NASA’s Hubble Space Telescope captures 11-billion-year old supernova in early universe

Astronomers have meticulously studied a supernova that occurred about 11.5 billion years ago, when a faraway star about 530 times bigger than our sun perished in a violent explosion that flung its outer layers of gas into the surrounding universe.

Scientists reported that NASA's Hubble Space Telescope had captured three photographs spanning eight days, beginning only hours after the blast. This is an impressive feat, given how long ago and far away the explosion happened.

These photographs provided the first detailed view at a supernova so early in the history of the universe, when it was less than a fifth of its present age, and the first sight of a supernova cooling swiftly following the initial explosion in a single series of images.

“The supernova is expanding and cooling, so its colour evolves from a hot blue to a cool red," said Patrick Kelly, an astronomy professor at the University of Minnesota.
Located in a dwarf galaxy, the doomed star exploded at the end of its relatively short life span as a red supergiant.

"Red supergiants are luminous, massive and large stars, but they are much cooler than most of the other massive stars - that is why they are red," Chen said. "After a red supergiant exhausts the fusion energy in its core, a core collapse will occur and the supernova explosion will then blast away the star's outer layers - its hydrogen envelope."

Six hours after the original burst, the first photograph reveals that the explosion was initially tiny but very hot, reaching temperatures of almost 99,725 degrees Celsius.

The second photo was taken around two days later, and the third was taken some six days after that. These two pictures show the expansion of the gaseous stuff emitted from the star. The intensity of the explosion is reduced by a factor of five in the second picture. The third picture shows temperatures that are one-tenth as high as the first.

According to Chen, the relic of the exploding star is likely a neutron star because to its extreme density.

Hubble was able to capture three photographs of the explosion's aftermath at various times due to a phenomenon known as strong gravitational lensing. A galaxy cluster in front of the exploding star, as seen from Earth, generated so strong gravitational forces that they acted as a lens, bending and amplifying the light from the supernova.

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"The gravity in the galaxy cluster not only bends the light from behind it, but also delays the light travel time because the stronger the gravity, the slower a clock moves," Chen said. "In other words, emission of light from a single source behind the lens can go through multiple paths toward us, and we then see multiple images of the source."

Gravitational lensing enabled Kelly to see the rapidly cooling supernova in a single set of images, calling it "just absolutely amazing."

"It's kind of like seeing a film reel in colour of the supernova evolving, and it's a much more detailed picture of any known supernova that existed when the universe was a small fraction of its current age," Kelly explained.

"The only other examples where we have caught a supernova very early are very nearby explosions," Kelly added. "When astronomers see more distant objects, they are looking back in time.”

(With inputs from Reuters)