Via Space.com: http://www.livescience.com/space/sci...nt_planet.html

This article brings up a question I've always had about the expulsion of the outer layers of a star during the red giant phase. How violent would that expulsion be?

This also begs the question of how the planet remained a gas giant during the loss of the star's outer layers.

Can't get the original article, as I don't subscribe to Nature.

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I don't know. That's why I'm asking--Noclevername

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Science is a way of thinking much more than it is a body of knowledge--Carl Sagan (1934-1996)

The title of this thread is somewhat misleading because V391 Pegasi is not yet a white dwarf. Anyway, the first white dwarf planets will be most likely discovered by the same method.

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Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
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I asked about this a while back...

http://www.bautforum.com/questions-a...ite-dwarf.html

Then don't these results contradict what Tim Thompson said:

?

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The dose makes the poison--Paracelsus (1493-1541) http://en.wikipedia.org/wiki/Paracelsus

I don't know. That's why I'm asking--Noclevername

Intelligence may not be clearly defined, but you know stupid when you see it--Noclevername

Science is a way of thinking much more than it is a body of knowledge--Carl Sagan (1934-1996)

Well for starters, the object in the OP isn't a proper white dwarf. For seconds, it's about three times the mass of Jupiter and not a flimsy little rockball like the Earth .

True enough, but it's former orbit has been estimated at 1 AU--earth orbit size--and, compared to the mass of a star, even a planet three times Jupiter's size is not that big.

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The dose makes the poison--Paracelsus (1493-1541) http://en.wikipedia.org/wiki/Paracelsus

I don't know. That's why I'm asking--Noclevername

Intelligence may not be clearly defined, but you know stupid when you see it--Noclevername

Science is a way of thinking much more than it is a body of knowledge--Carl Sagan (1934-1996)

You'd be surprised. You can stick Jupiter itself at 1 AU from a giant star that's 5000 times more luminous than Sol and even though the cloudtop temperature would be about 2350 K it still wouldn't lose its hydrogen (at least not from the temperature alone. The solar wind might knock a bit off, but I don't think it'd be enough to cause the planet to lose all its mass).

I'm wondering how the planet has gained momentum and is now farther from the star (unless "separated" somehow means surface-to-planet). I'm more used to the binary model where a secondary star inside the expanding/ejecting envelope loses momentum and spirals in. I don't see why a planet wouldn't do the same thing, unless maybe it's tidal-locked to the subdwarf.

As already mentioned, the host star in this case is not a white dwarf. V 391 Pegasi is a horizontal branch star, which means that it has passed through the red giant stage of stellar evolution, but has not yet gone through the asymptotic giant branch (AGB). So, from my earlier comments noted by Paracelsus: "They conclude that even planets as massive as Jupiter, and as far out as 3-5 AU, cannot survive the formation of a planetary nebula for a 1 solar mass star.". Planetary nebulae form after the AGB stage, and as my LAAS bulletin article points out, even Earth should survive (barely) the red giant stage of evolution of a 1 solar mass star (i.e., the sun). So the presence of a 3.5 Jupiter mass planet around V 391 Pegasi is not a contradiction of earlier information.

As it turns out, V 391 Pegasi is a highly unusual star, which lost far more mass during the red giant stage than one would expect (the Nature paper, not avalable online, points out that 98% of solar mass stars do not evolve as has V 391 Pegasi). As the star loses mass, planets migrate away from the star, a chase that I describe in my LAAS bulletin article. At 3.5 Jupiter masses the planet is too massive to succumb to gas drag in the stellar wind, and to far out (1 AU at first) to be swallowed by the star (which only reaches 0.7 AU). So again the survival of the planet does not look like a real surprise to me.

It's the AGB stage that will be fatal to Earth, and might be fatal to this planet. But V391 Pegasi will probably never get off the horizontal branch to become an AGB star, because it lost so much mass as a red giant. Starting out at 0.9 solar masses, it now sits at 0.5 solar masses. AGB star are characterized by carbon-oxygen cores, but V 391 Pegasi has a helium core. It might burn helium into carbon, but I doubt it with such a low mass, and I am pretty sure that a 0.5 solar mass star can't build the core temperature required to fuse carbon into oxygen. So I don't think this star is going to do anything dramatic. At this point, a 3.5 Jupiter mass planet at 1.7 AU from the star has a secure future.

Curiously, while I am unaware of any confirmed planets known around a white dwarf star (Livio, Pringle & Wood, 2005; Friedrich, et al., 2006), there is a planet in a triple system with a white dwarf and pulsar B 1257+12 (Wolszczan, 1994), and evidently another known system involving pulsar B 1620-26 in globular cluster M4 (Ford, et al, 2000). Thoise planets either survived a supernova (unlikely), or were more likely created in the fallback disks of the supernovae that created the pulsars (Menou, Perna & Hernquist, 2001; Currie & Hansen, 2007). Planets around pulsars beats planets around white dwarfs for weird in my book.

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The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell

OIC. Thanks for the clarification, Tim!

Yes, a planet orbiting a pulsar would be very strange--and probably not habitable, I would think.

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The dose makes the poison--Paracelsus (1493-1541) http://en.wikipedia.org/wiki/Paracelsus

I don't know. That's why I'm asking--Noclevername

Intelligence may not be clearly defined, but you know stupid when you see it--Noclevername

Science is a way of thinking much more than it is a body of knowledge--Carl Sagan (1934-1996)

V391 Pegasi is just a weirdo . I guess what happens to it depends on whether its outer layers are convecting and it can burn up all its hydrogen to become a Helium Dwarf, or if it's able to burn hydrogen in shells around the growing helium core... but I'd guess it'll just burn out eventually (after a long time).

@ Tim Thompson :

"Curiously, while I am unaware of any confirmed planets known around a white dwarf star (Livio, Pringle & Wood, 2005; Friedrich, et al., 2006), there is a planet in a triple system with a white dwarf and pulsar B 1257+12 (Wolszczan, 1994), and evidently another known system involving pulsar B 1620-26 in globular cluster M4 (Ford, et al, 2000). Those planets either survived a supernova (unlikely), or were more likely created in the fallback disks of the supernovae that created the pulsars (Menou, Perna & Hernquist, 2001; Currie & Hansen, 2007). Planets around pulsars beats planets around white dwarfs for weird in my book."

Yes indeed.

Except the pulsar planets around PSR 1257+12 were around a single pulsar & the milisecond pulsar-white dwarf-planet system was the one around PSR B1620-26 in Messier 4 -the globular cluster near the bright red supergiant Antares.

From my own compiled summary file of exoplanets (kept so I can keep 'em all straight) :

PSR B 1257+12 : Discovered in 1991 these pulsar planets were the first ever found. Four very low mass worlds orbit a pulsar with the inner three spaced like a half-sized model of our inner solar system and the outermost just 1/5th Pluto’s mass at a distance equivalent to the asteroid belt in our system.

&

PSR B 1620-26 b, “Methuselah” or “Genesis” planet : The oldest exoplanet and second to orbit a pulsar, it is located inside the globular cluster M4 orbiting a tight pulsar-white dwarf binary. The superjovian planet has the lowest mass but largest diameter in that system versus the Earth-sized white dwarf and city-sized pulsar! The Genesis planet has an estimated age of 12.7 billion years old.

Hope that helps.

(NB almost 2 years..)

I keep seeing this thread on the main page and can't help but feel sorry for the Caucasian dwarf.

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Meet the OOONG TOE.

This was covered at length in the latest issue of Scientific American. Ultimately, the Universe may well be chuckfull of planets.

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"Science is physics and astronomy." -Me
"There is absolutely no law in physics that prevents time travel." -Dr. Michio Kaku

I have no doubt that the Universe is teaming with planets. From our meager poking around in our local stellar neighborhood we are seeing hundreds of them. I suspect that most stars do have them, save the super massive ones that blow they're surrounding ring away. It's just a matter of finding the ones that can sustain life that is going to be the real search.

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Science may set limits to knowledge, but should not set limits to imagination.
Bertrand Russell (1872 - 1970)

Ooooo, I think I thought a thought. Ooo I did, I did, I did think a thought.

I am of the opinion that the formation of planets around stars is inevitable. If you've read the article in Scientific American, planets can apparently form even around dead stars. So, if they have the gut to form around such stars, why wouldn't we expect them to form around perfectly normal stars in the middle of their lives?

Seems pretty obvious to me that we're living in an ocean gloriously filled with planets of all kinds. And, given that, saying that life may not exist elsewhere is just complete nonsense, in my opinion.

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"Science is physics and astronomy." -Me
"There is absolutely no law in physics that prevents time travel." -Dr. Michio Kaku

Visibly... not visibly a white dwarf... for all we know it might not even be there any more.

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