Free Astronomy Magazine November-December 2022

38 NOVEMBER-DECEMBER 2022 ASTRO PUBLISHING S DSS J1448+1010 is a newly-dormant massive galaxy that was born when the Universe was at roughly half of its current age, and is nearing the com- pletion of a merger with another galaxy. During the course of this merger, the force of gravity flung what amounts to nearly half of the system’s star-form- ing gas away from the galaxy, leaving it unable to form new stars. This com- posite image combines blue/white data from the Hubble Space Telescope (HST) and red/orange data from the Atacama Large Millimeter/submillimeter Array (ALMA) to show the post-merger distribution of gas and stars from the now-dormant galaxy into streams of material known as tidal tails. [ALMA (ESO/NAOJ/NRAO), J. Spilker et al (Texas A&M), S. Dagnello (NRAO/AUI/NSF)] I n the Chajnantor Plateau, amazing picture of the ALMA antennas under the Milky Way. [Sergio Otarola, ALMA(ESO/NAOJ/NRAO)] burgh and a co-author of the paper. “But, there are many galaxies out there like J1448+1010 that we’re able to catch right in the middle of those crashes and study exactly what happens to them when they go through that stage. The ejection of cold gas is an exciting new piece of the quiescence puzzle, and we are excited to try to find more ex- amples of this.” Spilker added, “As- tronomers used to think that the only way to make galaxies stop forming stars was through violent, fast processes, like a bunch of super- novae exploding in the galaxy to blow most of the gas out of the galaxy and heat the rest. Our obser- vations show that it doesn’t take a ‘flashy’ process to cut off star forma- tion. The much slower merging process can also put an end to star formation and galaxies.” ones,” said Wren Suess, a cosmology fellow at the University of California Santa Cruz and a co-author of the paper. “We still don’t yet under- stand all of the processes that make galaxies stop forming stars, but this discovery shows just how powerful these major galaxy mergers are and how much they can affect how a galaxy grows and changes over time.” Because the new result is from a single observation, it is cur- rently unclear just how typical this tug-of-war and its resultant quies- cence may be. However, the discov- ery challenges long-held theories about how star formation stops and galaxies die and has provided scien- tists with an exciting new challenge: finding more examples. “While it’s pretty clear from this sys- tem that cold gas really can end up way outside of a merger system that shuts off a galaxy, the sample size of one galaxy tells us very little about how common this process is,” said David Setton, a graduate student in the department of physics and as- tronomy at the University of Pitts- !