Distant Red Giant Caught Devouring One of Its Planets

By Rebecca Boyle Posted 08.21.2012 at 2:28 pm 7 Comments

Red Giant Sun This artist's concept shows what might happen to the Earth when the sun enters its red giant phase. Astronomers believe they have found the first evidence of a red giant consuming one of its planets. Wikimedia Commons

Astronomers have glimpsed the first evidence of a dying star devouring one of its planets, a fate that may await the inner planets -- including Earth -- in our own solar system. The star in the new study swallowed its planet as it mushroomed into a red giant.

The star, BD+48 740, is older than the sun and about 11 times bigger. It’s located in the Perseus constellation. Astronomy professor Alex Wolszczan of Penn State was looking at it as part of a survey of old sun-like stars. The team is searching for exoplanets around red giants, partly because so few are known to exist -- this may be because they’ve been swallowed up already, Wolszczan and colleagues write.

The team, which included astronomers from Poland and Spain, performed a detailed spectral analysis of the star to see what it contained. They found lots of lithium, which is strange for such a huge, old star. Lithium mostly formed during the Big Bang, and it does not last very long inside stars, so the presence of the element indicated that the star must have swallowed a planet.

While observing the star, the team also found another planet, this one a lot larger than the putative planet the star already consumed. It’s about 1.6 times the size of Jupiter, as evidenced by its influence on the star, and it is in a very strange elliptical orbit. The team says this surviving planet’s orbit suggests the missing planet dived into the star and gave its sibling a boost of energy, kicking it out like a boomerang.

“The highly elongated orbit of the massive planet we discovered around this lithium-polluted red-giant star is exactly the kind of evidence that would point to the star's recent destruction of its now-missing planet,” study co-author Eva Villaver of the Universidad Autonoma de Madrid in Spain said in a statement.

The process is not something astronomers would normally see because it happens pretty quickly, at least relative to the star’s distance from Earth. But chemical analysis contains all the evidence they need. The study appears in Astrophysical Journal Letters.

[Penn State]

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7 Comments

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Robot

08/21/12 at 3:32 pm

Our Sun is predicted to become a red giant in approximately 5 billion years. So do not put off your plans to go to the movies tonight, lol! ;)

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ToomeyND

08/22/12 at 11:50 am

As the star turns into a Red Giant, its mass should not change, correct? Wouldn't that mean that the only way for it to absorb a planet would be for the star to grow around the planet? The planet's orbit should not change as the star "grows" as the star is not growing in mass, aka, not changing its gravitational properties.

Am I missing something?

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Llowelme

08/22/12 at 3:42 pm

The fact that the mass does not change is correct. It did absorb the inner planet which did add some mass but It is doubtful that was enough to effect this a measurable amount.

However that mass will be in a larger area. For example:

There are forces fighting each other in the sun right now. It is it's current size because those forces are balanced. Once the star begins to run short on the fuel is it now burning the balance of those forces will change and it will mushroom out. It has the same mass so the orbits of the planets will stay the same. Unfortunately the new size of the sun will cover the orbits of the 3 inner planets.

What changed about the orbit of the second planet described is due to the fact that not only do the planets interact with the sun. They also interact with each other. So by the first planet being consumed by the star it changed the orbit of the second.

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thumbpick

08/25/12 at 9:35 am

As the star expands the planet will spiral into the star eventually. Simply, because as the star expands, its gases reach the orbit of the planet. The planets' orbit will degrade because its speed will decrease as it collides with more and more particles of gas. A process similar to why satellite orbits decay around the Earth after colliding with air particles.

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quasi44

08/26/12 at 3:47 am

It will not go in the natural way with Earth and Sol though. I suspect that we'll be doing quantum tunneling or something to tap more energy from the sun within a couple hundred years or so. The costs will be gladly paid by then, with the full greenhouse effect blotting out all other stars but Sol.

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sam6302

08/26/12 at 1:57 pm

My math says 10100 AD. 7000 years of Meek rule ends with the destruction of the earth . Hell (io) on the earth. At the end of this year there is a possible solar event in Isaiah 30:26. There is sufficient BTU to cook us.

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sajin sasikumar

09/01/12 at 10:38 am

When the stars,the mass of the core of which is greater then the chandrasakar limit reaches the Red giant,correct? will our sun became above the chandrasakar limit?

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