Kelly McSweeney

Jul 7th 2021

Life in the Dark: Understanding Galaxy Death


Astronomers recently reported witnessing galaxy death for the first time. They used the Atacama Large Millimeter/Submillimeter Array (ALMA) telescopes in the Chilean desert to observe galaxy ID2299. They noticed that the galaxy is losing so much gas that it will soon go dark when it runs out of fuel for stars. In other words, the galaxy’s light appears to be dying.

“Galaxies are kind of living, evolving things, and as their physical processes take place, and as new chemical species emerge into the mix and planets form, the physics change,” says Northrop Grumman astrophysicist Jon Arenberg.

He explains that galaxy death is a misnomer, and it would be more accurate to say that ID2299 is transitioning to a new stage of life. Even when the galaxy goes black, it will still have mass — we just won’t be able to see it easily.

Death of ID2299

“When a galaxy stops making stars and the existing stars transition to the next stage of life, the galaxy gets dimmer and appears to die,” Arenberg says.

CBS News reports on the study, which was published in January 2020 in the journal Nature Astronomy. The galaxy is so far away that it took approximately nine billion years for its light to travel to Earth.

The astronomers calculated that the galaxy is losing the equivalent of 10,000 suns worth of gas each year, as CBS reports. Meanwhile, it appears to be making new stars that will quickly (in terms of the history of the universe) burn up the withering gas supply. Therefore, ID2299 appears to be using its gas supply relatively quickly, and it is expected to die in a few tens of thousands of years — which is very soon in terms of the history of the universe.

“This is the first time we have observed a typical massive star-forming galaxy in the distant universe about to ‘die’ because of a massive cold gas ejection,” said lead author Annagrazia Puglisi in a statement released by the European Southern Observatory (ESO).

When the gas associated with the luminous part of ID2299 or another galaxy disappears, astronomers will need to use a different instrument to observe the galaxy.

“Light is a continuum from gamma rays to radio waves,” Arenberg explained. “And since there will be matter in this galaxy, looking at it in the radio spectrum as it cools off hundreds of millions of years from now will still allow us to collect data. It’s a matter of using the right tool for the right question.”

What Happens When a Galaxy Dies?

Like many areas of astronomy research and science in general, galaxy death is not black and white. We don’t know much about what happens when galaxies go dark, but new scientific instruments are providing insight. Astronomers are using images from telescopes on land (such as ALMA) and space (such as the Hubble telescope and its forthcoming successor, NASA’s Webb Space Telescope) to peer into the universe to match observations with theories.

“ALMA is a relatively new instrument with tremendous capability,” says Arenberg. “It’s a groundbreaker, like Webb will be.”

One of the main scientific pillars of NASA’s Webb Telescope is understanding the assembly and evolution of galaxies. Soon, we will have answers to what happens when a galaxy dies. For now, we have theories.

“When a star dies and becomes a nova or supernova, it ejects the outer envelope that contains a lot of the evolved heavy elements that we’ll need for life and planets. Some of that gas is going fast enough to escape the galaxy,” Arenberg says. “Some of that gas is injected into the intergalactic medium and doesn’t come back to the original galaxy. So, there’s a very complicated set of dynamics that we’re now starting to be able to have instruments to understand.”

The astronomers who studied ID2299 were tipped off about the gas ejection when they noticed a stream of stars and gas called a tidal tail. They observed that this tail of gas ejection appears to be caused by two galaxies colliding and merging together.

“Our study suggests that gas ejections can be produced by mergers and that winds and tidal tails can appear very similar,” study co-author Emanuele Daddi explains in the ESO statement.

Don’t Quit Your Day Job

Scientists are working on collecting more data to better understand how galaxies transition from one phase to another.

“Objects that are close to our galaxy’s age are beautiful, elegant spirals or beautiful balls,” Arenberg says. “When we go back into the early universe, even as under-resolved as the images are, they’re kind of ugly and lumpy. They haven’t evolved these elegant structures through all of their complicated processes.”

So, now that we have observed a galaxy withering away, is there reason to panic about life on Earth?

“Don’t stop paying your mortgage,” Arenberg jokes. “The Sun will eventually ‘die’ and burn out, or move to a different stage of life, but that won’t be for billions of years.”

Interested in all things in outer space and exploration? We are, too. Take a look at open positions at Northrop Grumman and consider joining our team.