Wanting midway throughout the observable universe and anticipating to see particular person stars is taken into account a non-starter in astronomy, a bit like elevating a pair of binoculars on the moon in hopes of constructing out particular person grains of mud inside its craters. Because of a cosmic quirk of nature, nevertheless, a world staff led by astronomers on the College of Arizona’s Steward Observatory did simply that.
Utilizing NASA’s James Webb House Telescope, or JWST, the analysis group noticed a galaxy almost 6.5 billion light-years from Earth, at a time when the universe was half its present age. On this distant galaxy, the staff recognized a lot of particular person stars, made seen due to an impact referred to as gravitational lensing and JWST’s excessive gentle amassing energy.
Printed within the journal Nature Astronomy, the invention marks a record-breaking achievement — the most important variety of particular person stars detected within the distant universe. It additionally offers a strategy to examine one of many universe’s biggest mysteries — darkish matter.
Most galaxies, together with the Milky Manner, comprise tens of billions of stars. In close by galaxies such because the Andromeda galaxy, astronomers can observe stars one after the other. Nevertheless, in galaxies billions of light-years away, stars seem blended collectively as their gentle must journey for billions of light-years earlier than it reaches us, presenting a long-standing problem to scientists finding out how galaxies kind and evolve.
“To us, galaxies which can be very distant often appear like a diffuse, fuzzy blob,” stated lead examine writer Yoshinobu Fudamoto, an assistant professor at Chiba College in Japan and a visiting scholar at Steward Observatory. “However really, these blobs include many, many particular person stars. We simply cannot resolve them with our telescopes.”
Latest advances in astronomy have opened new prospects by leveraging gravitational lensing — a pure magnification impact attributable to the robust gravitational fields of huge objects. As predicted by Albert Einstein, gravitational lenses can amplify the sunshine of distant stars by elements of tons of and even hundreds, making them detectable with delicate devices like JWST.
“These findings have sometimes been restricted to only one or two stars per galaxy,” Fudamoto stated. “To review stellar populations in a statistically significant means, we’d like many extra observations of particular person stars.”
Fengwu Solar, a former U of A graduate scholar who’s now a postdoctoral scholar on the Middle for Astrophysics | Harvard & Smithsonian, came upon a treasure trove of such stars when he was inspecting JWST photos of a galaxy referred to as the Dragon Arc, situated alongside the road of sight from Earth behind an enormous cluster of galaxies known as Abell 370. Because of its gravitational lensing impact, Abell 370 stretches the Dragon Arc’s signature spiral into an elongated form — like a corridor of mirrors of cosmic proportions.
In December 2022 and 2023, JWST obtained two photos of the Dragon Arc. Inside these photos, astronomers counted 44 particular person stars whose brightness modified over time because of variations within the gravitational lensing panorama.
“This groundbreaking discovery demonstrates, for the primary time, that finding out giant numbers of particular person stars in a distant galaxy is feasible,” Solar stated — so long as nature is there to lend a serving to hand.
Nevertheless, even extraordinarily robust gravitational magnification from a galaxy cluster just isn’t adequate to enlarge particular person stars in galaxies even farther away. On this case, the invention was made potential by a serendipitous alignment of “fortunate stars.”
“Contained in the galaxy cluster, there are lots of stars floating round that aren’t certain by any galaxy,” stated co-author Eiichi Egami, a analysis professor at Steward Observatory. “When one in all them occurs to move in entrance of the background star within the distant galaxy alongside the road of sight with Earth, it acts as a microlens, along with the macrolensing impact of the galaxy cluster as a complete.”
The mixed results of macrolensing and microlensing dramatically improve the magnification issue, permitting JWST to choose up particular person stars that in any other case could be too far and faint to be detected in any respect.
As a result of the celebrities contained in the magnifying cluster transfer relative to the goal stars within the distant galaxy and Earth, the alignment of microlenses on this pure “telescope” modifications barely over quick timeframes — from a number of days to every week. When they’re completely aligned, the brightness and magnification of the distant stars improve dramatically, solely to fade once more shortly afterwards.
“By observing the identical galaxy a number of instances, we will spot stars in distant galaxies as a result of they seem to pop out and in of existence,” Fudamoto stated. “It is a results of the various efficient magnifications from the macro- and microlensing impact because the microlensing stars transfer out and in of the road of sight.”
The analysis staff fastidiously analyzed colours of every of the celebrities contained in the Dragon Arc and located that many are purple supergiants, much like Betelgeuse within the constellation of Orion, which is within the closing levels of its life. This contrasts with earlier discoveries, which predominantly recognized blue “supergiants” much like Rigel and Deneb, that are among the many brightest stars within the night time sky. Based on the researchers, this distinction in stellar sorts additionally highlights the distinctive energy of JWST observations at infrared wavelengths that would detect stars at decrease temperatures.
Future JWST observations are anticipated to seize extra magnified stars within the Dragon Arc galaxy. These efforts might result in detailed research of tons of of stars in distant galaxies. Furthermore, observations of particular person stars might present perception into the construction of gravitational lenses and even make clear the elusive nature of darkish matter.
This undertaking was supported by a number of funders together with NASA and NSF.
