Life in the Dark: Understanding Galaxy Death

Jan 27, 2020
Jul 7th 2021

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.

Galaxy ID2299, galaxy-11.ashx


Galaxy 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.”

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 WebbSpace Telescope) to peer into the universe to match observations with theories.

“ALMA, or the Atacama Large Millimeter/Sub-Millimeter Array, 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 only 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 just 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.

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.”


* The ALMA array has been constructed on the 5,000 m (16,000 ft) elevation on the Chajnantor plateau - near the Llano de Chajnantor Observatory and the Atacama Pathfinder Experiment. This location was chosen for its high elevation and low humidity, factors which are crucial to reduce noise and decrease signal attenuation due to Earth's atmosphere.

After searching the world over for the perfect place to receive millimetric and submillimetric waves, scientists identified a plateau where the conditions were unmatched: Chajnantor. In the middle of the Atacama desert in northern Chile, they found a vast expanse of plains at five thousand meters above sea level, where the climate’s extreme aridity presented the perfect conditions for receiving cosmic waves. At a high altitude, with a broad surface and favorable climate, ALMA had found its home.

However, they were not the first to discover this key site. Proof of this lies in the origin of the word Chajnantor, meaning “place of departure” in the Kunza language of the Atacameños, or Likan Antai, the original indigenous people who have been coming to this site to scrutinize the heavens for centuries.

Unlike the occidental worldview, concentrated on observing shiny objects in the sky, the Andean worldview distinguishes constellations while observing the dark sectors of the night sky, the same dark Universe that ALMA is currently investigating.

“Our ancestors were able to read the signs in the sky to survive the vagaries of climate and enjoy the bounty of Mother Earth (…) now we know that our ancestors are true observers of the heavens and the first true astronomers in Atacama,” indicates an Atacameño descendent in the extract of the book, “The Universe of Our Elders,”supported by ALMA.

All of ALMA’s operations are carried out in territory provided in a concession by the government of Chile in the Atacama desert, one of the driest places on Earth. Although the landscape is stark, there are communities that have lived here for a long time. The Atacameño people, known as Likan Antai, have raised llamas and alpacas here for hundreds of years, and still maintain this tradition, along with weaving and crafting of jewelry. They are currently the third-largest indigenous community in Chile.

ALMA, which observes the portion of the radio waves in millimetric and submillimetric wavelengths (found between the far infrared waves and the radio waves), we are able to fulfill the dream of opening a new window for high-resolution exploration of the Universe. This type of research is key to the future of astronomy, because it is where the dark universe is found.

In addition to the cosmic microwave background (an almost uniform glow across the sky, a consequence of the Big Bang), the Universe emits light that we can identify in three “groupings” of energy: high energy (ultraviolet, X-ray, gamma ray and cosmic background radiation), not so high energy (visible light) and low energy (infrared, microwave and radio wave).

For four centuries, man has studied visible light emissions thanks to the use of optic telescopes. The most energetic waves are absorbed by the ozone layer and are not able to penetrate the atmosphere; therefore they must be observed with space telescopes like the Hubble. Finally, the low energy groups could not previously be observed because they were blocked by the Earth’s atmosphere. However, these can now be captured by ALMA, thanks to its cutting edge technology and privileged location in the Chajnantor Plateau.

Aside from being sufficiently broad enough to house the 66 antennas, this site is also very high in altitude (5,000 meters above sea level), dry (located in the most arid desert in the world) and has the clearest skies (due to its distance from urban areas, it has less light and atmospheric pollution). This allows ALMA to capture far infrared waves.

Some of the most persistent questions in astronomy pertain to the origin of the galaxies, stars, planets and molecules that give rise to life. ALMA observes the light emitted by cold temperature objects in space, which allows us to untangle deep mysteries about planet formation or “digital fingerprints” of complex, even organic, molecules which inhabit the interstellar medium, of which to date little, if anything, is known.


Here we see a galaxy approaching its end as its stellar manufacturing medium is being ejected in a long tail thousands of lightyears long as the result of the gravity due to its collision with another galaxy. We know that once this medium is gone, stellar production will slow and future stars will be rich in the heavy metals resulting from the novae of dying Population I stars. Following that, the electromagnetic signature of the galaxies will move from infrared to radio. It is exciting to be alive today when new information seems to flood your inbox every day.
Last edited:
Jul 29, 2021
ID2299 is too far to influence the Milky Way, still direing and stunning, amazing
The merger mechanism contributes observations of surviving galaxies, including their host galaxy clusters and superclusters. Observing ‘local’ processes of the universe.
This event is observed and gathered valuable data, including that for simulations.