Most distant star yet discovered by Hubble

Using the Hubble Space Telescope, astronomers have observed the most distant star yet discovered.

Astronomers were trying to watch a gravitationally lensed supernova called Refsdal in the distant universe when they noticed an unexpected point source. The source turned out to be the universe's most distant star. Astronomers dubbed it Lensed Star 1.

The star is located 8.3 billion light-years away in the same galaxy as the Refsdal supernova. The light imaged by Hubble showcases the star as it existed just 4.4 billion years after the Big Bang and the birth of the universe.

Spectral analysis conducted using Hubble's instruments suggests the LS1 is a B-type supergiant star. Such stars burn twice as hot as the sun, between 11,000 and 14,000 degrees Celsius, giving them a bright blue appearance.

Bright or not, astronomers needed help to see LS1.

"Like the Refsdal supernova explosion the light of this distant star got magnified, making it visible for Hubble," Patrick Kelly, an astronomer at the University of Minnesota, said in a news release. "This star is at least 100 times farther away than the next individual star we can study, except for supernova explosions."

On its path from the distant universes to the lens of the Hubble Space Telescope, LS1's light was magnified by both the gravity of the surrounding galaxy cluster itself and the gravity of a high-mass compact object inside the cluster. The phenomenon is known as gravitational lensing.

"The discovery of LS1 allows us to gather new insights into the constituents of the galaxy cluster," said Steven Rodney, an astronomer at the University of South Carolina. "We know that the microlensing was caused by either a star, a neutron star, or a stellar-mass black hole."

By studying LS1, scientists hope to learn more about neutron stars and black holes inside the galaxy cluster MACS J1149-2223. Because these dark energy entities play a predominant role in the birth and evolution of galactic structures, researchers are hopeful that LS1 will offer clues to the nature dark matter and dark energy.

"If dark matter is at least partially made up of comparatively low-mass black holes, as it was recently proposed, we should be able to see this in the light curve of LS1," Kelly said. "Our observations do not favor the possibility that a high fraction of dark matter is made of these primordial black holes with about 30 times the mass of the sun."

In followup observations, astronomers discovered a second micro-lensed image of LS1.

"We were actually surprised to not have seen this second image in earlier observations, as also the galaxy the star is located in can be seen twice," said Jose Diego, a researcher at the Astronomical Institute of the Canary Islands. "We assume that the light from the second image has been deflected by another moving massive object for a long time -- basically hiding the image from us. And only when the massive object moved out of the line of sight the second image of the star became visible."

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