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Planet-Gobbling Star
crymeph0 writes "BBC is carrying a story about a star that mysteriously brightened three times last year. Scientists now know why. It's been eating gas-giant planets that orbit it! I'm just glad Earth isn't a tasty gas planet, or else we'd have to start making sacrifices to Sol to play it safe." It's hard to prove things from 20,000 light years away, but this explanation is interesting.
In stars where there is a much higher level of "metals" seem to generate more large planets than we have. It seems that in a star like this you may end up with 4-10 Jovian size planets. In the case of our solar system you have 2 very large planets and everything is far enough appart that it is stable. On the other hand if you had a bunch of planets at 10 Jovian masses it is inevitable that a few would be kicked out of the system and a few put into very close in orbits.
it all comes down to how much matter there is to create planets. The higher the densisty of heavy elements the faster things start to clump into planets, and the bigger the planets get.
Erlang Developer and podcaster
Perhaps we have a new standard candle in the making here. Perhaps this effect is closely tied to the starting mass and composition of the solar system of the star.. and thus the brightness is roughly the same for each event..
Just a thought :)
Simon
I imagined for a second an advanced civilization crashing gas giants into their sun to keep it alive a little longer. I am wrong, of course, and this is no doubt the work of gravity, but I would like to point out that if we ever decide that we would like to keep our Sun burning for an extra million years or so, the only way to do that will be to crash Jupiter into her. On the other hand, the energy expended to do that would probably be better expended in creating environs that can support life without a sun.
1. They're positing that eating one or three giant planets is enough new fuel to make the star brighten significantly? (I wish the article had the details on how much it actually brightened.) A typical gas giant is around 1/1000 the mass of the parent star. That's not a lot of new fuel, particularly when you consider that the star has way more hydrogen than that left over from main sequence burning.
:-)
2. My most recent understanding (and I admit that I'm only half paying attention to this) is that the planets-contaminate-stars model for the heavy element enrichment probably doesn't explain the observed enrichment. (Probably because the planet's bits would have to stay right near the star's surface over the long run. See mass ratio, above.)
I'm not saying that this model doesn't work, but I'm skeptical. I'd really want to see their stellar models showing how addition of a giant planet's mass of hydrogen on the surface of the red giant affects the luminosity. I'd also like to see evidence that this star had planets before the brightening. (I wouldn't be shocked if the data didn't exist. But I still want to see it.
It's a facinating theory, but there's a huge problem with it. Planetary orbits are highly unstable unless they are pretty widely spaced. It is therefore pretty much impossible that there were THREE planets anywhere near the same distance away from the sun.
Seeing it happen to three different stars in one year, OK. Seeing it happen three times to one star over thousands or millions of years, OK. But there's no was a single star ate 3 planets in a single year without some HUGE outside influence disrupting the orbits.
If the theory is right then it is of secondary interest, and whatever triggered the triple event is probably far more important and interesting.
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