Hubble Space Telescope spots oldest, farthest star known
Star light, star bright, how far you look tonight.
Astronomers announced Wednesday the discovery of the farthest and oldest star ever seen, a dot of light that shined 12.9 billion years ago, or 900 million years after the Big Bang that gave birth to the universe.
That means the light from the star traveled 12.9 billion light-years to reach Earth. The finding was part of efforts using the Hubble Space Telescope to search for some of the universe's farthest and earliest galaxies. By a lucky coincidence, the astronomers were able to discern 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 who is an author of a paper published Wednesday in the journal Nature that describes the discovery.
Usually, objects that far away are much too dim to be seen. But Einstein's theory of general relativity, which describes how gravity bends space, offers a handy workaround. A massive galaxy cluster fairly close to us can act as a lens to amplify light from much more distant stars and galaxies behind it.
A survey using the Hubble Space Telescope has been examining 41 galaxy clusters.
“When you look at a bunch of really massive galaxy clusters, there's a good chance that you can find some really highly magnified objects behind them,” Welch said.
The galaxy cluster typically magnifies the brightness of the object behind it by up to a factor of 10, Welch said.
The light is not magnified evenly, however. Ripples in space-time can create bright spots, much like ripples on the surface of a swimming pool create patterns of bright spots at the bottom of the pool. In examining one of the magnified distant galaxies, the astronomers found that a point of light lined up with one of the ripples and its shine was magnified by a thousandfold or more.
Because the universe is expanding, more distant objects are moving away faster. That shifts the frequency of light toward longer wavelengths. The star spotted by Welch and his colleagues possesses what astronomers call a red shift of 6.2, far higher than the previous record-holder for most distant single star. That star, reported in 2018, had a red shift of 1.5, corresponding to when the universe was about 4 billion years old.
The researchersnicknamed the new star Earendel — Old English for “morning star.” If it is a single star, the astronomers estimate that it is a big one — some 50 times the mass of our sun.