A research team led by Daniel Ivanov, a physics and astronomy graduate student in the Kenneth P. Dietrich School of Arts and Sciences at Pitt, has identified a strong candidate for one of the earliest known spiral galaxies with a stellar bar. These bright, elongated structures can strongly influence how galaxies grow and change over time. The Milky Way itself contains a stellar bar at its center.
The newly studied galaxy, named COSMOS-74706, appears to have existed about 11.5 billion years ago. By analyzing its light, researchers were able to determine its place in cosmic history and narrow down when barred structures may have first formed in the universe.
“This galaxy was developing bars 2 billion years after the birth of the universe,” Ivanov said. “Two billion years after the Big Bang.”
The results were presented at the 247th meeting of the American Astronomical Society.
What Is a Stellar Bar?
As the name suggests, a stellar bar is a straight, elongated feature that stretches across the central region of a spiral galaxy. “A stellar bar is a linear feature at the center of the galaxy,” Ivanov said. Rather than being a single object, the bar is made up of tightly packed stars and gas. When viewed from above or below the galaxy’s disk, this alignment creates the appearance of a bright line cutting through the middle.
These bars are more than just visually striking. They can shape a galaxy’s long term development by channeling gas from the outer regions inward. This inward flow can fuel the supermassive black hole at the galaxy’s core and reduce star formation across the surrounding disk.
Why This Discovery Stands Out
Other teams have previously reported possible barred spiral galaxies from even earlier periods. However, those findings relied on less precise measurements of redshift. In contrast, COSMOS-74706 was confirmed using spectroscopy, which provides more reliable distance data. In some earlier cases, the galaxy’s light was also distorted by passing near a massive object, an effect known as gravitational lensing.
In essence, Ivanov said, “It’s the highest redshift, spectroscopically confirmed, unlensed barred spiral galaxy.”
Although the galaxy dates back to a very early era, Ivanov was not entirely surprised. Computer simulations have suggested that stellar bars could begin forming at redshift 5, or roughly 12.5 billion years ago. Still, he noted that such objects are not expected to be common at that stage of cosmic history.
“In principle, I think that this is not an epoch in which you expect to find many of these objects. It helps to constrain the timescales of bar formation. And it’s just really interesting.”
Powered by the James Webb Space Telescope
The research relied in part on observations from the NASA/ESA/CSA James Webb Space Telescope. Data were obtained through the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127, which is supported by NASA. The project also received support from the Brinson Foundation.
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