Habitable zone around white dwarfs?

In article ,
"Greg Neill" wrote:

I'm not so sure that one can emphatically rule out the
possibility that such an accretion disk could not form
an orbiting body.

The process of accretion ONTO the body isn't dependent on it being fed. Cut off
the feed of matter TO the accretion disc, and I cannot see why the existing
disc would not continue to deed ONTO the body.

Much would depend upon where in their
life cycles the two stars are. With a two star system
it is also possible to imagine capture scenarios.

It might be worthwhile, for the sake of argument, to simply
suppose that such planets could exist and move on to
addressing the actual question. That is, where is the
habitable zone around a white dwarf and does at least some
of it lie outside the Roche limit.

Considering the surface T of WD's and the energetics of the processes around
it, I'm not sure there is one.



--
COOSN-174-07-82116: Official Science Team mascot and alt.astronomy's favourite
poster (from a survey taken of the saucerhead high command).

Official maintainer of the supra-cosmic space fluid pump (Mon and Tues only).

In article ,
Phineas T Puddleduck wrote:

The process of accretion ONTO the body isn't dependent on it being fed. Cut
off
the feed of matter TO the accretion disc, and I cannot see why the existing
disc would not continue to deed ONTO the body.

Much would depend upon where in their
life cycles the two stars are. With a two star system
it is also possible to imagine capture scenarios.

It might be worthwhile, for the sake of argument, to simply
suppose that such planets could exist and move on to
addressing the actual question. That is, where is the
habitable zone around a white dwarf and does at least some
of it lie outside the Roche limit.

Considering the surface T of WD's and the energetics of the processes around
it, I'm not sure there is one.


To add some more depth.....


I can understand the analogy between this and projected planetary formation
models, but here we have a much more compact object and the disc itself is a
much more energetic system then the original planetary nebula dynamics.

The formation of the accretion disc is a pretty high energy event, and even in
the death throes of the disc (as in from the time the disc is now no longer fed
from the parent star) I don't think much matter will survive the death of the
disc.

For the disc to form, the star's have to be reasonably close together and this
means that any planetary bodies that form are going to have pretty chaotic
orbital parameters - and that isn't going to change even when the second star
goes WD as the potential well is going to stay largely the same.

They are the reasons why I think the idea of planetary formation around WD's is
very unlikely. Given a T_eff of around 10^5K means the habitable zone would
have to be far out, which is going to require a LARGE accretion disc to form a
possible planet out far enough to be in this zone. The accretion disc may leave
some matter far out from it as it empties, but I don't think there would be
enough matter.

The lack of nuclear reactions in the WD means the habitable zone will creep
with time as well.

Factor in the complex planetary gravitational dynamics in a two star system, I
think any planet that was LIKELY to survive the death of the other star will
find it self in a very odd orbit. Any gravitational slingshot that would throw
a planet to a stable orbit to BOTH WD's will more likely expel the planet from
the system.

Hence why the phrase "one in a billion" springs to mind ;-)

http://www.journals.uchicago.edu/ApJ...704/17704.html
Talks about Planet/WD/Pulsar - whcih is almost certainly going to have NO
habitable zone ;-)

"M4 contains a unique stellar/planetary system. It consists of a central tight
binary composed of an 11 ms pulsar (PSR B1620-26) and a stellar companion
(thought to be the white dwarf that spun up the neutron star) together with a
distant object possessing either a planetary mass in a low-eccentricity orbit
or a stellar companion in a highly eccentric one (Lyne et al. 1988; McKenna &
Lyne 1988; Backer, Foster, & Sallmen 1993; Michel 1994; Rasio 1994; Thorsett et
al. 1999; Ford, Joshi, & Rasio 2000). The former scenario was deemed early on
to be the more probable one. The existence of this triple system is of great
cosmogonic significance since, if primordial, it could suggest the presence of
numerous solar systems that formed early in the history of the universe."




--
COOSN-174-07-82116: Official Science Team mascot and alt.astronomy's favourite
poster (from a survey taken of the saucerhead high command).

Official maintainer of the supra-cosmic space fluid pump (Mon and Tues only).

"Phineas T Puddleduck" wrote in message
news
In article ,
"Greg Neill" wrote:

I'm not so sure that one can emphatically rule out the
possibility that such an accretion disk could not form
an orbiting body.

The process of accretion ONTO the body isn't dependent on it being fed.
Cut off
the feed of matter TO the accretion disc, and I cannot see why the
existing
disc would not continue to deed ONTO the body.

Why does matter fall into the accreting attractor?
It does so because it sheds angular momentum via
frictional losses. I can posit that a throttling
of the feed would reduce the amount of friction
caused by new material entering on non-circular
orbits. What remains could have a chance to
condense into substantial bodies.


Much would depend upon where in their
life cycles the two stars are. With a two star system
it is also possible to imagine capture scenarios.

It might be worthwhile, for the sake of argument, to simply
suppose that such planets could exist and move on to
addressing the actual question. That is, where is the
habitable zone around a white dwarf and does at least some
of it lie outside the Roche limit.

Considering the surface T of WD's and the energetics of the processes
around
it, I'm not sure there is one.

Distance always mitigates luminosity.

"Phineas T Puddleduck" wrote in message
news
In article ,
Phineas T Puddleduck wrote:

The process of accretion ONTO the body isn't dependent on it being fed.
Cut
off
the feed of matter TO the accretion disc, and I cannot see why the
existing
disc would not continue to deed ONTO the body.

Much would depend upon where in their
life cycles the two stars are. With a two star system
it is also possible to imagine capture scenarios.

It might be worthwhile, for the sake of argument, to simply
suppose that such planets could exist and move on to
addressing the actual question. That is, where is the
habitable zone around a white dwarf and does at least some
of it lie outside the Roche limit.

Considering the surface T of WD's and the energetics of the processes
around
it, I'm not sure there is one.


To add some more depth.....


I can understand the analogy between this and projected planetary
formation
models, but here we have a much more compact object and the disc itself is
a
much more energetic system then the original planetary nebula dynamics.

The formation of the accretion disc is a pretty high energy event, and
even in
the death throes of the disc (as in from the time the disc is now no
longer fed
from the parent star) I don't think much matter will survive the death of
the
disc.

For the disc to form, the star's have to be reasonably close together and
this
means that any planetary bodies that form are going to have pretty chaotic
orbital parameters - and that isn't going to change even when the second
star
goes WD as the potential well is going to stay largely the same.

They are the reasons why I think the idea of planetary formation around
WD's is
very unlikely. Given a T_eff of around 10^5K means the habitable zone
would
have to be far out, which is going to require a LARGE accretion disc to
form a
possible planet out far enough to be in this zone. The accretion disc may
leave
some matter far out from it as it empties, but I don't think there would
be
enough matter.

The lack of nuclear reactions in the WD means the habitable zone will
creep
with time as well.

Factor in the complex planetary gravitational dynamics in a two star
system, I
think any planet that was LIKELY to survive the death of the other star
will
find it self in a very odd orbit. Any gravitational slingshot that would
throw
a planet to a stable orbit to BOTH WD's will more likely expel the planet
from
the system.

Hence why the phrase "one in a billion" springs to mind ;-)


http://www.journals.uchicago.edu/ApJ...704/17704.html
Talks about Planet/WD/Pulsar - whcih is almost certainly going to have NO
habitable zone ;-)

"M4 contains a unique stellar/planetary system. It consists of a central
tight
binary composed of an 11 ms pulsar (PSR B1620-26) and a stellar companion
(thought to be the white dwarf that spun up the neutron star) together
with a
distant object possessing either a planetary mass in a low-eccentricity
orbit
or a stellar companion in a highly eccentric one (Lyne et al. 1988;
McKenna &
Lyne 1988; Backer, Foster, & Sallmen 1993; Michel 1994; Rasio 1994;
Thorsett et
al. 1999; Ford, Joshi, & Rasio 2000). The former scenario was deemed early
on
to be the more probable one. The existence of this triple system is of
great
cosmogonic significance since, if primordial, it could suggest the
presence of
numerous solar systems that formed early in the history of the universe."

All I can say is, while this is interesting in and of itself,
it doesn't answer the original question of where what we call
the habitable zone would be for a white dwarf. Surely it's
largely a matter of luminosity and distance.

In article ,
"Greg Neill" wrote:

All I can say is, while this is interesting in and of itself,
it doesn't answer the original question of where what we call
the habitable zone would be for a white dwarf. Surely it's
largely a matter of luminosity and distance.

Given a 5000-1000K surface T for a WD, its going to be AU and above.

--
COOSN-174-07-82116: Official Science Team mascot and alt.astronomy's favourite
poster (from a survey taken of the saucerhead high command).

Official maintainer of the supra-cosmic space fluid pump (Mon and Tues only).

In article ,
"Greg Neill" wrote:

The process of accretion ONTO the body isn't dependent on it being fed.
Cut off
the feed of matter TO the accretion disc, and I cannot see why the
existing
disc would not continue to deed ONTO the body.

Why does matter fall into the accreting attractor?
It does so because it sheds angular momentum via
frictional losses. I can posit that a throttling
of the feed would reduce the amount of friction
caused by new material entering on non-circular
orbits. What remains could have a chance to
condense into substantial bodies.

Only on the outer edge, the inner edge of the outer material would still feel a
frictional force. There would in essence be no difference for that material, as
it still feels a frictional slowdown from inner material.

I don't think there is any loss of accretion rate, much as the material in a
bath continues going down the plughole even when you turn the tap off ;-)

Also remember that the material will also be largely (i.e almost exclusively)
of such low Z that there is no real chance of any solid bodies forming. Its
going to be largely H and He if its removed from the outer surface of the other
star.



--
COOSN-174-07-82116: Official Science Team mascot and alt.astronomy's favourite
poster (from a survey taken of the saucerhead high command).

Official maintainer of the supra-cosmic space fluid pump (Mon and Tues only).

Orbitan kirjutas:
Question:

Is it possible to have a planet form, perhaps from the accretion disk
of a binary star, that would be at a location close enough in to a
white dwarf that it would get an illumination from the residual
radiation of the white dwarf that would be the equivalent of the
amount of radiation that falls on the earth from the sun, or would
that theoretical orbit be far within the Roche limit for a white dwarf?

It would not last long. White dwarfs cool relatively fast, so a planet
which gets the equivalent amount of radiation from the dwarf at some
time would soon be getting less.

BOTE calculations: let´s say Roche limit is at 8 hours orbit
(actually, I think it is less, but only slightly).

Procyon B is 0,6 solar masses. Sun has about 3 hour orbit at surface
(700 000 km radius), therefore 8 hour orbit around 1,4 millions of km.
Procyon B would have 8 hour orbit slightly closer, about 1,2 millions
km.

At 1,2 millions of km, Procyon B should be brighter than Sun from
Earth. So, you might have a planet of Procyon B.

On Jun 4, 8:38 am, wrote:
Orbitan kirjutas:

Question:

Is it possible to have a planet form, perhaps from the accretion disk
of a binary star, that would be at a location close enough in to a
white dwarf that it would get an illumination from the residual
radiation of the white dwarf that would be the equivalent of the
amount of radiation that falls on the earth from the sun, or would
that theoretical orbit be far within the Roche limit for a white dwarf?

It would not last long. White dwarfs cool relatively fast, so a planet
which gets the equivalent amount of radiation from the dwarf at some
time would soon be getting less.

Is this true? I got the idea that it took about twice the
age of the current universe for white dwarfs to cool
down enough that they were no longer 'white'. This
being related to the idea that they had a small surface
area from which they radiated energy.

Of course, the small size of the white dwarfs themselves
would be another factor along these lines.

'Red dwarfs', or small main sequence stars, have the
problem that they are so dim that their 'habitable
zones' are so close to the star that they will 'tidally
lock' any planets so far in, making them always
present the same side to the sun.

As far as the 'white dwarfs' are concerned, there
is the fact that the giant phases previous to their
formation in non-binary systems would envelope
anything that close in within the earlier solar
system that would have existed while the
star was on the main sequence.





BOTE calculations: let´s say Roche limit is at 8 hours orbit
(actually, I think it is less, but only slightly).

Procyon B is 0,6 solar masses. Sun has about 3 hour orbit at surface
(700 000 km radius), therefore 8 hour orbit around 1,4 millions of km.
Procyon B would have 8 hour orbit slightly closer, about 1,2 millions
km.

At 1,2 millions of km, Procyon B should be brighter than Sun from
Earth. So, you might have a planet of Procyon B.

On Jun 3, 5:16 pm, Phineas T Puddleduck
wrote:
In article ,
Phineas T Puddleduck wrote:





The process of accretion ONTO the body isn't dependent on it being fed. Cut
off
the feed of matter TO the accretion disc, and I cannot see why the existing
disc would not continue to deed ONTO the body.

Much would depend upon where in their
life cycles the two stars are. With a two star system
it is also possible to imagine capture scenarios.

It might be worthwhile, for the sake of argument, to simply
suppose that such planets could exist and move on to
addressing the actual question. That is, where is the
habitable zone around a white dwarf and does at least some
of it lie outside the Roche limit.

Considering the surface T of WD's and the energetics of the processes around
it, I'm not sure there is one.

To add some more depth.....

I can understand the analogy between this and projected planetary formation
models, but here we have a much more compact object and the disc itself is a
much more energetic system then the original planetary nebula dynamics.

The formation of the accretion disc is a pretty high energy event, and even in
the death throes of the disc (as in from the time the disc is now no longer fed
from the parent star) I don't think much matter will survive the death of the
disc.

For the disc to form, the star's have to be reasonably close together and this
means that any planetary bodies that form are going to have pretty chaotic
orbital parameters - and that isn't going to change even when the second star
goes WD as the potential well is going to stay largely the same.

They are the reasons why I think the idea of planetary formation around WD's is
very unlikely. Given a T_eff of around 10^5K means the habitable zone would
have to be far out, which is going to require a LARGE accretion disc to form a
possible planet out far enough to be in this zone. The accretion disc may leave
some matter far out from it as it empties, but I don't think there would be
enough matter.

The lack of nuclear reactions in the WD means the habitable zone will creep
with time as well.

Factor in the complex planetary gravitational dynamics in a two star system, I
think any planet that was LIKELY to survive the death of the other star will
find it self in a very odd orbit. Any gravitational slingshot that would throw
a planet to a stable orbit to BOTH WD's will more likely expel the planet from
the system.

Hence why the phrase "one in a billion" springs to mind ;-)

http://www.journals.uchicago.edu/ApJ...L/v597n1/17704...
Talks about Planet/WD/Pulsar - whcih is almost certainly going to have NO
habitable zone ;-)

"M4 contains a unique stellar/planetary system. It consists of a central tight
binary composed of an 11 ms pulsar (PSR B1620-26) and a stellar companion
(thought to be the white dwarf that spun up the neutron star) together with a
distant object possessing either a planetary mass in a low-eccentricity orbit
or a stellar companion in a highly eccentric one (Lyne et al. 1988; McKenna &
Lyne 1988; Backer, Foster, & Sallmen 1993; Michel 1994; Rasio 1994; Thorsett et
al. 1999; Ford, Joshi, & Rasio 2000). The former scenario was deemed early on
to be the more probable one. The existence of this triple system is of great
cosmogonic significance since, if primordial, it could suggest the presence of
numerous solar systems that formed early in the history of the universe."

--
COOSN-174-07-82116: Official Science Team mascot and alt.astronomy's favourite
poster (from a survey taken of the saucerhead high command).

Official maintainer of the supra-cosmic space fluid pump (Mon and Tues only).- Hide quoted text -

- Show quoted text -

Considering a similar subject, is it rather well
established that planets around pulsars were
formed at the time that the initial star formed,
and simply survived the supernova explosion
that formed the neutron star/pulsar, or are
some or most planets around pulsars, thought
to be the product of phenomenon that happened
after the pulsar formed?

Orbitan kirjutas:
On Jun 4, 8:38 am, wrote:
Orbitan kirjutas:

Question:

Is it possible to have a planet form, perhaps from the accretion disk
of a binary star, that would be at a location close enough in to a
white dwarf that it would get an illumination from the residual
radiation of the white dwarf that would be the equivalent of the
amount of radiation that falls on the earth from the sun, or would
that theoretical orbit be far within the Roche limit for a white dwarf?

It would not last long. White dwarfs cool relatively fast, so a planet
which gets the equivalent amount of radiation from the dwarf at some
time would soon be getting less.

Is this true? I got the idea that it took about twice the
age of the current universe for white dwarfs to cool
down enough that they were no longer 'white'. This
being related to the idea that they had a small surface
area from which they radiated energy.

Procyon B is hotter than Sun, at about 7500 K, at the age of 1,7
milliards of years. Keid B, of slightly lower mass, has temperature of
about 13 500 K - which should mean 10 times the luminosity. Perhaps
because it is younger. Both are white.

Of course, the small size of the white dwarfs themselves
would be another factor along these lines.

'Red dwarfs', or small main sequence stars, have the
problem that they are so dim that their 'habitable
zones' are so close to the star that they will 'tidally
lock' any planets so far in, making them always
present the same side to the sun.

As far as the 'white dwarfs' are concerned, there
is the fact that the giant phases previous to their
formation in non-binary systems would envelope
anything that close in within the earlier solar
system that would have existed while the
star was on the main sequence.





BOTE calculations: let´s say Roche limit is at 8 hours orbit
(actually, I think it is less, but only slightly).

Procyon B is 0,6 solar masses. Sun has about 3 hour orbit at surface
(700 000 km radius), therefore 8 hour orbit around 1,4 millions of km.
Procyon B would have 8 hour orbit slightly closer, about 1,2 millions
km.

At 1,2 millions of km, Procyon B should be brighter than Sun from
Earth. So, you might have a planet of Procyon B.