planet schmanet, it's probably a brown dwarf!

I think this new "planet" detected in a 13 billion year old
star system is most likely really a brown dwarf. Ahh, but
you say that 2.5 MJup. is too low to be a brown dwarf!
Firstly, no, we don't really know that, not yet. Secondly,
let's assume for the moment that the mass limit assumption
for brown dwarfs holds, imagine this scenario. You've got
3 stars in a system, a really massive star (a few solar
masses), a kinda low mass star (just under one solar mass,
or thereabouts), and a dinky brown dwarf around a dozen MJ.
Now, the big star goes off the main sequence really soon,
turns into a red giant then supernovas. It's just a hunch,
but I'm betting that the blast from a type-II supernova is
gonna brush off a teensy weensy bit of the outer atmosphere
of a friend the brown dwarf. Then you've got the other
star, which spends several billion years on the main
sequence, but eventually it too goes into a red giant phase.
First it heats up and its outer atmosphere balloons up,
and then it blows off that outer atmosphere in the creation
of enormously powerful stellar winds (which create a
temporary planetary nebula). This is just a hunch too,
but I bet both the red giant phase and the strong stellar
winds phase might, just might, strip off a wee bit of the
brown dwarfs mass. Ahh, but wait, there's more! There was
almost certainly a scuffle involving the stars when they
first got together and the poor little brown dwarf was
tossed around quite a bit, there's plenty of opportunity
in that, I think, for a fair amount of mass loss. So
you've got three events that are likely to remove a fair
amount of mass from a brown dwarf, are they powerful enough
to remove 80% of the mass of a brown dwarf? I don't think
that question has been answered satisfactorily yet. Nor has
the question of the true mass distribution of objects which
coalesce directly from stellar nebulae (i.e. stars, including
brown dwarfs.


I think there is a chance this object is a planet (i.e.
was formed from a proto-planetary disc), but so far I don't
think enough evidence has been presented to dismiss the
possibility that it might be a brown dwarf which has lost
mass.

"Christopher M. Jones" wrote:

I think this new "planet" detected in a 13 billion year old
star system is most likely really a brown dwarf. Ahh, but
you say that 2.5 MJup. is too low to be a brown dwarf!
Firstly, no, we don't really know that, not yet.

These are just terms that we use but haven't defined yet, so saying,
"It's not an X, it's a Y" is at this point pure semantics. I'm not
familiar with any widespread acceptance of your use of the term _brown
dwarf_ to mean "very large gas giant that evolved as the center of a
protoplanetary disk, as opposed to on the periphery of one," and as I
pointed out in the thread we were both involved in when this last came
up, even that distinction is arbitrary and unclear -- all one has to do
is consider multiple star systems formed from the same protostellar
cloud to see that such a hard dividing line can't be all that
significant in a classification system. Reduce the mass of the smaller
star, and at some point it becomes "less than a star" and at some other
point it becomes "just a planet." Where you draw those lines are
arbitrary (the second much more so!), but it's a continuous spectrum.

I think there is a chance this object is a planet (i.e.
was formed from a proto-planetary disc), but so far I don't
think enough evidence has been presented to dismiss the
possibility that it might be a brown dwarf which has lost
mass.

I don't know, this sounds like an astonishingly large amount of sheer
speculation based on a system we know so very little about.

--
Erik Max Francis && && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ You are inspiration to my life / You are the reason why I smile
\__/ India Arie

(Brian Davis) writes:

Christopher M. Jones wrote:
[...]
This is just a hunch too, but I bet both the red giant phase
and the strong stellar winds phase might, just might, strip
off a wee bit of the brown dwarfs mass.

Why? A hunch is a bit rough here. The stellar wind wouldn't touch a
brown dwarf (magnetic fields), and heating by a red giant phase couldn't
drive off much at all. This is not a very good mass loss mechanism.

The "pulsar wind," consisting of mostly of highly energetic electron/positron
ambiplasma plus a smattering of ions and a LOT of energetic X-rays and
gamma rays, might be another matter. (We are talking here about electrons,
positrons and ions with cosmic-ray scale energies; the "rigidity" of the
planetary magnetic field is likely to be insufficient to deflect them...
We have observed at least one pulsar "evaporating" a companion star this way,
and stars typically have stronger magnetic fields than planets...)


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

"Erik Max Francis" wrote:
"Christopher M. Jones" wrote:

I think this new "planet" detected in a 13 billion year old
star system is most likely really a brown dwarf. Ahh, but
you say that 2.5 MJup. is too low to be a brown dwarf!
Firstly, no, we don't really know that, not yet.

These are just terms that we use but haven't defined yet, so saying,
"It's not an X, it's a Y" is at this point pure semantics.

I beg to differ. My own definitions of X and Y are quite clear
(formation via condensing nebula or via a proto-planetary disc).
I think that my definitions are the only ones that really make
sense in regard to planets vs. stars. I also think that they
are the same basic definitions as the most popular or at least
the "leading" definitions (i.e. the definitions used by those
who's work is the most important in the field). Furthermore, I
am very confident that eventually they will be the official and
standard and majority accepted definitions. Nevertheless, I
will admit that this definitional area of star vs. planet is one
which is rather craptistic at the moment, and there's a lot of
"accepted definitions and conventions" which are not helpful and
some which are in fact detrimental. And, I'll also admit that
this whole topic (definitions and all) is very short on
observational evidence and especially statistics at the moment.

Given all that, I'll still stick by my definitions. In the
future I'll try to be more careful to explain what I mean more
precisely rather than using shorthand, non-standard definitions.
For now, just assume that when I say "brown dwarf" or "star" I
mean an object which condensed directly from a nebula, either
alone or in parallel with the formation of other stars, and when
I say "planet" I mean an object which condensed from a proto-
planetary disc, which itself was formed after and in parallel
with the condensation of its parent star.


I'm not
familiar with any widespread acceptance of your use of the term _brown
dwarf_ to mean "very large gas giant that evolved as the center of a
protoplanetary disk, as opposed to on the periphery of one," and as I
pointed out in the thread we were both involved in when this last came
up, even that distinction is arbitrary and unclear -- all one has to do
is consider multiple star systems formed from the same protostellar
cloud to see that such a hard dividing line can't be all that
significant in a classification system. Reduce the mass of the smaller
star, and at some point it becomes "less than a star" and at some other
point it becomes "just a planet." Where you draw those lines are
arbitrary (the second much more so!), but it's a continuous spectrum.

Proto-planetary disc formation is a long process in comparison
to proto-stellar nebula collapse. Of special interest is the
process by which the material in the disc becomes enriched in
ices and dust and depleted in gases, as well as the formation
of the disc shape itself. Of secondary interest is the
difference between the process of gravitational collapse of a
gas cloud vs. accretion. Now, it looks like there are
formation processes for gas rich planets from proto-planetary
discs which do not necessarily rely on accretion and which
blur the line somewhat between star formation and planet
formation, but not completely. There are many distinguishing
characteristics between the two formation processes and their
results, but I don't really feel like delving into that
discussion right at the moment, as it's a long one, perhaps
sometime later. For the mean time, note that the major
difference lies in the composition of the materials going into
the formation of the object. Proto-planetary discs are
enriched to a high degree in dusts and ices (i.e. "metals").
Even for Jovian planet formations the increase in abundances
of dusts and ices in the planetary makeup is enormous (even
though they might still be very minor constituents in
comparison to H and He).

Also, as I've said before, but perhaps not forcefully enough,
I think the distinction between planets and brown dwarfs
based on mass is bogus in the extreme. Obviously, pulsars,
white dwarfs, black holes, and main sequence stars of 1 solar
mass are *not* the same objects nor necessarily have the same
origins, but by the brown dwarf / planet system they would be
presented as equivalent objects. That's just stupid. It's a
more extreme case of the man with a hammer problem, not only
does everything look like a nail but the world is divided
into only two important categories, nails and non-nails.


I think there is a chance this object is a planet (i.e.
was formed from a proto-planetary disc), but so far I don't
think enough evidence has been presented to dismiss the
possibility that it might be a brown dwarf which has lost
mass.

I don't know, this sounds like an astonishingly large amount of sheer
speculation based on a system we know so very little about.

Precisely. That's what I take issue with. That's why I
think it's critically important to consider alternatives
to the narrow mule-headed view that if it's under 13 MJ
it's a "planet".

Even more so since the significance put on this discovery
has been very, very clearly due to the assumed formation
route of the object. Which, if it were a planet by *my*
definition would mean it was formed from a metal enriched
proto-planetary disc. And, obviously, if this system
dates back to the dawn of the Universe or thereabouts
there was very little chance of the possibility of such a
metal enriched *anything*.


Getting back to alternate hypothesis for the formation of
this 2.5 MJ object, I thought of another scenario for
substantial mass loss. The theory in the paper is that
the stellar system was assembled after the fact due to
stellar encounters near the center of a dense globular
cluster (specifically, the posit that the pulsar nee
massive star entered the system of the white dwarf nee
red dwarf plus "planet" and caused a reorginazation where
the planet ended up in orbit of the binary stars). Their
very own scenario has the "planet" only a few AU from the
white dwarf star during its earlier lifetime. By that
it's enormously plausible that the object was well within
the stellar atmosphere or very near it during the star's
red giant phase for a considerable period of time and
consiquently burned off a lot of mass.

"Brian Davis" wrote:
Upshot: in all likelyhood, it really is a 2.5 MJup object.

For clarity's sake I'll make this short. There is no good
evidence at all that a 2.5 MJup object is necessarily only
a "planet" and never a "brown dwarf".

In article ,
"Christopher M. Jones" writes:
... imagine this scenario. You've got
3 stars in a system, a really massive star (a few solar
masses), a kinda low mass star (just under one solar mass,
or thereabouts), and a dinky brown dwarf around a dozen MJ.
Now, the big star goes off the main sequence really soon,
turns into a red giant then supernovas. It's just a hunch,
but I'm betting that the blast from a type-II supernova is
gonna brush off a teensy weensy bit of the outer atmosphere
of a friend the brown dwarf.

"Teensy weensy" sounds about right. Why not try calculating the
momentum in the supernova ejecta and what fraction intercepts the
brown dwarf? How much atmosphere can that strip away?

I suspect direct heating might be more of an issue but haven't done
the calculation. (It doesn't look simple. While the heating is
intense, a large fraction of the heat will probably be reradiated.
Now that I think about it, it isn't obvious to me that neutrino
heating is negligible.)

Then you've got the other
star, which spends several billion years on the main
sequence, but eventually it too goes into a red giant phase.
First it heats up and its outer atmosphere balloons up,
and then it blows off that outer atmosphere in the creation
of enormously powerful stellar winds (which create a
temporary planetary nebula). This is just a hunch too,
but I bet both the red giant phase and the strong stellar
winds phase might, just might, strip off a wee bit of the
brown dwarfs mass.

I think you'll lose that bet, but let's see the calculation.

Ahh, but wait, there's more! There was
almost certainly a scuffle involving the stars when they
first got together and the poor little brown dwarf was
tossed around quite a bit, there's plenty of opportunity
in that, I think, for a fair amount of mass loss.

As others have said, there is no obvious mechanism for mass loss via
gravitational interactions.

You are right, I think, to be skeptical of any proposed formation
scenario. We simply have too few examples and know too little about
planet formation to be sure of anything in this subject. Still, it's
an intriguing observation.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)

"Christopher M. Jones" wrote:

For clarity's sake I'll make this short. There is no good
evidence at all that a 2.5 MJup object is necessarily only
a "planet" and never a "brown dwarf".

Even if we accept your definitions (based on a distinction that as far
as I know the astronomical community does not weigh in strongly on),
there's no reason to think that it isn't, either. In your response, we
saw you speculate _quite_ wildly in order to try to get a body with the
right mass that once had a greater mass, in order to back up your
hypothesis.

This sounds more like pure guesswork and handwaving than astrophysics.
Maybe it was once a Real Honest to God Brown Dwarf (whatever one might
mean by that) but had most of its mass stripped away by aliens who
wanted to use it for fusion fuel? We're literally in that same realm of
speculation here.

--
Erik Max Francis && && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ It is much safer to obey than to rule.
\__/ Thomas a Kempis

(Brian Davis) wrote in message om...

snip

First, the research are proposing a late capture sequence for the
objects - they are not thought (to my knowledge?) to be co-eval. Not
that this invalidates your theory, but it brings up one of my own -
that assuming a formation time for the 2.5 MJup object that is the
same as the globular might be pushing it. Doesn't work for blue
stragglers, and this might be a similar "recent" object. I wonder if
anyone here knows how far out the 2.5 MJup object is? The binary pair
at the center has a 6 month orbit, so it's got to be out a ways...
what's the expected lifetime for such a system in the heart of M4,
with more than a few disturbing influences swinging around?

snip

I seem to recall hearing that the odds are pretty good that the system
survives. It turns out that even in a crowded globular cluster,
there's a lot of space between stars. Passes near enough to
significantly perturb a planet would be rare (er, over a few billion
years).


Karl Hallowell

Erik Max Francis writes:

"Christopher M. Jones" wrote:

Precisely. That's what I take issue with. That's why I
think it's critically important to consider alternatives
to the narrow mule-headed view that if it's under 13 MJ
it's a "planet".

The terminology isn't even _that_ well nailed down; the 13 Jupiter mass
limit is a common convention, but as far as I know it has no official
endorsement as a classification criterion by the IAU -- which has _no_
objective classification criteria for practically any of the terms that
are used to identify substellar objects.

It _does_, however, have a semi-objective basis in that the 13 M_Jupiter
dividing line is the point at which the object becomes massive enough to
start fusing deuterium in its core. So, it may not be a "star" in the
usual sense of the word, but it's not exactly a "planet," either...

It should be noted that one of the reasons why the IAU has not yet managed
to decide on and "official" definition of terms like "planet" is that
nearly every definition of "planet" that anyone has been able to come up with
is falsified by some obeject within our own solar-system... :-/


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

"Gordon D. Pusch" wrote:

It _does_, however, have a semi-objective basis in that the 13
M_Jupiter
dividing line is the point at which the object becomes massive enough
to
start fusing deuterium in its core. So, it may not be a "star" in the
usual sense of the word, but it's not exactly a "planet," either...

The 13 Jupiter mass dividing line is "arbitrary" in the sense that you
could have picked some other dividing line, but it definitely is
specific and indicative of a characteristic somewhere between planets
and stars, as you say.

It should be noted that one of the reasons why the IAU has not yet
managed
to decide on and "official" definition of terms like "planet" is that
nearly every definition of "planet" that anyone has been able to come
up with
is falsified by some obeject within our own solar-system... :-/

Indeed. A planet is what the IAU says is a planet; there is no, and has
never been, any objective definition. The same is certainly true of
brown dwarfs, which I'm not even sure the IAU has ever used as an
official designation (though they may have).

Enthusiasts tend to severely overestimate the usefulness of objective
criteria for defining asteroids, comets, planets, and so on. What
matters is the object and its properties, not which classification name
we attach to it.

--
Erik Max Francis && && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ Of war men ask the outcome, not the cause.
\__/ Seneca