An Incredible Massive Disk Galaxy Discovered In The Very Early Universe

Artist's 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

Researchers have discovered the most distant rotating massive disk galaxy ever observed. Although disk galaxies like the Milky Way are common throughout the universe, none have been discovered as big and as far back as this one, which formed when the universe was 10 percent the age it is now. The study of Galaxy DLA0817g is published in Nature.

Nicknamed the Wolfe Disk after the late astronomer Arthur M. Wolfe, it rotates at 272 kilometers per second (170 miles) and weighs 72 billion times the mass of the Sun. The observations, conducted by the Atacama Large Millimeter/submillimeter Array (ALMA), clash with traditional models that expect a massive disk galaxy such as DLA0817g to be well-formed around 6 billion years after the Big Bang, which is not as early at this one.

“While previous studies hinted at the existence of these early rotating gas-rich disk galaxies, thanks to ALMA we now have unambiguous evidence that they occur as early as 1.5 billion years after the Big Bang,” lead author Marcel Neeleman, of the Max Planck Institute for Astronomy, said in a statement.

The Wolfe Disk as seen with ALMA (right - in red), VLA (left - in green) and the Hubble Space Telescope (both images - blue). ALMA (ESO/NAOJ/NRAO), M. Neeleman; NRAO/AUI/NSF, S. Dagnello; NASA/ESA Hubble

Galaxies are believed to form through many mergers of smaller galaxies as well as by capturing hot clumps of gas. The process is chaotic and leads to a messy galaxy that only settles to become a more relaxed, well-ordered object after billions of years. Clearly, another mechanism is necessary to explain the Wolfe Disk.

“We think the Wolfe Disk has grown primarily through the steady accretion of cold gas,” co-author J. Xavier Prochaska, from the University of California, Santa Cruz, added. “Still, one of the questions that remains is how to assemble such a large gas mass while maintaining a relatively stable, rotating disk.”

The galaxy is forming stars at a rate 10 times higher than our own galaxy. This is among the highest during that epoch of the universe, but far from the highest ever. This was estimated thanks to the use of the Karl G. Jansky Very Large Array (VLA) and the NASA/ESA Hubble Space Telescope.

The galaxy was first discovered in 2017 while the team was studying the light of a distant luminous quasar, a particular type of active galaxy. The emission from the quasar was altered by the large cloud of hydrogen surrounding the Wolfe Disk, allowing for the discovery of a much fainter galaxy.

“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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