Could a star not have planets ?

[Tom]

Given the formation of our own solar system, how could a star not form a solar system from surrounding debris ?

Also, if planets form in a binary star system, what do the orbits look like ?

 

[Farmer]

Also, if planets form in a binary star system, what do the orbits look like ?

To good approximation, their orbits will be conic sections focused at the center of mass of the 3-body system (star, star, planet). Since the planet will have mass much smaller than the stars, it will look like a normal orbit, except instead of about the center of the Sun, as is with the Solar system, it will be about the center of mass of the binary system.

 

[R.Danneskjold]

Given the formation of our own solar system, how could a star not form a solar system from surrounding debris ?

Even if the formation of our solar system was a given (as in the nebular hypothesis is just that: a hypothesis), why would we assume that a newborn star is always surrounded by a vast amount of debris or that it forms the same way as ours?

 

[SMOGZINN]

Given the formation of our own solar system, how could a star not form a solar system from surrounding debris ?

I can think of several theoretical ways.

All the extra matter also fell into the star formation. I would suppose that would happen if the matter was exceptionally well distributed originally.

Another large body could sweep the solar system clean of extra matter and then fall into the star or escape.

The star forming region could have strong enough wind to push the stars debris cloud to escape velocity.

Another large gravity field passes close enough to the start to strip all the extra debris from it.

 

[Tom]

Thanks, that's what Im looking for, some theories.

I'm starting from the most observable example solar system we have, ours. I think a logical deduction is that's what happens, unless there's good evidence it doesn't always happen, or good theories of how it could not happen.

Given the theory of our solar system, it seems to me that debris that's too far from the sun to fall into the sun, will be attracted to itself and form planets. The exception in our own solar system, the asteroid belt, only exists because it's held that way by planetary gravity, correct ?

So it's not an argument against our solar system being an exception, because it requires planets to exist.

 

[MrScott81]

Given the extraordinary size of our universe, I can't imagine that it has never happened before.

 

[Biftheunderstudy]

Well, the reality is almost certainly much more complicated than simple self gravitation.

There are many problems currently faced by planetessimal formation. A couple of them are:

How do you go from dust to about metre sized objects? This is difficult to get working in models, many simulations start with metre sized objects which can accrete from there.

How long does the whole thing take? There are constraints on how long planet formation can take, and a simple cloud of dust takes too long to form planets if you assume simple self attraction. i.e. there is other physics happening.

How do you get a planet the size of jupiter in an orbit the size of mercury's? Exo-planet statistics show a large number of planets in this regime.

Next, think about the environment of a forming star, its usually in a dense stellar environment like a cluster...how does this affect planet formation?

How do you get planets around pulsar/neutron stars ?!?

This is just the tip of the ice berg, its not clear at all why some stars form planets and others don't.

 

[Merad]

Also, if planets form in a binary star system, what do the orbits look like ?

Depends on how the system is setup. Get this and play with it all you want.

 

[Gibsons]

I remember hearing about some extragalactic stars - idea was that a binary system gets too near a large black hole. One of them is captured by the black hole and maybe consumed, the other gets flung out of the galaxy at high speed. Could an event like this strip it of any associated planets?

 

[Sunny129]

I remember hearing about some extragalactic stars - idea was that a binary system gets too near a large black hole. One of them is captured by the black hole and maybe consumed, the other gets flung out of the galaxy at high speed. Could an event like this strip it of any associated planets?

yes, such an encounter could possibly strip a star of its planets.

btw, not all such encounters result in a member of a binary star system getting consumed - it could just as well go into orbit about the black hole while the other is flung out of the system.

 

[ArisVer]

Given the extraordinary size of our universe, I can't imagine that it has never happened before.

Also, i can see no reason why a star must have planets.

 

[Tom]

Also, i can see no reason why a star must have planets.

But that isn't how science works. What is observable is our Sun has planets, and some other stars appear to have planets.

Do we actually know there are stars WITHOUT planets ?

I'm not saying we don't, I'm asking if we know they exist ?

 

[Evadman]

Do we actually know there are stars WITHOUT planets ?

Conclusively proven that a specific star has no planet sized objects in orbit? I don't believe it is possible to prove that with our current tech. The tech to find planets is in its infancy; using the same tech (transits and wobble) can't remove the possibility of a planet being in orbit on a star.

 

[silverpig]

I'm pretty sure there aren't any planets around a neutron star...

 

[Sunny129]

I'm pretty sure there aren't any planets around a neutron star...

there most definitely are planets around some neutron stars. in addition, there exists strong evidence that planets can not only end up orbiting neutron stars, but may also form around them:

http://science.nasa.gov/science-news/science-at-nasa/2006/05apr_pulsarplanets/Planets Around Dead Stars

 

[Fallen Kell]

To good approximation, their orbits will be conic sections focused at the center of mass of the 3-body system (star, star, planet). Since the planet will have mass much smaller than the stars, it will look like a normal orbit, except instead of about the center of the Sun, as is with the Solar system, it will be about the center of mass of the binary system.

Unless, of course, the 2 stars are orbiting each other, or in the case of 1 star is orbiting the other star, there would most certainly be some stranger orbits as the center of gravity of the system would constantly be shifting on those two cases.

 

[ArisVer]

There is also a good chance not to find any planets in stars belonging to very small constellations.

 

[Sunny129]

There is also a good chance not to find any planets in stars belonging to very small constellations.

could you elaborate on this? i don't see your logic...

 

[silverpig]

there most definitely are planets around some neutron stars. in addition, there exists strong evidence that planets can not only end up orbiting neutron stars, but may also form around them:

http://science.nasa.gov/science-news/science-at-nasa/2006/05apr_pulsarplanets/Planets Around Dead Stars

Eh, they haven't discovered any planets around the stars, but it does seem likely from the remnants that they could form. I was thinking of this though:

Any planets around the stars that gave rise to pulsars would have been incinerated when the stars blew up. The pulsar disk discovered by Spitzer might represent the first step in the formation of a new, more exotic type of planetary system, similar to the one found by Wolszczan in 1992.

So at least for a good long time, there aren't any planets around every neutron star. They may form new planets, or may capture some, but they get all blowed up.

 

[silverpig]

could you elaborate on this? i don't see your logic...

He probably means tight clusters of many stars. There aren't any stable orbits and the planets would likely get flung out of the system.

 

[ArisVer]

could you elaborate on this? i don't see your logic...

IF. If the distance between the stars of a small constellation is small, let's say star to star around the size of our solar system, then the gravities of the stars would have different effects of any planets rotating in the area. As a result those planets caught in the gravity field of that constellation would eventually get drawn into a star. This is close to what Fallen Kell said.


And, no, we do not know whether there are stars without planets. We can only guess what other solar systems are like when comparing them to our solar system.

And i do not know what can be seen with a telescope.

 

[Biftheunderstudy]

Remember, its thought that *all* stars form in dense stellar environments (clusters). In fact, our own solar system shows strong evidence in the form of elements only found in a supernova (http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2966.2010.16921.x/full). A likely explanation for these elements is that the solar system was near a supernova early in its lifetime. If you do the statistics, you can work out the stellar density required for the solar system to be near a supernova and how big that cluster must have been based on this.

*edit*
In addition, we observe that around 50% of stars are found in a binary system. Further a large percentage (I forget the exact amount, somewhere around 20%) of these stars are in triple or higher systems.
*edit*

Also, look up the Kepler mission to find exo planets. There are a lot of really interesting patterns emerging about planet formation.

A quick search on web of knowledge shows quite a few papers on planetary systems around pulsars.

A relatively recent paper by Hagai Perets (a pretty big name in this field) is about planetary systems around evolved binaries, this is a mixture of the comments about binary systems and evolved stars so it is particularly relevant.

 

[JeffreyLebowski]

Well, the reality is almost certainly much more complicated than simple self gravitation.

There are many problems currently faced by planetessimal formation. A couple of them are:

How do you go from dust to about metre sized objects? This is difficult to get working in models, many simulations start with metre sized objects which can accrete from there.

How long does the whole thing take? There are constraints on how long planet formation can take, and a simple cloud of dust takes too long to form planets if you assume simple self attraction. i.e. there is other physics happening.

How do you get a planet the size of jupiter in an orbit the size of mercury's? Exo-planet statistics show a large number of planets in this regime.

Next, think about the environment of a forming star, its usually in a dense stellar environment like a cluster...how does this affect planet formation?

How do you get planets around pulsar/neutron stars ?!?

This is just the tip of the ice berg, its not clear at all why some stars form planets and others don't.

They already know that small dust size particles do tend to clump together in low/zero G.
There's video of an astronaught with a bag of something( i don't remember what was in it), but it is full of small particles and they start clumping together with no external actions.
I saw it on The Universe or something. If I find the video I'll post it.

 

[Sunny129]

Eh, they haven't discovered any planets around the stars, but it does seem likely from the remnants that they could form.

did you miss this part of the article?

The finding represents the missing piece in a puzzle that arose in 1992, when Aleksander Wolszczan of Pennsylvania State University found three planets circling a pulsar called PSR B1257+12. Those pulsar planets, two the size of Earth, were the first planets of any type ever discovered outside our solar system. Astronomers have since found indirect evidence the pulsar planets were born out of a dusty debris disk, but nobody had directly detected this kind of disk until now.

I was thinking of this though:

Any planets around the stars that gave rise to pulsars would have been incinerated when the stars blew up. The pulsar disk discovered by Spitzer might represent the first step in the formation of a new, more exotic type of planetary system, similar to the one found by Wolszczan in 1992.

So at least for a good long time, there aren't any planets around every neutron star. They may form new planets, or may capture some, but they get all blowed up.

note what the article specifically says about when the planet(s) are incinerated - it happens during the supernova that creates the neutron star, not during the lifetime of the neutron star itself. i don't disagree with you that neutron stars exist for some period of time without planets, the duration of which is debatable. but if a neutron star endures an epoch without planets, i would tend to think that it is because 1) planets have not yet formed out of the debris disk orbiting it (assuming a debris disk exists in the first place), 2) it hasn't yet captured any planets with its gravity, or 3) any previously existing planets it may have had in the past were flung out of their orbits by an external gravitational influence. but i can't imagine that a "planet-less" epoch would be induced by the radiation of the pulsar vaporizing any existing planets...perhaps gaseous planets, but not rocky planets like the ones found in our inner Solar System.

IF. If the distance between the stars of a small constellation is small, let's say star to star around the size of our solar system, then the gravities of the stars would have different effects of any planets rotating in the area. As a result those planets caught in the gravity field of that constellation would eventually get drawn into a star. This is close to what Fallen Kell said.

ok, now your logic makes sense to me. you threw me through a loop when you mistook constellations for star clusters. you see, the constituent stars of a constellation/asterism are generally not members of a common star cluster (open or globular), regardless of how large or small the constellation may be. take the small constellation Lyra for instance, which contains the bright star Vega, and approximates the shape of a small square/rhombus. while i haven't researched it myself, i'd be willing to be that if you research the 4 stars that comprise the constellation Lyra, you'll find that their distances from us vary greatly, perhaps by orders of magnitude. so while they appear to be close together in the sky, one star may be 100 times farther away from us than another (i.e. its a depth perception issue). therefore , the constituent stars of a constellation typically are 99% of the time not gravitationally bound. for the stars of a cluster on the other hand, you're assertion makes perfect sense...particularly globular clusters, as their stars are typically more densely packed than those of an open cluster.

 

[pw38]

I've learned to never underestimate the ability for nature to surprise us. To answer though of course it's possible to have a star form without planets. There's quite a few variables that can ensure this happens. Look at open or globular clusters to see examples of numerous stars that most likely don't have planets. Open clusters would be more apt to produce planet forming systems than a globular cluster but it's not a guarantee.