Astronomers discover 12.5-billion-year-old disk galaxy

Sophie Lewis

For decades, astronomers have attempted to piece together the mystery of how galaxies, stars and planets formed from an empty universe. They recently stumbled upon a gargantuan system that formed just 1.5 billion years after the Big Bang — and it challenges some of the accepted theories of how all galaxies in the universe may have formed.

According to a study published Wednesday in the journal Nature, the 12.5 billion-year-old rotating galactic disk formed much earlier than astronomers thought possible for a galaxy of its size. They renamed galaxy DLA0817g the "Wolfe Disk," after late astronomer Arthur M. Wolfe.

Disk galaxies, as the name suggests, are disk-shaped systems of stars, including spiral systems like our Milky Way. Previous observations showed these types of galaxies formed gradually, and did not reach a large mass until much later in their development. 

Using one of the most powerful telescopes in the world, the Atacama Large Millimeter/submillimeter Array (ALMA), located in Chile, scientists found the Wolfe Disk, which they said grew to a mass of 70 billion suns when the universe was just one-tenth its current age. It is the most distant of its kind ever observed, about 1 billion light years farther from us compared to other known disk galaxies. 

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Artist impression of the Wolfe Disk, a massive rotating disk galaxy in the early, dusty universe. The galaxy was initially discovered when ALMA examined the light from a more distant quasar (top left). NRAO/AUI/NSF, S. Dagnello

Astronomers said they observed the galaxy spinning at 170 miles per second, similar to the Milky Way. It was also teeming with massive stars. 

"The star formation rate in the Wolfe Disk is at least ten times higher than in our own galaxy," J. Xavier Prochaska, coauthor of the paper, said in a press release. "It must be one of the most productive disk galaxies in the early universe."

"Its shape and rotation (much like our Milky Way) are surprising, as we didn't expect to see such a 'grown-up' disk when the universe was this young," lead author Marcel Neeleman told CBS News on Wednesday. "This directly challenges some models of how we think galaxies form."

The prevailing theory for the formation of galaxies is the "hot mode" scenario, in which hot gas slowly cools over a long period of time to form a disk. By that logic, most galaxies would only start to have well-formed shapes around 6 billion years after the Big Bang. But this research suggests that another method of growth – "cold mode accretion," where cool gas forms a galaxy much faster — may have dominated. 

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The Wolfe Disk as seen with ALMA (right - in red), VLA (left - in green) and the Hubble Space Telescope (both images - blue). In radio light, ALMA looked at the galaxy's movements and mass of atomic gas and dust and the VLA measured the amount of molecular mass. In UV-light, Hubble observed massive stars.  ALMA (ESO/NAOJ/NRAO), M. Neeleman; NRAO/AUI/NSF, S. Dagnello; NASA/ESA Hubble

The researchers said they don't believe the discovery was a one-off. Rather, they believe galaxies like the Wolfe Disk are relatively common in the early universe.

"The fact that we found the Wolfe Disk using this method, tells us that it belongs to the normal population of galaxies present at early times," said Neeleman. "When our newest observations with ALMA surprisingly showed that it is rotating, we realized that early rotating disk galaxies are not as rare as we thought, and that there should be a lot more of them out there."

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