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(UPI)   Astronomers say dying stars may still host habitable planets, as well as the Oscars   (upi.com) divider line 4
    More: Interesting, planets, planetary habitability, white dwarfs, James Webb Space Telescope, astronomers, metallicity, Electromagnetic Spectrum, Earth-like planets  
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1455 clicks; posted to Geek » on 24 Apr 2013 at 11:42 PM (1 year ago)   |  Favorite    |   share:  Share on Twitter share via Email Share on Facebook   more»



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2013-04-25 11:48:13 AM  
1 votes:

simplicimus: Silly Questions: Don't white stars have a considerable gravity pull? Would't the planets be tidally locked?


They have no more gravity than an ordinary star of the same mass.  What you are thinking of is their extreme surface gravity but that's simply because they're smaller.

On the other hand, this article makes little sense.  I can't imagine an orbit in which a planet could be lifebearing around a white dwarf where it wasn't sterilized (or more likely destroyed) by the previous red giant phase.  Last I knew it wasn't settled whether the Earth will burn or not but even if we escape it will be a close call where the surface of the planet melts.  Once the red giant phase is over we will be much too far out to maintain life zone temperatures, not to mention that our volatiles will be gone.

Ed Grubermann: A planet in orbit around a white dwarf is would have to be incredibly close to the star in order to get any heat from it. Close enough that it would have been blown to bits when the star went super-nova. Possibly so close that it would have had to have been inside the original start before it exploded.


Stars big enough to supernova don't leave behind white dwarfs.  You get a white dwarf when a star below 1.44 solar masses runs out of helium.  It's too small to ignite carbon, the fires go out and it shrinks to an object of Earthlike size.  You basically have a great ball of carbon that's being squeezed so hard the electrons are squashed out of their orbits and wander freely.

dragonchild: Any planets in the Goldilocks zone before its expansion & collapse would be roasted clean, yes, but a lot can happen in several billion years -- the star could capture another planet, an outer planet could spiral inwards, or an inner (sterilized) planet can gradually accumulate water & an atmosphere from comet impact debris. To me, the biggest obstacle is that the white dwarf's temperature doesn't really stabilize on a "life needs time to evolve" timescale until it gets relatively cool. These things start out hotter than white-hot (emitting x-rays and UV) and over the course of several billion years will cool to surface temperatures lower than that of the Sun today. That makes the Goldilocks zone enough of a moving target to pose problems for life. An ideal candidate planet would orbit close to a cool white dwarf, but that means it starts out getting blasted by X-rays and UV.


Also, anything close enough in to be in the Goldilocks zone will be tidally locked.
2013-04-25 07:38:53 AM  
1 votes:

JasonOfOrillia: You can migrate to a dying star system if you want, Subby, but I'm going for a little more upside potential with a young system.


Why don't you have a seat over there?  Seriously, the upside to a white dwarf is that it's very stable.  They decay slowly and some of them pulse, but unlike actively fusing stars they're not going to flare, so you can orbit one pretty closely.

simplicimus: Would't the planets be tidally locked?


Depends on its distance, but tidal locking doesn't automatically doom a planet.  It presents problems, but life has options when there's a whole planet to work with.  For perspective, large patches of the Earth are almost inhospitable to life and there's ice on Mercury.

Darth_Lukecash: Huh, I thought a white dwarf wouldn't have any planets close enough, especially if it expanded.


The expansion makes a star very tenuous.  It doesn't get destroyed; it will continue orbiting inside the red giant.  That said, orbiting inside a giant star is the ultimate slow-roast.

2chris2: A planet which was any distance at all from a white dwarf would be a frozen rock. A planet which was close to one would, back before the star became a white dwarf, have had all of its atmosphere blasted away. So I'm not sure how you get a planet with life orbiting a white dwarf.

Any planets in the Goldilocks zone before its expansion & collapse would be roasted clean, yes, but a lot can happen in several billion years -- the star could capture another planet, an outer planet could spiral inwards, or an inner (sterilized) planet can gradually accumulate water & an atmosphere from comet impact debris.  To me, the biggest obstacle is that the white dwarf's temperature doesn't really stabilize on a "life needs time to evolve" timescale until it gets relatively cool.  These things start out hotter than white-hot (emitting x-rays and UV) and over the course of several billion years will cool to surface temperatures lower than that of the Sun today.  That makes the Goldilocks zone enough of a moving target to pose problems for life.  An ideal candidate planet would orbit close to a cool white dwarf, but that means it starts out getting blasted by X-rays and UV.
2013-04-25 04:59:17 AM  
1 votes:

simplicimus: Silly Questions: Don't white stars have a considerable gravity pull? Would't the planets be tidally locked?


The gravity pull would be less that the original star since it had previously blown away it outer layers. The only way I see to have a habitable star around a white dwarf is to have one accrete around it after the star blows up and loses a considerable chunk of mass (and gravity). Seems in most situations the planets would have been engulfed by the previous red giant that was there, have its atmosphere blown away, and/or likely get tossed into space or a very elliptical orbit.
2013-04-25 02:38:08 AM  
1 votes:
A planet which was any distance at all from a white dwarf would be a frozen rock.  A planet which was close to one would, back before the star became a white dwarf, have had all of its atmosphere blasted away.  So I'm not sure how you get a planet with life orbiting a white dwarf.
 
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