Galactic gas scarcity: a cosmic crisis!

Leif Larsen August 2, 2023 Science

TOLEDO, Ohio (WTVG)

In 2021, astronomer Kate Whitaker at UMass Amherst was part of a team tasked with taking on space and time, answering some weird questions we still have about the early universe.

Light and Time

Even though we can’t easily perceive it, light takes a certain amount of time to travel, so those distant features are really a snapshot of billions of years in the past finally reaching us. The Milky Way isn’t the most massive galaxy out there, but some of our neighbors fit the bill.

Exploring the Early Universe

“The way you want to do it is not in an archaeological sense,” Whitaker said. “Would we want to go looking at dinosaur bones? No, we want to go and look at when the dinosaurs were roaming! When we look at those galaxies in the nearby universe, we see that they’re all red and dead and old. It means they formed a really long time ago, then something happened to shut them down.”

The only reason they were able to see those old galaxies that had shut down star formation, was because other galaxies were in the way… counterintuitive, but true.

Strong Gravitational Lensing

“Those galaxies in the foreground bent spacetime,” Whitaker said, “so we had more light coming to our detector of those background galaxies than we would have normally. This is called ‘strong gravitational lensing’… so we use our time machine, and we add in a magnifying glass, and combine those two things to try and do cutting-edge science.”

Gas Shortage Mystery

Initially, the thought was some undiscovered shutoff valve for that cold gas serving as fuel for the cloud to collapse, ignite and form stars… then they found the gas simply wasn’t there.

“In the early universe, there was lots of gas everywhere flowing into galaxies… so for some reason, THESE galaxies use up their gas, they’re running on empty and don’t seem to be re-accreting,” Whitaker said.

Possible Explanations

Whitaker says it’s a super-small sample size — funny to think about, considering the scale — but the team has a few working theories.

“It could be that it’s all there, but gas has to be cold to form stars. We think that all galaxies have a supermassive black hole, and those are known to heat gas. We don’t see any cold gas, but that doesn’t mean there isn’t hot gas in these galaxies,” Whitaker said.

Those black holes are also known to eject cold gas and perhaps blew much of it away in select cases. Future research has been granted for a similar though wider gaze into the cosmos, using the Atacama Large Millimeter Array.

Simulations and Understanding the Universe

“We also want to take a look into simulations where we’re trying to mock the universe, and try to understand — with all the physical ingredients we know — how do you form a galaxy?” Whitaker said.