Starlight, star bright, how far do you see tonight.
Astronomers announced on Wednesday the discovery of the farthest and oldest star ever seen, a bright spot that shone 12.9 billion years ago, or just 900 million years after the Big Bang that gave birth to the Universe.
That means the light from the star has traveled 12.9 billion light-years to reach Earth.
The find was part of efforts to use the Hubble Space Telescope to search for some of the universe’s farthest and earliest galaxies. By a happy coincidence, the astronomers were able to distinguish a single star system within one of those galaxies.
“It was an unexpected surprise to find something so small,” said Brian Welch, a graduate student at Johns Hopkins University in Baltimore, author of a paper published Wednesday in the journal Nature describing the discovery.
Usually objects that are far away are much too faint to be seen. But Einstein’s general theory of relativity, which describes how gravity bends space, offers a handy solution. A massive cluster of galaxies quite close to us can act as a lens to amplify light from much more distant stars and galaxies beyond.
A study using the Hubble Space Telescope has examined 41 galaxy clusters. “If you look at a bunch of very massive galaxy clusters, there’s a good chance you can find some very highly magnified objects behind them,” said Mr. welch.
Learn more about the James Webb Space Telescope
After traveling nearly a million miles, the James Webb Space Telescope arrived at its destination. It will observe the cosmos for years.
The cluster of galaxies typically increases the brightness of the object behind it by a factor of 10, Mr Welch said.
However, the light is not magnified evenly. Ripples in space-time can create bright spots, just as ripples on the surface of a swimming pool create patterns of bright spots at the bottom of the pool. While examining one of the magnified distant galaxies, the astronomers found that a point of light aligned with one of the ripples, and its brilliance was magnified a thousandfold or more.
“The Milky Way is sort of stretched out in this long crescent-shaped arc,” said Mr. welch. “And then the star is just part of that.”
As the universe expands, more distant objects move faster. That shifts the frequency of light to longer wavelengths. The star that Mr. Welch and his colleagues have found what astronomers call a redshift of 6.2, much higher than the previous record holder for the most distant single star. That star, reported in 2018, had a redshift of 1.5, which is equivalent to when the universe was about four billion years old.
The researchers nicknamed the new star Earendel — Old English for “morning star.” If it’s a single star, the astronomers estimate it to be a large one — about 50 times the mass of our sun. It can also be a system of two or more stars.
The alignment of Earendel and the galaxy cluster will continue for years to come, so Earendel will be one of the targets during the first year of observations by the newly launched James Webb Space Telescope, which has a larger mirror than Hubble and collects light at the longer infrared wavelengths. .
The Webb observations will be able to measure brightness over a spectrum of wavelengths. That will help astronomers determine the star’s temperature. “We really need that spectrum to be able to say with some kind of absolute certainty that this is a star as opposed to any other kind of object,” Mr Welch said.
Mr. Welch said later, more detailed observations by Webb could identify Earendel’s composition. The Big Bang produced only the lightest elements, such as hydrogen and helium. Thus, the earliest stars are expected to contain lower concentrations of heavier elements, which are created by fusion reactions within stars and in the explosions of dying stars. The current hypothesis is that with less of the heavier elements, more of the early stars should have been large and bright.
“It looks like it’s pretty hot and pretty massive,” Steven Finkelstein, an astronomer at the University of Texas at Austin who was not involved in the study, said of Earendel.
But this one star alone would not be enough to prove the case of larger stars in the early Universe. “But it certainly supports that,” said Dr. Finkelstein. “If you start to build up a large number, and many of them appear to be quite massive, then the evidence would grow stronger that more massive stars are the norm in the distant universe.”
The Webb telescope should also be able to find other distant, magnified stars like Earendel, although it’s not yet clear how many happen to be lined up with a gravitational lens. It would even be able to see some stars with a redshift 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,” said Dr. Finkelstein.
