Scientists have identified a star that, they say, survived a massive explosion and eventually became brighter than before.
The star is a species known as a “white dwarf.” These are very dense objects with a mass roughly equal to that of the sun. But they can be as big as planets like Earth. A white dwarf is formed when the star burns up all of its central nuclear fuel and loses its outer layers.
Astronomers have observed the white dwarf star with the Hubble Space Telescope. The telescope is operated by the American space agency NASA.
Hubble has discovered “the oldest burned-out stars in our Milky Way galaxy”, NASA reported† Some old white dwarf stars seen by Hubble are estimated to be 12 to 13 billion years old. That is almost as old as the universe itself.
The observed star is in a universe called NGC 1309. It is about three quarters the size of our Milky Way. The white dwarf is about 108 million light-years from Earth. A light year is the distance light travels in a year.
The observation team said the white dwarf at one point reached a mass 1.4 times the mass of the sun. This led to thermonuclear reactions in the center of the star that triggered a supernova event.
NASA describes a supernova as an “extremely bright, super-powerful explosion of a star”. A supernova occurs at the end of a star’s life. The scientists say the supernova should have killed the white dwarf star, but it didn’t.
The investigation was led by a team from Las Cumbres Observatory in California. The lead writer of a study who described the finding was astronomer Curtis McCully.
He told Reuters news agency: “During the explosion, radioactive material was produced. This is what drives the brightness of the supernova.” He added that some of the material “remained in the remains” remnant star” and acted as fuel to heat it.
“We were quite surprised that the star itself had not been destroyed, but had actually survived and is brighter than it was before it exploded,” McCully said.
There are different types of supernova events. Each depends on the size and chemical composition of the star and the strength of the explosion.
This observed white dwarf produced an unusual type of supernova called “Type Iax”, the Las Cumbres Observatory said in a statement† The team said this kind is less bright and fainter than traditional “Type Ia” supernovae.
Scientists believe that this kind of supernova does not destroy the white dwarf. Instead, it leaves an “undead” remnant. This theory is confirmed by the new observations, the research team said.
‘We have named these objects’zombie stars for this reason. They died, but not completely,” McCully said. Previous experiments with supernova activity had suggested that in some cases white dwarf stars were able to survive these types of events. “It’s exciting to think that this told us something about the actual physics of these supernovae,” McCully added.
Scientists have discovered about 50 such supernovae. But until now, they hadn’t been able to identify the surviving white dwarf star.
Scientists believe that our sun will probably also become a white dwarf one day. This happens in about 97 percent of the stars. But the event involving our sun is not expected to happen for another 5 billion years.
I’m Bryan Lynn.
Reuters and the Las Cumbres Observatory reported on this story. Bryan Lynn has adapted the report for VOA Learning English.
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Words in this story
universe † n. one of the independent groups of stars in the universe
remnant † n. a piece of something that lasts when the rest of that thing disappears
zombie – n. a corpse walking around, as depicted in fictional stories
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