Space

Astronomers spot "invisible" galaxies at the dawn of the universe

Astronomers spot "invisible" g...
Left: Hubble's visible-light view of a region of space. Right: ALMA's view of the same area in radio waves, revealing a previously hidden galaxy
Left: Hubble's visible-light view of a region of space. Right: ALMA's view of the same area in radio waves, revealing a previously hidden galaxy
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Left: Hubble's visible-light view of a region of space. Right: ALMA's view of the same area in radio waves, revealing a previously hidden galaxy
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Left: Hubble's visible-light view of a region of space. Right: ALMA's view of the same area in radio waves, revealing a previously hidden galaxy

Astronomers have spotted two “invisible” galaxies hiding near the dawn of the universe. The team used radio waves to peer behind a curtain of dust that was obscuring them from view, and the find suggests that there were far more galaxies in the early universe than previously thought.

The Hubble Space Telescope is one of our most powerful cosmic eyes, able to see objects more than 13 billion light-years away. And because space and time are so intertwined, the objects it sees at that distance are seen as they were 13 billion years ago, allowing astronomers to effectively look back in time to the universe’s early childhood.

But Hubble can’t see everything. It watches the skies mostly in ultraviolet and visible wavelengths of light, with some near-infrared capability. Other telescopes, scanning the cosmos in other wavelengths, can reveal new details – and that’s exactly what happened here, as astronomers investigated a well-studied region of space using the Atacama Large Millimeter Array (ALMA), which captures radio waves.

"We were looking at a sample of very distant galaxies, which we already knew existed from the Hubble Space Telescope,” says Pascal Oesch, an author of the study. “And then we noticed that two of them had a neighbor that we didn’t expect to be there at all. As both of these neighboring galaxies are surrounded by dust, some of their light is blocked, making them invisible to Hubble.”

The two newly discovered galaxies have been named REBELS-12-2 and REBELS-29-2, and although the light from them has traveled 13 billion years to reach us, the galaxies are actually much farther away than that now. Thanks to the expansion of the universe, the galaxies are now a staggering 29 billion light-years away, making them among the most distant known galaxies.

Their discovery also raises some intriguing new questions about the early universe. The team calculated that between 10 and 20 percent of galaxies from around that time may be hiding behind dust clouds, meaning our models of the evolution of the universe could be off by a wide margin.

"We are trying to put the big puzzle about the universe’s formation together and answer the most basic question: ‘Where does it all come from?’” says Oesch. “The invisible galaxies that we’ve discovered in the early universe are some of the first building blocks of the mature galaxies we see around us in the universe today. So that’s where it all began.”

And soon, we should have even more powerful instruments to find these hidden galaxies. The James Webb Space Telescope (if it ever actually launches) will specialize in infrared imaging of the cosmos, which is perfect for seeing deeper into space than ever before. That’s because the expansion of the universe is stretching light from more distant objects further towards the infrared end of the spectrum. If all goes to plan, Webb should finally launch on December 22.

The new study was published in the journal Nature.

Source: University of Copenhagen

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