in paper Announced today Astronomical JournalThe astronomers analysed the evolution of giant galaxies at redshifts 4 to 8 selected from the JWST Cosmic Evolution Early Emission Survey (CEERS).
A composite color image of the very red quasar-like object A2744-QSO1. Image courtesy of Furtak. others., doi:10.1038/s41586-024-07184-8.
“We still see more galaxies than expected, but none of them are massive enough to 'break' the universe,” said Katherine Kworowski, a graduate student at the University of Texas at Austin.
Galaxies that appear excessively massive are likely to harbor black holes that are rapidly eating away at gas, according to a new study.
Friction between the fast-moving gas releases heat and light, making these galaxies much brighter than they would be if light were emitted only by stars.
This extra light can make galaxies appear to contain more stars, and therefore more massive, than we would normally assume.
When scientists remove these galaxies, which they call “little red dots,” from their analysis, the remaining early galaxies are not so massive that they fit the predictions of the Standard Model.
“This means there is no crisis with regard to the standard model of cosmology,” Professor Steven Finkelstein said.
“When you have a theory that has stood the test of time for a long time, you need overwhelming evidence to really disprove it, and that's simply not the case.”
They've solved the main dilemma, but a less troubling one remains: there are still about twice as many massive galaxies in the Webb data from the early universe than would be expected from the standard model.
One possible explanation may be that stars formed more quickly in the early universe than they do today.
“Maybe early in the universe, galaxies were better at turning gas into stars,” Kurowski said.
Star formation occurs when hot gas cools enough to succumb to gravity and condense into one or more stars.
But as the gas contracts, it heats up and creates outward pressure.
In our region of the universe, the balance of these opposing forces tends to make the process of star formation very slow.
But some theories suggest that the early universe was denser than it is today, which could have made it harder for gas to escape during star formation, speeding up the process.
At the same time, astronomers are analyzing spectra of the tiny red dots that Webb has spotted, and the CEERS team and others are finding evidence of fast-moving hydrogen gas that is characteristic of black hole accretion disks.
This supports the idea that at least some of the light from these compact red objects comes from gas swirling around black holes rather than from stars, strengthening Kurowski and his colleagues' conclusion that black holes are probably not as massive as astronomers originally thought.
However, further observations of these intriguing objects are underway, which should help solve the mystery of how much light is coming from the star and how much is coming from the gas around the black hole.
In science, answering one question often gives rise to a new one.
Although the authors show that the Standard Model of cosmology is likely not broken down, their work points out the need for new ways of thinking about star formation.
“So there's still curiosity. Not everything is fully understood, which is why this kind of science is fun to do, because if one paper explained everything or there were no more questions to answer, it would be a very boring field,” Kurowski says.
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Katherine Choworowski others2024. Evidence for shallow evolution of bulk density in massive galaxies at z = 4-8 from CEERS. AJ 168, 113;doi:10.3847/1538-3881/ad57c1
Source: www.sci.news
