Rogue planets may be more numerous than stars in our galaxy

[Kamen Rider Blade]

Ars Technica | Rogue planets may be more numerous than stars in our galaxy

This could make for more interesting stories in the future in ST featuring more Rogue Planets than the single one that we've seen.

 

[Asbo Zaprudder]

I assume one can formulate an initial mass function (IMF) for planets as one does for stars. As for the stellar version, this function would change over time as the Universe started off with only hydrogen, helium and a small amount of lithium. Heavier elements only came along later through nuclear synthesis, p-, r- and s-processes in supernova explosions, neutron star collisions, asymptotic giant branch stars and so on. I also expect that the fraction of planets that are ejected from stellar systems might be estimated. On the IMF spectrum of stellar bodies, the least massive would be brown dwarfs and even bodies that resemble planets. However, I've only seen IMF curves that go as low as 0.01 solar masses. For masses m greater than one solar mass M, the number drops as a power law (m/M)^−2.35, so 10-solar mass stars are about 200 times less numerous than solar mass stars. For less massive stars or bodies that don't make it as stars, the IMF function is very uncertain and there is theoretical controversy about assuming a single IMF that covers the whole substellar and stellar mass range. Microlensing observations seem like an excellent way to investigate this.

The link given is broken, BTW. It should be:

Lots of Earth-mass rogue planets could be found by NASA’s Roman telescope | Ars Technica

 

[Kamen Rider Blade]

The link given is broken, BTW. It should be:

Thanks, I fixed it on the original post.

 

[Asbo Zaprudder]

I've just had a thought that rogue planets might function as nucleation seeds that grow into stars if they were to pass through nebulae, molecular clouds, supernova remnants and so on and accrete material to themselves via their gravitational attraction. However, this is just a random thought - it doesn't sound implausible, but I don't know how significant it would be as one possible cause of stellar formation. It's the sort of scenario whose likelihood can probably only be estimated by computer modelling.

One 2011 study indicated an upper limit of 0.25 Jupiter-mass free-floating or wide-orbit planets for every main-sequence star in the Milky Way - so perhaps as many as 100 billion such planets. One would expect a similar or larger number of smaller mass rogue planets. The estimated number of non-rogue planets in stellar systems in the Milky Way is usually put at between 100 billion and 200 billion.

 

[Kamen Rider Blade]

I've just had a thought that rogue planets might function as nucleation seeds that grow into stars if they were to pass through nebulae, molecular clouds, supernova remnants and so on and accrete material to themselves via their gravitational attraction. However, this is just a random thought - it doesn't sound implausible, but I don't know how significant it would be as one possible cause of stellar formation. It's the sort of scenario whose likelihood can probably only be estimated by computer modelling.

One 2011 study indicated an upper limit of 0.25 Jupiter-mass free-floating or wide-orbit planets for every main-sequence star in the Milky Way - so perhaps as many as 100 billion such planets. One would expect a similar or larger number of smaller mass rogue planets. The estimated number of non-rogue planets in stellar systems in the Milky Way is usually put at between 100 billion and 200 billion.

It sounds very much possible, but the time frame to validate is over Millions to Billions of years fo that to happen.

Also, what are the chances that a specific Rogue Planet with enough base mass moves into a Nebulae that is dense enough to have enough gaseous matter.

So it seems like it's almost down to dumb chance, but given that space is constantly expanding, those chances gets very hard to predict with the universe constantly expanding at a relatively consistent rate.

 

[Asbo Zaprudder]

We're unlikely to validate it visually as the accretion process for protostars takes of the order of a hundred thousand years. However, we're not talking new physics, so a simulation that generates falsifiable predictions regarding star formation rate as opposed to other mechanisms, such as random density fluctuations, is probably good enough.

The expansion of the Universe has no meaningful effect over galactic scales where local gravitational effects dominate. That's why galaxies collide and merge - as our own Milky Way gakaxy appears to be doing with the Andromeda galaxy M31.

 

[Kamen Rider Blade]

We're unlikely to validate it visually as the accretion process for protostars takes of the order of a hundred thousand years. However, we're not talking new physics, so a simulation that generates falsifiable predictions regarding star formation rate as opposed to other mechanisms, such as random density fluctuations, is probably good enough.

The expansion of the Universe has no meaningful effect over galactic scales where local gravitational effects dominate. That's why galaxies collide and merge - as our own Milky Way gakaxy appears to be doing with thr Andromeda galaxy M31.

Spoiler: Isaac Arthur - Is Our Galaxy Going To Collide With Andromeda¿ #SHORTs

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[Asbo Zaprudder]

Yeah, that video doesn't disagree with the concensus view about what happens in galactic clusters over timespans far greater than a human lifetime. The timescales and distances are also orders of magnitude greater than those involved in star and planet formation.

 

[Kamen Rider Blade]

Yeah, that video doesn't disagree with the concensus view about what happens in galactic clusters over timespans far greater than a human lifetime. The timescales and distances are also orders of magnitude greater than those involved in star and planet formation.

I concur, but you're missing the fact that it's more than just our Milky Way & Andromeda Galaxy's on a collision/merger course, other local galaxies may be in on it too like Triangulum Galaxy.

But the time scale for that is HUGE and long after our remains are space dust.

Imagine trying to sustain the UFP for "Billions of years".

That's going to be difficult.

 

[Asbo Zaprudder]

Yes, none of that is news to me - galaxies collide. A direct collision between M33 and M31 is predicted to happen in about 2.5 Ga, but they've interacted in the past sometime between -2 and -8 Ga. A collision between our galaxy and M31 will happen in about 4 Ga - although it's now thought that this interaction will probably be glancing rather than direct. However, the exact dynamics aren't certain. We know more about these external galaxies than we do about our own. We have observational evidence that the milky way has probably had several close encounters with other galaxies. As for the UFP's life expectancy, I suggest applying Lindy's Law or the Doomsday Argument.

Lindy effect - Wikipedia
Doomsday argument - Wikipedia

As the UFP doesn't exist and might well never exist, it's impossible to estimate how long such a fictional entity would survive.

 

[Asbo Zaprudder]

Talking of galaxy interactions, it seems that it's very unlikely that their central supermassive black holes ever merge except on timescales much longer than the current age of the Universe. Which begs the question, how did they get so massive in the first place? I assume they must have formed very early on from density fluctuations and acted as attractors in galaxy formation. I did my academic studies so long ago that I don't know what the concensus view is on this topic.

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[publiusr]

It seems our Sun is bright in gamma rays..a rocky planet in the grip of a fusion furnace might be a reverse nuke..fusion triggering a fission of the core’s elements?

 

[Asbo Zaprudder]

Sort of an inverse Teller-Ulam design? Perhaps - the primary in that does not need to be a fission device - it just needs to supply a copious flux of X-rays, which are applied to the fission-fusion spark plug.

Nuclear weapon - Fission, Fusion, Delivery | Britannica

It has been confirmed recently that the Earth's inner core itself has a core. I have wondered if such a core might consist of dense fissionable elements that decay over time releasing heat energy. Such heat could be important for sustaining life on a rogue planet. I doubt your proposed mechanism would have sufficient gamma ray flux to reach such a core and compress it, however. The pusher is typically a doped aerogel, not thousands of kilometres of rock and metal. If the compression were asymmetric, you'd get an ineffective squirt.

 

[publiusr]

Some think we have a solid crystal of epsilon iron in the core.

 

[Asbo Zaprudder]

Based on seismic P wave speed anisotropy data, it has been suggested that the iron atoms in the inner core might be arranged body-centred cubic (BCC) rather than hexagonal-close-packed (HCP) as in ε-iron.

Iron in Earth’s core might be cubic, not hexagonal – Physics World

However, I don't know to what phase that would correspond. It seems very unlikely that it's α-iron, which is BCC. The research has certainly moved on from 2018, however. The inner inner core proposal of this year (2023) being one example.

 

[Asbo Zaprudder]

A video referencing the research that suggest that rogue planets might outnumber all bound planets by a factor of as much as ten to one.

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We're going to have to wait for results from the Nancy Grace Roman Space Telescope to get a tighter estimate.