How long after the Big Bang did stars and galaxies begin to form? A difficult question to answer because much of the light from the first stars shifted deep into the infrared during the billions of years it spent traveling to Earth. One of Webb’s design goals was to create a telescope that could pick up this light and tell us something about the early history of the universe. And the early data are so promising that astronomers seem to be racing to find the most distant galaxy ever observed.
Now, a new study examining the properties of a series of distant galaxies shows that one of them appears to be larger than the Milky Way just 700 million years after the Big Bang. If the results hold, the number of galaxies of this size may be difficult to reconcile with the forces we think built the universe.
dig deep
The technique for finding early galaxies is fairly simple. Early stars and galaxies were embedded in a universe filled with hydrogen atoms, which become ionized when they absorb certain wavelengths of light in the UV range. This absorption creates a unique signature in light arriving from distant galaxies. But although it took billions of years to reach us, the feature was redshifted by the expansion of the universe and now appears deep in the infrared portion of the spectrum. If we can identify , we can determine how far apart the galaxy is.
For the new study, a team of astronomers searched the galaxy for patches of sky and was able to identify two specific features due to the ionization of hydrogen. This resulted in a group of 13 galaxies with redshifts from 500 million years to 900 million years from the Big Bang. This means that light from them traveled about 13 billion years before reaching Earth.
Just knowing the galaxy is out there helps. But it is also possible to estimate some of their properties, telling us how quickly galaxies formed and evolved. These estimates are based on the ratio of hydrogen feature intensity to deeper infrared light, which includes much of the starlight emitted by these galaxies.
There are several ways to model the properties of these galaxies, and the research team has done all of them. One of them used five different configurations. This was intended to provide a range of values under the assumption that the actual value is likely to fall within this range.
big one
The brightest of these galaxies is unexpectedly large. The upper bound of that mass estimate is about 10.11 It is twice the mass of the Sun and larger than the Milky Way by this estimate. However, it seems that many stars exist about 700 million years after the Big Bang. A galaxy with this mass has never been seen at this distance before. There appeared to be at least two of her mates nearby, which may have been part of the cluster, which may have affected growth.
However, although it is the largest member of this sample, the overall sample tends to be unexpectedly large. In fact, when these galaxies are represented, most of the stars in the early Universe were in massive galaxies. Or they have not been very successful in finding low-mass galaxies at these distances. Given our current understanding of what happened, it is difficult to form so many high-mass galaxies. The regular matter that makes up its many stars. These galaxies “defy limits set by the number of baryons available in the most massive dark matter halos,” the researchers note.
The alternative, of course, is that the mass estimate is somehow wrong. One possibility is that the method used to estimate mass was developed using a slightly more recent example, and thus gives less accurate results when used on more distant galaxies.
Luckily, it takes time to figure out what’s going on. This had been previously imaged by Hubble, so he was just one of the small regions of the sky chosen for study. There are undoubtedly additional regions for which we already have data, and they should tell us whether the trend toward massive galaxies is a general feature of the early Universe.
Nature, 2023. DOI: 10.1038/s41586-023-05786-2 (About DOI).
