“These are essentially dead galaxies, but they're not small. They're massive galaxies with a lot of gravity,” Giavalisco said. “So why is it that a galaxy that potentially has all the gravity it needs to attract gas and keep making babies and keep forming stars, for some reason does not do that?"
“The quenching of the star-formation activity is a process that happens quickly in the history of the universe and we don’t know how,” he added.
One possibility is that these galaxies harbor monster-sized black holes that radiate out so much heat, gas in the galaxies can’t cool down to form stars.
Another idea it there are too many massive, hot stars squeezed together into too small of a space, generating so much heat that, like the black hole theory, gas cannot cool and form new stars.
“The galaxy dies, essentially self-strangulated," Giavalisco said. "But why does this only happen to spheroidal galaxies and not to disk galaxies? It’s not obvious. And why so quickly?”
The study, headed by BoMee Lee of the University of Massachusetts, pushes back the time frame for when modern galaxies emerged to about 2.5 billion years after the universe’s creation some 13.8 billion years ago. Previous galaxy surveys studied objects that formed about 5 billion years after the Big Bang.
“This is the only comprehensive study to date of the visual appearance of the large, massive galaxies that existed so far back in time,” astronomer Arjen van der Wel with the Max Planck Institute for Astronomy in Germany, added in a statement.
“The galaxies look remarkably mature, which is not predicted by galaxy formation models to be the case that early on in the history of the universe,” van der Wel said.
The research appears in The Astrophysical Journal.