The unprecedented power of the James Webb Space Telescope allows it to look farther back in space and time than ever before – and in doing so, it’s revealed puzzling galaxies that seem to be too advanced for their age. Now astronomers have proposed a new explanation for them – starburst galaxies – which mercifully spare the standard model of cosmology.
To look through space is to look through time. If astronomers look at a star 100 light-years away, for example, they’re seeing it as it was 100 years ago, because its light took that long to reach us. So when you extend that to the very fringes of the observable universe, you can actually see more than 12 billion years into the past – a period called the “cosmic dawn,” as the first stars fired up and formed early galaxies.
James Webb was the first telescope powerful enough to see this far back in space and time. Astronomers were expecting to see still-forming “protogalaxies,” but to their surprise the telescope spotted galaxies that seem to be quite advanced and mature, similar to those around today. And not just one or two anomalies, but dozens. This isn’t just weird, it potentially uproots our entire understanding of how galaxies form, and may even bring into question the standard model of cosmology itself.
So for the new study, a team of astrophysicists led by Northwestern University investigated alternative ideas using powerful computer simulations. In doing so they identified one possibility that produces signatures matching James Webb’s observations.
The simplest way to estimate a galaxy’s mass and size, especially from a huge distance, is its brightness, and this was done with the early galaxies Webb spotted. But the team’s simulations showed that galaxies at the cosmic dawn could reach the same level of brightness with much lower masses – all they had to do was go through a period of rapid star formation, something the simulated galaxies did on their own.
“The key is to reproduce a sufficient amount of light in a system within a short amount of time,” said Guochao Sun, lead author of the study. “That can happen either because the system is really massive or because it has the ability to produce a lot of light quickly. In the latter case, a system doesn’t need to be that massive. If star formation happens in bursts, it will emit flashes of light. That is why we see several very bright galaxies.”
Modern galaxies like the Milky Way tend to show steady star formation over time, but the simulations suggest that early galaxies with low masses were more likely to go through “starburst” phases followed by periods of relative quiet, until those older stars died and fueled the formation of the next generation in another starburst period.
“Most of the light in a galaxy comes from the most massive stars,” said Claude-André Faucher-Giguère, senior author of the study. “Because more massive stars burn at a higher speed, they are shorter lived. They rapidly use up their fuel in nuclear reactions. So, the brightness of a galaxy is more directly related to how many stars it has formed in the last few million years than the mass of the galaxy as a whole.”
Of course, just because it’s possible in a simulation doesn’t mean that’s how it happened in the real universe. Follow-up Webb observations, using other techniques to measure the mass of these galaxies, could help confirm the starburst hypothesis and let the standard model of cosmology breathe a sigh of relief – or put it back on the chopping block. After all, how does starburst formation explain the presence of other advanced structures like bar galaxies earlier than they should have arisen?
The research was published in the Astrophysical Journal Letters.
Source: Northwestern University