Hubble spots most distant single star ever seen, near dawn of universe
Hubble has spotted the most distant single star ever seen, about 12.9 billion light-years from Earth. The light from this star was emitted not long after the Big Bang, and has been magnified by a foreground galaxy and stretched out by the expansion of the universe.
The star has been nicknamed Earendel, which is apparently an Old English word meaning “morning star” or “rising light.” And that’s fitting for a star that we’re viewing as it was a mere 900 million years after the beginning of the universe. That makes it by far the most distant individual star ever observed – the previous record holder, a blue supergiant by the name of Icarus, is almost 4 billion light-years closer.
That said, these numbers can get a bit confusing. Earendel’s 12.9-billion-light-year distance and Icarus’ 9 billion are in terms of what’s known as lookback time, using the present day as a point of reference. As such, it’s taken 12.9 billion years for Earendel’s light to reach us here on Earth, but in that time the expansion of the universe means the star is now a staggering 28 billion light-years away. Or at least it would be – Earendel is likely long dead by now.
The rate of this universal expansion is one tool used to measure such incredible distances. As light travels through the cosmos, the expanding universe stretches out its wavelengths, shifting it towards the red end of the spectrum. Calculating this redshift can reveal how far away the source was – the greater the redshift number, the further the distance. In this case, Earendel’s redshift was 6.2, which is absolutely huge compared to Icarus’ redshift of just 1.5.
Although whole galaxies and clusters have been seen at even greater distances, it’s much harder to make out individual stars so far away. As such, the astronomers had a bit of help from a much closer galaxy, which warped spacetime itself thanks to its immense gravity. This bent the light from Earendel and magnified it, making it visible to Hubble through a phenomenon known as gravitational lensing. A lucky alignment between Earth and Earendel made the star pop out from its host galaxy, with its light magnified thousands of times over.
By accounting for the lensing, the astronomers were able to estimate that Earendel has a mass more than 50 times that of the Sun. There is a chance that it’s not one lone star, but a binary system of two, but that doesn’t diminish the achievement of detecting it from so far away.
The astronomers weren’t able to measure other properties of Earendel, such as its temperature, spectrum and whether it’s one or two stars, but these details could be revealed by the James Webb Space Telescope, which is due to begin observations within a few months.
The research was published in the journal Nature. The work is described in the video below.
Source: ESA Hubble