There’s more to a galaxy than meets the eye. Galaxies’ bright stars seem to spiral serenely against the dark backdrop of space. But a more careful look reveals a whole lot of mayhem.
“Galaxies are just like you and me,” Jessica Werk, an astronomer at the University of Washington in Seattle, said in January at a meeting of the American Astronomical Society. “They live their lives in a constant state of turmoil.”
Much of that turmoil takes place in a huge, complicated setting called the circumgalactic medium, or CGM. This vast, roiling cloud of dust and gas is a galaxy’s fuel source, waste dump and recycling center all in one. Astronomers think the answers to some of the most pressing galactic mysteries — how galaxies keep forming new stars for billions of years, why star formation abruptly stops — are hidden in a galaxy’s enveloping CGM.
“To understand the galaxies, you have to understand the ecosystem that they’re in,” says astronomer Molly Peeples of the Space Telescope Science Institute in Baltimore.
Yet this galactic atmosphere is so diffuse that it’s invisible — a liter of CGM contains just a single atom. It has taken almost 60 years and an upgrade to the Hubble Space Telescope just to begin probing distant CGMs and figuring out how their constant churning can make or break galaxies. [Continue reading…]