About 13.8 billion years ago, our universe was born.
But the newborn universe didn’t look like it does today, with elegant, star-filled galaxies strewn in all directions. Instead of stars and galaxies, the early universe was filled with gas and dark matter.
As dark matter coalesced into clumps, it pulled in gas and triggered stars, and thus galaxies, to form. This star and galaxy formation ramped up over a few billion years, reaching its peak 10 billion years ago. But new details from a distant galaxy reveal it was a couple of billion years ahead of the game.
In a new study published today in Science, two researchers describe what could be spiral arms in an unexpected place — a giant, extremely luminous galaxy about 12.3 billion years ago — offering a new puzzle for astronomers to ponder.
“This was before the peak of cosmic star formation and maybe the formation of galaxies,” Takafumi Tsukui of the Graduate University of Advanced Studies, Japan, and the National Astronomical Observatory of Japan, tells Inverse. He and advisor Satoru Iguchi conducted the new study.
WHAT’S NEW — Previously, astronomers had found galaxies with spiral arms that had formed as early as about 10 to 11 billion years ago.
Astronomers find snapshots of galaxies from billions of years in the past by looking deep into space. Since light travels through a vacuum at a set speed, pointing a telescope at a galaxy that’s a billion light-years away means we see what that galaxy looked like a billion years ago.
The spiral arms discovered by Tsukui and Iguchi come from a time when the universe was little more than a billion years old, a time when little matter had coalesced into galaxies, let alone “grand design” spiral galaxies like the Milky Way.
This galaxy, called BRI 1335-0417, is a dramatic one. It’s forming about 5,000 solar masses worth of stars per year, the researchers estimate. For comparison, the Milky Way is forming something like one to two solar masses’ worth of stars per year, though there may have been small bursts in star formation in the past. BRI 1335-0417 also has a quasar in its center — a supermassive black hole that’s actively gobbling up nearby mass.
“It's a different beast from a regular spiral galaxy today,” Alice Shapley of the University of California, Los Angeles, who studies galaxy formation and evolution, tells Inverse. (Shapley was not involved in the study.)
HOW THEY DID IT — Tsukui and Iguchi looked at data of this early-universe galaxy from the archives of the Atacama Large Millimeter/submillimeter Array (ALMA) observatory in Chile. Analyzing images of the galaxy showed what looks like two spiral arms in the galaxy.
Larger galaxies break down into a few different types, including disc, elliptical, and irregular galaxies. Disc galaxies (including spiral galaxies like the Milky Way) are called this because of their relatively flat plane of stars.
What’s especially interesting about the galaxy BRI 1335-0417, Shapley says, is that it’s forming stars so intensely and contains a quasar in its center. A galaxy like this is often the product of two galaxies smashing together and merging, she says. If that’s what happened to BRI 1335-0417, the galaxy somehow managed to form a disc and spiral arms in the time since such a collision.
“It’s telling us something interesting about the conditions in which you can have a disc in a galaxy,” Shapley says.
But what was even more revealing, Tsukui says, was looking at how fast gas in this galaxy was rotating around the galaxy center.
- The velocities of gas at different points in the galaxy match a typical pattern found in galaxies with discs, implying that this galaxy has a fairly well-defined disc.
- The rotation speeds of gas in the arm-like structures match the rotation speeds of the disc, suggesting the structures could be arms within the disc rather than streams of gas outside it.
“This velocity-resolved image was also important for us to identify the spiral arms in this galaxy,” Tsukui says.
A European Southern Observatory video on how galaxies come together.
WHY IT MATTERS — Understanding the features of galaxies is a key part of understanding how galaxies form and evolve over time. For example, the presence of spiral arms in a galaxy can affect how gas moves within a galaxy and encourage dense structures to form in galaxy centers, like the bar in the center of the Milky Way.
David Law, an astronomer at the Space Telescope Science Institute who led a 2012 study describing a spiral galaxy from about 10 billion years ago, says this finding is another important clue toward understanding the spiral galaxies that formed early in the universe’s history.
“It really adds one more piece into that puzzle — that these kinds of galaxies really are present out in the very distant universe,” he tells Inverse.
WHAT’S NEXT — To understand how the disk and spiral arms formed in this galaxy, researchers who run simulations of galaxies forming over time will need to see what conditions lead to a galaxy with BRI 1335-0417’s eclectic mix of properties.
More detailed observations of the galaxy, as well as searches for more galaxies in the early universe with spiral structures, will also be important for learning more about these objects and how they come to be.
“The more of these objects we find, the better,” says Law. “Then that gives us a sample that we can start to study.”
Abstract: Spiral galaxies have distinct internal structures including a stellar bulge, disk and spiral arms. It is unknown when in cosmic history these structures formed. We analyze observations of BRI 1335–0417, an intensely star-forming galaxy in the distant Universe, at redshift 4.41. The [C II] gas kinematics show a steep velocity rise near the galaxy center and have a two-armed spiral morphology, which extends from about 2 to 5 kiloparsecs in radius. We interpret these features as due to a central compact structure, such as a bulge; a rotating gas disk; and either spiral arms or tidal tails. These features had formed within 1.4 billion years after the Big Bang, long before the peak of cosmic star formation.