Astronomers have discovered a distant rotating disk-shaped galaxy that’s incredibly unique and shouldn’t even exist. Located around 12.3 billion light-years away from Earth, DLA0817g (or the Wolfe Disk) appeared to be a normal disk-shaped galaxy that rotates at a speed of approximately 170 mi/s. It measures approximately 100,000 light-years across and about 70 to 80 billion suns can fit in it.
However, studies have determined that it was formed several billions of years prior to what was previously believed – at the same time as other galaxies like our own Milky Way were going through violent mergers.
It has been long thought that galaxies took their shape over a period of billions of years, but the Wolfe Disk contradicts that theory. Many of the universe’s galaxies have a rapidly rotating disk-shape that only formed about six billion years after the Big Bang. However, the Wolfe Disk’s shape formed just 1.5 billion years after the Big Bang – 4.5 billion years earlier than what was thought to be possible.
Marcel Neeleman, who is the lead author of the study (which can be read here), explained this further, “Most galaxies that we find early in the universe look like train wrecks because they underwent consistent and often ‘violent’ merging,” adding, “These hot mergers make it difficult to form well-ordered, cold rotating disks like we observe in our present universe.”
Co-author J. Xavier Prochaska weighed in by stating, “We think the Wolfe Disk has grown primarily through the steady accretion of cold gas,” adding, “Still, one of the questions that remains is how to assemble such a large gas mass while maintaining a relatively stable, rotating disk.”
Researchers first discovered the Wolfe Disk in 2017 when they were studying a quasar and noticed that part of its light was being absorbed when it traveled through a hydrogen gas envelope in the galaxy. At that point, they used the ALMA (Atacama Large Millimeter/submillimeter Array) radio observatory in order to determine how fast the galaxy’s disk was spinning.
“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,” Neeleman explained. “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.”
Additionally, they used the National Science Foundation's Karl G. Jansky Very Large Array (VLA) and the NASA/ESA Hubble Space Telescope to study the galaxy and discovered that 12.3 billion years ago, stars were being formed at an exceptional rate – over ten times higher than our own Milky Way galaxy. This exceptional discovery suggests that the Wolfe Disk was “one of the most productive disk galaxies in the early universe.” Pictures of the Wolfe Disk galaxy can be seen here.