Hubble telescope reveals the explosion of a huge star in detail
By Will Dunham
WASHINGTON (Reuters) – About 11.5 billion years ago, a distant star, about 530 times larger than our sun, died in a catastrophic explosion that blew its outer layers of gas into the surrounding cosmos, a supernova documented in detail by astronomers.
Researchers said Wednesday that NASA’s Hubble Space Telescope managed to capture three separate images over an eight-day period, starting just hours after the detonation — a feat even more remarkable considering how long ago and far away it happened.
The images were discovered in a 2010 review of Hubble observational archive data, according to astronomer Wenlei Chen, a University of Minnesota postdoctoral researcher and lead author of the study published in the journal Nature.
They provided the first glimpse of a supernova cooling rapidly after the first explosion in a single series of images and the first in-depth look at a supernova this early in the universe’s history, when it was less than a fifth its current age.
“The supernova expands and cools, so the color evolves from warm blue to cool red,” said Patrick Kelly, an astronomy professor and co-author at the University of Minnesota.
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The doomed star, a type called a red supergiant, resided in a dwarf galaxy and exploded at the end of its relatively short lifespan.
“Red supergiants are luminous, massive and large stars, but they are much cooler than most other massive stars — that’s why they’re red,” Chen said. “After a red supergiant has exhausted the fusion energy in its core, the core will collapse and the supernova explosion will then blow away the star’s outer layers — its hydrogen shell.”
The first image, taken about six hours after the initial blast, shows that the explosion started relatively small and fiercely hot — about 180,000 degrees Fahrenheit (100,000 degrees Kelvin/99,725 degrees Celsius).
The second image is from about two days later and the third from about six days after. These two images show the gaseous material ejected from the star expanding outward. In the second image, the explosion is only a fifth as hot as in the first. In the third image it is only a tenth as hot as the first.
The remnant of the exploded star most likely became an incredibly dense object called a neutron star, Chen said.
A phenomenon called strong gravitational lensing explains how Hubble was able to obtain three images at different times after the explosion. The enormous gravitational pull exerted by a cluster of galaxies in front of the exploding star from Earth’s perspective served as a lens — bending and magnifying the light coming from the supernova.
“Gravity in the galaxy cluster not only bends light from behind, but also slows down light’s travel time because the stronger the gravity, the slower a clock moves,” Chen said. “In other words, the emission of light from a single source behind the lens can go to us through multiple paths, and then we see multiple images of the source.”
Kelly called the ability to see the rapidly cooling supernova in a single sequence of images thanks to gravitational lensing “just absolutely amazing.”
“It’s like seeing a reel of film evolve in color from the supernova, and it’s a much more detailed picture of every known supernova that existed when the universe was a small fraction of its current age,” Kelly said.
“The only other examples where we’ve caught a supernova very early are nearby explosions,” Kelly added. “When astronomers see objects more distant, they look back in time.”
(Reporting by Will Dunham, editing by Rosalba O’Brien)
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