, sometimes a hundred times greater than our own Milky Way.

In theory, these “starburst” galaxies should have become supersized — but until now, no one has known why they didn’t.

Using a new telescope perched high above Chile’s Atacama desert, where the ultra-dry air provides great viewing conditions, astronomers have seen billowing clouds of hydrogen and other gases — the fuel for making new stars — fleeing a starburst galaxy called NGC 253.

Some 11.5 million light-years away, NGC 253 was discovered in 1783 by Caroline Herschel, sister of William Herschel, the first person to spot Uranus. It has been dubbed the “Silver Coin” or “Silver Dollar” galaxy because of its round, shiny form. In spite of its name, the orientation of NGC 253 is slightly askew when viewed from Earth. This gives sky-gazers an excellent chance to pore over the clusters of stars near its center.

These clusters are where stars are being formed — and they are also an exit point for massive ejections of gas, according to the investigators.

“We can clearly see for the first time massive concentrations of cold molecular gas being jettisoned by expanding shells of intense pressure, created by young stars” emitting particles, said Alberto Bolatto of the University of Maryland in College Park. “The amount of gas we measure gives us very convincing evidence that some growing galaxies blow out more gas than they take in, slowing star formation down to a crawl.”

The other main theory to explain the dearth of high-mass galaxies is that the precious gas is gobbled up by supermassive black holes at the centers of galaxies.

But there is no indication that NGC 253′s central black hole is active, says the paper, published in the journal Nature.

Measurements by the ALMA telescope at the European Southern Observatory in Chile estimate that the galaxy’s stellar fuel is fleeing at between 40 km and 250 km per second.

Despite this great speed, the gas could take millions of years to completely escape the galaxy’s gravitational clutch. It may even get recycled by the galaxy to create new stars, but only further observations can confirm the theory.