New research supported by Yingjie Cheng, a University of Washington postdoctoral researcher in astronomy, uncovered a contender for one of the earliest observed spiral galaxies containing a stellar bar - a notable visual feature that can play an important role in the evolution of a galaxy.
This finding helps constrain the timeframe in which bars could have first emerged in the universe. Analysis of light from the galaxy, called COSMOS-74706, places it on the cosmic timeline at about 11.5 billion years ago, or just two billion years after the birth of the universe.
The research team presented its findings at the 247th meeting of the American Astronomical Society on Jan. 8. A published study is forthcoming.
"Stellar bars are typically seen in mature, well-evolved galaxies, so finding one just two billion years after the Big Bang is remarkable," said Cheng, who completed this work as a doctoral student at the University of Massachusetts Amherst. "This discovery shows that massive disk galaxies were already dynamically organized at very early times, offering new insight into how galaxies assembled and evolved in the young universe."
While at Amherst, Cheng led the analysis of the galaxy's physical properties and evolutionary history.
The "bar" in a barred galaxy isn't an object itself, but a dense collection of stars and gas that is aligned in such a way that, in images taken perpendicular to a galactic plane, there appears to be a bright line bisecting the galaxy.
Despite appearing like a permanent feature, stellar bars are fluctuating density waves that form as the result of some kind of instability in the galaxy. They can be the result of "tidal perturbations," gravitational forces caused by something outside of the galaxy.
"If you have a close interaction with a nearby galaxy, that can actually trigger the global instability that leads to the formation of a stellar bar," said lead author Daniel Ivanov, a graduate student in astronomy at the University of Pittsburgh.
Even without outside influences, a stable disc can slowly become unstable on its own. Over time, this process can naturally lead to the formation of stellar bars. They likely appear and disappear multiple times over the life of a galaxy.
Stellar bars can play a role shaping their galaxy's evolution by funneling gas inward from the outer reaches of a galaxy, feeding the supermassive black hole in the center.
The team members made their discovery as they were developing a catalog of barred and non-barred galaxies in a particular region of space. During this work, a couple of galaxies were flagged for their unusually high redshifts. This is an indication of how long the light had been traveling and, therefore, how long ago it was emitted.
Other researchers have reported earlier barred spiral galaxies, but the analysis of those are less conclusive because the methods used to measure the lights' redshifts are not as definitive as spectroscopy, the method used to validate COSMOS-74706.
Ivanov wasn't necessarily surprised to find a barred spiral galaxy so early in the universe's evolution - in fact, some simulations suggest bars forming as early as 12.5 billion years ago.
But, he said: "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."
This research was funded by NASA and The Brinson Foundation.
