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Jun 15th 2018

Zombie Star Diaries — The Life and “Death” of iPTF14hls

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What happens when a star dies? Depends on the mass of the star. Consider the sun: In around 5 billion years, our star will run out of hydrogen and begin fusing helium, turning it into a red giant that engulfs the Earth. Once exhausted, it will fade into a white dwarf, according to Universe Today. But there are more exciting ways to go, according to Space.com: Some massive stars can go out with a bang as Type II supernovae, exploding and briefly outshining entire galaxies. “Zombie star” iPTF14hls decided to come back from the dead, confounding scientists with atypical supernova behavior. Is this zombie star really rising from a stellar grave?

Simple Supernova or Zombie Star?

Supernovae aren’t complicated: Large stars — more massive than the sun — have enough mass and pressure to fuse carbon and heavier elements, causing their cores to rapidly become heavier and surpass the Chandrasekhar limit, which causes them to implode. This causes even greater core density and pressure and eventually the implosion “bounces” off the core, spraying stellar material (light and energy) into space, according to Space.com.

Space.com notes that, over the course of 100 days, supernovae follow a predictable brightness curve and then fade away to become superdense neutron stars or black holes. Unless, of course, we’re talking about iPTF14hls. According to Astronomy Now, the supernova was first discovered in September 2014 and behaved like any run-of-the-mill dying star. But then it got weird: Months later, researchers noticed the star getting bright again — and it’s done so five times over the last few years. Even stranger? Scientists found evidence of another supernova explosion at the same location back in 1954. Some experts suggest this could be evidence of “pulsational pair-instability supernova” theory, which suggests that massive stars could generate both matter and antimatter in their cores, in turn leading to a series of explosions before the final curtain call. The problem? Energy released by iPTF14hls is more than the theory predicts. As a result, there’s no good explanation (yet) for this ever-exploding zombie.

Myriad Mysteries

Exactly what happens when a star dies — and why it won’t stay dead — aren’t the only stellar mysteries under investigation. Scientists from MIT are struggling to understand the origins of a supermassive black hole at the center of a quasar formed around 690 million years after the Big Bang. With a mass more than 800 million times that of our sun, the black hole shouldn’t exist given the conditions of the early universe, meaning there’s more science needed to explain exactly what’s causing the phenomenon.

Dark matter is also on the list of top-tier stellar mysteries, since there should be more of it than regular matter in the universe, yet scientists have never directly confirmed its existence. According to NASA, new data suggests that dark matter might have two energy states separated by 3.5 kiloelectron volts (keV), accounting for consistent X-ray absorption near the center of black holes and consistent emission from hot gas at the edges; understanding energy states could help zero in on dark matter itself, or amount to another red herring.

Other mysteries, such as Jupiter’s strange “switching” jet stream, may finally have a solid explanation. On Earth, the jet stream changes direction every 28 months as atmospheric waves produced by tropical storms rise from the troposphere. On Jupiter, the switch occurs every four years, but until recently, scientists had no idea why. According to Phys.org, new measurements from NASA’s Infrared Telescope Facility in Hawaii, suggest that gravity waves produced by convection in the low atmosphere are acting to restore overall equilibrium and leading to the jet stream shift.

Space is full of mysteries that defy current understanding. New technologies, however, combined with the unquenchable need of humankind to know what’s out there, are helping scientists discover supermassive objects, investigate the potential presence of aliens and keep a close eye on that one really weird zombie star.

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