The Hubble telescope shows the explosion of a giant star in detail
About 11.5 billion years ago, a distant star about 530 times larger than our Sun died in a cataclysmic explosion that blew its outer layers of gas into the surrounding cosmos, a supernova that astronomers have documented in blow-by-blow detail .
Researchers said Wednesday NASA’s Hubble Space Telescope managed to capture three separate images over an eight-day period that began just hours after the detonation — an achievement even more remarkable considering how long and far away it took place.
The images were discovered during a review of archival data from the 2010 Hubble observation, according to astronomer Wenlei Chen, a postdoctoral researcher at the University of Minnesota and lead author of the study published in the journal Nature.
They provided the first look, in a single image set, of a supernova that cooled rapidly after the initial explosion, and the first detailed look of a supernova so early in the history of the Universe when it was less than a fifth of its present age.
“The supernova expands and cools, changing its color from a hot blue to a cool red,” said Patrick Kelly, professor of astronomy at the University of Minnesota and co-author of the study.
The doomed star, a guy called the red supergiant, lived in a dwarf galaxy and exploded at the end of its relatively short lifespan.
“Red supergiants are luminous, massive, and large stars, but they’re much cooler than most other massive stars — that’s why they’re 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 shell.”
The first image, about six hours after the initial explosion, shows how the explosion started out relatively small and intensely hot — about 180,000 degrees Fahrenheit (100,000 degrees Kelvin/99,725 degrees Celsius).
The second picture is from about two days later and the third about six days later. 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 picture it is only a tenth as hot as in 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 capture three images at different times after the explosion. The tremendous gravitational pull of a galaxy cluster in front of the exploding star from Earth’s perspective served as a lens — bending and magnifying the light emanating from the supernova.
“Gravity in the galaxy cluster not only bends the light behind it, but also retards the travel time of light, because the stronger the gravity, the slower a clock moves,” Chen said. “In other words, light emission from a single source behind the lens can come at us in multiple ways, and we then see multiple images of the source.”
Kelly called the ability to see the rapidly cooling supernova in a single image set, thanks to gravitational lensing, “just absolutely amazing.”
“It’s like seeing a supernova evolve in color, and it’s a much more detailed picture of every known supernova that existed when the universe was only a small fraction of its current age,” Kelly said.
“The only other examples where we’ve caught a supernova very early on are explosions in close proximity,” Kelly added. “When astronomers see more distant objects, they are looking back in time.”