Science. One in five galaxies are still hidden from telescopes

11-23-2021 With the help of the giant radio telescopes ALMA (Atacama Large Millimeter Array) in the Atacama Desert in Chile, the two invisible galaxies suddenly appeared. NASA research and technology policy

Madrid, 23 years old (European press)

Astronomers at the University of Copenhagen’s Cosmic Dawn Center have discovered two previously unseen galaxies in the distant universe.

Light from these two unseen galaxies, named REBELS-12-2 and REBELS-29-2, have traveled about 13 billion years to reach us.

Their discovery suggests that as many as one in five distant galaxies are still hidden from our telescopes, camouflaged by cosmic dust. New knowledge is changing perceptions of the evolution of the universe since the Big Bang.

The two galaxies were invisible to the optical lens of the Hubble Space Telescope. But with the help of the giant ALMA radio telescopes (Atacama Large Milimeter Array) in the Atacama Desert in Chile, which can pick up radio waves emitted from the coldest and darkest depths of the universe, the two invisible galaxies suddenly appeared.

“We were looking at a sample of very distant galaxies, which we already knew existed from the Hubble Space Telescope. Then we noticed that two of them had neighbors that we didn’t expect to be there at all. Because both galaxies are neighboring, explains Associate Professor Pascal Oche of the Center for Cosmic Dawn.” At the Niels Bohr Institute in a statement that galaxies are surrounded by dust, and part of their light is obscured, making them invisible to Hubble.

The new discovery, published in Nature, indicates that the early universe contained many more galaxies than previously assumed. They simply hide behind the dust, which consists of small particles of stars. However, it can now be detected thanks to the highly sensitive ALMA telescope and the method the researchers use.

By comparing these new galaxies with previously known sources in the early universe, roughly 13 billion years ago, researchers estimate that between 10 and 20 percent of these early galaxies may still be hidden behind curtains of cosmic dust.

“Our discovery shows that up to one in five of the first galaxies may be missing from our map of the sky. Before we begin to understand when and how galaxies formed in the universe, we first need a proper account,” says Pascal Ochs.

To aid in this mission, the Webb Telescope – which will be launched in late December – will look deeper into the universe and contribute new insights into its origins. This, among other things, will help Cosmic Down researchers at the Niels Bohr Institute see cosmic dust.

“The next step is to identify galaxies that we’re missing, because there’s a lot more than we think. This is where the James Webb Telescope is going to be a big step forward. It will be much more sensitive than Hubble and will be able to investigate longer wavelengths, allowing us to see these galaxies.” Easily hidden,” says Pascal Auch.

“We are trying to piece together the great mystery about the formation of the universe and answer the fundamental question: ‘Where does all this come from?’ “The invisible galaxies that we discovered in the early universe are some of the first building blocks of the mature galaxies we see around us in the universe today. That’s where it all started.”

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