Fade away

Galaxy-scale interactions

Just as each successive smartphone companies release includes a higher-resolution camera for sharper, more detailed photos, each new instrument astronomers build reveals the universe in ever-finer detail. In this case, that new instrument is the Commonwealth Scientific and Industrial Research Organisation’s (CSIRO) Australian Square Kilometer Array Pathfinder (ASKAP) array, containing 36 radio antennas whose data is combined into a single wide-field image of the sky. Researchers have now used the ASKAP array to image the Small Magellanic Cloud (SMC), one of the Milky Way’s small satellite galaxies, in three times more detail than ever before. The new view has allowed them to see that the tiny galaxy is quickly losing hydrogen — and with it, its ability to form new stars.The results, published October 29 in Nature Astronomy , identify “a powerful outflow of hydrogen gas from the Small Magellanic Cloud,” said Naomi McClure-Griffiths of the Research School of Astronomy and Astrophysics at The Australian National University (ANU), lead author of the paper, in a press release . The outflow, which astronomers believe may have formed between 25 million and 60 million years ago, stretches at least 6,500 light-years from the galaxy’s center. The team estimates the outflow contains about 107 solar masses of material, which amounts to about 3 percent of the galaxy’s total atomic gas. What’s more, the SMC is losing gas up to ten times faster than it is currently forming stars.“The implication is the galaxy may eventually stop being able to form new stars if it loses all of its gas,” McClure-Griffiths said. In that case, she added, it will “gradually fade away into oblivion. It's sort of a slow death for a galaxy if it loses all of its gas.”Of course, the SMC’s story is already set to end in tragedy — ultimately, the tiny dwarf will be swallowed up, or “cannibalized,” by the Milky Way, all of its stars, gas, dust, and dark matter ending up as part of our own galaxy, with few traces of the dwarf left behind.Several decades ago, astronomers first observed a “tail” of gas — mostly hydrogen — trailing the Large and Small Magellanic Clouds, stretching more than 100° on the sky. Called the Magellanic Stream, the tail is believed to have resulted from gravitational interactions between the Milky Way and one or both dwarfs, though the exact cause is still debated and numerous factors likely contribute to its current length and shape. “The result [from this study] is also important because it provides a possible source of gas for the enormous Magellanic Stream that encircles the Milky Way,” McClure-Griffiths said.