Gravitational Lensing Helps Scientists Discover Most Distant Star Yet!

Astronomers got a bonus surprise recently when they used the Hubble Space Telescope to study a far off supernova. They discovered the most distant star ever observed by humans!

An international team of astronomers led by Patrick Kelley of the University of Minnesota, USA, Jose Diego from the  Instituto de Física de Cantabria, Spain, and Steven Rodney of the University of Southern California, USA were studying the gravitationally lensed supernova "Refsdal" (heuc1525) when a point of light brightened in the same galaxy that hosted the supernova. This point of light turns out to be a hot (about twice the temperature of the Sun), blue supergiant star (LS1) that is a pretty significant find.

“Like the Refsdal supernova explosion, the light of this distant star got magnified, making it visible for Hubble,” says Patrick Kelly. “This star is at least 100 times farther away than the next individual star we can study, except for supernova explosions.”

How old is this star? Well, the light scientists observed from it was emitted "only" 4.4 billion years  after the Big Bang, when the universe was only 30 percent of its current age. Astronomers were only able to see this light because of a phenomenon called gravitational or cosmic lensing. This allowed the light from the star to be magnified 2000 times.

“The star became bright enough to be visible for Hubble thanks to a process called gravitational lensing,” explains Jose Diego. Gravitational lensing occurs when objects of huge mass create a magnifying effect on objects behind them. You can read another article where I explain it in more detail here. 

But that's not all. Scientists were able to ascertain that the gravitational lensing was due to more than just the mass of the galaxy cluster, but by a giant source of mass that wasn't visible to them. They believe this mass was from a compact object about three times the mass of the Sun. This caused an effect called gravitational microlensing.

“The discovery of LS1 allows us to gather new insights into the constituents of the galaxy cluster. We know that the microlensing was caused by either a star, a neutron star, or a stellar-mass black hole,” explains Steven Rodney.

This means that because of the discover of this super old star, astronomers will be able to learn more about black holes and neutron stars and their effects on other objects around them. This is important because black holes and neutron stars aren't visible--they must be studied indirectly, via their effects rather than by direct observation. Studying this will help astronomers understand what galaxy clusters are made of, and also will help them to understand dark matter, one of the great mysteries of our universe. 

“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. Our observations do not favour 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,” says Kelly.

Looking back at data from previous studies of the Refsdal supernova, scientists realized that in fact, they did detect this star earlier, in 2016. But the interesting thing is that in a subsequent image, the star isn't there. They hypothesize that this is because a massive dark object moved in front of it, blocked the Hubble's view. The star came back into sight after the object moved past. This gives even more clues to what galaxy clusters are made of.

Astronomers are excited to study these new developments with the new tech of the James Webb Space Telescope, set for launch in May 2020.  Soon, we'll be able to study the oldest stars and reach to the beginnings of the universe in more detail than ever before. 

Melanie R. Meadors is the author of fantasy stories where heroes don't always carry swords and knights in shining armor often lose to nerds who study their weaknesses. She’s been known to befriend wandering garden gnomes, do battle with metal-eating squirrels, and has been called a superhero on more than one occasion. Her fiction has appeared in Circle Magazine, Prick of the Spindle, and in the anthology Champions of Aetaltis. She studied astronomy and physics at Northern Arizona University and has published some non-fiction in the field of astronomy and library sciences. She's the co-editor of the anthology MECH: Age of Steel and editor of Hath No Fury, and she is a blogger and general b*tch monkey at The Once and Future Podcast.