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Would holes in the Oort cloud be a record of what has passed through it?

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    $\begingroup$ You should be aware that nobody has ever observed anything in the Oort cloud. It's existence is infered from long period comets. But anything about the detailed distribution of objects is hypothetical. Remember also that objects in the cloud are not fixed, they move in orbits around the sun. $\endgroup$
    – James K
    Oct 25, 2023 at 20:41
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    $\begingroup$ So the answers to your questions are "nobody knows" and "probably not" $\endgroup$
    – James K
    Oct 25, 2023 at 20:43
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    $\begingroup$ A buddy asked me for documentaries on either the Oort Cloud or the Kuiper Belt. There's like one and a half of them, all of which are speculation and neither of them were very good. $\endgroup$
    – Mazura
    Oct 26, 2023 at 7:06
  • $\begingroup$ Recently asked: astronomy.stackexchange.com/questions/55039/… $\endgroup$ Oct 26, 2023 at 14:46
  • $\begingroup$ Note that Oort cloud entities are prone to perturbations and so they can gravitate/accumulate to bodies with bigger mass. Have a read: articles.adsabs.harvard.edu//full/1992MNRAS.259...37C/… $\endgroup$ Oct 26, 2023 at 14:52

2 Answers 2

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The Oort Cloud has not been directly observed.

The Oort cloud is still theoretical. We're pretty sure it's there, but we don't have direct evidence. The objects that make it up are too small, too dark, and too far away to observe. We only see comets when they get close enough to the sun for the surface ice to start to burn off and produce a tail of dust behind it. In the "freezer" of the theorized Oort cloud, it would be like trying to see a lump of coal on a moonless night.

The question of whether there are holes in the Oort cloud presupposes we have a good map of the area, which we don't.

If an object made a big hole in the cloud, it would vanish over time.

The Oort cloud (assuming it exists) is made up of many small objects in orbits in a wide range of orientation, distance, and eccentricity. What that means is the orbital period of any given two objects are almost certain to be wildly different, and their paths crisscross throughout the cloud.

If you were to, say, fire a massive laser into the cloud, burning away every object in a huge area (this is not recommended), the hole would vanish over time. It might be possible for a while to detect a "thinness" in one direction over another, but it would probably be impossible to spot after a few thousand years (if you could even see oort objects). Removing those objects would end up just thinning out the oort cloud in general, but not with any directionality.

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    $\begingroup$ There would be more high energy cosmic rays coming through holes perhaps. $\endgroup$
    – user52681
    Oct 25, 2023 at 20:54
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    $\begingroup$ Although we don't know exactly how many object are in the OOrt cloud, they are certainly pretty spaced out (it's not like a cloud on earth, nor like a starwars asteroid field) There's enough gaps to let light and cosmic rays through. $\endgroup$
    – James K
    Oct 25, 2023 at 21:22
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    $\begingroup$ Long period comets come from an Oort cloud. There is AFAIK no alternative credible model. $\endgroup$
    – ProfRob
    Oct 25, 2023 at 23:01
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    $\begingroup$ @Adrdav22 We are pretty sure that a star passed through the Oort cloud 70,000 years ago. This is Scholz's star. We know its trajectory and we can see that it came well within the supposed oort cloud. Gl710 will do so in the not-so-distant future too. We don't know about any "holes" $\endgroup$
    – James K
    Oct 26, 2023 at 14:14
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    $\begingroup$ Doubtful. As I said, the chaotic orbits of oort objects are probably going to mean any disruptions smooth out across the whole cloud in a (astronomically) short time. $\endgroup$ Oct 26, 2023 at 15:12
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Maybe, but not likely.

Let's look at something similar - the Asteroid Belt.

The Asteroid Belt between Mars and Jupiter (not really "between" since some of it extends past Jupiter, and depending on your definition, some is inside Mars' orbit, all the way close to the sun).

The Belt has several gaps and clusters. This is Not even close to scale. Most of those dots are as small as 300 feet.

enter image description here

The Belt's total mass is quite tiny, about the total mass of Pluto. We've tracked many objects there and have a good idea of the total mass.

The Oort cloud's total mass is estimated to be somewhere between the mass of Earth and the mass of Saturn. Saturn isn't really a "large" object astronomically. The Oort cloud is estimated to be 1 to even 3 light-years thick. Scattering the mass of Saturn across even one light year would basically be dust. The distance between objects, even tiny ones, could be multiple AU.

If we go with 3 ly, then the area of the cloud in 2 dimensions is about 27ly squared. It's in 3 dimensions, and lets say it is 1 ly thick. That's 27 cubic light years of volume to fit the planet Saturn.

It is much less dense than the Belt.

As a side note, when NASA sends out a probe past the Belt, they track some of the larger objects and plot a course to not hit them, and ignore everything else since the distance between asteroids is mind-bogglingly-huge.

Thus, since we don't track anything through the Belt this way, it would work even less for the cloud.

But, we have to define "large" in your question. If you mean like a black hole, or Betelgeuse, then probably not in a billion years. Its gravity would have totally wrecked the whole system, since its size is about the orbit of Jupiter. (Not the size of Jupiter, its diameter is the orbit of Jupiter. It is extra-large.)

Since we are estimating the size of the cloud, and Pluto's orbit is about 5 light-hours vs a few light-years of the cloud, Pluto's orbit gets rounded out.

It is a very interesting theory, and if we could measure the objects in the Cloud, closely, and in real-time, if it exists, then we might could track something planet or star-sized that moved through it.

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  • $\begingroup$ @Adrdav22 If I'm not mistaking that is the average density in between galaxies, and considering how much empty space there is that is still a mind boggling large amount of matter. $\endgroup$
    – Michael
    Oct 27, 2023 at 15:20
  • $\begingroup$ "The Oort cloud is estimated to be 1 to even 3 light-years thick...." Interesting: if Alpha Centauri has its own Oort cloud, the gap between clouds should be of the same order as an average Oort cloud. $\endgroup$ Oct 27, 2023 at 21:27
  • $\begingroup$ @Adrdav22, A=pi r ^2. If r is ~3, then A ~ 27. Since all these are speculation/hypothesis, it very well could be wrong. $\endgroup$
    – MikeP
    Oct 28, 2023 at 3:03
  • $\begingroup$ @MikeP is the "three LY thick" counting the radius (i.e. distance from sun or us to the outer "edge") or the diameter? $\endgroup$ Oct 28, 2023 at 20:56
  • $\begingroup$ @Michael I got my calculation wrong. It should have been the mass of Saturn 10^26 kg in 27 light years cubed (10^48 m^3) This is 10^ -22 kgm^3 one billion times larger than my first calculation. $\endgroup$
    – user52681
    Oct 29, 2023 at 13:52

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