Galaxies formed in the first billion years following the Big Bang should have had long and healthy lives. They were blessed with abundant supplies of cold hydrogen gas, which is exactly what they needed to continue star formation.
New observations have shown that "quenched" galaxies have stopped star formation. Astronomers don't know why.
An international team of astronomers studied a group of six early galaxies with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Hubble Space Telescope. Nature published the results of this research recently.
These galaxies were chosen because they had little star formation and were "quenched".
Astronomers had previously believed that something stopped star formation in these otherwise rich galaxies.
"The largest galaxies in our Universe created their stars quickly and furiously in a remarkable amount of time. "Gas, the fuel for star formation, should be abundant at these early times of the Universe," stated Kate Whitaker (lead author and assistant professor of Astronomy at the University of Massachusetts in Amherst).
We believed that the quenched galaxies would have slowed down just a few billions of years after the Big Bang. Our new research has shown that the brakes were not actually applied to early galaxies. Instead, they were running on gas.
These galaxies are usually so far away that it's impossible to resolve. However, the REQUIEM team (for REsolving QUIEscent Magnified Galaxies) devised a way to do this: They used gravitational lenses around nearby galaxies in order to magnify the images.
It is very difficult to see the details of a galaxy in detail using any telescope if it isn't creating many new stars. REQUIEM solves this problem by studying galaxies with gravitationally lensed light. This means that their light is stretched and magnified when it bends and warps around galaxies closer to the Milky Way. Justin Spilker is a coauthor of the new study and a NASA Hubble postdoctoral fellow at Texas A&M University.
"In this way gravitational lensing combined with the sensitivity and resolution of Hubble and ALMA acts as a natural telescope. This makes dying galaxies appear larger and brighter than in reality. It allows us to see what's happening and what's not.
Contrary to what was expected, the team discovered that there was no sudden decrease in the galaxies' ability to convert cold gas into stars. Instead, stars had a lack of cold gas.
Christina Williams, co-author of the research and an astronomer at Arizona University, said that while we don't know why this happens, it could be because the primary gas supply to the galaxy is cut off or that a supermassive dark hole injects energy that keeps the gas hot.
This basically means that the galaxies cannot refill their fuel tanks and therefore are unable restart the engine for star production.
What is the secret to removing cold gas from galaxies, then? Astronomers are still stumped. They will continue to observe the galaxy to uncover clues.
Whitaker stated, "We still have much to learn about the origins of the largest galaxies in the Universe" and the reasons they stopped star formation while so much cold gas was available.
"The simple fact that these giant beasts of space formed 100 billion stars in less than a billion years, then shut down star formation is a mystery that we all would love to solve. REQUIEM has given us the first clue."
Universe Today originally published this article. You can read the original article.
