Interstellar storm prevents birth of new stars
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Stars like the Sun are big balls of glowing gas. They are born from clouds of gas and dust. Gravity causes those clouds to contract and collapse. Eventually, new stars are born. So if a galaxy contains a lot of gas, you would expect many new stars to form.
But in the galaxy NGC 1266, this appears not to be the case. Close to the centre of the galaxy is an enormous amount of gas and dust. It’s massive enough for the formation of a few hundred million stars like our Sun. Remarkably, the birth rate of new stars in the galaxy is fifty times lower than expected.
Using ALMA, astronomers have now discovered why. It’s because the galaxy has a supermassive black hole in its core. The black hole gobbles up matter from its immediate surroundings. But it also ‘burps’, as if it is eating too quickly. The burps are in the form of two jets of matter, being spewed away into space.
Sometimes, such jets are powerful enough to blow away most of the gas in a galaxy. Of course, not many new stars can form if there’s almost no gas left. But in the case of NGC 1266, the black hole is not nearly so powerful. The jets are not able to blow away all of the surrounding gas.
In stead, star formation is halted because of turbulent motions in the gas. The jets slam into the thick surrounding gas clouds. The jets are almost completely stopped, but the gas becomes very chaotic. It’s as if you’re pointing your garden hose at the surface of a pond: the water from the hose is stopped, but the surface of the pond becomes very turbulent.
If gas is too turbulent, it cannot easily collapse into new stars. That’s why so few stars are being born in NGC 1266, even though there’s plenty of gas around.
Until now, astronomers thought that black holes in the cores of galaxies needed to be very powerful to prevent the birth of new stars. The new ALMA observations reveal that less powerful black holes can also do the trick.
NGC 1266 is a galaxy at a distance of some 100 million light years. It can be seen with a big telescope, in the constellation Eridanus the River. It is a so-called lenticular galaxy. These galaxies usually don’t contain a lot of gas, probably because they collided and merged with a smaller galaxy in the past. However, in NGC 1266 there’s a lot of gas and dust surrounding the supermassive black hole in the galaxy’s core.
NGC 1266 was studied by a group of astronomers led by Katherine Alatalo of the California Institute of Technology in Pasadena. Katherine and her colleagues not only used ALMA for their observations; they also used a smaller array of radio antennas in California, called CARMA. The new results have been published in The Astrophysical Journal.