A Treasure Trove Of Unseen Stars Seen Beyond The ‘Dragon Arc’

Eddie Gonzales Jr. – MessageToEagle.com – An international team of astronomers photographed over 40 stars in a distant galaxy whose light dates to when the universe was half its current age.

Abell 370, a galaxy cluster located nearly 4 billion light-years away from Earth features several arcs of light, including the “Dragon Arc” (lower left of center). These arcs are caused by gravitational lensing: Light from distant galaxies far behind the massive galaxy cluster coming toward Earth is bent around Abell 370 by its massive gravity, resulting in contorted images. Credit: NASA

Looking halfway across the observable universe and expecting to see individual stars is considered a non-starter in astronomy, a bit like raising a pair of binoculars at the moon in hopes of making out individual grains of dust inside its craters. Thanks to a cosmic quirk of nature, however, an international team of astronomers did just that.

Using NASA’s James Webb Space Telescope (JWST), postdoctoral researcher Fengwu Sun at the Center for Astrophysics | Harvard & Smithsonian (CfA) and his team observed a galaxy nearly 6.5 billion light-years from Earth, at a time when the universe was half its current age. In this distant galaxy, the team identified 44 individual stars, made visible thanks to an effect known as gravitational lensing and JWST’s high light collecting power.

Published in the journal Nature Astronomy, the discovery marks this record-breaking achievement – the largest number of individual stars detected in the distant universe. It also provides a way to investigate one of the universe’s greatest mysteries – dark matter.

“This groundbreaking discovery demonstrates, for the first time, that studying large numbers of individual stars in a distant galaxy is possible,” Sun, a co-author on the study, said. “While previous studies with the Hubble Space Telescope found around seven stars, we now have the capability to resolve stars that were previously outside of our capability. Importantly, observing more individual stars will also help us better understand dark matter in the lensing plane of these galaxies and stars, which we couldn’t do with only the handful of individual stars observed previously.”

CfA’s Sun found this treasure trove of stars while inspecting JWST images of a galaxy known as the Dragon Arc, located along the line of sight from Earth behind a massive cluster of galaxies called Abell 370. Due to its gravitational lensing effect, Abell 370 stretches the Dragon Arc’s signature spiral into an elongated shape – like a hall of mirrors of cosmic proportions.

The research team carefully analyzed colors of each of the stars inside the Dragon Arc and found that many are red supergiants, similar to Betelgeuse in the constellation of Orion, which is in the final stages of its life. This contrasts with earlier discoveries, which predominantly identified blue “supergiants” similar to Rigel and Deneb, which are among the brightest stars in the night sky. According to the researchers, this difference in stellar types also highlights the unique power of JWST observations at infrared wavelengths that could reveal stars at lower temperatures.

“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,” said Sun. “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.”

Sun, in particular, is excited for the next opportunity to study these red supergiants. “We know more about red supergiants in our local galactic neighborhood because they are closer and we can take better images and spectra, and sometimes even resolve the stars. We can use the knowledge we’ve gained from studying red supergiants in the local universe to interpret what happens next for them at such an early epoch of galaxy formation in future studies.”

Most galaxies, including the Milky Way, contain tens of billions of stars. In nearby galaxies such as the Andromeda galaxy, astronomers can observe stars one by one. However, in galaxies billions of light-years away, stars appear blended together as their light needs to travel for billions of light-years before it reaches us, presenting a long-standing challenge to scientists studying how galaxies form and evolve.

“To us, galaxies that are very far away usually look like a diffuse, fuzzy blob,” said lead study author Yoshinobu Fudamoto, an assistant professor at Chiba University in Japan. “But actually, those blobs consist of many, many individual stars. We just can’t resolve them with our telescopes.”

Recent advances in astronomy have opened new possibilities by leveraging gravitational lensing – a natural magnification effect caused by the strong gravitational fields of massive objects. As predicted by Albert Einstein, gravitational lenses can amplify the light of distant stars by factors of hundreds or even thousands, making them detectable with sensitive instruments like JWST.

“These findings have typically been limited to just one or two stars per galaxy,” Fudamoto said. “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 magnified stars in the Dragon Arc galaxy. These efforts could lead to detailed studies of hundreds of stars in distant galaxies. Moreover, observations of individual stars could provide insight into the structure of gravitational lenses and even shed light on the elusive nature of dark matter.

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Written by Eddie Gonzales  Jr. – MessageToEagle.com Staff Writer