Spinning Ancient Galaxy Suggests Universe’s First Stars Quickly Merged into Disks | Science

Astronomers have detected the rotation of a galaxy dating back just 550 million years after the big bang, when the universe was 4% of its current age. The rotation suggests that this small galaxy was not an amorphous blob but rather an organized disk, much like the Milky Way and similar galaxies that took over 13 billion years to mature. This is further evidence that galaxies are growing and evolving faster than theorists predicted.

Merging stars into a disc so soon doesn’t contradict existing theories, but stretches them, says Sarah Bosman of the Max Planck Institute for Astronomy, who was not involved in the research. “It’s pretty much possible this soon.”

The stars in this pioneer galaxy were also mature, indicating that they formed 300 million years earlier, when the universe was only 250 million years old. That’s good news for the upcoming James Webb Space Telescope, which launched last year and is expected to start science operations next month. If those early galaxies gave birth to many stars in one burst, they’ll likely be “bright enough for Webb to see,” says Richard Ellis, an astronomer at University College London and co-author of the new study. Astronomers hope the $10 billion instrument will reveal multitudes of early galaxies, rather than just the largest and brightest outliers, so they can understand how these early agglomerations formed and evolved.

The galaxy, called MACS1149-JD1 or just JD1 for short, is not the most distant galaxy known, but it is now the most distant galaxy with everything known about its dynamics. The team, including Ellis, discovered JD1 in 2018 as an indistinct spot in images from the Atacama Large Millimeter/submillimeter Array (ALMA), a collection of 66 radio telescopes high in the Chilean Andes, and the Very Large Telescope of the European Southern Observatory, also in Chile. From her color, Ellis and her colleagues knew that at least some of her stars were mature, as they tend to blush with age. But the team did not know how these stars were organized.

They decided to take a closer look with ALMA. Such telescope arrays have the ability to “zoom out” by spreading the dishes further apart and combining their signals through a process called interferometry. The team observed JD1 when the dishes were spread over an area 2.5 kilometers in diameter, giving the sharpness of vision of a single dish of this size.

When astronomers look at such distant objects, their light is shifted toward the red end of the spectrum as photons are stretched by the expansion of the universe as they fly. The degree of this “redshift” tells astronomers how far away the object is. Along with the new high-resolution image from JD1, the researchers were also able to see tiny redshift differences across the face of the galaxy, the kind of variations one would expect from a rotating object in which part was moving towards the observer and the other was moving away from it. . As the team reports today in Astrophysical Journal LettersThere was a speed difference of 120 kilometers per second between one side of the galaxy and the other. “We were really excited when we saw the velocity map,” says Ellis.

The researchers put the velocity distribution into a galaxy model and it fitted well for a disk galaxy with a mass between 1 billion and 2 billion suns. It’s tiny compared to the Milky Way, which contains 1 trillion solar masses, and so JD1 spins slower than our galaxy, at about a quarter of our galaxy’s speed. Finding a spinning galaxy so early in the history of the universe is “surprising”, says Bosman, but the data is “completely consistent with a disk”.

Astronomers won’t have to wait long to find out if JD1 is one of a kind or if disk galaxies were common in the early universe. Beginning in just a few weeks, the Webb Telescope is expected to find many more galaxies in the universe’s first half billion years. “We’ll go from single-digit numbers to hundreds,” Bosman says. “At least I hope so!”