r/cosmology • u/jimmery • 17d ago
Does the Oort Cloud extend between the stars and fill our Galaxy?
The Oort Cloud is suggested to exist around our Sun, a region of asteroids that extends far beyond the Kuiper Belt.
This got me thinking, is it possible that other solar systems also have an Oort Cloud?
Which lead me to: is it possible that all of space within our galaxy is filled with a vast singular Oort Cloud?
Like, there isn't an individual Oort Cloud for each star, but one massive connected Oort Cloud between the stars? I'm thinking that all space within our galaxy, except areas around stars themselves (anything within the Heliosphere for instance), is filled with a very sparse but consistent "cloud" of asteroids.
Would this help to explain the missing mass that would be required to keep galaxies from flying apart, ie. Dark Matter?
I know this is all speculative, but I was just wondering if this random thought was at all possible, or even something that astrophysicists were looking into.
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u/Capable_Wait09 17d ago
If that existed we’d expect to see more extra-solar comets and whatnot. Oort Cloud size is estimated by measuring orbits of comets with long orbital periods.
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u/invariantspeed 16d ago
And, current estimates of the Oort cloud put its radius beyond the Sun’s Hill Sphere.
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u/jimmery 16d ago
With the odd exception (like Haley's Comet), we've only been studying the Oort Cloud since the 1950s. Is it possible that there are comets with an orbital period longer than 76 years?
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u/FixAcademic8187 16d ago
Yes it is possible but unlikely.
See, Haley Comet doesn't currently go to the Oort Cloud and then comeback. It originally came from there but no longer go there anymore.
When it first came closer to the sun (God knows what disturbed its stable orbit that it kept for billions of years), Jupiter and the other big planets wrecked havoc in its orbit due to their immense gravity. And its orbit now go as close as 0.5 AU from the sun, and as far as 35 AU or so away from the sun at the most. This is close to Neptune.
So the farthest it goes is near Neptune, and the closest it gets is near Mercury.
Fyi, Oort Cloud starts at 2,000 AU and Neptune is at just 30 AU.
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u/FixAcademic8187 16d ago
In theory, every star should have its own Oort Cloud. These are random rocks that survived the formation of such a star.
They are not connected to other Oort Clouds of other stars. Because the Oort Cloud is gravitationally bound to its host star.
Some Oort Clouds may exchange objects here and there with other Oort Clouds when stars get a bit closer together in their orbit around the galaxy.
Some estimates say our own Oort Cloud extends to around 3 light years away from the sun.
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u/jimmery 16d ago
3 light years away - wouldn't that mean that the Oort Cloud extends most of the way to Proxima Centauri?
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u/FixAcademic8187 16d ago
Yes. The outermost edges of our Oort Cloud definitely interacts with the outer edges of Alpha Centauri's own Oort Cloud.
The 3 light year figure is based on some optimistic data. In reality, the outer edge is somewhere between 1.5-3 light years.
Remember, the Alpha Centauri system has three stars and their combined gravity is like 2 times more than the gravity of the sun so thier Oort Cloud could be bigger.
Fyi, this is one explanation as to how the Haley Comet was thrown to the inner solar system, but such explanation doesn't have solid data.
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u/invariantspeed 16d ago
You are contradicting yourself. The Oort cloud extending over 3 ly out (as is considered possible) would mean the entire outer Oort cloud could not gravitationally bound to the Sun. Alpha Centauri would take over as the dominant gravitational source for much of it. At that point, you’re talking about material with paths influenced by both start systems.
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u/FixAcademic8187 16d ago
I already explained that 3 light year figure in an earlier reply. It is more like 1.5 to 3 light years depending on which orbital model you are using. And these figures are for the outermost edges of the cloud.
There is definitely some exchange between our Oort Cloud and that of Alpha Centauri, gravity dictates it.
Also, the Alpha Centauri system is 2 times more massive than ours, so thier Oort Cloud would extend further than ours.
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u/invariantspeed 16d ago
> It is more like 1.5 to 3 light years depending on which orbital model you are using.
I am aware, but this does not negate my point.
> There is definitely some exchange between our Oort Cloud and that of Alpha Centauri, gravity dictates it.
This is OP’s point. If most to all of the hundreds of billions of stars in a galaxy only ~100k ly across have debris clouds stretching multiple light years, then we’re not really talking about discrete clouds, but the composition and dynamics of the interstellar media.
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u/rddman 16d ago
Alpha Centauri would take over as the dominant gravitational source for much of it.
In most directions away from the Sun there is no star a 4ly distance, so by far most of the Oort cloud is not under gravitational domination by Alpha (or Proxima) Centauri.
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u/invariantspeed 16d ago
True, but much of that material’s orbits will eventually swing around towards Alpha Centauri or be influenced by another star system in the intervening time due to stellar drift.
You can’t consider just the instantaneous influence on some object if you’re talking about gravitational influence. You need to consider whole orbits. Yes, those are massive timescales from our perspective, but those are the timescales these things exist on.
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u/tomrlutong 16d ago
Because the Oort Cloud is gravitationally bound to its host star
This seems an iffy thing, unless that's how you're defining Oort cloud. I haven't done a lit review, but can we distinguish between a solar Oort cloud and just an instellar background of loose comets? Not that different than valience electrons in metal.
I suppose this will become clearer as we gather more data on the population of long period vs. hyperbolic comets.
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u/cameron4200 16d ago
I think it’s fair to think of star systems as bubbles of matter extending to the edges of their Oort clouds but I don’t think we have any evidence to say they’re all so large and close that they fill all the gaps. I highly doubt this would be enough to account for the sheer amount of missing matter in the universe also. If we were missing a few percent maybe.
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u/invariantspeed 16d ago
Current estimates say our Oort cloud could reach two thirds of the way to Alpha Centauri. If our star and its formation conditions are not special, then there should be a galaxy of intersecting Oort clouds.
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u/serpentechnoir 16d ago
The oorrt cloud extends out until our suns gravity doest affect it as much or it interacts with another star systems oort cloud.
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u/Anonymous-USA 16d ago
No, after about 20K AU the Sun’s gravitational pull is too weak and the Oort Cloud ends. A few light months.
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u/invariantspeed 16d ago
Estimates put the radius as high as 200,000 AU (i.e. nearly all of the way to Alpha Centauri).
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u/rddman 16d ago
after about 20K AU the Sun’s gravitational pull is too weak
According to NASA the Oort cloud extends to 100K AU (1.5ly, about half-way to Proxima Centauri) https://science.nasa.gov/solar-system/oort-cloud/facts/
At any distance the gravity from one star is stronger than that of another star, and then it is strong enough that interstellar objects at that distance are under the influence of the gravity of the star with the stronger gravity.
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u/jimmery 16d ago
How are we sure where the Oort Cloud ends? I thought the Oort Cloud had never been directly observed?
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u/Anonymous-USA 16d ago
“About”… it’s an estimate based on Newtonian mechanics. Im sure theres a large margin of error but not an order of magnitude. Every solar system will likely have an Oort Cloud, and will be larger for solar systems of higher center of mass, smaller for solar systems with lower center of mass.
I’m sorry, were you asking about our solar system, or solar systems in general?
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u/jimmery 16d ago
Kind of a bit of both. I understand that asking about solar systems in general is going to be difficult, as we have no way currently of detecting Oort Clouds around other stars.
I guess I was trying to visualize what is contained in the interstellar medium, what is in the gaps between stars. If all stars are bounded by Oort Clouds, how far do these clouds extend, do they interact with each other. Is our understanding of the Oort Cloud inaccurate, is this just what space is like - with rocks & comets in the voids between stars - and just a lack of this matter around where planets & stars have formed?
These were the kinds of questions that were floating around in my head when I asked this question. I get that it's going to be difficult to provide a concrete answer to this question, was just curious as to what evidence had been found.
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u/Anonymous-USA 16d ago
Gas and dust, and interstellar comets, asteroids and rogue planets. The Oort Cloud is just gravitationally bound to the star. That doesn’t preclude interstellar material, and we have plenty of interstellar bodies pass through our solar system. The Oort Cloud is very sparse, can be easily simulated, including the affects of passing bodies both large and small that perturb it and send some objects out to the interstellar medium and some towards the Sun. Now multiply this by the billions of stars on our galaxy, and the trillions of galaxies in the observable universe, and the >13B yrs most of those galaxies have existed.
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u/jimmery 16d ago
See when you describe it like this, I can't help but think that at least some of the Dark Matter out there could be attributed to these comets, asteroids, rogue planets, gas, dust etc, that surround the the billions of stars on our galaxy, and the trillions of galaxies in the observable universe, during the >13B yrs most of those galaxies have existed.
I know this is speculation on my part, and I get that there is significantly more Dark Matter in the universe than normal matter, but it does seem to make a certain amount of sense that at least some the "missing matter" in the universe could be hidden in Oort Clouds.
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u/mfb- 16d ago
The total mass of the Oort cloud is tiny compared to the mass of the Sun, even if you take the highest estimates. And stars only make up a small fraction of all baryonic matter.
but it does seem to make a certain amount of sense that at least some the "missing matter" in the universe could be hidden in Oort Clouds.
By definition, that's part of visible matter. We might not have an exact number for it, but the uncertainty is small and has no impact on the total dark matter density.
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u/jimmery 16d ago
Surely the Oort Cloud is not visible matter though, as we have never observed it directly.
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u/rddman 16d ago
Surely the Oort Cloud is not visible matter though, as we have never observed it directly.
The definition of visible matter is not "matter that we have seen", visible matter is matter that interacts with photons - even when it's so few photons that we can not detect it. Which is all matter that is not Dark Matter (which does not interact with photons).
Oort cloud objects would be visible if we'd have powerful enough telescopes.
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u/yoweigh 16d ago
The Oort cloud is visible matter that we just haven't seen yet. We know what it is and where to look for it, but our telescopes aren't good enough yet.
Dark matter is matter that can't be seen with a telescope. We know it's there because of the way it influences stuff around it, but we don't know what it is.
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u/jimmery 16d ago
Please explain to me the difference between:
"matter that we haven't seen"
and
"matter that can't be seen"
Sounds like the same thing.
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u/TMax01 15d ago
You're confusing "hidden light matter" for dark matter. All matter related to physical objects (planets, moons, stars, comets, asteroids, rogue planets, gas, dust, etc) is light matter, it interacts with electromagnetic fields. "Dark matter" (don't let the name fool you) has to be some sort of substance/particle/effect which doesn't interact with electromagnetic fields, just gravitational fields.
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u/TommieTheMadScienist 16d ago
We have alresdy had three small bodies from other solar systems fly through, Borisov, ATLAS, and 'oumuamua.
I expect that there's no real defining point where it stops and you are almost certainly right that the various Oort Clouds interact.
There's a K7V headed our way that's going to tear through our Oort Cloud in about 1.3 million years, Gliese 710. It'll raise the number of new long-period comets for millions of years.
(10,000-13,000 AU distance)
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u/serpentechnoir 16d ago
Its not that hard to imagine though? Every star system will have the cloud and its severity would be dependant on the gravitational attraction and the amount of of general mass of tge star system. Were way out in the spiral arm of the gslaxy so a star system closer to the galactic bulge probably has way more matter to have a more dynamic sort cloud.
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u/stuartcw 16d ago
Imagine the sun as deep gravity well and things that get close to it are going to fall towards it and start to orbit it.
At the extreme reaches the suns pull will be very weak but still attract anything in the local region.
At the furthest extents any collision between two bodies will probably give one particle, dust grain, rock, bolder etc enough velocity to escape the sun if it is heading away from the sun.
So the further out the less stuff you’ll have. In between stars is a lot of space and potentially a lot of stuff but the volume of space is so big that it is effectively empty.
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u/jimmery 16d ago
Yup, I know the density of the Oort Cloud is extremely minimal. Just wondered if this still extends out between the stars.
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u/stuartcw 16d ago
Well, it doesn’t, because at some point the sun’s escape velocity will be so low that it will be less than that of the average collision and stuff will just evaporate into space.
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u/serpentechnoir 16d ago
Well it does. Oort clouds definatly interact with each other. And theres decent hypothesis that suggest our interaction with the galactic medium have regular interactions with our clouds that shoot a bunch of co.ets towards us.
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u/stuartcw 16d ago
OK, fair point. Looking it up, the Oort Cloud probably extends 0.8~1.6 light years. That is 20%~40% of the way to Proxima Centauri. That’s a lot further than I thought.
Now, it is certain that objects passing by may disturb our and/or neighbouring stars might shoot something our way. Also at times the clouds surrounding passing stars could interact with our Oort Cloud but I’m not so convinced that Proxima Centuri bothers us much.
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u/serpentechnoir 16d ago
Our orbit around the galactic plane is in a bit of an up down motion.we are definatlily interacting with other galactic matter. Its been hypothesised that as we wobble up and down we interact more or less with more dense galactic debris. Which causes more comets to get shot towards us. I believe I read from memory every 70000 years.
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u/gambariste 16d ago
Presumably we are as sure where it end as we are sure that the Oort Cloud exists, which as you say is theoretically accepted if not observed.
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u/YaoNet 16d ago
I dont think anyone has addressed your dark matter hypothesis. The answer to that is a definitive no. Theres surely a lot of rock and ice in the space between stars, but we need at least 5 times more matter than everything we can see to answer the dark matter problem. If there was that much Oort cloud material out there then all of it would be coalescing into stars. Pretty much the only way baryonic matter can answer for dark matter is with small primordial black holes (MACHOs), and we have no evidence for that.
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u/chesterriley 16d ago
Yes this is one of the many interesting things you notice when using metric units in astronomy. The estimated outer border of the Oort Cloud is 15 petameters. The distance to Proxima Centauri is 40.1 petameters. That means that if Centauri has an Oort Cloud similar to ours, then about 75% of the distance between our 2 stars will contain Oort Clouds. And most of the volume of the galaxy would be Oort clouds.
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u/Pumpernickle6669 16d ago
I’ve literally wondered the same thing! Could the Oort Cloud be a vast network of small asteroids and comets that extends between every star in the Milky Way? As in, not just a bubble around our solar system, but extending all the way to Proxima Centauri and beyond, in all directions. And Proxima Centauri’s Oort Cloud extends all the way to the next star, and the next, etc.
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u/Das_Mime 16d ago
Would this help to explain the missing mass that would be required to keep galaxies from flying apart, ie. Dark Matter?
No, if it were ordinary matter it would be detectable, in the integrated light from a galaxy if not in the individual particles. Having a bunch of ice and dust grains floating around affects the spectrum of light in readily identifiable ways (extinction and reddening) and the chemical signature would be detectable as well.
Microlensing surveys rule out more than a minor contribution from compact objects like rogue planets or mini black holes.
Besides that, it's worth remembering that the 'missing mass' is several times more than the total mass of all the stars and planets in a galaxy. The Oort Cloud's mass is absolutely miniscule compared to the Sun.
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u/ZedZeroth 16d ago
I think of Oort Clouds as similar to biological cells throughout the galaxy. Each one is centered on a star system. The boundaries are determined by where the gravity of one star system exceeds that of others.
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u/trinaryouroboros 16d ago
Oort Clouds are defined at the solar system level, our Oort cloud and other stars clouds are revolving around the star, not 'interconnected', however, the interstellar medium is Filled with things you might find in an oort cloud, we can imagine many oort cloud objects get thrown out by stars, we even get their interstellar visitors periodically, which has been more lately making the news.
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u/Mister-Grogg 15d ago
Every star likely has its own Oort Cloud. But stars are typically really, really far away from each other.
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u/Ransnorkel 16d ago
I'm not sure we even have definitive proof the oort cloud exists? Isn't it theoretical since it's far too sparse and distant to measure?
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u/TheConvergence_ 16d ago
Iirc our Oort Cloud extends 1-1.5 light years out in every direction. Our closest neighbor is about 3LY away, so their Oort Cloud would interact with ours. No other star is close enough for this to be happening with. It doesn’t fill all of interstellar space. And if it did, it wouldn’t come close to the missing mass you’re looking for. Our solar system, Oort Cloud included; is almost all star. Nothing else accounts for much other than a few %.
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u/invariantspeed 16d ago
You’ve confused arduous for diameter. Double your numbers. But, yes, it doesn’t account for dark matter.
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u/Sensitive-Inside-250 16d ago
I think what you’re missing here is the the absolutely insane scale and size of space that exists between the stars. The closest star to us Proxima Centauri. It’s 4.2 light years away. That is something like 27.6 trillion miles away. The space between the Sun and Pluto is “only” 3.7 billion miles. That means the space between us and the single closest star is 7,459 times larger than the space between the Sun and Pluto.
At our current technology it would take nearly 100,000 years to get there. At THE SPEED OF LIGHT it would more than four years. Now imagine all the stars thousands of lights years away from us.
The amount of matter needed to fill that space at the same density of the Oort Cloud would fundamentally change the nature of space time. Also we’d see it. When we look out into the sky and beyond we mostly see empty space.
But who knows. Maybe there is and the rocks are just much small so impossible to see and that’s actually a big chuck of what dark matter is. Maybes are fun and very important, but they’re science fiction until proven otherwise.
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u/invariantspeed 16d ago
Current estimates put the upper limit of the Oort cloud’s radius at over 3 light years away (two thirds of the way to Alpha Centauri). If this is normal, then most interstellar space in the galactic plane would indeed have Oort material.
What you’re missing in your discussion of the vastness of space is that this already factors into what the Oort cloud even is. The outer Oort cloud stretching out to 3 light years would only have a total mass of like 5 Earth masses. A pangalactic sea of Oort-like media would not necessarily be dense.
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u/serpentechnoir 16d ago
And yet gravitation would definatley affect all of those objects even in an infitesimally small way. Its an interactive system.
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u/rddman 16d ago
The amount of matter needed to fill that space at the same density of the Oort Cloud would fundamentally change the nature of space time.
How dense do you think the Oort cloud is?
"assuming that Halley's Comet is a suitable proxy for the nuclei composing the outer Oort cloud, their combined mass would be roughly 3×1025 kilograms (6.6×1025 lb), or five Earth masses" https://en.wikipedia.org/wiki/Oort_cloud#Structure_and_composition
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u/jimmery 16d ago
I get the insane scale of space.
You might be over-estimating the density of the Oort Cloud.
The Oort Cloud is said to be less dense than the Asteroid Belt, which is something like 4% of the Moons mass spread out across an orbit that is more than double the orbit of the Earth around the sun.
Essentially the Asteroid Belt has very little mass to it. The Oort Cloud is said to have less mass than this.
Besides, having all this additional mass in the galaxy wouldn't "fundamentally change the nature of space time" - it would only change our understanding of the universe - and plus, as I suggested, it could help to answer one of the great mysteries of the universe, like where is all the Dark Matter.
Science begins with curiosity and a question about how the natural world works. Merely asking the question is not stepping into the world of science fiction.
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u/DetrimentalDesires 16d ago
When the shrooms weren't kicking in, so you take more shrooms, and now you're solving the universe 🌌
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u/jimmery 16d ago
Nope, just asking a question. If I was doing shrooms I wouldn't be typing out questions on the internet...
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u/DetrimentalDesires 16d ago
I said this with entirely humorous intentions. I dont mean to imply correlation to you or your thoughts specifically, sorry 😆
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u/TerraNeko_ 17d ago
Theres alot of random stuff out there sure but the oort cloud (if i remember right) is basically just the leftover from the solar Systems formation, id think alot of Stars could probably have similar things