Massive Rotating Disk in Early Universe Flips Galaxy-Formation Theories

ALMA radio image of the Wolfe Disk, seen when the universe was only 10% of its current age. (ALMA (ESO / NAOJ / NRAO), M. Neeleman; NRAO /AUI /NSF, S. Dagnello)

(CN) — Star-gazing instruments in the Chilean desert have observed a massive rotating-disk galaxy formed more than 12 billion years ago when the universe was young — a discovery that challenges models for gradual galaxy formation. 

Most galaxies in our 13.8 billion-year-old universe — including our Milky Way — developed their large mass slowly and over billions of years, according to traditional formation models.

Galaxy development simulations predict that massive galaxies form by merging with or absorbing smaller galaxies and hot clumps of gas, according to the study titled “A Cold, Massive, Rotating Disk 1.5 Billion Years after the Big Bang.”

But the new evidence collected by the Atacama Large Millimeter/Submillimeter Array (ALMA) project in Chile shows at least one galaxy reached its large mass at an earlier point in the evolution of the cosmos.

The galaxy observed by ALMA — categorized as Galaxy DLA0817g — is the most distant rotating-disk galaxy ever observed, according to the study published Wednesday in the journal Nature.

Study lead author Marcel Neeleman said in a statement ALMA’s powerful observation tools made it possible to study the galaxy.

“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,” said Neeleman, who is with the Max Planck Institute for Astronomy in Heidelberg, Germany.

Joe Pesce, astronomy program director at the National Science Foundation — which funds the telescope — said in a statement ALMA allows researchers to explore uncharted areas of the cosmos.

“This observation epitomizes how our understanding of the universe is enhanced with the advanced sensitivity that ALMA brings to radio astronomy,” Pesce said.

The disk galaxy, nicknamed the Wolfe Disk after the late astronomer Arthur M. Wolfe, spins at a rate of 170 miles per second, like the Milky Way.

The Wolfe Disk, a massive rotating-disk galaxy in the early universe, was discovered in 2017 when a stargazing project in the Chilean desert examined light from a distant quasar (top left) absorbed in hydrogen gas surrounding the galaxy. (Courtesy of NRAO / AUI / NSF, S. Dagnello)

In most simulations, galaxies develop a well-formed disk around 6 billion years after the Big Bang. But the Wolfe Disk appears to have formed when the universe was only 10% of its current age, according to Neeleman.

“Most galaxies that we find early in the universe look like train wrecks because they underwent consistent and often ‘violent’ merging,” said Neeleman. “These hot mergers make it difficult to form well-ordered, cold rotating disks like we observe in our present universe.”

The rapid growth suggests other factors were at play, according to a statement by study coauthor and University of California, Santa Cruz, researcher J. Xavier Prochaska.

“We think the Wolfe Disk has grown primarily through the steady accretion of cold gas,” Prochaska said. “Still, one of the questions that remains is how to assemble such a large gas mass while maintaining a relatively stable, rotating disk.”

Prochaska said researchers also used the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) and the NASA/European Space Agency Hubble Space Telescope to study the Wolfe Disk.

Using powerful radio wavelengths, ALMA captured the galaxy’s atomic gas mass and movements while the VLA measured the disk’s molecular mass, which is the fuel for star formation. 

“The star formation rate in the Wolfe Disk is at least ten times higher than in our own galaxy,” Prochaska said in the statement. “It must be one of the most productive disk galaxies in the early universe.”

Researchers discovered the Wolfe Disk in 2017 while using ALMA to examine the light from a quasar, a distant and bright object that gives off an enormous amount of energy.

The Wolfe Disk was only revealed when light from the distant quasar was absorbed as it passed through the galaxy’s massive reservoir of hydrogen gas.

Galaxies from the early universe that project fainter light can be found by astronomers using the light absorption method, researchers said. 

“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 said. “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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