A star in a galaxy that is now more than 27 billion light years away may allow us to understand the very first stars after the big bang
A star more than 27 billion light years from Earth is the most distant individual one we have seen. Because light takes time to travel across the universe, this means that we are seeing the star as it existed just 900 million years after the big bang, providing a potentially valuable window into the early universe.
Brian Welch at Johns Hopkins University in Maryland and his colleagues spotted the star with the Hubble Space Telescope using a process called gravitational lensing. This involves a relatively nearby galaxy or cluster of stars warping and magnifying the light from a more distant object, behaving like a lens through which we can view astronomical objects that would otherwise be too faint.
The galaxy in which this new star resides is nicknamed the Sunrise Arc for the shape into which gravitational lensing stretched its light, and the researchers dubbed the new star Earendel, a word from Old English – the language of the Anglo-Saxons – meaning “morning star” or “rising light”.
We can’t be sure exactly how much the star is being magnified by lensing, making our understanding of its size uncertain, but it is most likely between 50 and 100 times the mass of the sun.
The accelerating expansion of the universe means that while the light from Earendel took about 12.8 billion years to reach us, it is now probably about 27.7 billion light years away. “It’s getting back to a time when [our] universe was a lot different than it is today,” says Welch. Further observations of the star could allow researchers to determine exactly how stars in the early universe were different from those that formed more recently.
Depending on the actual size of Earendel, it could also help solve the mystery of how supermassive black holes formed in the early universe. “If it does turn out to be a really, really massive star, then it could be the sort of thing that could form an intermediate black hole that could be the seed to a supermassive black hole,” says Welch.
The researchers have been awarded observation time on the James Webb Space Telescope to examine Earendel and find out its true size and temperature.
Journal reference: Nature, DOI: 10.1038/s41586-022-04449-y
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