A week later, astronomers discovered a galaxy deeper in time

Zoom / The James Webb Space Telescope continues to deliver on its promise to discover the first galaxies.


Data from the Webb Space Telescope has only been in the hands of astronomers for the past few weeks, but they’ve been waiting for it for years, and it looks like the scans are in place. The result was like a race against time as new discoveries found objects that formed much closer to the Big Bang that produced our universe. Last week, such a search for a galaxy that existed less than 400 million years after the Big Bang appeared. This week, a new scan revealed a galaxy that formed just 233 million years after the universe began.

This discovery is a happy byproduct of work aimed at answering a larger question: how many galaxies should we expect to see at different times after the Big Bang?

In time

As we reported last week, the early universe was opaque to light at all wavelengths carrying more energy than is needed to ionize hydrogen. This energy is in the ultraviolet part of the spectrum, but the redshift caused by the 13 billion years of expansion of the universe has moved this cutoff point to the infrared part of the spectrum. To find galaxies from this era, we need to look for objects that are not visible at shorter infrared wavelengths (meaning the light was once above the hydrogen cutoff) but appear at lower energy wavelengths.

The deeper the boundary between the visible and the invisible in the infrared, the stronger the redshift and the further away the object is. The further 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 shifts in galactic dynamics that occurred at a particular 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 in the first galaxies are absorbed by the Earth’s atmosphere and must therefore be imaged from space. This was one of the design goals of the Webb Telescope.

The new work has focused on examining the luminosity function of galaxies that formed shortly (astronomically speaking) after the Big Bang. But while cataloging early galaxies, researchers discovered what appears to be the oldest galaxy ever photographed.

Job choice

The researchers used two data sources to reconstruct what galaxies looked like at different times. One was produced by analyzing work done with an infrared telescope (ESA’s view of the telescope) and the Spitzer Space Telescope, both of which imaged galaxies that were relatively older when they produced the light that now reaches Earth—about 600 million years or around after the big bang. Other embedded data generated by Webb, including datasets analyzed in the Report Us article And the area was filmed in The first public image. In all cases, the researchers were looking for the same thing: things that were present at the longer infrared wavelengths but absent at the shorter ones.

In total, the team identified 55 distant galaxies, 44 of which had never been observed before. 39 of them come from web data, and that number includes the two ancient galaxies identified last week. The numbers are not very accurate for higher redshifts as they are based on only one or two galaxies. But in general, the trend is toward a gradual decline in visible objects a few hundred million years from the Big Bang, without abrupt changes or cuts.

But the amazing thing is that there is data for a galaxy at a very high redshift (z=16.7, for those who understand this). This places it less than 250 million years after the Big Bang. This distance depends in part on whether the first wavelength filter in which the object appears appears very faint there, indicating that it is faint at the wavelengths allowed by the filter. 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 matter of a billion suns in the form of stars. Scientists estimate that it may have started forming stars 120 million years after the Big Bang, and definitely 220 million years ago.

The researchers are completely convinced 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 another independent confirmation of previous galaxy discoveries, it greatly increases our confidence in these discoveries. All of this suggests that the new telescope lives up to its promise, at least when it comes to early galaxies.

The big question now is what will emerge when they aim for high-lensing regions that might be able to zoom in on objects to the point where we can image structures in these early galaxies. We’ve probably already done this, but we’ll have to wait for the descriptions to appear in the arXiv file.

arXiv file. Abstract number: 2207.12356 (About arXiv).

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