NASA's HaloSat Satellite Shows How Recycled Gas from Stars Surrounds the Milky Way

Observations made by a small spacecraft called HaloSat have shown that the Milky Way galaxy is surrounded by a clumpy halo of hot gases that is continually being supplied with material ejected by birthing or dying stars. A halo is a large region filled with hot gas that surrounds a galaxy, also known as a “circumgalactic medium.” The heated gaseous halo around the Milky Way was the incubator for the Milky Way’s formation some 13 billion years ago and could help solve a longstanding puzzle about where the missing matter of the universe might reside. “That suggests the circumgalactic medium is related to star formation, and it is likely we are seeing gas that previously fell into the Milky Way, made stars, and now is being recycled into the circumgalactic medium.” Every galaxy has a circumgalactic medium, and these regions are crucial to understanding not only how galaxies formed and evolved but also how the universe progressed from a kernel of helium and hydrogen to a cosmological expanse teeming with stars, planets, comets, and all other sorts of celestial constituents. The satellite has been observing the Milky Way’s circumgalactic medium for evidence that the missing baryonic matter may reside there. “So it turns out with HaloSat alone, we really can’t say whether or not there really is this extended halo around the Milky Way,” Kaaret said.