WEBVTT - How Do White Dwarf Stars Shred Planets?

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<v Speaker 1>Welcome to Brainstuff, a production of iHeartRadio, Hey Brainstuff, Lauren Bolebaum. Here.

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<v Speaker 1>When our Sun runs out of hydrogen fuel in roughly

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<v Speaker 1>five billion years, it will swell into a huge, red

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<v Speaker 1>giant star, violently shedding hot layers of plasma and cooking

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<v Speaker 1>the inner planets to a crisp as it goes. All

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<v Speaker 1>that will be left behind is an expanding bubble of

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<v Speaker 1>cooling gas, creating a beautiful planetary nebula with a white

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<v Speaker 1>dwarf in the middle, shining bright like a stellar diamond.

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<v Speaker 1>Though we know this is the fate of our star,

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<v Speaker 1>what of the planets in our Solar system? But what

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<v Speaker 1>exactly will happen to Earth long after we're gone. Astronomers

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<v Speaker 1>from the University of Warwick in the UK took a

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<v Speaker 1>stab at answering this question back in twenty nineteen and

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<v Speaker 1>came up with a rudimentary warning guide for planets that

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<v Speaker 1>find themselves in this grim scenario. While our planet's fate

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<v Speaker 1>isn't necessarily clear, the study, which is published in the

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<v Speaker 1>journal Monthly Notices of the Royal Astronomical Society, revealed that

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<v Speaker 1>when it comes to contending with a white dwarf star,

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<v Speaker 1>only the tiniest worlds will survive. Why is that, Well,

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<v Speaker 1>we know that many white dwarf star systems have quantities

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<v Speaker 1>of dust surrounding them, and through spectroscopic measurements, dust has

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<v Speaker 1>been found polluting these star's atmospheres. The implication is clear.

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<v Speaker 1>These star systems used to have rocky planets, plus asteroids

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<v Speaker 1>and comets and orbit, but through extreme tidal interactions with

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<v Speaker 1>their white dwarf, were torn to shreds and ground to dust.

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<v Speaker 1>But why do planetary bodies get blended when they're in

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<v Speaker 1>the orbit of a white dwarf. These exotic stellar objects

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<v Speaker 1>contain nearly the entire mass of the dead star that

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<v Speaker 1>they came from, in a blob of degenerate matter only

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<v Speaker 1>the size of Earth. With this extreme density comes an

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<v Speaker 1>incredibly powerful gravitational field and tidal forces. Anything that strays

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<v Speaker 1>too too close to a white dwarf will be pulled

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<v Speaker 1>in by that powerful gravity. But there's a much wider

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<v Speaker 1>zone of destruction around such a star within which planets

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<v Speaker 1>or other orbiting bodies will be destroyed. Within this zone,

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<v Speaker 1>a planet, for example, will experience a much more powerful

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<v Speaker 1>tidal force on the star facing side than on the

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<v Speaker 1>side facing away, depending on what that planet is made

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<v Speaker 1>of and how well it holds together due to its

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<v Speaker 1>own gravity and a number of other factors. At a

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<v Speaker 1>certain distance, the tidal shear through the planet will be

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<v Speaker 1>too much, and it will be literally pulled like taffy

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<v Speaker 1>until it's pulled right apart. This is known as the

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<v Speaker 1>destruction radiusmarked by an ominous dusty ring around a white dwarf.

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<v Speaker 1>To understand where a variety of planets of different sizes

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<v Speaker 1>might be safe, the researchers carried out dynamic simulations of

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<v Speaker 1>different planets in orbit around a star like our Sun,

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<v Speaker 1>as it dies and passes through the red giant phase

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<v Speaker 1>to become a white dwarf. This violent phase of a

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<v Speaker 1>star's life will disturb the orbit of the planets around it,

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<v Speaker 1>possibly dragging them to their dusty deaths or flinging them

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<v Speaker 1>to wider orbits. Interestingly, the researchers found that it isn't

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<v Speaker 1>just the mass and composition of planets that affect how

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<v Speaker 1>sensitive they are to the tidal shear. It's also their

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<v Speaker 1>viscosity or the resistance they have to being deformed. Think

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<v Speaker 1>if you had a glass of water and a glass

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<v Speaker 1>of nacho cheese, If you poked the surface of the water,

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<v Speaker 1>it would easily deform around your finger. You'd feel basically

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<v Speaker 1>no resistance at all. This is low viscosity. Now, if

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<v Speaker 1>you poked the nacho cheese, I mean, you'd still be

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<v Speaker 1>able to deform its surface, but it would give you

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<v Speaker 1>a little bit more resistance because it has a higher viscosity. Now,

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<v Speaker 1>think about if you poke the glass itself, It's not

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<v Speaker 1>going to deform at all from a mere poking. Of

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<v Speaker 1>the three, it has the highest viscosity under these particular circumstances. Anyway,

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<v Speaker 1>the physics is complicated. But back to white dwarfs. The

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<v Speaker 1>researchers found that if all other variables were controlled for

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<v Speaker 1>low viscosity, exoplanets of a similar consistency to say, Saturn's

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<v Speaker 1>moon Enceladus, which they called a relatively homogeneous dirty snowball

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<v Speaker 1>because of its thick iso layers surrounding a small core,

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<v Speaker 1>would be dragged to its doom if it resides within

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<v Speaker 1>anywhere up to five times of the white dwarf's destruction radius.

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<v Speaker 1>At the other extreme, a high viscosity world might live

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<v Speaker 1>comfortably if it orbited the white dwarf at just twice

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<v Speaker 1>its destruction radius. Recently, astronomers discovered a dense, heavy metal

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<v Speaker 1>object around a white dwarf that's embedded inside a dusky disc.

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<v Speaker 1>It's believed that this object, which isn't much bigger than

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<v Speaker 1>a large asteroid, was the metal core of a larger

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<v Speaker 1>planet that was destroyed by tidal shear, leaving its high

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<v Speaker 1>viscosity metallic core behind. As the search for exoplanets, that

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<v Speaker 1>is planet's orbiting other stars becomes more sophisticated, we're going

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<v Speaker 1>to observe more worlds in white dwarf star systems, So

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<v Speaker 1>the researchers hope that these simulations will act as a

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<v Speaker 1>guide that will help us understand what those exoplanets are

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<v Speaker 1>made of. Although this simulation has provided some key insights

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<v Speaker 1>to what it takes to avoid being dragged to a

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<v Speaker 1>dusty death, it only simulated relatively homogeneous objects. When it

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<v Speaker 1>comes to our planet, the problem becomes more complex because

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<v Speaker 1>of all the layers of atmosphere, water, rock, and inner

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<v Speaker 1>metallic core that our planet contains. But in summary, it

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<v Speaker 1>pays to be tiny and mighty and composed of heavy

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<v Speaker 1>metals if you want to have a snug orbit around

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<v Speaker 1>a white dwarf without being dragged to your death. As

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<v Speaker 1>for Earth's fate, we'll have to wait and see, but

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<v Speaker 1>in all honesty, you probably won't want to be there

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<v Speaker 1>when our red giant sun switches to broil. A note

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<v Speaker 1>that long before the Sun runs out of hydrogen and

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<v Speaker 1>puffs up into a red giant let alone before it

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<v Speaker 1>becomes a white dwarf, it will become a lot hotter

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<v Speaker 1>than it is now, irradiating the inner planets. This, combined

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<v Speaker 1>with powerful solar winds, will likely blast away our atmosphere,

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<v Speaker 1>undoubtedly destroying any and all life that remains. So today's

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<v Speaker 1>episode is based on the article white dwarfs can shred

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<v Speaker 1>planets to pieces on HowStuffWorks dot com, written by Ian O'Neil.

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<v Speaker 1>Brainstuff is production of iHeartRadio in partnership with hostuffworks dot

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<v Speaker 1>Com and is produced by Tyler klang A. Four more

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