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Durakken
2008-Nov-11, 11:33 PM
When a binary, trinary, or greater star system forms is it likely that it will have anywhere near the number of planets in our solar system, terrestrial or gaseous...

it seems to me that it would be unlikely that there would be many planets in a multi star system and if there are it's even more unlikely they'd be gaseous but i read that about 60% would be able to support life, but how much metal might they have in them and how often might they appear...

On a side note... anyone got any clue how many black holes are in a 1000ly^2 range on average?

StupendousMan
2008-Nov-12, 12:18 AM
On a side note... anyone got any clue how many black holes are in a 1000ly^2 range on average?

Well, if you are talking about ordinary stellar-mass black holes, a good starting point would be to take a census of the number of stars with mass greater than, say, 20 solar masses. After all, it is those very massive stars which can turn into black holes. In the disk of a spiral galaxy, the density of these very massive stars might be reasonably large; in the halo, probably not.

Of course, that's just a starting point, since all you can see are the CURRENT massive stars, while it's the entire set of all PAST massive stars which could have created black holes. So you'd have to do quite a bit of modeling to make the estimate.

On the observational side, the MACHO project and its kin (EROS and OGLE) can provide some limits on the density of black holes in the Milky Way; that was one of their original goals. Go to ADS and do some reading!

Eroica
2008-Nov-13, 11:15 AM
When a binary, trinary, or greater star system forms is it likely that it will have anywhere near the number of planets in our solar system, terrestrial or gaseous...If a binary system has two stars each about the size of the Sun, then it probably formed from about twice as much material as was in the Solar nebula, so why shouldn't it be able to form at least as many planets as the Solar System?

As for trinary and higher multiple systems, they always consist of close binaries and more distant singletons (eg the Alpha Centauri system), so the same principle applies.

Durakken
2008-Nov-13, 11:49 AM
My thinking is that it takes more material to form those stars and thus would have less material to form the planets, but of course i didn't think about bigger nebulas...

so would 3-8 planets be about right? with a 50/50 chance on it being terrestrial/gaseous?

cjameshuff
2008-Nov-13, 01:33 PM
My thinking is that it takes more material to form those stars and thus would have less material to form the planets, but of course i didn't think about bigger nebulas...

That, and gas giants/stars would tend to eject planets or disrupt their formation. Look at our own system...0.39 AU, 0.72 AU, 1 AU, 1.5 AU...then nothing but a sparse field of rocks (well, and Ceres) until you reach Jupiter at 5.2 AU.



so would 3-8 planets be about right? with a 50/50 chance on it being terrestrial/gaseous?

If you look at initial formation, probably considerably more small, rocky planets, most of them having been ejected from the system or collided or been disrupted by near misses when the system was younger.

AndreasJ
2008-Nov-13, 03:19 PM
On a side note... anyone got any clue how many black holes are in a 1000ly^2 range on average?

I assume you meant 1000 ly^3?

Also, are looking for the average black hole density of the universe at large (it's very close to zero) or that of, say, our galaxy (I don't know it but it should be appreciable).

Durakken
2008-Nov-13, 05:38 PM
I assume you meant 1000 ly^3?

Also, are looking for the average black hole density of the universe at large (it's very close to zero) or that of, say, our galaxy (I don't know it but it should be appreciable).

squared...1000x1000x1 is what i am looking for but cubed can be used to find this too as it should be the same percent any way you look at it.

i have to imagine it less than 1% though as i don't think that there would be more blackholes than stars...

And I mean in our galaxy...

if you take and multiply it out there is 50 trillion lys for stars...1% of that is 500billion, but half of that is empty space (meaning the average density is 2%), but then about half of the space that has stars in it has a denser population...which means that the core has 3% density while the arms have 1%... so for black holes it has to be similar, but less than the overall number of stars...

Ilya
2008-Nov-13, 05:55 PM
Unless the stars in question are VERY far apart, a multiple star system does not have as many stable orbits. Alpha Centauri A and B come within 11.2 AU (Sun-Earth distance) of each other at closest approach; thus planets can exist only within about 2.5 AU from either one.

astromark
2008-Nov-13, 06:23 PM
The OP is a little more complex than Yes / No...
In order to know how many black holes within a distance from us we need to know how many stars with mass sufficient to form such and what percentage of them might have already done so... That could be a lifetimes work. Would you accept the idea that in the central bulge and spiral arms the massive high energy stars might be more than those found out in the suburbs.
As to planets, I would guide you to consider that the planetary disks and the way they settle over time leads me to think that planets are the normal. Terrestrial and gaseous. Binary systems are a indicator of vast planetary disks. I trust you will not find a easy number to answer your questions. Much research will enlighten you further. Much information has been researched well and finding it on the net is in itself a weeks work.

Eroica
2008-Nov-14, 11:51 AM
Unless the stars in question are VERY far apart, a multiple star system does not have as many stable orbits. Alpha Centauri A and B come within 11.2 AU (Sun-Earth distance) of each other at closest approach; thus planets can exist only within about 2.5 AU from either one.I have read that a planetary orbit will be stable if the separation of the stars at periapsis is more than three times the planet's aphelion distance.

So Alpha Centauri A and B could each have stable terrestrial planets like the four in our Solar System.

Ilya
2008-Nov-14, 02:12 PM
Well, yes. "Within 2.5 AU" does include Mars orbit.

timb
2008-Nov-14, 03:07 PM
Planets don't only have to have stable orbits, but they must have had a way to get there. In Planet formation in the habitable zone of alpha Centauri B, Thebault et al. find


We study here if such habitable planets can form, by numerically investigating
the planet-formation stage which is probably the most sensitive to binarity effects: the mutual
accretion of km-sized planetesimals. Using a state-of-the-art algorithm for computing the im-
pact velocities within a test planetesimal population, we find that planetesimal growth is only
possible, although marginally, in the innermost part of the HZ around 0.5AU. Beyond this
point, the combination of secular perturbations by the binary companion and gas drag drive
the mutual velocities beyond the erosion limit.


The situation regarding aCen A seems rather worse. The problem is that the affect of the companion dynamically excites the planetesimals, leading to much greater collision velocities. These high speed collisions tend to break up the planetesimals, rather than agglomerate them into planetary embryos.

Eroica
2008-Nov-18, 10:07 AM
Good point, timb! I never considered that problem.

Eroica
2008-Nov-21, 09:08 AM
Planets don't only have to have stable orbits, but they must have had a way to get there. In Planet formation in the habitable zone of alpha Centauri B, Thebault et al. find... The situation regarding aCen A seems rather worse. The problem is that the affect of the companion dynamically excites the planetesimals, leading to much greater collision velocities. These high speed collisions tend to break up the planetesimals, rather than agglomerate them into planetary embryos.
Terrestrial Planet Formation in Binary Systems (http://arxiv.org/abs/0705.3444v1) by Quintana and Lissauer seems to disagree:


Our simulations show that giant and stellar companions not only truncate the disk, but hasten the accretion process by stirring up the planetary embryos to higher eccentricities and inclinations. Terrestrial planets similar to those in our Solar System formed around individual stars in simulations with the binary periastron (closest approach) greater than about 5 AU.

In simulations of the Alpha Centauri System (with various parameters), they consistently got a few terrestrial planets in stable orbits.

AndreasJ
2008-Nov-21, 09:44 AM
squared...1000x1000x1 is what i am looking for but cubed can be used to find this too as it should be the same percent any way you look at it.
A block of 1000 x 1000 x 1 light years has a volume of 1,000,000 cubic light years.

i have to imagine it less than 1% though as i don't think that there would be more blackholes than stars...

And I mean in our galaxy...

if you take and multiply it out there is 50 trillion lys for stars...1% of that is 500billion, but half of that is empty space (meaning the average density is 2%), but then about half of the space that has stars in it has a denser population...which means that the core has 3% density while the arms have 1%... so for black holes it has to be similar, but less than the overall number of stars...

I can't make much sense of this. You seem to be saying that the galaxy is 2% stars by volume? That's many orders of magnitude too high.

Durakken
2008-Nov-22, 07:30 PM
There are 1million stars in a 1000ly^3 area, or 1,000,000,000, or if you cut it down that is 1/1000 which is .5%

If you consider the size of the galaxy is 100,000x100,000x1,000(or 5,000) you get 10,000,000,000,000 light years... 0.5% of that is 50 billion(or 250 billion) stars... of course that is if you take the entire area...

unfortunately 50-70% of that space is empty so that number is lowered to 25-125billion or less...which means there is 3-15 times more than that in the core... or a ~1.5-7.5% in the core...averaging that out at the largest extents of those numbers...and realizing that 3/4 of that is .5% and 1/4 is 7.5% then the average population density is ~2.25%

And just so noone says that is not what i said initially... your right, but it still works out the same. The difference is that i'm only taking the average of two zones in the original and not taking into account the fact that there is more spiral arm than there is core and i used a bigger number of 1% out of a mistake.

formulaterp
2008-Nov-23, 01:59 AM
What the heck does it mean to say the average density is 1%?

1% of what?

Hornblower
2008-Nov-23, 02:08 AM
What the heck does it mean to say the average density is 1%?

1% of what?
He appears to be saying, in very awkward language, that roughly one cubic light year out of every 100 contains a star. My question is, what does this have to do with the opening question about the possibilities of planets in multiple star systems?

timb
2008-Nov-23, 03:01 AM
Terrestrial Planet Formation in Binary Systems (http://arxiv.org/abs/0705.3444v1) by Quintana and Lissauer seems to disagree:



In simulations of the Alpha Centauri System (with various parameters), they consistently got a few terrestrial planets in stable orbits.

That simulation involving embryos, not planetesimals. It assumed that largish planetary embryos already existed at the start of the simulation. The simulation I referred to is more refined and examines the preceding stage when embryos form. It casts serious doubt on the ability of planetesimals to agglomerate into embryos in the aCen system(s).

AndreasJ
2008-Nov-23, 12:37 PM
He appears to be saying, in very awkward language, that roughly one cubic light year out of every 100 contains a star. My question is, what does this have to do with the opening question about the possibilities of planets in multiple star systems?
It's got something to do with the other opening question about black hole density.

Unfortunately, nobody seems willing to try and estimate the number of black holes in the Galaxy (or at least to put it where I can google it). The number of current black hole progenitor stars is estimatable, but extrapolating backwards with any sort of reliability would require knowledge of the historical evolution of the stellar mass distribution function. (In particular, a primordial generation of massive population III stars might've produced a big crop of black holes, but nobody knows much about that theoretical bunch.) The honest answer is probably we don't know.

Hornblower
2008-Nov-23, 01:56 PM
It's got something to do with the other opening question about black hole density.Perhaps this should be split into two threads. The two questions are unrelated, and the black hole question appeared as a relatively inconspicuous afterthought.


Unfortunately, nobody seems willing to try and estimate the number of black holes in the Galaxy (or at least to put it where I can google it).This may not be lack of willingness so much as lack of interest. Unless such a black hole is part of a binary system such as Cygnus X-1, it is going to be virtually unobservable, and such objects would be rare enough as to be only a very minor component in the overall gravitational dynamics of the galaxy.


The number of current black hole progenitor stars is estimatable, but extrapolating backwards with any sort of reliability would require knowledge of the historical evolution of the stellar mass distribution function. (In particular, a primordial generation of massive population III stars might've produced a big crop of black holes, but nobody knows much about that theoretical bunch.) The honest answer is probably we don't know.

Eroica
2008-Nov-23, 02:39 PM
That simulation involving embryos, not planetesimals. It assumed that largish planetary embryos already existed at the start of the simulation. The simulation I referred to is more refined and examines the preceding stage when embryos form. It casts serious doubt on the ability of planetesimals to agglomerate into embryos in the aCen system(s).:sad: Sigh ... I so want there to be terrestrial planets in the Alpha Centauri system, but it seems I just have to accept that it's unlikely.

Durakken
2008-Nov-24, 06:19 AM
so am i getting this right in that if there are planets around binary they are 5AU + out and no more than 4 terestrials? and definitely no gas giants?

timb
2008-Nov-24, 07:13 AM
:sad: Sigh ... I so want there to be terrestrial planets in the Alpha Centauri system, but it seems I just have to accept that it's unlikely.

Who knows, there might be, but so far there's no reason to fire up the Jupiter 2. It's odd that the planet finders haven't done long period radial velocity studies. It's the closest system, and similar to the Sun. I suppose the fact that it is a binary discourages them.

astromark
2008-Nov-24, 08:16 AM
Unfortunately, and I would really like to be wrong, cos there's a drink or two involved on this... but... at this time we have not confirmed the presence of any planetary objects in orbit around Alpha cent A or B. We know its a possibility that has not been confirmed. I want it to be confirmed. It would be the news so many want to hear. So lets get the Enterprise built and get it out there. Now. How do we convince the politicians that this would be a worthy avenue for billions of bucks.?

Michael Noonan
2008-Nov-24, 08:50 AM
Unfortunately, and I would really like to be wrong, cos there's a drink or two involved on this... but... at this time we have not confirmed the presence of any planetary objects in orbit around Alpha cent A or B. We know its a possibility that has not been confirmed. I want it to be confirmed. It would be the news so many want to hear. So lets get the Enterprise built and get it out there. Now. How do we convince the politicians that this would be a worthy avenue for billions of bucks.?

Don't forget the Energia-Buran programme (http://news.bbc.co.uk/1/hi/sci/tech/7738489.stm). It has greater capacity and dollar for dollar value probably a better investment if it could be brought back on line.

cjameshuff
2008-Nov-24, 03:08 PM
Who knows, there might be, but so far there's no reason to fire up the Jupiter 2. It's odd that the planet finders haven't done long period radial velocity studies. It's the closest system, and similar to the Sun. I suppose the fact that it is a binary discourages them.

You sure they haven't? A lack of findings makes for little news.
I wonder if the rotational axis is known. It might be in a bad orientation for such techniques to work.

Tau Ceti's still a decent candidate.

timb
2008-Nov-24, 09:26 PM
You sure they haven't? A lack of findings makes for little news.
I wonder if the rotational axis is known. It might be in a bad orientation for such techniques to work.


79o, almost face on. There's the problem. Searching arxiv I see some (unsuccessful) attempts to find sub-stellar companions by astrometry and direct imaging, but these would only be sensitive to giant planets, which are a priori improbable.