Starlight, shining star, how far the night looks.
Astronomers announced on Wednesday the discovery of the farthest and oldest star ever seen, a point of light that brightened 12.9 billion years ago, or just 900 million years after the Big Bang that gave birth to the universe.
This means that the light from the star traveled 12.9 billion light years to reach Earth.
The result was part of an effort to use Hubble Space Telescope To search for some of the oldest and farthest galaxies in the universe. By lucky coincidence, astronomers were able to discern a single star system within one of those galaxies.
said Brian Welch, a graduate student at Johns Hopkins University in Baltimore, and author of A research paper published Wednesday in the journal Nature describes the discovery.
Usually, distant objects are too dark to be seen. But Einstein’s general theory of relativity, which describes how gravity bends space, offers a useful solution. A nearby massive galaxy cluster can act as a lens to amplify the light from stars and distant galaxies behind them.
A survey using the Hubble Space Telescope examined 41 galactic clusters. “When you look at a group of really massive galaxy clusters, there’s a good chance you’ll find some very massive objects behind them,” said Mr. Welch.
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Mr. Welch said that a galaxy cluster typically magnifies the brightness of the object behind it by up to 10 times.
However, the light is not magnified equally. Ripples in spacetime can create luminous spots, like ripples on the surface of a swimming pool that create patterns of luminous spots at the bottom of the pool. Examining a distant, magnified galaxy, astronomers found that a point of light aligned with one of the ripples, and its luminosity was amplified by a thousandfold or more.
“The galaxy is kind of stretched out in this long crescent-shaped arc,” said Mr. Welch. “And then the star is just one component of that.”
As the universe is expanding, distant objects are moving faster. This shifts the frequency of the light towards longer wavelengths. The star spotted by Mr. Welch and his colleagues has what astronomers call a redshift of 6.2, much higher than the previous record for the most distant individual star. This star, which was reported in 2018, had a red shift of 1.5, which corresponds to when the universe was about four billion years old.
The researchers called the new star Earendel – in Old English the “morning star”. If it’s a single star, astronomers estimate it’s a massive star — about 50 times the mass of our sun. It can also be a two or more star system.
The Earendel alignment and the galaxy group will last for years, so Earendel will be one of the targets during the first year of observations by the newly launched group. James Webb Space Telescopewhich has a larger mirror than Hubble and collects light at longer infrared wavelengths.
Webb’s observations will be able to measure brightness across a spectrum of wavelengths. This will help astronomers determine the temperature of the star. “We really need that spectrum to say with some kind of absolute certainty that this is a star compared to another kind of thing,” Mr. Welch said.
Mr. Welch said that later, more detailed observations by Webb could determine Earendel’s composition. The Big Bang produced only the lightest elements, such as hydrogen and helium. The first stars are thus expected to contain lower concentrations of heavier elements, which arise from fusion reactions within stars and in the explosions of dying stars. The current hypothesis is that with fewer heavier elements, the first stars should be large and bright.
“It looks very hot and very massive,” Stephen Finkelstein, an astronomer at the University of Texas at Austin who was not involved in the research, said of Earndale.
However, this star alone would not be enough to prove the state of the largest stars in the early universe. “But he definitely supports that,” said Dr. Finkelstein. “If you start to form a large number, and many of them appear to be very massive, the evidence will become stronger and stronger that more massive stars are the norm in the distant universe.”
The Webb telescope should also be able to find distant magnifying stars like Earendel, although the number of stars lined up by chance with a gravitational lens remains invisible. It may even be able to identify some stars at a red shift between 10 and 20, which corresponds to a period between 100 million and 500 million years after the Big Bang.
“That’s right in that window when we think the first stars are forming,” Dr. Finkelstein said.
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