An international research team was able to find 6 huge galaxies completely devoid of cold hydrogen clouds responsible for the formation of new stars, and the strange thing is that these galaxies existed early in the history of the universe, that is, 3 billion years after its inception, at a time when it was assumed that All galaxies are active.
To reach these results, which were published in the journal Nature and announced by NASA, which participated in the study in an official statement on September 22, the research team used data from the “Hubble” space telescope, and they also used the Atacama Large Millimeter/ Submillimeter Observatory Array (ALMA).
When the universe was about 3 billion years old, just 20% of its current age, it experienced the most prolific period of star birth in its history. But when NASA’s Hubble Space Telescope and ALMA observations in northern Chile gazed toward cosmic objects in this period, they found something odd: six early, massive, “dead” galaxies that had run out of the cold hydrogen gas needed to make stars.
“At this point in our universe, all galaxies should be forming lots of stars. It’s the peak epoch of star formation,” explained lead author Kate Whitaker, assistant professor of astronomy at the University of Massachusetts, Amherst. Whitaker is also associate faculty at the Cosmic Dawn Center in Copenhagen, Denmark. “So what happened to all the cold gas in these galaxies so early on?”
Live Fast, Die Young
These sorts of dead galaxies don’t appear to rejuvenate, even through later minor mergers and accretions of nearby, small galaxies and gas. Gobbling up things around them mostly just “puffs up” the galaxies. If star formation does turn back on, Whitaker described it as “a kind of a frosting.”
About 11 billion years later in the present-day universe, these formerly compact galaxies are thought to have evolved to be larger but are still dead in terms of any new star formation.
These six galaxies lived fast and furious lives, creating their stars in a remarkably short time. Why they shut down star formation so early is still a puzzle.
Whitaker proposes several possible explanations: “Did a supermassive black hole in the galaxy’s center turn on and heat up all the gas? If so, the gas could still be there, but now it’s hot. Or it could have been expelled and now it’s being prevented from accreting back onto the galaxy. Or did the galaxy just use it all up, and the supply is cut off? These are some of the open questions that we’ll continue to explore with new observations down the road.”
Sources:
https://www.nature.com/articles/s416-7
https://www.nasa.gov/feature/goddard/2021/hubble-finds-early-massive-galaxies-running-on-empty