A strange, zombie-like galaxy has been spotted in the distant universe. This undead galaxy stopped forming stars for 20 million years before coming back to life in a burst of activity, and it could help explain a cosmic mystery about the earliest galaxies.
鈥淲e鈥檝e seen galaxies going through bursts of star formation, and we鈥檝e also seen galaxies that are no longer forming stars, but this is the first instance of seeing a galaxy that鈥檚 stopped forming stars and then gone through this sort of rejuvenation process,鈥� says at the University of Geneva in Switzerland.
Roberts-Borsani and his colleagues observed the galaxy, called A2744-YD4, using the James Webb Space Telescope (JWST). Because of the time the light took to travel to the telescope, they saw the galaxy as it was just 650 million years after the big bang, making it one of the earliest galaxies to form.
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The researchers found signatures of bright, young stars as well as dimmer, older ones, which has never been seen before in one galaxy. The ages of the stars implies that after about 100 million years of forming stars, the galaxy went quiet for around 20 million years. Then聽it started churning out stars again.
This behaviour could be explained by mergers with other galaxies, which could provide fresh fuel for star formation to a dead galaxy, or it could be due to gas getting blown away by supernovae and then falling back into the galaxy. The process has never been seen before, so figuring out what caused it may be crucial for our understanding of the most distant galaxies.
鈥淵oung stars can easily outshine old ones, so in order to accurately infer the masses of galaxies, we need to know whether there could be an older population that is outshone by bright young stars,鈥� says at Northwestern University in Illinois. 鈥淣eglecting this possibility can introduce major errors in our census of the galaxy population 鈥� with fundamental implications for theoretical models.鈥�
The main such errors would be in our calculations of these galaxies鈥� masses and ages. When the glare from the young stars hides the old ones, the galaxies look younger and less massive than they are.
When JWST began sending back pictures of the early universe, it found many galaxies that were bigger and older than expected. This led some researchers to suspect that our previous idea of early galaxies as steady and consistent in their star formation might be wrong. Bursts and lulls in the activity of these star factories could explain the new observations.
鈥淚f this bursty behaviour is confirmed, then that can explain some of these puzzling JWST observations,鈥� says at the Flatiron Institute in New York. 鈥淭here have not been any smoking-gun observations for the kind of bursty star formation that would be needed, but this is such evidence.鈥�
This is only one galaxy, so whether or not this behaviour is common remains to be seen. If it is, though, it could prove to be a major paradigm shift in how we view the early universe. 鈥淲e expect that in the first few hundred million years of the universe, basically all galaxies should be undergoing this very bursty, violent mode of star formation,鈥� says Hayward. 鈥淏ut we鈥檒l of course need much larger samples to prove that this is a ubiquitous phenomenon.鈥�
arXiv
