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An inside out planetary nebula has given astronomers insight into what might happen in our own solar system someday, and it's that time of year again to search for shooting stars.

Hosted by: Hank Green

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Sources:

https://www.amsmeteors.org/2018/08/viewing-the-perseid-meteor-shower-in-2018/
https://www.space.com/32868-perseid-meteor-shower-guide.html
https://press.nature.com/wp-content/uploads/files/2018/07/41550_2018_551_OnlinePDF.pdf
https://www.iaa.csic.es/en/news/strange-case-hubi1-inside-out-stellar-corpse

Images:

http://chandra.harvard.edu/photo/2012/pne/
https://www.iaa.csic.es/en/news/strange-case-hubi1-inside-out-stellar-corpse
https://commons.wikimedia.org/wiki/File:Mz_3,_BD%2B30-3639,_Hen_3-1475,_and_NGC_7027-_Planetary_Nebulas_-_Fast_Winds_from_Dying_Stars_(2940653103).jpg
http://spacetelescope.org/images/potw1010a/
https://www.nasa.gov/image-feature/goddard/hubble-finds-a-little-gem
https://en.wikipedia.org/wiki/File:Phot-21-96.gif
https://www.eso.org/public/usa/images/potw1531a/
https://commons.wikimedia.org/wiki/File:Perseids_2015.jpg
https://commons.wikimedia.org/wiki/File:Perseiden_2014.png
https://commons.wikimedia.org/wiki/File:Comet_Swift_EE-Barnard_4_and_6_April_1892.jpg
https://www.nasa.gov/topics/solarsystem/features/watchtheskies/perseid-meteor-shower-aug11-12.html
https://en.wikipedia.org/wiki/File:Nursery_of_New_Stars_-_GPN-2000-000972.jpg
[♪ INTRO].

When people talk about space, it’s often on scales so large they’re almost incomprehensible:. Thousands of light-years.

Hundreds of millions of years. Billions of galaxies. But some of the universe’s most beautiful sights are much more fleeting, like planetary nebulas, glowing, colorful shells of gas that only last for about 10,000 years or so.

And this week, a paper published in Nature Astronomy reported the first one that appears to be inside out. Despite the name, planetary nebulas have nothing to do with actual planets. They got their name in the 1700s, when astronomers saw them as smears of light in their telescopes, not single points like stars, but disk-like objects that looked more like planets.

We’ve known they’re not planets for a long time, but the name stuck. Instead, planetary nebulas are a type of stellar remnant, or what’s left over after a star dies. Stars like our Sun aren’t massive enough to undergo a supernova explosion, so their death throes are far less violent.

The outer layers of the star, or stellar envelope, are shed into interstellar space, and the core collapses into a super dense white dwarf. The electromagnetic radiation emitted from that core reacts with the particles from the envelope and other matter in the area. Sometimes those particles absorb the energy and reemit it at other wavelengths, producing a rainbow of colors.

Other times, the photons of light emitted from the white dwarf are so energetic they knock electrons off their parent atoms entirely, creating charged ions. Normally, the stuff closer to the white dwarf is more ionized than the stuff farther away, because it gets hit with the most radiation. But this planetary nebula is the first one we’ve seen that has it the other way around, and astronomers think that’s because the inner shell is excited by shocks from what’s known as a “born again” event.

Basically, the stellar remnant at the center, imaginatively named IRAS 17514-1555, underwent a sort of thermal pulse and its nuclear engine fired up again, expanding the star from a white dwarf back into a red giant. Yeah. It’s an undead star.

This isn’t the first “born again” event we’ve ever seen. For example, there’s also Sakurai's Object, which was discovered back in 1996 in the area of the sky near the constellation Sagittarius. But this is the first time we’ve seen one with an inside-out nebula, and the researchers think it’s happening as the star in its center rapidly cools back down from its second shot at life, whereas Sakurai’s Object is still heating up.

In the past 4 decades, IRAS 17514’s brightness has dropped by a factor of 10,000, and in the process, it’s been ejecting large amounts of carbon-rich material at speeds faster than the nebula is expanding. That creates a shockwave in the nebula, which heats up the material just in front of it enough to ionize atoms that usually wouldn’t be. Meanwhile, less-ionized particles are left in its wake.

That leads to more highly-ionized material outside of the less-ionized stuff; in other words, an inside-out nebula. But besides being a totally unique object in the astronomy books, this planetary nebula can teach us a lot. For one, it’s a missing piece of the story of how low-mass stars turn into metal-rich white dwarfs surrounded by planetary nebulas.

And according to models, the star that became IRAS 17514 had a mass only 10% larger than our own Sun. So we might be looking at what could happen in our own solar system in billions of years. We’ll never know for certain, ‘cause we’ll all be dead by then, but it’s sometimes good just to know, you know?

In the meantime, there’s another beautiful astronomical sight you can catch this very weekend: The Perseid meteor shower. It’s caused by the comet 109P/Swift-Tuttle, which last passed by Earth in 1992 on its way around the Sun. The comet was actually discovered back in 1862, by Lewis Swift and Horace Tuttle, but since one orbit takes over a hundred years to complete, we didn’t have enough data to predict when exactly it would come around again.

But each time Swift-Tuttle does, it leaves a trail of dust in Earth’s orbit. Every year, our planet crashes into that trail and some of the tiny pieces of space debris rain down. But they do not make it very far.

They strike the Earth’s atmosphere at 59 kilometers per second and get burned away pretty quickly, creating a meteor shower. Meteor showers get their names from where they appear to come from in the sky. We see Swift-Tuttle’s remnants coming from the constellation Perseus, so it gets the name the “Perseids.” The Earth has lots of regularly occurring meteor showers throughout the year.

But since this one happens in August, when the evening weather is nicer, at least in the Northern Hemisphere, the Perseids is one of the more popular. This year, we entered Swift-Tuttle’s dust trail back on July 17th, and won’t leave until August 24th, but we’ll be entering the densest area on August 12th. So this weekend, you can expect to see about one meteor per minute.

Assuming you don’t have any clouds raining on your parade, you’ll be able to see meteors streaking across all parts of the sky in the Northern Hemisphere. But they will be more visible in areas with less light pollution. And lucky for all of us, one major source of light pollution, the Moon, won’t be visible, since it’s a new moon on Saturday.

So if you can find the time this weekend, check out what the universe has to offer! Thanks for watching this episode of SciShow Space News! To keep up with the latest discoveries and learn about some of the most fascinating things in the universe, just go to youtube.com/scishowspace and subscribe.

Also, if you want to celebrate your love of space with posters on your walls or shirts on your torso, check out DFTBA.com/SciShow [♪ OUTRO].