Another Hubble Goodie II

Cosimo

Cosimo

Cosimo

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Last time we had Saturn, this time we have:

Hubble Finds a Star Eating a Planet​


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"The Star That Ate My Planet" may sound like a B-grade science fiction movie title, but this is really happening 600 light-years away. Like a moth in a candle flame, a doomed Jupiter-sized planet has moved so close to its sunlike parent star that it is spilling its atmosphere onto the star. This happens because the planet gets so hot that its atmosphere puffs up to the point where the star's mavity pulls it in. The planet will likely be completely devoured in 10 million years. Observations by Hubble's new Cosmic Origins Spectrograph measured a variety of elements in the planet's bloated atmosphere as the planet passed in front of its star. The planet, called WASP-12b, is the hottest known world ever discovered, with an atmosphere seething at 2,800 degrees Fahrenheit.
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The full Story:

The hottest known planet in the Milky Way galaxy may also be its shortest-lived world. The doomed planet is being eaten by its parent star, according to observations made by a new instrument on NASA's Hubble Space Telescope, the Cosmic Origins Spectrograph (COS). The planet may only have another 10 million years left before it is completely devoured.

The planet, called WASP-12b, is so close to its sunlike star that it is superheated to nearly 2,800 degrees Fahrenheit and stretched into a football shape by enormous tidal forces. The atmosphere has ballooned to nearly three times Jupiter's radius and is spilling material onto the star. The planet is 40 percent more massive than Jupiter.

This effect of matter exchange between two stellar objects is commonly seen in close binary star systems, but this is the first time it has been seen so clearly for a planet.

"We see a huge cloud of material around the planet, which is escaping and will be captured by the star. We have identified chemical elements never before seen on planets outside our own solar system," says team leader Carole Haswell of The Open University in Great Britain.

Haswell and her science team's results were published in the May 10, 2010 issue of The Astrophysical Journal Letters.

A theoretical paper published in the science journal Nature last February by Shu-lin Li of the Department of Astronomy at the Peking University, Beijing, first predicted that the planet's surface would be distorted by the star's mavity, and that gravitational tidal forces make the interior so hot that it greatly expands the planet's outer atmosphere. Now Hubble has confirmed this prediction.

WASP-12 is a yellow dwarf star located approximately 600 light-years away in the winter constellation Auriga. The exoplanet was discovered by the United Kingdom's Wide Area Search for Planets (WASP) in 2008. The automated survey looks for the periodic dimming of stars from planets passing in front of them, an effect called transiting. The hot planet is so close to the star it completes an orbit in 1.1 days.

The unprecedented ultraviolet (UV) sensitivity of COS enabled measurements of the dimming of the parent star's light as the planet passed in front of the star. These UV spectral observations showed that absorption lines from aluminum, tin, manganese, among other elements, became more pronounced as the planet transited the star, meaning that these elements exist in the planet's atmosphere as well as the star's. The fact the COS could detect these features on a planet offers strong evidence that the planet's atmosphere is greatly extended because it is so hot.

The UV spectroscopy was also used to calculate a light curve to precisely show just how much of the star's light is blocked out during transit. The depth of the light curve allowed the COS team to accurately calculate the planet's radius. They found that the UV-absorbing exosphere is much more extended than that of a normal planet that is 1.4 times Jupiter's mass. It is so extended that the planet's radius exceeds its Roche lobe, the gravitational boundary beyond which material would be lost forever from the planet's atmosphere.
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Source

What an amazing universe we live in, what next? :)
 
I'd appreciate it if someone would help me understand something about this.

That planet is orbiting very close to its star.

Is it the speed of the orbit creating centrifugal force that prevents the stars mavity from sucking the planet in ?

If so, and this is where my brain approaches melt down, then as the planet loses material to the star it becomes lighter, less mass, so would the stars mavity have a greater effect and begin to decay the planets orbit pulling it into the star ?
 
eddie_slovik said:
I'd appreciate it if someone would help me understand something about this.

That planet is orbiting very close to its star.

Is it the speed of the orbit creating centrifugal force that prevents the stars mavity from sucking the planet in ?

If so, and this is where my brain approaches melt down, then as the planet loses material to the star it becomes lighter, less mass, so would the stars mavity have a greater effect and begin to decay the planets orbit pulling it into the star ?
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It might be simpler to not think of centrifugal force, simply things that are travelling want to go in a straight line, and will do unless acted upon by something else. So here the planet is subject to mavity from the star that pulls its motion circular. Interestingly though getting lighter should move it away from the star, so it's probably already in a decaying orbit such that the loss of mass won't be sufficient to counter the inward motion.
 
Centrifugal force doesn't really exist, when you go round a corner in a car really fast and feel yourself pushed out to the side, you aren't being pushed OUT at all. Your body is trying to carry on moving in a straight line, and the car door is actually pushing you IN to keep you inside the car.

The same with planets, it is the gravitational force of the star that stops the fast moving planets from flying off into space. This is called a centripetal force, and works in the opposite direction to how people assume centrifugal force acts.

Mass is irrelevant, a tiny satellite a fixed distance from the earth would have to travel at the same speed as a bigger one to maintain the same orbit. It's the same with hump back bridges - if you go over a hump back bridge at 30mph on your bike and don't take off, but go over it again at 40mph and do take off then it means that a car or even a truck would take also off at 40mph, (although in reality depends on how much of the hump is absorbed by your suspension...).

If you look at newton's law of universal gravitation F=(G*m1*m2)/r you'll see that the gravitational force is proportional to the mass of both objects, so as the mass of one decreases the force attracting them decreases and all stays equal.

To take it further however, you could say that the mass of the star is increasing because it is taking matter from the planet whose mass is decreasing, and that would mean that the planet would have to accelerate to maintain it's orbit around the increasingly more massive star, which obviously it can't, so then yes it would gradually move towards it.

That's the limit of my old A-level physics! - I'm sure someone else can go into the fact that Newton's laws are less useful the bigger (or smaller) you go...
 
jimmymctavish said:
If you look at newton's law of universal gravitation F=(G*m1*m2)/r you'll see that the gravitational force is proportional to the mass of both objects, so as the mass of one decreases the force attracting them decreases and all stays equal.
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You've got that backwards, if I have two bodies, A & B with mass 3 and 2, which are 5 units apart F = 1.60152 × 10-11 m3 kg-1 s-2
If B loses 1 mass onto A now F = 1.06768 × 10-11 m3 kg-1 s-2
Additionally losing mass towards the star will provide a reactive force pushing the planet away.
 
OK now you've made me think! Always dangerous.

The force between the bodies will decrease as the disparity in the 2 masses increases, i.e. the maximum force will always be when the bodies are of equal mass.

As the mass of the planet decreases (and the star increases), the gravitational force between the bodies will decrease. Since the planet is now of a smaller mass it will require a smaller gravitational force to remain at the same radius of orbit, and as the gravitational force has decreased then that may well be what happens.

You have to do a F=ma or a=F/m to work out whether the planets orbit will decay or not. If the ratio of F:m stays the same then a (acceleration) will stay the same, and it is acceleration which keeps it in orbit.

In your example (i'll change constant G to 1 for simplicity as it doesn't change anything in this case)

State 1:

Ma = 3
Mb = 2
r = 5
G = 1

F = (1*3*2)/5 = 1.2

therefore acceleration of planet B = a = F/m = 1.2/2 = 0.6

That's the acceleration required to keep the planet in orbit.

In state 2:

Ma = 4
Mb = 1
r = 5
G = 1

F = (1*4*1)/5 = 0.8

The acceleration on planet B is now a = F/m = 0.8/1 = 0.8

That's a greater acceleration than is required to keep the planet in orbit (>0.6), and so the planet moves toward the star.

Which is what I finished on saying above.

I see your point about the mass leaving the planet toward the star causing an opposite force repelling the planet from the star, but I don't think it applies since the mass being lost isn't being ejected by the planet, it's being pulled by the star. It's like saying removing blutack from the a wall causes the wall to be repelled away from you.
 
jimmymctavish said:
OK now you've made me think! Always dangerous.

The force between the bodies will decrease as the disparity in the 2 masses increases, i.e. the maximum force will always be when the bodies are of equal mass.

As the mass of the planet decreases (and the star increases), the gravitational force between the bodies will decrease. Since the planet is now of a smaller mass it will require a smaller gravitational force to remain at the same radius of orbit, and as the gravitational force has decreased then that may well be what happens.

You have to do a F=ma or a=F/m to work out whether the planets orbit will decay or not. If the ratio of F:m stays the same then a (acceleration) will stay the same, and it is acceleration which keeps it in orbit.

In your example (i'll change constant G to 1 for simplicity as it doesn't change anything in this case)

State 1:

Ma = 3
Mb = 2
r = 5
G = 1

F = (1*3*2)/5 = 1.2

therefore acceleration of planet B = a = F/m = 1.2/2 = 0.6

That's the acceleration required to keep the planet in orbit.

In state 2:

Ma = 4
Mb = 1
r = 5
G = 1

F = (1*4*1)/5 = 0.8

The acceleration on planet B is now a = F/m = 0.8/1 = 0.8

That's a greater acceleration than is required to keep the planet in orbit (>0.6), and so the planet moves toward the star.

Which is what I finished on saying above.

I see your point about the mass leaving the planet toward the star causing an opposite force repelling the planet from the star, but I don't think it applies since the mass being lost isn't being ejected by the planet, it's being pulled by the star. It's like saying removing blutack from the a wall causes the wall to be repelled away from you.
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I forgot to account in my previous post for my assumption that the orbit would increase, I started to do the maths for this, then found this site :) http://cseligman.com/text/stars/masslosseffects.htm

Btw, the law of gravitation is over r^2, not r :)
 
That's an interesting site, although it's talking about the star losing mass as the inevitable result of nuclear fusion (presumably) rather than the planet losing mass due to it being all vaccuumed up by the immense mavity of a very nearby star.

Still if you want to account for that then I admit I can't compete :p

Btw, the law of gravitation is over r^2, not r :)
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Oh yeah! It was a hard night last night... :D
 
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