Could dark matter form planet sized objects?

[imatfaal]

Is it possible for objects the size of planets to be made of dark matter?

 

It is highly unlikely for dark matter to clump together.*

 

It is gravitationally attracted to itself - so like normal matter, it will tend to draw in but, and whilst this seems a minor quibble it is important, it has no easy way to lose its kinetic energy, momentum, and angular momentum. Normal matter is able to dissipate energy by way of heat and radiation after an interaction involving the electromagnetic force; two things bump into each other, release a photon or a more, move away from each other more sluggishly; lots of things bounce about and get hot giving off infrared; etc.

 

Dark matter does not interact in this manner (if it did we would be able to see it glow and we wouldn't have called it dark) and thus it forms lose ever-moving filaments, halos, and clouds rather than the more solid stuff required for planetary formation. Very simplistically, DM has no obvious way fo slowing down; so whilst it may be attracted to other bits of DM it will not be able to get together with them - but will end up in an orbit with them.

 

* But as we don't know too much about dark matter any notion in this area is pretty speculative

 

If you wish to continue this line of investigation - we will split this off to a new thread (pm me and I will do so)

[Mordred]

 

It is highly unlikely for dark matter to clump together.*

 

It is gravitationally attracted to itself - so like normal matter, it will tend to draw in but, and whilst this seems a minor quibble it is important, it has no easy way to lose its kinetic energy, momentum, and angular momentum. Normal matter is able to dissipate energy by way of heat and radiation after an interaction involving the electromagnetic force; two things bump into each other, release a photon or a more, move away from each other more sluggishly; lots of things bounce about and get hot giving off infrared; etc.

 

Dark matter does not interact in this manner (if it did we would be able to see it glow and we wouldn't have called it dark) and thus it forms lose ever-moving filaments, halos, and clouds rather than the more solid stuff required for planetary formation. Very simplistically, DM has no obvious way fo slowing down; so whilst it may be attracted to other bits of DM it will not be able to get together with them - but will end up in an orbit with them.

 

* But as we don't know too much about dark matter any notion in this area is pretty speculative

 

If you wish to continue this line of investigation - we will split this off to a new thread (pm me and I will do so)

This is probably one of better explanations I've seen on any forum. Well thought out and concise.+1

[Moontanman]

 

It is highly unlikely for dark matter to clump together.*

 

It is gravitationally attracted to itself - so like normal matter, it will tend to draw in but, and whilst this seems a minor quibble it is important, it has no easy way to lose its kinetic energy, momentum, and angular momentum. Normal matter is able to dissipate energy by way of heat and radiation after an interaction involving the electromagnetic force; two things bump into each other, release a photon or a more, move away from each other more sluggishly; lots of things bounce about and get hot giving off infrared; etc.

 

Dark matter does not interact in this manner (if it did we would be able to see it glow and we wouldn't have called it dark) and thus it forms lose ever-moving filaments, halos, and clouds rather than the more solid stuff required for planetary formation. Very simplistically, DM has no obvious way fo slowing down; so whilst it may be attracted to other bits of DM it will not be able to get together with them - but will end up in an orbit with them.

 

* But as we don't know too much about dark matter any notion in this area is pretty speculative

 

If you wish to continue this line of investigation - we will split this off to a new thread (pm me and I will do so)

 

Isn't dark mater supposed to analyte if it comes into contact with it's self?

 

Has the hypothetical Mirror Matter been discounted completely?

 

https://en.wikipedia.org/wiki/Mirror_matter

 

When I was corresponding with Robert Foot he had suggested Mirror planets would be invisible as would Mirror stars but they could affect each other gravitationally...

 

http://xxx.lanl.gov/abs/astro-ph/0102294

Edited December 4, 2016 by Moontanman

[imatfaal]

 

Isn't dark mater supposed to analyte if it comes into contact with it's self?

....

 

Not that I have heard - neither mirror matter, antimatter, or even normal matter has that characteristic. Anti and Normal will annihilate. Mirror and Normal will interact only gravitationally as neither the strong, nor weak nor the electromagnetic will have any effect transmitted by the mirror gauge bosons - gravity / the graviton is its own mirror boson and thus will have effect

Has the hypothetical Mirror Matter been discounted completely?

 

Not that I can tell - I don't think there has been a great deal of progress on finding the DM particle*. If it is weakly interacting massive particle that would be hard enough - but mirror matter would be even harder to find.

 

* note the last paper suggesting this listed by wiki is 1995 - so maybe unfashionable rather than disproved

 

...When I was corresponding with Robert Foot he had suggested Mirror planets would be invisible as would Mirror stars but they could affect each other gravitationally...

 

http://xxx.lanl.gov/abs/astro-ph/0102294

 

I think the idea is that they would be invisible to US and would only affect US gravitationally - to themselves everything would be normal

[AbstractDreamer]

One question that springs to mind is if DM "orbits/swirls/forms halos/gathers/loosely collects" around galaxies, then why might it not swirl around real nebulae, solar systems, stars, planets, asteroids?

 

Or why might it not gather in the middle of galaxies, instead of surrounding it?

 

If it tends to swirl surrounding matter, then would there not be even more swirling around bigger super clusters than small galaxies? Do any observations support this?

On the other hand, if it is difficult for it to "gather", why would it gather at all? Would it it not be evenly spread out throughout the universe (rather than "form halos" around galaxies). Collisions alone would not cause it to coalesce, they will just be redirected off into space. Perhaps something akin to brownian motion.

Also if DM ever did manage to form into a object of significant size, there's no reason for it ever to fall apart (unless it collides with something)?

Is DM affected by the strong and weak fundamental forces, or just gravity?

Edited December 5, 2016 by AbstractDreamer

[Moontanman]

Some Dark matter candidates do act as their own anti particles.

 

https://en.wikipedia.org/wiki/Dark_matter

 

 

 

Non-baryonic matter[edit]

Candidates for nonbaryonic dark matter are hypothetical particles such as axions or supersymmetric particles. The three neutrino types already observed are indeed abundant, and “dark”, and matter, but because their individual masses – however uncertain they may be – are almost certainly tiny, they can only supply a small fraction of dark matter, due to limits derived from large-scale structure and high-redshift galaxies.^[90]

Unlike baryonic matter, nonbaryonic matter did not contribute to the formation of the elements in the early universe ("Big Bang nucleosynthesis")^[13] and so its presence is revealed only via its gravitational effects. In addition, if the particles of which it is composed are supersymmetric, they can undergo annihilation interactions with themselves, possibly resulting in observable by-products such as gamma rays and neutrinos ("indirect detection").^[90]

[Mordred]

One question that springs to mind is if DM "orbits/swirls/forms halos/gathers/loosely collects" around galaxies, then why might it not swirl around real nebulae, solar systems, stars, planets, asteroids?

 

Or why might it not gather in the middle of galaxies, instead of surrounding it?

 

If it tends to swirl surrounding matter, then would there not be even more swirling around bigger super clusters than small galaxies? Do any observations support this?

 

On the other hand, if it is difficult for it to "gather", why would it gather at all? Would it it not be evenly spread out throughout the universe (rather than "form halos" around galaxies). Collisions alone would not cause it to coalesce, they will just be redirected off into space. Perhaps something akin to brownian motion.

 

Also if DM ever did manage to form into a object of significant size, there's no reason for it ever to fall apart (unless it collides with something)?

 

Is DM affected by the strong and weak fundamental forces, or just gravity?

DM as far as we know only interacts with the weak force and gravity. Yes we do have evidence that DM clusters around large scale structures. Yes it's highly likely to be present within Galaxies etc. There is even some thought as to being present within stars. We don't know for sure on that one. However it is viable. Edited December 5, 2016 by Mordred

[AbstractDreamer]

According to wiki there's 4.6% baryonic matter and 23% dark matter.

 

Assuming gravitational constant G is the same for both types, I would expect baryonic matter (BM) to gather and coalesce around dark matter, rather than vice versa. Unless some time in our past the ratios were reversed, particularly around the early formative periods. I recall reading that the ratios evolve over time. It would seem DM is less susceptible to entropy than BM, unless "weak decay" for DM follow different mechanics.

[Mordred]

Well DM starts collected before Baryonic matter. Its a little complex to explain why. However it has a lot to do with thermal equilibrium and when particles drop out of thermal equilibrium. Which isn't easily explained.

 

One of the articles I posted to you covers this without detailing DM itself.

[Janus]

One question that springs to mind is if DM "orbits/swirls/forms halos/gathers/loosely collects" around galaxies, then why might it not swirl around real nebulae, solar systems, stars, planets, asteroids?

There have forwarded that the Solar system has swept-up extra DM as it orbits the galaxy, but since the total DM spread out in the volume of the Solar system adds up to be equal to the mass of a small asteroid, it is not exactly noticeable.

Or why might it not gather in the middle of galaxies, instead of surrounding it?

The expected density profile for DM does have it having a slightly higher density near the core of the galaxy than at the fringes. Don't think of DM surrounding the galaxy, think of the Galaxy as embedded in a cloud of DM.

On the other hand, if it is difficult for it to "gather", why would it gather at all? Would it it not be evenly spread out throughout the universe (rather than "form halos" around galaxies). Collisions alone would not cause it to coalesce, they will just be redirected off into space. Perhaps something akin to brownian motion.

It isn't that it doesn't gather, just that the mechanisms that cause it to gather don't lead to it happening very quickly. We are talking about the loss of energy through gravitational radiation and gravitational "slingshot" type interactions that rob speed from one particle and eject another. The thing is that DM "clumping" happens over very long time scales and the universe just isn't old enough for it to form very compact structures

Also if DM ever did manage to form into a object of significant size, there's no reason for it ever to fall apart (unless it collides with something)?

The forces pulling it apart would have to be gravitational as well (it can't collide in the normal sense). If it were to pass to close to a another massive body, tidal forces could pull it apart. In fact, tidal forces likely play a roll in preventing such DM bodies from forming in the first place. Average DM density is lower than average galactic density, so out to quite a far distance from the visible galaxy boundary, tidal forces will keep DM spread out..