The galaxy cluster Abell 370, as seen by the Hubble Space Telescope (HST). (Image: NASA, ESA, and J. Lotz and the HFF Team / SWNS)
It is believed to be the first time so many stars have been identified in one cluster.
Physicists studying a distant galaxy using a telescopic technique called “gravitational lensing” found 44 previously unknown astral bodies.
The research shows how the stars were behaving eight billion years ago, giving glimpses into the population of stars at “cosmic noon” – the Middle Ages of the Universe.
The research was led by the Centre for Frontier Science at Chiba University, Japan, and involved more than 45 international partners, including Durham University’s Centre for Extragalactic Astronomy and the Jodrell Bank Centre for Astrophysics, Manchester University.
The international team used observations from the James Webb Space Telescope (JWST) and gravitational lensing to study a galaxy known as the Dragon Arc, located behind a massive cluster of galaxies called Abell 370.
The researchers explained that, in gravitational lensing, a foreground galaxy cluster bends the light from a more distant object and magnifies it, allowing scientists to study the distant object.
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.
Using the technique, and high-resolution images from the JWST, taken across a full year, the team was able to identify 44 previously unknown stars in the Dragon Arc.
They observed that the brightness of the individual stars changed over the course of the study due to variations in the gravitational lensing landscape.
The findings, published in the journal Nature Astronomy, show what the galaxy is made of in a way not previously achieved.
They also tell scientists more about “dark matter” – a mysterious substance that binds together galaxies, creating the environment for stars, planets and life to exist.
Durham University’s Dr David Lagattuta said: “When the team made this discovery, we knew that, given the size of the dots seen in the JWST images, the most logical explanation was that these were individual stars, seen for the first time, which is a hugely exciting discovery.
“We know these are stars that have not been seen before by comparing them to previous image of the Dragon Arc which do not show these bright dots.
“Other possibilities such as these findings being a cluster of stars or exploding supernovae simply did not fit the data.
“It would be a huge coincidence to find so many supernovae all in the same galaxy and all exploding at the same time.
“Supernovae also tend to suppress star formation, but spectroscopy tells us the Dragon Arc is still actively forming stars.”
He added: “We also reasoned that these objects had to be individual stars, rather than star clusters, since the size of what we’re seeing – after accounting for the extreme lensing magnification – is much too small to fit in the tens of hundreds of bright stars in a star cluster at once.
Dr Lagattuta says many of the stars identified through the study are “red supergiants” – a type of star that has been difficult to identify outside of the Milky Way because they are covered in a layer of cosmic “dust” which makes them almost invisible to telescopes.
The JWST enabled the research team to peer through the dust more easily, revealing the hidden stars inside.
Professor Mathilde Jauzac, also of Durham University, said: “This is the first time, that we are aware of, that so many stars have been discovered in one cluster.
“This finding enables us to see what the galaxy is made of in ways not possible before.
“This provides a fascinating and unique view into the behaviour of stars at the critical ‘cosmic noon’, the Middle Ages of the Universe.”
She added: “We know that in the early stages of the Universe there is lots of gas and early ‘protostars’ and then by nine to 10 billion years ago star formation peaks and everything is turning on.
“We also know that stars in the early Universe were born and behaved in a different way to today.
“It is roughly in the cosmic noon, that these behaviours start to change.
“So, this new study provides an insight into stars at this point in time.”
The research team hopes to continue its study by taking further images of the Dragon Arc to help differentiate between different stellar populations being magnified by the cluster.