A galaxy remarkably similar in shape to our own Milky Way, yet significantly bigger and dating back to the universe’s infancy, has been observed by astronomers.
This cosmic relic, dubbed J0107a, offers a glimpse into a time 11.1 billion years ago, when the universe was merely a fifth of its current age.
Observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile and NASA’s James Webb Space Telescope revealed J0107a’s surprising spiral structure, complete with a central bar of stars and gas – a hallmark of the Milky Way.
However, the similarities end there. J0107a dwarfs our galaxy in mass, weighing in at over 10 times greater, and boasts a star formation rate approximately 300 times higher.
Despite this increased activity and mass, J0107a is more compact than the Milky Way.
The discovery of such a mature and massive galaxy so early in the universe’s timeline raises intriguing questions about the speed and processes of galactic formation.
“The galaxy is a monster galaxy with a high star formation rate and plenty of gas, much more than present-day galaxies,” said astronomer Shuo Huang of the National Astronomical Observatory of Japan, lead author of the study published this week in the journal Nature.
“This discovery raises the important question: How did such a massive galaxy form in such an early universe?” said study co-author Toshiki Saito, an astronomer at Japan’s Shizuoka University.
While some galaxies that are undergoing star formation at a similar rate to J0107a exist in today’s universe, almost all of them are ones that are in the process of a galactic merger or collision. There was no sign of such circumstances involving this galaxy.
J0107a and the Milky Way have some commonalities.
“They are similarly huge and possess a similar barred structure. However, the Milky Way had plenty of time to form its huge structures, while J0107a didn’t,” Mr Saito said.
In the first few billion years after the Big Bang event 13.8 billion years ago that initiated the universe, galaxies were turbulent entities and were much richer in gas than those existing currently – factors that fostered extreme bursts of star formation.
While galaxies with highly organised structures like the barred spiral shape of the Milky Way are common now, that was not the case 11.1 billion years ago.
“Compared to other monster galaxies in the distant universe (dating to an earlier cosmic epoch) whose shapes are usually disturbed or irregular, it is unexpected that J0107a looks very similar to present-day spiral galaxies,” Mr Huang said.
“Theories about the formation of present-day galactic structures may need to be revised,” he added.
The Webb telescope, as it peers across vast distances back to the early universe, has found that galaxies with a spiral shape appeared much earlier than previously known. J0107a is now one of the earliest-known examples of a barred spiral galaxy.
About two thirds of spiral galaxies observed in the universe today possess a bar structure. The bar is thought to serve as a form of stellar nursery, bringing gas inward from the galaxy’s spiral arms. Some of the gas forms what are called molecular clouds. Gravity causes the contraction of these clouds, with small centers taking shape that heat up and become new stars.
The bar that is part of J0107a measures about 50,000 light years in length, Mr Huang said. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).
The Webb telescope “has been studying the morphology of early massive galaxies intensely recently. However, their dynamics are still poorly understood”, Mr Saito said.
