from the it's-not-dead-it's-just-resting dept.
You'd think large galaxies in the early universe would have had plenty of 'fuel' left for new stars, but a recent discovery suggests that wasn't always the case. Astronomers using the Hubble Space Telescope and the Atacama Large Millimeter/Submillimeter Array (ALMA) have found six early galaxies (about 3 billion years after the Big Bang) that were unusually "dead" — that is, they'd run out of the cold hydrogen necessary for star formation. This was the peak period for star births, according to lead researcher Kate Whitaker, so the disappearance of that hydrogen is a mystery.
The team found the galaxies thanks to strong gravitational lensing, using galaxy clusters to bend and magnify light from the early universe. Hubble identified where stars had formed in the past, while ALMA detected cold dust (a stand-in for the hydrogen) to show where stars would have formed if the necessary ingredients had been present.
The galaxies are believed to have expanded since, but not through star creation. Rather, they grew through mergers with other small galaxies and gas. Any formation after that would have been limited at most.
From CNET we read:
"The most massive galaxies in our universe formed incredibly early, just after the Big Bang happened," Kate Whitaker, a professor of astronomy at University of Massachusetts-Amherst and lead author of a new study, said in a statement. "But for some reason, they have shut down. They're no longer forming new stars."
It turns out, some old galaxies merely ran low on star fuel, or cold gas, early on in their lifetimes. The results of the group's study were published Wednesday in the journal Nature and could rewrite our knowledge of how the universe evolved.
Katherine E. Whitaker, Christina C. Williams, Lamiya Mowla, et al. Quenching of star formation from a lack of inflowing gas to galaxies, Nature (DOI: 10.1038/s41586-021-03806-7)