The Dragon Arc is a distant star system that we see highly warped due to gravitational lensing from a cluster of galaxies that is closer to us. However, this effect has recently allowed scientists to see individual stars there.
Observing stars in a distant galaxy
In astronomy, it is believed that looking halfway across the observable Universe and hoping to see individual stars is like raising binoculars to the Moon in hopes of seeing individual grains of dust in its craters. However, thanks to a cosmic quirk of nature, an international team of astronomers has done just that.
Using NASA’s James Webb Space Telescope, doctoral student Fengwu Sun of Harvard and Smithsonian Institution’s Center for Astrophysics (CfA) and his team observed a galaxy nearly 6.5 billion light-years away from Earth at a time when the Universe was half its current age. The team identified 44 individual stars in this distant galaxy, which became visible due to an effect known as gravitational lensing and JWST’s high ability to collect light.
The discovery, published in the journal Nature Astronomy, records the largest number of individual stars found in the distant Universe. It also opens the way to investigate one of the greatest mysteries of astronomy – dark matter.
“This groundbreaking discovery demonstrates for the first time that studying a large number of individual stars in a distant galaxy is possible,” said Sun, a co-author of the study.
Gravitational lensing of the Dragon Arc
CfA’s Sun found this treasure trove of stars while studying JWST images of a galaxy known as the Dragon Arc, located along the line of sight from Earth behind a massive galaxy cluster called Abell 370. Through a gravitational lensing effect, Abell 370 stretches the characteristic spiral of the Dragon Arc into an elongated shape similar to a space-scale hall of mirrors.
The research team carefully analyzed the colors of each of the stars within the Dragon Arc and found that many of them were red supergiants, similar to Betelgeuse in the constellation Orion, currently in the final stages of its life. This contrasts with previous discoveries that predominantly identified blue “supergiants” like Rigel and Deneb, which are among the brightest stars in the night sky.
This difference in star types also highlights the unique power of JWST’s infrared observations to detect stars with lower temperatures, the researchers said.
“When we discovered these individual stars, we were actually looking for a background galaxy that is lensing-magnified by the galaxies in this massive cluster,” Sun said. “But when we processed the data, we realized that there were what appeared to be a lot of individual star points. It was an exciting find because it was the first time we were able to see so many individual stars so far away.”
Most galaxies, including the Milky Way, contain tens of billions of stars. In neighboring galaxies, such as the Andromeda Galaxy, astronomers can observe stars one by one. However, in galaxies billions of light years away from us, stars appear to be mixed, as their light travels billions of light years before reaching us. This is a longtime challenge for scientists studying how galaxies form and evolve.
Prospects of gravitational lensing of galaxies
Recent progress in astronomy has opened up new possibilities through the use of gravitational lensing, a natural magnification effect caused by the strong gravitational fields of massive objects. As Albert Einstein predicted, gravitational lenses can amplify the light of distant stars by hundreds or even thousands of times, making them available for detection by sensitive instruments such as JWST.
“These findings were typically limited to only one or two stars per galaxy,” the scientists note. “To study stellar populations in a statistically meaningful way, we need many more observations of individual stars.”
Future JWST observations are expected to capture more enlarged stars in the Dragon Arc galaxy. This effort could lead to detailed studies of hundreds of stars in distant galaxies. Moreover, observations of individual stars can provide insight into the structure of gravitational lenses and even shed light on the elusive nature of dark matter.
According to phys.org
