It’s rough being a dwarf galaxy. Hot on the heels of the discovery that the Large and Small Magellanic Clouds collided – with the smaller galaxy inevitably coming off worst – we learn the Small Magellanic Cloud (SMC) is losing so much gas it will soon be unable to form new stars. Astronomers had previously predicted dwarf galaxies would struggle to hold onto their gas, but this is the first time the process has been seen directly.
“Soon” is measured in astronomical time so we are no danger of losing sight of one of the three galaxies visible to the naked eye. The SMC will continue forming stars for hundreds of millions of years. Indeed, Professor Naomi McClure-Griffiths of the Australian National University told IFLScience that, in the light of expectations that the SMC will eventually be absorbed into the Milky Way, it is not clear which sort of death will come first.
Even if star formation does cease, making it a dead galaxy in astronomer's terminology, the SMC will have a beautiful corpse. Many of its existing stars have fuel to last for billions of years.
Nevertheless, the discovery confirms theories about the evolution of small galaxies, as well as being a demonstration of the amazing power of radio astronomers' exciting new tool.
Hot young stars emit powerful winds, like the solar wind but at speeds of up to 10,000 kilometers per second (one-thirtieth of the speed of light or 22 million mph), McClure-Griffiths noted. Supernova explosions provide an even more powerful burst of energy. “The SMC had periods 25-60 million years ago when it formed a lot of new stars,” McClure-Griffiths told IFLScience. Some of these have now gone through their entire life cycle to become supernovae.
In a large galaxy, gas carried along by these winds has a long journey to reach the edge, and plenty of gravitational force pulling the other way. McClure-Griffith provides evidence in Nature Astronomy the SMC is too small for this, and the gas given such powerful impetus escapes, joining the band of hydrogen known as the Magellanic Stream.
Although astronomers detected the Magellanic Stream decades ago, the radio telescopes in which it was visible lacked the sensitivity to tell if the SMC was a source.
The Australian Square Kilometer Array Pathfinder provided McClure-Griffiths with this resolution. She collected images three times more detailed than any previously taken of the SMC at hydrogen's wavelengths, allowing her to trace the connections between patches of gas into the dwarf galaxy's heart.
As its name suggests, the Pathfinder is only a test run for the Square Kilometer Array telescope to be built at the same site. McClure-Griffiths gleefully described the SKA as a “dream come true” that will be 40 times more powerful still.