Brian Welch, a PhD candidate in the Department of Physics and Astronomy, discovered a new star—the farthest star ever observed. The discovery paves the way for a new means to study the distant universe.
The star, Earendel, is one of millions of stars observed in data collected from the Hubble Space Telescope’s Reionization Lensing Cluster Survey program. Welch’s research focuses on distant galaxies using gravitational lensing, where massive foreground objects distort and magnify the light from background objects—a process that was pivotal to the Earendel discovery.
The find is a huge leap further back in time from the previous single-star record holder, detected by Hubble in 2018. That star existed when the universe was about 4 billion years old, or 30% of its current age, at a time that astronomers refer to as “redshift 1.5.” Scientists use the word “redshift” because as the universe expands, light from distant objects is stretched or “shifted” to longer, redder wavelengths as it travels toward us.
12.9 billion years away
The newly detected star is so far away that its light has taken 12.9 billion years to reach Earth, appearing to us as it did when the universe was only 7% of its current age, at redshift 6.2. The smallest objects previously seen at such a great distance are clusters of stars embedded inside early galaxies.
“We almost didn’t believe it at first; it was so much farther than the previous most-distant, highest redshift star,” Welch says. He is lead author of the paper describing the discovery, published in the March 30 journal Nature with co-author Dan Coe at the Space Telescope Science Institute in Baltimore.
Because Welch made the discovery, he had the chance to choose the star’s nickname. He thought Earendel, an Old English word meaning “morning star,” was fitting, as he says the star is seen during the era often referred to as the cosmic dawn.
The star nicknamed Earendel (indicated with arrow) is positioned along a ripple in spacetime that gives it extreme magnification, allowing it to emerge into view from its host galaxy, which appears as a red smear across the sky.
