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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.
so it's just a case if indigestion, then?
"As the harald of Galactus, I beseech you to welcome your new Earth-gobbling overlord."
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
Star devours planets
By Dr David Whitehouse
BBC News Online science editor
The mystery of an erupting star may be explained by the realisation that it has been engulfing planets.
Last year, the usually well behaved star V838 Monocerotis dramatically brightened three times, and astronomers were at a loss to explain why.
The latest suggestion is that the expanding red-giant star was swallowing three gas planets that were orbiting it.
Astronomers are looking carefully at the observations as what happened to those planets may one day also happen to the Earth.
Previously unexplained
V838 Monocerotis is located about 20,000 light-years away in the constellation Monoceros (the Unicorn).
The outbursts were detected last year by Australian amateur astronomer Nicholas Brown.
The star was seen to brighten to more than 600,000 times our Sun's luminosity.
Astronomers had previously been unable to explain what transformed a dim star into the brightest, cool, supergiant star in the Milky Way.
The Hubble Space Telescope's Advanced Camera for Surveys had earlier recorded a dramatic image detecting a burst of light spreading into space and reflecting off shells of dust around the troubled star.
Now, in research soon to be published in the journal Monthly Notices of the Royal Astronomical Society, Dr Alon Retter and Dr Ariel Marom, from Sydney University, suggest the activity can be explained by the expanding star swallowing nearby planets.
Three planets, three meals
The researchers say that V838 Monocerotis flared because it was fuelled as it engulfed three orbiting planets. It could be the first evidence for an event that had been predicted but not knowingly observed.
Support for this assessment, say the astronomers, is provided by the study of the shape of the light curve and comparison between the observed properties of the star and several theoretical studies.
In addition to the gravitational energy generated by the process, there may also have been a rapid release of nuclear energy as fresh hydrogen was driven into the hydrogen-burning region of the star.
Some researchers believe that planet swallowing may be common and may explain why so many stars have enhanced levels of metals in their surface regions. The metals may have come from engulfed planets.
CMDRTACO CHECK YOUR EMAIL!
Somebody call Commodore Decker and Captain Kirk!
Is the star brighter, or is everything else just darker?
Orson Wells?
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
*cue cool music*
Unicron: For a time, I considered sparing your wretched little planet, Cybertron! But now, you shall witness... its DISMEMBERMENT!
El riesgo vive siempre!
Prevacid stock has spiked sharply up.
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
If our sun some day decides to turn into a Planet-Gobbling Star, let me know. I will go to the church and pray to the Almighty to send the devilish sun to Hell !!
Someone get Skywalker and Solo, ASAP!
Goo goo g'joob.
Prilosec went over-the-counter Monday...
I saw the headline and figured "Oh no! Carnie Wilson is off her diet again!"
Don't blame Durga. I voted for Centauri.
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.
OK, its more a Jupiter bar -- a chewy metallic hydrogen center covered in rich fluffy methane-ammonia clouds. What every growing star needs for a burst of energy.
How many orbits does it take to get to the center of a gas-giant lollipop?
Two wrongs don't make a right, but three lefts do.
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.
Yeah, I thought it said "Planet Gobbling Star" too.
I, for one, welcome our new star-gobbling plan...this is like shooting fish in a barrel.
IN SOVIET RUSSIA...man, this is just too easy.
Interesting that the star would actually get noticeably brighter, though! Isn't is strange that it ate three planets in such a short time period?
And incidentally, if they were right about the brightness coming from an infusion (haha) of hydrogen, those planets must have been extremely large - most planets (ours included) don't have a strong enough gravitational field to keep hydrogen within its sphere (haha again) of influence.
Planets taste like chicken!
Ceci n'est pas un post.
If it's 20,000 LY away it didn't brighten 3 times last year (that we know of)... rather it brightened 3 times in one year approximately 20,000 years ago.
I just know there is a good joke in there *somewhere* with gas-guzzling, solar power, and SUVs... I just can't get my mind around it yet...
"Your superior intellect is no match for our puny weapons!"
Read Niven's A World Out Of Time (multiple meanings in the title) for a similar idea. It's one if his first "State" books.
SPOLIERS BELOW
Basically, something else gets dropped into Jupiter. And there's some fascinating ideas on how to move a planet around.
You cannot apply a technological solution to a sociological problem. (Edwards' Law)
south for the winter or hearty meal ? you decide
There are places where the networks are not touching,and there are places where they are-Boeing's Lori Gunter
It sounds kinda cool to go ahead and fuel our sun with a giant gas planet, but then the resulting burst of energy would probably decimate all life on our planet. "Oops! Sorry! My bad..."
Then again, it just has ya thinking about "hm, well we could shoot all our nukes or other sources of fuel to the sun to feed it in controllable ammounts." This also rids our planet of them. But like you said...all that time, effort, and energy could be spent on other forms of life preservation and exploration. Sure is fun stuff to think about.
"He uses statistics as a drunken man uses lampposts...for support rather than illumination." - Andrew Lang
That's no star!
It is times like this that the need for a "Duh!" -1 moderation is screamingly obvious.
I live ze unknown. I love ze unknown. I am ze unknown.
I had this idea. What if we could atach retro-rocket boosters to an astroid (or comet) and redirect it's path toward Mars. Hopefully the release of energy from impact would warm up the planet and maybe melt some of that ice in to water. Thus, giving it a thicker atmosphere.
Life is not for the lazy.
Kick ass. Now that's why we need a space program!
"To confine our attention to terrestrial matters would be to limit the human spirit." -Stephen Hawking
The mechanical (potential + kinetic) energy E of a small mass m and velocity v a distance r from mass M is given by
E=mv^2/2-GMm/r
If we assume m is orbiting in an approximately circular orbit (the argument works even if the radius is slowly decaying), then v = (GM/r)^.5. Thus
E = mGM/(2r)- GMm/r
= -GMm/(2r)
Differentiating w/ respect to radius,
dE/dr = GMm/(2r^2)
. Suppose m is the mass of 10 Jupiters and M is 5 solar masses, and that m is at the surface of M at ~ 4 solar radii (astronomers can't agree whether the star is a red giant or a pre-red giant, so these numbers are very mushy.). To release our sun's output of energy over an entire year, m's orbit would only have to decay 15 kilometers. Notice also that once m is inside M, M becomes a variable that decreases to 0 at r=0 (the force of gravity at the center of a spherically symmetrical mass is 0). This means that at a certain point inside M, the amount of energy m is losing per unit change in radius actually starts to decrease the closer to the center of M it gets (assuming M is proportional to r^a with a>2 near the center). Also one might suspect that m wouldn't be able to descend much further then the layer of M with the same density as the core of m. All-in-all, it seems like most of the energy and the contents of the planet will be deposited in the outermost layers of the star.
"I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
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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- - You can't take something off the Internet! That's like trying to take pee out of a swimming pool.
You made a mistake, though. (The same one I made at first with this calculation.) The planet is being engulfed by the star, which is expanding out to it. Which means that the planet isn't moving inwards to the star, the star is moving out to *it*. So the star doesn't gain the PE from the planet's orbit, at least not much. If the planet does move inward into the star, most of that energy comes at the expense of moving more fo the star upwards against the star's gravity. (You'd basically have convection. The denser materials would allow for some gain in energy, but not much. That which would be released would do so deep in the interior of the star, taking (estimate ahead) thousands of years to reach the surface. At which point, the energy spike would be spread out over many years due to diffusion. (Note that energy from the Sun takes about a million years to leak out. However, I'll knock 3 orders of magnitude off to allow for a star that is less opaque.)
...the redundant rating is for.
Nobody made any mistakes, because nobody knows what really happened. Elsewhere there are examples of gas giants orbiting within 3-7 million miles of their stars' surfaces. Perhaps the enormous mass loss rate is bleeding the gas giant of its orbital angular momentum and essentially driving it into the star that is frying it. Or if the star is rotating slower than the planet is revolving around it (the previously mentioned evaporating gas giants have a period of 3-4 days, about a tenth of the rotational period of our own sun), then the induced tidal bulges will cause the planet to transfer its orbital angular momentum to the star's rotational angular momentum (and this could increase convection, allowing the star's energy to escape faster as light). Notice that in this case the planet is transferring energy to the star without even touching it while simultaneously falling towards it (the reverse process is happening here on Earth, where the rapidly rotating Earth is using its tidal bulges to slowly increase the orbital radius of the Moon, and we've actually been able to measure that increase). So there are a variety of ways a star could eat a planet. You seem to favor the expanding red giant model, so I'll quote from this article:
"In principle, that explanation seems OK," says John Lattanzio, director of the Centre for Stellar and Planetary Astrophysics at Monash University. But he says the star was too hot to have been a red giant. "It was probably one that was on its way there - that could fit the parameters."
And also the equation in my previous post is surprisingly robust. It should work quite well once the planet dips into the outer layers of star, no matter whether the star grew to meet it or it fell in. Also, one factor that I ignored but that works in my favor is the mass lot rate of m. The energy per unit radius lost by the planet decreases linearly with a decrease in m. Therefore the planet will be losing most of its energy when it still has most of its mass and before it gets far enough into the star that the force of gravity actually weakens (note that I've been treating M as the mass of the star interior to the radius of the planet's orbit, outside M is merely the mass of the star, but inside it decreases to 0). Once the star ate the first planet, it did increase in size, so your idea of how it eats is valid for the second and third planets.
"I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
I agree that the BBC article is woefully short of details, like how much additional energy was released, and the like. But before rejecting the conclusion out of hand, keep in mind that we're not entirely sure about a lot of "core" facts about our own planetary neighbors:
You need that core in standard formation models before you can accrete the hydrogen and helium gas.
According to this space.com article from 2001, extrasolar gas giants are throwing doubt on the "accretion" model of planet formation:
In the traditional view, Jupiter first formed a rocky core several times the size of Earth, which then attracted a still larger outer envelope of gas. This process is known as "accretion."
If this is the case, the large gaseous planet would have taken a very long time -- current estimates range between 10 million and a billion years -- to develop by the gradual build-up of material.
However, recent observations of distant stars suggest that planets have at most a few million years to gather up as much dust and gas as they can before the protoplanetary disk that feeds them disappears. There simply isn't enough time for massive planets like Jupiter to form.
If these new theories (yes, just theories) are correct, then you have a lot of very dense Hydrogen and Helium held together by its own gravity, not a big, rocky core. This makes the gas giants just small, dirty versions of the sun.
Of course, there are those who go the other way... Iron-core Sun, anyone?
It's a great time to be interested in the sky... fewer and fewer of the questions I got "right" on the middle school science test would be correct today.
Stressed? Me? Of course not. Stress is what a rubber band feels before it breaks, silly.
Red giants are quite large. Even the Sun in that phase will probably be large enough to reach Earth's orbit. An F-class star is larger, so we can assume that these weren't hot Jupiters that got envelopped.
And, yes, distance DOES matter. If the planet never falls into the star (the star rises and meets it instead) you don't get to extract that gravitational potential energy. It's as simple as that.
And you're being pretty blithe invoking tides. Since tidal forces fall of like 1/r^3, you'd need a monster of a planet to induce significant tides in the star. (And if you did transfer that angular momentum, the planet would be moving away from the star, not towards it.)
So it isn't quite a red giant yet. Even your article stated it was probably on the way there, meaning it was getting quite large. Older data on this star claim it was a red giant already (see the AAVSO site I quoted elsewhere), so either way, this is a big mother of a star.
Finally, so that the planet does just fall into the star so it hits the surface and basically gives up all of its energy. What will you see? Yep, a brief flash of energy, then it'll calm down again because the energy has been transfered over. It won't last months.
I quite simply cannot see a reasonable way to get the energy that they require, either through fusion or energy from the engulfing. I need to see the actual paper to be absolutely sure, but the burden to convince is very much on the authors on this one. (And what happened to waiting to hold press conferences until the goddamn paper came out, anyway?)
...a Beowulf cluster of those things!
You thought it, but only I had the courage to say it.
And you're being pretty blithe invoking tides. Since tidal forces fall of like 1/r^3, you'd need a monster of a planet to induce significant tides in the star.
Well, which is it? When you say that "the star rises and meets it", you seem to be describing the inducement of a tidal bulge or Roche lobe. You then complain that I am invoking a tidal bulge. And while you say "Since tidal forces fall of like 1/r^3, you'd need a monster of a planet to induce significant tides in the star," it should be obvious that the closeness of the planet is far more important than mass. The force goes as r^-3, so it takes only a small decrease in r for a large increase in force, while the tidal force is only linear in m. Also, you'll have to explain how the planet would be moving out from the star if the star's 'day' is greater than the planet's year, as I basically don't believe you. It goes against what I was taught about the orbits of Phobos and Deimos, one of which is doomed to crash into Mars or get crushed into a ring in the process, and one is not. But ultimately to me it didn't matter how the planet got to surface of the star. :Like you, I was interested in modeling it once the planet and star atmospheres had contacted each other. That's when the real fireworks begin. We're merely disagreeing as to the height in the star's atmosphere that the planet descends to before it is transferring the maximum mount of power to the star. Once the two objects are touching, the tidal forces have to be important, but that would be a more complicated model than I am willing to work on at the moment. But yes, I am anxious to see the "goddamn paper."
"I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
And remember my sun, if you're going to eat a gas-giant, please don't forget the Bean-O. Solar wind can be most disruptive.
Never pet a burning dog.
If you eat a gas giant, I suppose you can reasonably anticipate a celestial fart...