Astronomers have newly discovered 44 stars that were born when the universe was about half its current age (approximately 13.7 billion years). They detected faint light using a powerful space telescope and took advantage of the phenomenon of light bending due to gravity to capture starlight coming from deep space. This is the first time such a large number of stars have been discovered simultaneously from distant space.
On the 6th (local time), a joint research team including scientists from 13 countries, such as Chiba University in Japan, the Harvard-Smithsonian Center for Astrophysics in the United States, and the Chinese Academy of Sciences, announced in the international journal Nature Astronomy that they discovered 44 stars in a distant galaxy located 6.5 billion light-years away from our Milky Way. The researchers noted, "The stars reported this time are the most ever discovered in deep space," adding, "This opens the way to find more individual stars in deep space, which will provide clues for future research on dark matter related to galaxy formation and cosmic evolution."
Most galaxies, including the Milky Way, contain billions of stars. In galaxies close to Earth, such as the Milky Way and Andromeda, individual stars can be observed, but galaxies billions of light-years away are too far for their many starlights to be seen clearly, appearing as blurred masses. Because the stars in distant galaxies are difficult to observe individually, how galaxies evolve has remained a challenge for scientists.
Recently, gravitational lensing, which frequently appears in astronomy, has opened new possibilities. Predicted by the genius physicist Albert Einstein, gravitational lensing is the phenomenon where starlight bends and shines brighter as it passes by massive celestial objects like stars or planets. It acts like a huge magnifying glass that can magnify faint starlight from deep space thousands of times.
The research team examined images captured by the James Webb Space Telescope (JWST) of the National Aeronautics and Space Administration (NASA) in 2022 and 2023, from a region of space that corresponds to being 6.5 billion light-years away, when the universe was half its current age, and discovered a "treasure trove of stars." They found that the galaxy behind the massive galaxy cluster Abell 370, located 4 billion light-years from Earth, appeared elongated due to the effects of gravitational lensing. The research team discovered 44 stars in this distorted image, referred to as the "Dragon arc."
According to the paper, an analysis of the stars' colors revealed that most of the newly discovered stars are confirmed to be red giants and supergiants similar to Betelgeuse in the constellation Orion. Red giants and supergiants, which eject gas and dust before exploding into supernovae, correspond to relatively late stages in a star's life. The researchers explained, "Many facts have already been revealed through red giants discovered in galaxies close to Earth, and we can use this knowledge to interpret what happens during the early stages of galaxy formation."
The James Webb Space Telescope is a space telescope equipped with a 6.5-meter diameter mirror, developed to measure faint infrared light emitted by stars in the distant universe. Since its launch on Christmas in 2021, it has been observing the deep universe from a location 1.5 million kilometers from Earth. Scientists expect that by utilizing the James Webb Space Telescope and the effects of gravitational lensing, they can identify even more faint stars in distant galaxies.
Scientists liken the task of finding stars in the distant universe to searching for dust particles in a lunar crater with binoculars. Even with the previous utilization of NASA's Hubble Space Telescope, only seven stars were discovered.
Fengwu Sun, a postdoctoral researcher at the Harvard-Smithsonian Center for Astrophysics and a co-author of the paper, stated, "This research is the first to show that it is possible to study a large number of individual stars in distant galaxies," adding, "Now we have the ability to dissect stars that were previously beyond our capability."
The research team is looking forward to observing even larger stars in the Dragon arc in the future. Astronomers believe that identifying more individual stars will accelerate research into one of the universe's greatest mysteries: dark matter.
Professor Yoshinobu Hudamoto, the lead author of the study from Chiba University in Japan, noted, "To study the population of stars in a statistically meaningful way, more information about individual stars is necessary," adding, "Observations of individual stars can provide insights into the structure of gravitational lensing and help illuminate the nature of dark matter."
Reference materials
Nature Astronomy (2024), DOI: https://doi.org/10.1038/s41550-024-02432-3