Astronomers Have Discovered A Pair Of Merging Galaxies From The Dawn Of Time

Artist's impression of two starbursting galaxies beginning to merge in the early universe. NRAO/AUI/NSF

Merging is a key mechanism in the evolution of galaxies and astronomers believe every galaxy, big or small, eventually collides with many others over its lifetime. And now research might have found an extraordinary early example of it.

The ADFS-27 galactic pair comprises two massive hyper-luminous galaxies merging just 1 billion years after the Big Bang. In a study reported in the Astrophysical Journal, the international team explained how these two objects are incredible star-making factories.

“Discovering a hyper-luminous starburst galaxy is an extraordinary feat, but discovering two – this close to each other – is amazing,” lead author Dominik Riechers, from Cornell University, said in a statement. “It’s nearly 13 billion light-years away and in its frenzied star-forming action, we may be seeing the most extreme galaxy merger known.”

The team estimates that the two galaxies have about 50 times more star-forming gas than our own galaxy, and are forming stars 1,000 times quicker than the Milky Way. The gas is enough to allow them to maintain this extraordinary rate for at least 100 million years. The object resulting from the merger is thought to be a progenitor for the massive galaxies we see at the center of galaxy clusters in the modern universe.

“Finding these galaxies – about 30,000 light-years apart – helps astronomers to understand how very extreme structures form, as they continue to birth stars and become even more massive,” explained Riechers. “These galactic progenitors help us to understand massive galaxies of the present day, as we’ve tried to understand how these actually form. In other words, this discovery is helping astronomers to understand the timeline of the cosmos.”

The Herschel image (middle square) and the ALMA image (right). NRAO/AUI/NSF, B. Saxton; ESA Herschel; ESO APEX; ALMA (ESO/NAOJ/NRAO); D. Riechers

This special object was first observed with the European Space Agency’s Infrared Herschel Telescope. Observations were then followed up with the Atacama Large Millimeter/submillimeter Array (ALMA). This allowed the researchers to discover that the source Herschel spotted was actually two objects.

“We can now see distant galaxies in exquisite detail, as we were able to uncover the compact, starburst nature of this merger pair – known only as a dusty blob in the good old days,” co-author and doctoral candidate T.K. Daisy Leung, also at Cornell, added.

The pair cannot be seen at visible wavelengths because they are far away and extremely dusty. The team hopes to combine the ALMA data with observations by the new James Webb Space Telescope, which will launch in 2019.

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