Lauren Fuge
Astronomers may have just witnessed a new way for galaxies to “die”, using the super-sensitive Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.
The array of 66 radio telescopes, sprawled across the Atacama Desert about 1400 km north of Chile’s capital Santiago, watched as a galaxy nine billion light-years away ejected nearly half of its star-forming gas into space.
Key research points
- A radio telescope array has observed a galaxy losing 46% of its total star-forming gas
- Without this gas, the galaxy will stop creating stars within a few tens of millions of years and “die”
- The ejection of gas was likely caused by a galaxy merger – suggesting a new mechanism by which galaxies end their lives
The astronomers suspect this cataclysmic event was triggered by two galaxies colliding and merging to form a new one – inspiringly called ID2299. This massive disruption event provides fresh insight into the mechanisms that can halt star formation, adding another piece to the complex puzzle of how galaxies evolve and die.
The research appears in Nature Astronomy.
“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,” says lead researcher Annagrazia Puglisi, from Durham University, UK, and the Saclay Nuclear Research Centre (CEA-Saclay) in France.
Previous evidence has indicated that such ejections of star-forming gas can be caused by high-speed galactic winds blasted out from newly formed massive stars, or the powerful activity of black holes spinning at the hearts of massive galaxies.
“Our study suggests that gas ejections can be produced by mergers,” says co-author Emanuele Daddi, of CEA-Saclay.
The clue that led to this conclusion came from a “tidal tail” – an elongated stream of stars and gas extending out into interstellar space. Usually, these features are faint, but the team managed to capture ID2299’s when it was just launching into space and so still relatively bright.
Daddi points out that winds and tidal tails can appear very similar. Previous research that observed winds driving galactic gas out into space could have actually seen tidal tails instead.
“This might lead us to revise our understanding of how galaxies die,” Daddi says.
The observed ejection makes up an astonishing 46% of the ID2299’s gas, and it’s spewing out at a remarkable rate – equivalent to 10,000 Suns worth of gas per year. This means the galaxy is rapidly losing the material it needs to create new stars.
The gas left in ID2299 won’t last long either: the galaxy is also busy forming stars hundreds of times quicker than our own Milky Way, consuming the leftover material.
The team estimates that ID2299 will shut down in just a few tens of millions of years – and when its stars eventually wink out, it will go dark forever.
Spotlight: galaxy deaths
- Galaxies start to “die” when they lose or consume all their star-forming gas, so new stars can’t be born
- Existing stars will eventually burn through their fuel and go dark, bringing the galaxy to its true end
- Stars like our Sun can only last for around 10 billion years, but smaller, cooler red dwarf stars can last for trillions years