Rare cosmic alignment provides glimpse of most distant star ever observed

Astronomers were using images taken by Hubble Space Telescope to study a supernova when they detected an unusually strong source of light later determined to be a star.


A rare cosmic alignment has offered astronomers a glimpse of a star nine billion light-years from Earth—the most distant ever observed.

The star, MACS J1149 Lensed Star 1, or simply Icarus, is a B-type star, commonly referred to as a blue supergiant. Icarus is hotter, larger, and brighter than our sun, but its distance from Earth makes it impossible for modern telescopes to spot.

However, a phenomenon called gravitational lensing rendered the supergiant visible to astronomers. In simple terms, gravitational lensing is explained by a key tenet of Einstein’s relativity: mass bends light. Massive objects, such as galaxy clusters, have strong gravitational fields—so strong that if a galaxy cluster comes between your line of sight and a distant star, the cluster’s gravitational field will bend and magnify the light from the distant star, similar to how a convex lens on a magnifying glass makes objects appear bigger.


(Photo: NASA)

Gravitational lensing typically magnifies distant objects by a magnitude of 50. However, a well-aligned individual star could theoretically boost that magnification by a factor of many thousands, as researchers wrote in an article published in Nature Astronomy.

“A single star in a foreground lens, if precisely aligned with a background star, can magnify the background star thousands of times,” reads a statement from the University of California, Berkeley. “In this case, a star about the size of our sun briefly passed directly through the line of sight between the distant star Icarus and Hubble, boosting its brightness more than 2,000 times.”


(Photo: NASA, Kelly et al.)

As it happens, the alignment of Icarus means there will likely be more gravitational lensing occurrences during which astronomers can observe the star—even ones that could magnify its brightness by 10,000 times instead of 2,000.  

“There are alignments like this all over the place as background stars or stars in lensing galaxies move around,” said Alex Filippenko, a professor of astronomy at UC Berkeley and one of many co-authors of the report. “[It offers] the possibility of studying very distant stars dating from the early universe, just as we have been using gravitational lensing to study distant galaxies... For this type of research, nature has provided us with a larger telescope than we can possibly build!”

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