Astronomers have used the Atacama Large Millimeter/submillimeter Array (ALMA) to look for a specific signal from a galaxy that existed 13.4 billion years ago, when the Universe was only 500 million years old. Although ALMA could not detect this signal, the researchers were able to determine some important properties of this galaxy, called MACS1149-JD1. This galaxy is one of the earliest known, observed only 500 million years after the Big Bang. It has a very high rate of star formation and contains almost no heavy elements like carbon, oxygen and nitrogen.

In their ALMA observations, the team searched for a specific emission line from neutral oxygen. This line is commonly seen in more evolved, massive galaxies in the present-day Universe, but the astronomers predicted it would be weak or absent in MACS1149-JD1 because of the galaxy's low metal content and small size.

The non-detection of the neutral oxygen line indicates that MACS1149-JD1 is indeed a very young galaxy with little chemical enrichment. This suggests that the first galaxies were likely very different from the galaxies we see today, and that they did not form through the same processes.

Further observations with ALMA and other telescopes will help astronomers to better understand the formation and evolution of the earliest galaxies.