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What exactly is a ‘Zombie Star,’ and how does it compare to other stars and supernovas? We’ve also learned more about how the haze over Pluto plays a role in its temperature.

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Sources:

http://www.keckobservatory.org/recent/entry/LCO_supernova
https://www.nature.com/articles/nature24030
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.18.379
http://iopscience.iop.org/article/10.3847/1538-4357/836/2/244/meta;jsessionid=D94FCFB34EBFF404AAC91DF857F18175.ip-10-40-2-120

http://nature.com/articles/doi:10.1038/nature24465
http://pluto.jhuapl.edu/Participate/learn/What-We-Know.php?link=Plutos-Atmosphere
http://www.skyandtelescope.com/astronomy-news/plutos-atmosphere-confounds-researchers-032520166/
http://adsabs.harvard.edu/full/1989BAAS...21..981E

Images:

https://en.wikipedia.org/wiki/File:Keplers_supernova.jpg
https://en.wikipedia.org/wiki/File:IPTF14hls.png
https://en.wikipedia.org/wiki/File:Pluto-01_Stern_03_Pluto_Color_TXT.jpg
https://en.wikipedia.org/wiki/File:Pluto-BlueSkyFinal_PIA21590.jpg
https://commons.wikimedia.org/wiki/File:New_horizons_(NASA).jpg
https://en.wikipedia.org/wiki/File:MVIC_sunset_scan_of_Pluto.jpg
Astronomers are always finding weird stuff in the universe.

But sometimes, their discoveries are especially strange… and maybe a little spooky. According to a paper published last week in Nature, astronomers have found a star about 500 million light-years away that just won’t quit.

It appears to have died and come back to life multiple times, almost like… a zombie star. When really large stars run out of fuel, they can explode in gigantic, beautiful explosions called supernova. And scientists can describe them using graphs called light curves.

A light curve shows you how bright an object is over some amount of time. For a supernova, the curve should look really bright at first, because it’s exploding, and then it should taper off as everything disperses and cools. Normally, a supernova doesn’t stay bright for long: only about 100 days.

And it only happens once because, well, the star is dead after that. But the light curve for this new supernova, called iPTF14hls, which is so easy to remember, has all kinds of fun bumps in it, like it’s pulsing. And even though we discovered it in 2014, it’s still really bright three years later.

It’s also way brighter than your average, garden-variety supernova! So far, we’ve recorded it being almost three and a half billion times as bright as the Sun, while regular supernova usually aren’t more than 500 million times brighter. But the weirdest part is that this object might have exploded before!

After seeing how strange it was, the team searched through previous research for similar phenomena, and they found an explosion recorded in the same spot in 1954! So, it seems like the star died about 60 years ago, but then made a comeback and exploded again. Right now, there isn’t a full explanation for its behavior, but part of it may have to do with its mass.

The team calculated that, before it exploded, the star was at least 50 times the mass of the Sun, and probably a lot bigger than it. And even though we’ve found thousands of supernova, we haven’t yet seen a star that big die, so it could work differently than expected. Another, even cooler option is that this may be the first recorded pulsational pair-instability supernova, or PPISN.

This is something scientists have modeled, but never observed in real life. The idea is that, a star that’s massive and hot enough might start manufacturing pairs of electrons and their antimatter opposite: positively-charged particles called positrons. And creating these pairs might drive the supernova’s weird pulses.

Making them uses up energy that the star would normally use to stop itself from collapsing. But since it is used up, the star contracts. That causes more elements to burn in the star’s core, which gives off a bunch of extra light, until the star eventually cools down and expands.

And then the cycle begins again. So, more pulses. Still, the team also doesn’t think a PPISN could fully explain what’s happening, because we think those supernova get rid of most of their hydrogen early on, while this one has lots of hydrogen leftover.

Plus, in this recent explosion, the mystery supernova has about ten times more energy than what PPISNs should. So it remains under close observation! This week, astronomers reported another mystery in the journal Nature, but this time, it was about Pluto, and they’ve solved it!

As it turns out, Pluto is super cold, which believe it or not, is unexpected. Okay, we already knew it must be kinda cold, because it’s tiny and billions of kilometers from the Sun. But after New Horizons flew by in 2015, we found that it’s about 40 degrees Celsius cooler than we thought.

According to new research, that’s probably because it has a unique atmosphere. Studying an object’s atmosphere is crucial to understanding its temperature, because atmospheres are normally fluffy, regulating planetary blankets. On most planets, it’s the gases in the atmosphere that do the regulating, like how carbon dioxide influences Earth’s temperature.

But on Pluto, it’s not the gases: It’s haze, or something a little like smog. From previous research, we already knew that Pluto has a somewhat hazy atmosphere, because light passing close to its surface was dimmer than we’d expect. New Horizons confirmed that, but it also found that the hazes are more abundant and stretch higher than we thought: about 700 kilometers above the surface.

Still, that didn’t explain why Pluto is so cold. But before we could learn more, New Horizons flew off farther into the Kuiper Belt, so we couldn’t gather the data to explore this temperature problem. And that’s where modeling stepped in.

A team of scientists built a new and improved model of Pluto’s atmosphere, and they found that, if they set it up so that hazes were the main thing controlling Pluto’s temperature, the model matched the New Horizons data! In other words, Pluto’s atmospheric hazes are mainly what’s making it so cold, not its gases. That haze is likely made of lots of bigger hydrocarbons, which formed when light drove certain chemical reactions, a lot like how smog can form on Earth.

Those molecules are really great at sucking up energy, but they’re also great at radiating it away. The hydrocarbons distribute the heat among themselves really rapidly, then force a lot of that heat into the upper atmosphere, where it spreads into space. And that leaves Pluto extra chilly.

As far as we know, the only place in the solar system with a temperature controlled by hazes like this is Pluto! And since hazes seem to play an important role in the atmosphere of some exoplanets, this research might also help us explore worlds farther away. That little dwarf planet just keeps impressing us!

So this week, all kinds of expectations are being thrown overboard in the solar system! And I’m sure that is not the last time I’ll say that. Thanks for watching this episode of SciShow Space!

If you’d like to keep up with the latest news from around the universe, you can go to youtube.com/scishowspace and subscribe.