Strange 'zombie' star has died multiple times

Astronomers have discovered a supernova that has exploded and 'died' multiple times throughout its long history.
By Jose Jefferies | Nov 11, 2017
Despite erupting constantly over the last three years, a giant supernova known as iPTF14hls refuses to die, according to a report published in the journalNature.

This shocking discovery comes from astronomers at the University of California, Santa Barbara who found, not only that the star has been exploding for some time, but it may also have had two such outbursts in the past. Such activity has never been recorded in a supernova before.

"A supernova is supposed to be a one-time thing the star explodes, it's dead, it's done, it can't explode again," explained astrophysicist Iair Arcavi, a researcher at the University of California, Santa Barbara, according to Science News. "It's the weirdest supernova we've ever seen It's like the star that keeps on dying."

Astronomers first found iPTF14hls in September 2014 using the Intermediate Palomar Transient Factory. Though it first appeared like a regular type 2 supernova -- which typically glow for about 100 days before starting to dim -- further study of the body revealed that it got brighter over time.In addition, data collected from September 2014 to June 2016 showed that the supernova remained bright for more than 600 days.

Typically, gas kicked out of an exploding star begins to slow and cool as it expands. However, iPTF14hls remained extremely hot warm during the entire observation, and the outer gas layers did not slow down as they should have. That suggests the gas may have already cooled, which means that an earlier explosion took place sometime between 2010 and 2014.

This discovery adds credence to the theory that stars between 95 and 130 times the mass of the sun can explode several times. Though astronomers have postulated that idea for sometime, such cycles have never been observed before now.

The reason that process occurs is because those stars get so hot that they turn gamma rays into electrons and positrons. Without that internal energy, the star's core collapses and triggers a partial explosion that ejects a large amount of mass. Then, the electrons and positrons recombine back into gamma rays after the blast and hold up the remaining stellar core.

According to that theory, stars are able to blow up several times before finally dying. Eventually, the remains of such supernovae would collapse into a black hole roughly 40 times the mass of the sun.

Though that reasoning is sound, the model also suggests that those large stars would blow off all of their hydrogen in the first explosion. That does not fit with iPTF14hls because it expelled 50 times the mass of the sun in hydrogen in 2014, and the amount of energy in the most recent explosion is also greater than it should be.

Researchers are not sure what is causing the supernova to explode multiple times. However, as they may be able to glimpse inside the core when theouter layers of gas cool and become transparent. The team plans to continue monitoring the distant body to see what happens next.

"This process can repeat every few years or every few decades," said Arcavi, according toThe Washington Post. "It's an attractive theory because it explains why we may have seen this thing explode multiple times."


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