The data from the Webb Space Telescope has only gotten into the hands of astronomers over the past few weeks, but they’ve been waiting for this for years, and it looks like the analyzes are in place. The result was like a race back in time, as new discoveries found objects that formed much closer to the Big Bang that produced our universe. Last week, one such search revealed a galaxy that existed less than 400 million years after the Big Bang. This week, a new analysis revealed a galaxy that appeared just 233 million years after the emergence of the universe.
This discovery is a happy byproduct of work designed to answer a more general question: How many galaxies should we expect to see at different time points after the Big Bang?
Back in time
As we reported last week, the early universe was opaque to light at any wavelengths carrying more energy than is required to ionize hydrogen. This energy is in the ultraviolet portion of the spectrum, but the red shift caused by the 13 billion years of expansion of the universe has shifted this cutoff point to the infrared portion of the spectrum. To find galaxies from this time, we have to look for objects that are not visible at shorter infrared wavelengths (meaning the light was once above the hydrogen cut-off point), but appear in lower-energy wavelengths.
The deeper the boundary between visible and invisible in infrared, the stronger the redshift, and the farther away the object. The farther away an object is, the closer the time is to the Big Bang.
Studies of these galaxies can tell us something about their individual properties. But identifying a large group of early galaxies can help us determine how quickly they formed and identify any changes in galactic dynamics that occurred at a specific time in the universe’s past. This change over time in the frequency of visible objects is called the ‘luminosity function’, and some work has been done to describe the luminosity function of early galaxies. But the infrared wavelengths of the first galaxies are absorbed by the Earth’s atmosphere, and therefore must be imaged from space. This was one of the design goals of the Webb Telescope.
The new work focused on examining the luminosity function of galaxies that formed shortly (astronomically speaking) after the Big Bang. But when creating a catalog of early galaxies, researchers discovered what appears to be the oldest galaxy ever photographed.
The researchers used two data sources to reconstruct the appearance of galaxies at different time points. One was produced by analyzing work done with the ground-based Infrared Telescope (the European Space Agency’s VISTA telescope) and the Spitzer Space Telescope, both of which are images of galaxies that were relatively older when they produced the light that now reaches Earth – about 600 million years or more after the Big Bang . Other data included that was generated by Webb, including the datasets analyzed in the paper we reported and an area depicted in the first public image release. In all cases, the researchers looked for the same thing: things that were present at the longer infrared wavelengths but absent on the shorter ones.
In all, the team identified 55 distant galaxies, 44 of which had not been observed before. Thirty-nine of them come from Web data, and that number includes the two ancient galaxies identified last week. The numbers are not particularly accurate for higher redshifts, as they are based on only one or two galaxies. But in general, the trend is for a gradual decrease in visible objects within a few hundred million years of the Big Bang, without sharp changes or cuts.
But the amazing thing is that there is data for a galaxy at a very large redshift (z = 16.7, for those who understand this stuff). This puts it at less than 250 million years after the Big Bang. This distance depends in part on the fact that the first wavelength filter in which the object appears appears to be very faint there, indicating that it is faint at the wavelengths the filter allows. This indicates that the hydrogen-induced light cutoff is near the edge of the filter band.
Like the distant galaxies described last week, it also appears to have the equivalent of a billion suns of material in the form of stars. Researchers estimate that it may have started forming stars 120 million years after the Big Bang, and certainly did so by 220 million years ago.
The researchers are quite confident that this new galaxy is a real discovery: “After extensive research, we cannot currently find any reasonable explanation for this object, other than a new redshift galaxy.” And by adding a second independent confirmation of previous galaxy discoveries, it greatly increases our confidence in those discoveries. All of this suggests that the new telescope delivers on promises, at least in terms of early galaxies.
The big question now is what will appear when they are aimed at regions with high lenses, which may be able to zoom in on objects to a point where we can image the structures within these early galaxies. We’ve probably already done that, but we’ll have to wait for the descriptions to appear in the arXiv file.
arXiv file. Bare number: 2207.12356 (about arXiv).