[Bored chemist]

So please show me one star that the gravity of the galactic disc pulls it inwards.

The Sun.
If gravity was not pulling it in then it would no longer be in the galaxy.

[Dave Lev (OP)]

Quote from: Dave Lev on Today at 16:37:48
Do we see any star that is falling into the galactic disc from outside?

We see entire galaxies of stars falling into each other.
How could we hope to spot a single star doing it? We have only been looking in detail at the sky for 100 years or so.
So, no star has been seen to move more than 100  light years.
That's time to over about 1/500 of the diameter of the Milky way.
It's unlikely that we would spot it.

As we can spot those Hypervelocity stars, we also should be able to spot at least several  in falling stars - if there were any falling in stars.
However, there is not even a single falling in star. Not in 100 Years and not in one billion years due to the following:
1. Do you agree that for any star in the galaxy there is at least one outside? Therefore, the open space isn't empty. it should be full with stars.
2. The radius of the MY galactic disc is almost 50,000 Ly. So, just think how many stars should be collide with the galaxy per year.
3. We see so many hypervelocity stars that are ejected from the galaxy, while we couldn't find even one in those 100 years that fall in.
4. How many years are you going to wait until you would understand that our galaxy doesn't pull in any star from outside?
5. Actually, the MW galaxy acts as a mighty Star sprinkler. It ejects stars at any given moment. So the gravity of the galaxy pushes way many stars.
6. Any new born star must be ejected eventually from the arm/galactic disc. That's how the galaxy works (if you like it or not)
7. So, as any spiral galaxy acts as a giant star sprinkler, we have so many stars outside the galaxies.

 

If gravity pushed then orbits would not happen.
We would not be here.

We are here as our Sun had been created at the center of the galaxy
We are still holding our self in the Orion arm.
Sooner or later we will be ejected outwards from the spiral arm and the galactic disc
If we will be ejected alone, we will gain ultrahigh velocity and considered as Hypervelocity star that had been ejected from the galaxy . (very dangerous for us...)
.
If we will be lucky and be ejected with many nearby stars (cluster) we will be more protected and move away from the galactic disc at lower velocity.

If gravity was not pulling it in then it would no longer be in the galaxy.

Gravity works locally.
Therefore, the sun doesn't orbit around the center of the galaxy. It orbits around its twin.
Yes, there must be a twin for our sun.
Therefore it moves upwards and downwards several times (about four times) before it set one full cycle around the galaxy in about 240 MLy.
You have to consider the Orion arm as some sort of star' cluster.
So, the central mass of the Sun/twin is orbiting at a cluster that we currently call Orion arm.
Therefore, it moves at high velocity (about 220Km/s) not because of dark matter, but due to the local gravity force in the local spiral arm. Hence, in theory D there is no need for dark matter.
Currently, we are near the edge of the arm facing outwards.
However, don't worry, we will move back inwards later on.
Think about a star cluster. Stars are moving inwards and outwards constantly in a cluster.
In the same token, the Sun might consider that it orbits in a star' cluster, while the galaxy holds by gravity the whole cluster that is called Orion arm.

[Bored chemist]

Do you understand that everything that is in an orbit is falling in?

Anyway gravity sucks.

[Halc]

I would like to add that even if you have one million asteroids orbiting at 10R and you try to shoot them randomly in the direction of earth, It is quite clear to me that even if they hit with each other the chance that one of them will set a circular orbit at R is virtually Zero.

As I said, there's no need for them to be in orbit at all. They can just be passing by and be at the right place at the right time. My orbiting example was simply the easiest one to compute.

You said "NEVER EVER", and two of us have demonstrated you wrong. So you move the goal post I seen and now declare it merely improbable.  Given a random hit, I'd agree it's not very probable, but you're letting me control things at a distance, which makes it as probable as my ability to measure accurately.  One hit is all it takes, not a million.

Based on Newton (V= M G /R^2), in order to set it radius R its velocity should be 10^-2 V = about 3.15V
V is the velocity at 10R.
So, if we wish to decrease the circular orbit radius by 10 we must increase the velocity by 3.15

Still using the inappropriate formula at all times I see.  In fact, the 1R orbit is lower energy than a 10R one, so the trick would be to slow it down, which is what I'm doing with my collisions.  I gave the appropriate formula in my post. Yours is for a stable circular orbit, which isn't going to get our object down from 10 to 1 now is it?

I claim that in any direction/velocity that you would push (from 10R in the direction of the Earth) this asteroid it would never set a circular orbit around the earth at lower radius.

But you've backed off that claim and stated it to be merely improbable now. You're admitting you're wrong it seems, but of course you're also wrong about the promised payment.

2.Circular orbit - Let's assume that something had been created. The chance to get an circular orbital system between two objects that came from the deep space in the direction of each other is virtually zero.

And yet our moon is such an object, the result of a two-body collision, and having a nearly circular orbit.

Phobos is in a circular orbit, which is measurably decreasing every year, so that's another example of an orbit dropping, this time without any interference by a 3rd object.

I can think of other real examples that invoke GR, such as the merger of two black holes, which originate from 'deep space', or at least outside of each other's orbits, and they reduce their circular orbit from 10R to 1R all without collision or rockets.  Of course the radius doesn't stop at 1R, it keeps going down as the angular momentum is radiated away in the form of gravity waves.  But you asked, and that is a very real example that has actually been empirically measured.  Pay up, or shut up.  I would certainly accept the latter, but you're not going to do that either.

3. Increasing the Circular orbital velocity - Let's assume that a star (S2) is orbiting around a main object as a SMBH.

This is something you've repeatedly denied.

This is my point of view

My kid's point of view is that her invisible friend hides her glasses now and then. Your personal point of view has far less self-consistency than that. At least the existence of the invisible friend is not easily falsified, so she's one up on you.

[Kryptid]

Do we see any star that is falling into the galactic disc from outside?
Why we see so many Meteors falling on earth due to gravity and NOT EVEN ONE STAR falling into the galactic disc?

You have actually created a situation where you "can't lose". If we find a star that is heading towards our galaxy, all you will do is claim that it will eventually be pushed aside before it can enter. Any star that is already in our galaxy, on the other hand, will be one that you claim never came from outside in the first place. For example, I can link you to this source about stars in our galaxy that probably came from outside of it, but you will simply claim that they originated in our own galaxy instead, won't you? https://www.cnn.com/2020/07/12/world/milky-way-stars-nyx-scn-trnd/index.html#:~:text=(CNN)%20Astronomers%20have%20found%20a,Greek%20goddess%20of%20the%20night.

It's interesting to note what they say about the Nyx stars in that link, though:

The cluster of 250 stars are rotating with the Milky Way's galactic disk, where most of the galaxy's stars are located. But the Nyx stars are also moving toward the center of the galaxy.

That contradicts what you claimed earlier when you said:

However, all the stars in the arms MUST be drifted outwards over time.

I am about to predict the future! Oh! Oh! I see... I SEE... I see Dave trying to argue that the stars aren't actually moving towards the center of the galaxy! He is going to say there is a mistake of some kind!

[Dave Lev (OP)]

If we find a star that is heading towards our galaxy, all you will do is claim that it will eventually be pushed aside before it can enter. Any star that is already in our galaxy, on the other hand, will be one that you claim never came from outside in the first place. For example, I can link you to this source about stars in our galaxy that probably came from outside of it, but you will simply claim that they originated in our own galaxy instead, won't you? https://www.cnn.com/2020/07/12/world/milky-way-stars-nyx-scn-trnd/index.html#:~:text=(CNN)%20Astronomers%20have%20found%20a,Greek%20goddess%20of%20the%20night.

It's interesting to note what they say about the Nyx stars in that link, though:

Thanks
This article doesn't fulfill my request.
I have asked if we see any star that is falling into the galactic disc from outside (not about the center itself).
However, it is still very interesting article due to the following:

1. Born outside - "The stars that are born outside the Milky Way have different chemicals than the ones that are born here," Necib said.
There is no further explanation about the different chemicals than the ones that are born here
Does it mean that all the 400 Billions stars in the Milky Way have the same unique chemicals?
Can you please elaborate about it? What is so unique in the chemicals of all the stars that had been created in the Milky Way?
What kind of different chemicals our scientists have found in all of those 250 stars.

2. Cluster radius:
It is stated:
"This new star cluster has been named Nyx, for the Greek goddess of the night. They are within the vicinity of our sun's location in the galaxy and extend about 6,000 light-years above and below the plane of the Milky Way galaxy if you were to view it from the side."
"The cluster of 250 stars are rotating with the Milky Way's galactic disk, where most of the galaxy's stars are located. But the Nyx stars are also moving toward the center of the galaxy."
So, this cluster is located near our sun (within the vicinity of our sun's location in the galaxy). Therefore, it is about 28,000 Ly from the center of the galaxy.
At that location the thickness of the galactic disc is only 1KLY.
So how could it be that suddenly out of the blue there will be a cluster which gets to 6000 Ly above and below the galactic disc?
Is this realistic?

3. Star density near the sun location:
The density of star near our location is exactly 64 per 50LY radius. Our scientists have found that the total number stars per 100LY is exactly 512.
Therefore, by using the same density, the number of the stars per 6000Ly should be :
(6000/100) ^ 3 * 512 = 216,000 * 512 = 110,592,000 stars  or about 100 M stars in a cluster with a radius of 6000Ly.

So, somehow, we see here a cluster with a radius of 6000 Ly that only has 250 stars.
The real meaning of that is a density of only one star per 1000Ly. (6^3=216, or almost 250)
How can we consider that ultra low density as a cluster?
This is clear unrealistic idea. Could it be that we actually see two clusters or some stream of stars? One cluster/stream of stars at 6000 below the disc and the other is 6,000 Ly above the disc?.
However, I have full confidence that if we will measure their velocity with regards to the galactic disc, we should find that all of them are drifting away from the galactic disc. (above or below the disc)

4. Cluster Location:
As it is stated:  "This new star cluster has been named Nyx, for the Greek goddess of the night. They are within the vicinity of our sun's location in the galaxy and extend about 6,000 light-years above and below the plane of the Milky Way galaxy if you were to view it from the side."
What does it mean that: "They are within the vicinity of our sun's location in the galaxy"?
It should be quite close to the Sun location, however how close?
How far from our location and how far from the galaxy center this cluster is located?
Is it part of any nearby arm, or is it stays there by itself?
Can we see exactly the location of all the stars above and below the disc including there movment direction?

5. Moving toward the center of the galaxy:
"The cluster of 250 stars are rotating with the Milky Way's galactic disk, where most of the galaxy's stars are located. But the Nyx stars are also moving toward the center of the galaxy."
Well stars at the galactic disc can't move in the direction of the center.
However, if 125 stars are located at 6000 Ly above the disc and the other 125 are located below the disc and all of them are moving away from the disc, than they have already disconnected from the disc. In this case, as they move upwards/downwards from the disc, they can move in the direction of the center. However, They will NEVER EVER fall back again at the galactic disc.
In any case, can we really measure their exact distance from the center of the galaxy and verify if they are really decreasing this radius?


Conclusion:
A cluster with a density of one star per 1000Ly can't be considered as a cluster
Why they do not try to verify if the stars are falling into the galactic disc?
They surly have error in this verification.
However, I mostly appreciate to get further explanation of that "different chemicals" issue.

He is going to say there is a mistake of some kind!

You are absolutely correct!

[Bored chemist]

What kind of different chemicals our scientists have found in all of those 250 stars.

It's the ratios of the elements that are different.

Did you read the Nature article?
https://www.nature.com/articles/s41550-020-1131-2.epdf?sharing_token=e71tq_0EyC0COzNCPhCZW9RgN0jAjWel9jnR3ZoTv0Mq3fdQAZsAtY7Q6FxuakNtbhEKxyKIugF0KF-bGpOgZ-N5JSk5uFieMqObpFVfPmM06zaRRIpzeuO4q-y_nYNg_22QCyrOJFRwmp8TQFHO6uzbX7mBwCm9o3YehpbzhWOZ2h__FvoH7QKCV7to902XBJ4KZrw8OCIx5VTVGYnq8MgSxJRqcxLJU3McXJfyDydGU5qpTDI7xWu-PTKFNv0bi2JJb2Mg8x2HmSOigg5solRV_nUfYG5SH038jilL4_U%3D&tracking_referrer=edition.cnn.com

[Bored chemist]

So how could it be that suddenly out of the blue there will be a cluster which gets to 6000 Ly above and below the galactic disc?

Because it's in the process of collision.
That's the point.

[Kryptid]

Ha! I knew that you were going to be in denial!

In any case, can we really measure their exact distance from the center of the galaxy and verify if they are really decreasing this radius?

Yes. We can know the direction that a star is moving by look at its redshift. You might want to look it up.

[Dave Lev (OP)]

Ha! I knew that you were going to be in denial!

Well, even our scientists don't know for sure the source of those stars. They clearly claim that: "further spectroscopic follow-ups (for example, from APOGEE-2, 4MOST and WEAVE) are needed to validate these conclusions."
https://www.nature.com/articles/s41550-020-1131-2.epdf?sharing_token=e71tq_0EyC0COzNCPhCZW9RgN0jAjWel9jnR3ZoTv0Mq3fdQAZsAtY7Q6FxuakNtbhEKxyKIugF0KF-bGpOgZ-N5JSk5uFieMqObpFVfPmM06zaRRIpzeuO4q-y_nYNg_22QCyrOJFRwmp8TQFHO6uzbX7mBwCm9o3YehpbzhWOZ2h__FvoH7QKCV7to902XBJ4KZrw8OCIx5VTVGYnq8MgSxJRqcxLJU3McXJfyDydGU5qpTDI7xWu-PTKFNv0bi2JJb2Mg8x2HmSOigg5solRV_nUfYG5SH038jilL4_U%3D&tracking_referrer=edition.cnn.com
For the small subset for which we have data, Nyx stars have abundances that are comparable to both the thick disk (Fig. 2) and dwarf galaxies29–31. However, the small dispersion in the chemical abundances for Nyx does suggest a single progenitor origin, especially given the coherence in velocity space. Given the small subset of Nyx stars with abundances, and the large measurement uncertainties from RAVE-on, further spectroscopic follow-ups (for example, from APOGEE-2, 4MOST and WEAVE) are needed to validate these conclusions."
So, why in the other articale they were so sure that those stars came from outside?
As they don't come from outside, it is clear that all of those stars had been created in the galaxy itself.
Velocity: It is stated that the average speed is 250 Km/s
The Sun is velocity is 220Km/s. So, as both are moving with the galactic disc, how could it be that our scientists claim that they are lagging by 90Km/s with regards to the galactic disc.
"It is clearly prograde, moving with the Galactic Disk, but lagging in velocity by ~90 km s−1. The 232 most likely stars to belong to Nyx are coherent in velocity, with total average speed 250 km s−1 and dispersion of 48 km s−1."
How could it be?

Cluster or stellar stream?
"In the article it is clearly stated that they specifically claim for a stellar stream as I was expecting:
So it isn't a cluster by definition.
In any case, as the distance between the stars is about 2KPC (6000Ly) how can we even consider it as a stream?
"Here we present evidence for a new prograde stellar stream in the vicinity of the Sun, whose interpretation provides a hint that such a merger occurred in our Galaxy"
However, as I have already pointed, our scientists don't know for sure the source of those stars and therefore, they can't claim that it is "a merger occurred in our Galaxy".
Conclusion:
This article is very confusing.
we really don't know the correct locations of the star.
We don't know if they are locatedd near a spiral arm or far away from any arm.
We don't know the source of those stars
Why they claim that they are coming (falling in) from a dwarf galaxy while they claim clearly that "further spectroscopic follow-ups (for example, from APOGEE-2, 4MOST and WEAVE) are needed to validate these conclusions."?
How could it be that the stars are moving at 250Km/s and still lagging by 90 km/s?

Yes. We can know the direction that a star is moving by look at its redshift. You might want to look it up.

Once we understand what do we really see, we can consider if what we see is realistic.

[Bored chemist]

Ha! I knew that you were going to be in denial!

Well, even our scientists don't know for sure the source of those stars. They clearly claim that: "further spectroscopic follow-ups (for example, from APOGEE-2, 4MOST and WEAVE) are needed to validate these conclusions."
https://www.nature.com/articles/s41550-020-1131-2.epdf?sharing_token=e71tq_0EyC0COzNCPhCZW9RgN0jAjWel9jnR3ZoTv0Mq3fdQAZsAtY7Q6FxuakNtbhEKxyKIugF0KF-bGpOgZ-N5JSk5uFieMqObpFVfPmM06zaRRIpzeuO4q-y_nYNg_22QCyrOJFRwmp8TQFHO6uzbX7mBwCm9o3YehpbzhWOZ2h__FvoH7QKCV7to902XBJ4KZrw8OCIx5VTVGYnq8MgSxJRqcxLJU3McXJfyDydGU5qpTDI7xWu-PTKFNv0bi2JJb2Mg8x2HmSOigg5solRV_nUfYG5SH038jilL4_U%3D&tracking_referrer=edition.cnn.com
For the small subset for which we have data, Nyx stars have abundances that are comparable to both the thick disk (Fig. 2) and dwarf galaxies29–31. However, the small dispersion in the chemical abundances for Nyx does suggest a single progenitor origin, especially given the coherence in velocity space. Given the small subset of Nyx stars with abundances, and the large measurement uncertainties from RAVE-on, further spectroscopic follow-ups (for example, from APOGEE-2, 4MOST and WEAVE) are needed to validate these conclusions."
So, why in the other articale they were so sure that those stars came from outside?
As they don't come from outside, it is clear that all of those stars had been created in the galaxy itself.
Velocity: It is stated that the average speed is 250 Km/s
The Sun is velocity is 220Km/s. So, as both are moving with the galactic disc, how could it be that our scientists claim that they are lagging by 90Km/s with regards to the galactic disc.
"It is clearly prograde, moving with the Galactic Disk, but lagging in velocity by ~90 km s−1. The 232 most likely stars to belong to Nyx are coherent in velocity, with total average speed 250 km s−1 and dispersion of 48 km s−1."
How could it be?

Cluster or stellar stream?
"In the article it is clearly stated that they specifically claim for a stellar stream as I was expecting:
So it isn't a cluster by definition.
In any case, as the distance between the stars is about 2KPC (6000Ly) how can we even consider it as a stream?
"Here we present evidence for a new prograde stellar stream in the vicinity of the Sun, whose interpretation provides a hint that such a merger occurred in our Galaxy"
However, as I have already pointed, our scientists don't know for sure the source of those stars and therefore, they can't claim that it is "a merger occurred in our Galaxy".
Conclusion:
This article is very confusing.
we really don't know the correct locations of the star.
We don't know if they are locatedd near a spiral arm or far away from any arm.
We don't know the source of those stars
Why they claim that they are coming (falling in) from a dwarf galaxy while they claim clearly that "further spectroscopic follow-ups (for example, from APOGEE-2, 4MOST and WEAVE) are needed to validate these conclusions."?
How could it be that the stars are moving at 250Km/s and still lagging by 90 km/s?

Yes. We can know the direction that a star is moving by look at its redshift. You might want to look it up.

Once we understand what do we really see, we can consider if what we see is realistic.

None of it matters because you still run into these.

As I have stated, there are two possibilities for falling in objects:
Fall in and collide with the main object or be pushed away.

Why don't  you consider the third possibility?
Don't you understand it?
Most people would get to grips with it quite easily.
They thing falls towards something, and then misses it.

Since you don't seem to understand basic physics, you are not in a position to criticise it, but let's see how you did.

(1) Gravity does not push - Yes It does

It plainly does not.
But you don't understand how something can get close to something and then miss.
This says a lot about you...

2) Black holes don't break the conservation laws  - Black hole does not break the conservation laws and also does not evaporate as Hawking had claimed. There is no negative particles. BH has the ability to create new positive particle pair and give them extra kinetic energy by its high gravity energy.

Unless it evaporates in the process of creating new particles, what you have described is a breach of the conservation laws.
It's just that you don't seem to be bright enough to recognise this.

(3) Even if they did, it wouldn't help because they wouldn't build a universe that looks like this one - Yes it does. The Rocket over rocket system can do it easily.

That wouldn't work anyway,, but it doesn't matter.
The "rocket over rocket "idea is a breach of GR.

(4) Even if they could, you still need to explain where the first one comes from - The Universe and its infinite space was always there

No.
Because Olber.
Also because the conservation laws.

(5) This simply isn't true "The Black body radiation in the CMB is a clear indication that our Universe is Infinite in its size." - Yes it is. I have already explained this issue. You would never ever get a black body radiation outside the cavity (in the open space). Only if you are located at the cavity itself (or monitor the radiation in the cavity by a tiny hole) you could find the Black body radiation.

That's not a sensible explanation.
Inside of a finite, large, universe that was once very hot, you expect a CMB.

As I have pointed out, what if we are in a big (but finite) box with black walls at 2.7K?
That would be finite, and we would see BBR .

(6) Even if it was true, this wouldn't be a valid deduction "Therefore, it also must be infinite in its age." - Yes it is. In order to set an infinite Universe from a single BH you must use infinite time.

Other mechanisms (those which are  not a pile of junk) do not start from a singe BH and make it grow by magic.

(7) We know that it's finite, thanks to Olber - This is a fiction. Our Universe is infinite. Olber theory could work only if in the all the galaxies in the infinite universe are moving at a velocity which is lower than the speed of light relative to our location.

No, because some of them would be moving towards us (very fast).

Now, since it's clear that you are wrong about all that, why not just accept that you are wrong?

[Kryptid]

The Sun is velocity is 220Km/s. So, as both are moving with the galactic disc, how could it be that our scientists claim that they are lagging by 90Km/s with regards to the galactic disc.

The speed of stars in the galactic disk is not uniform. In general, those closer to the center will move faster. It's also important to remember that there can be differences in relative velocity in different directions. The Nyx cluster might be moving at an overall velocity of 250 km/s while it is moving more slowly than that in the direction of the galactic rotation.

"In the article it is clearly stated that they specifically claim for a stellar stream as I was expecting:
So it isn't a cluster by definition.
In any case, as the distance between the stars is about 2KPC (6000Ly) how can we even consider it as a stream?

All you are doing is arguing semantics. A stream can be a cluster. Cluster is just another name for "group". A stream of water is group of water molecules, so it can also be considered a cluster of water molecules.

Once we understand what do we really see, we can consider if what we see is realistic.

Redshift tells us both whether an object is moving towards or away from the Earth and what its relative velocity is. That's been well understood for many decades.

[Dave Lev (OP)]

Quote
2.Circular orbit - Let's assume that something had been created. The chance to get an circular orbital system between two objects that came from the deep space in the direction of each other is virtually zero.

And yet our moon is such an object, the result of a two-body collision, and having a nearly circular orbit.

How the moon had been created:
https://en.wikipedia.org/wiki/Origin_of_the_Moon
"Theia, an early protoplanet the size of Mars, hit Earth in such a way that it ejected a considerable amount of material away from Earth. Some proportion of these ejecta escaped into space, but the rest consolidated into a single spherical body in orbit about Earth, creating the Moon. "
This is a pure imagination:
If two solid bodies at that size collide with each other, they both would be broken  to several/many smaller objects.
Then the broken objects would collide again and again with each other and break themselves to death.
None of those broken objects would regain the nice round ball shape of a planet or moon.

We have an excellent example for the outcome of collision
It is calls - Ceres
This Object was a real planet in the past.
The Cerest with the Million asteroids are the left over from a mighty collision.
So, the idea that collision could create new planet or moon is a pure fiction.
Collision can only destroy the object!
Please remember that all the planets and moons in the solar system had been created from the same giant gas cloud (Similar to G1 and G2.) near the SMBH and at the same time.
As almost 98% of the matter is based on Hydrogen and helium, the solid matter in the Moon (or the planet) was less than 2% from the total matter in their creation time.
So, the moon and the earth were born as a compact gas clouds. Over time the solid matter moved inwards due to gravity, while most of the hydrogen and helium have been evaporated to the open space.
This is the only way to get a nice ball shape of a solid planet or moon.
We actually have a solid prove for that.
The gravity force between the Sun/Moon is more than twice stronger than the gravity force of the Moon/earth gravity.
So, why the Moon orbits around the earth and not around the sun?
The answer is quite simple:
The current mass of the moon or the earth is less than 2% from their mass in the creation date.
So, each one of them had almost 50 times its current mass.
They were also closer to each other.
Therefore, during the creation process, the Moon had been locked to earth by their higher gravity force.
This also proves that objects do not change the hosting object even if their gravity force had been reduced dramatically.
Hence, if an object is coming from the open space it will continue to the open space or collide with the nearby object.
It would never ever set a circular orbital cycle with that object.

Given a random hit, I'd agree it's not very probable, but you're letting me control things at a distance, which makes it as probable as my ability to measure accurately.  One hit is all it takes, not a million.

In our real universe a planet, moon or even asteroids are not elastic ball.
If you hit it you break it.
So, if you hope that by collision with other asteroids you can force this asteroid to orbit around the earth, then this is a fiction.
After one or two collisions you would end up with millions of broken objects.
If you could set a simulation in a computer, you would see that not even one tiny object would be bound by gravity to earth.
Meteor are perfect examples for that activity.
A group of asteroids cross the path of the earth while they orbit around the Sun.
Those asteroids that fall in considered as meteors.
All the other continue in their path and totally neglect the earth.
None of those asteroids that orbit the sun will start orbiting the Earth.
Hence, the wishful hope that somehow objects that came from the open space could orbit around each other (while they have no engine) is just a pure imagination.

Phobos is in a circular orbit, which is measurably decreasing every year, so that's another example of an orbit dropping, this time without any interference by a 3rd object.

I have also discussed about Phobos.
I totally disagree with the assumption that its radius is decreasing.
If I remember it correctly, our scientists based this assumption on a difference of only 0.7 sec per full orbital cycle while they monitor it from outside by a probe.
This is really unrealistic assumption.
The 0.7sec is clearly falling in the error range while the probe is also orbiting Mars.
If we wish to get better understanding, we had to monitor it from inside or to monitor its orbital velocity.
As it drifts in, its orbital velocity should be faster.
Please let me know if you have better example for an object that drifts inwards and increases its orbital velocity during this process.

[Bored chemist]

None of those broken objects would regain the nice round ball shape of a planet or moon.

Why is the Earth round then?
It was formed by countless collisions.

So, why the Moon orbits around the earth and not around the sun?
The answer is quite simple:

The Moon does orbit the Sun.
The path it traces is slightly perturbed by the motion round the Earth. It is close to a 13 sided polygon with rounded corners.

Why invent some tosh to explain something that's not true?

[Bored chemist]

The 0.7sec is clearly falling in the error range while the probe is also orbiting Mars.

What makes this "clear"?
A decent digital watch would measure better than that.

[Bored chemist]

I totally disagree with the assumption that its radius is decreasing.

It isn't an assumption, it's a measurement.

What you are saying there is "I do not agree with reality".
You might want to think about that.

[Kryptid]

If I remember it correctly, our scientists based this assumption on a difference of only 0.7 sec per full orbital cycle while they monitor it from outside by a probe.

No, it was measured from the surface. A lander there was able to measure (not assume, not theorize, not simulate, but actually measure) that the time it takes for Phobos to orbit Mars is slowly decreasing. So this means it's either speeding up, coming closer to Mars, or both.

The 0.7sec is clearly falling in the error range

Support that statement with evidence. Do you have authoritative information about the error range of the measurements?

[Dave Lev (OP)]

Quote from: Dave Lev on Yesterday at 21:35:43
If I remember it correctly, our scientists based this assumption on a difference of only 0.7 sec per full orbital cycle while they monitor it from outside by a probe.

No, it was measured from the surface. A lander there was able to measure (not assume, not theorize, not simulate, but actually measure) that the time it takes for Phobos to orbit Mars is slowly decreasing. So this means it's either speeding up, coming closer to Mars, or both.

Would you kindly introduce this interesting article about Phobos.

[Kryptid]

Would you kindly introduce this interesting article about Phobos.

After looking into it further, it seems that it was indeed measured by a spacecraft as you said. That was a mistake on my part. One article describing the measurement is here: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2004JE002376

The Mars Orbiter Laser Altimeter (MOLA) instrument on the Mars Global Surveyor spacecraft has observed 15 transits of the shadow of Phobos across the surface of Mars, and has directly measured the range to Phobos on one occasion. The observed positions of Phobos and its shadow are in good agreement with predictions from orbital motion models derived from observations made prior to 1990, with the notable exception that Phobos is gradually getting ahead of its predicted location. This effect makes the shadow appear at a given location earlier than predicted, and the discrepancy is growing by an amount which averages 0.8 s/yr.

The instrument time is related to the spacecraft clock with submillisecond precision [Neumann et al., 2001], and spacecraft time is maintained by the Mars Global Surveyor project with accuracy better than 30 milliseconds relative to UTC.

As stated above, the overall accuracy of the laser altimeter is in the range of +30 milliseconds (+0.03 seconds). That uncertainty is significantly smaller than the measured value of 0.8 seconds per year, so you can't blame the measured decrease in orbital time of Phobos on uncertainty.

[Dave Lev (OP)]

Thanks Kryptid

After looking into it further, it seems that it was indeed measured by a spacecraft as you said. That was a mistake on my part. One article describing the measurement is here: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2004JE002376

In the article it is stated that the measurement was based on "the shadow of Phobos across the surface of Mars":

The Mars Orbiter Laser Altimeter (MOLA) instrument on the Mars Global Surveyor spacecraft has observed 15 transits of the shadow of Phobos across the surface of Mars,

However, Phobos isn't a nice round object.
https://en.wikipedia.org/wiki/Phobos_(moon)
Dimensions   27 × 22 × 18 km[5]
Mean radius   11.2667 km (1.76941 mEarths)
So, how do we know for sure if we measure the shadow of Phobos while it is 27Km, 22Km or 18Km?
It is clear that the shadow time could be different from size to size.
How our scientists couldn't consider this possibility?
There is also the issue of the eccentricity of phobos orbital cycle:
Periapsis   9234.42 km[5]
Apoapsis   9517.58 km[5]
Semi-major axis   9376 km[5] (2.76 Mars radii)
Eccentricity   0.0151[5]
How do we know if we set the measurements at the Periapsis, Semi-major axis or exactly at the Semi-major axis.
At each location the velocity is different.
I assume that there might be some other issues as the accuracy of the probe velocity and location.
So, how our scientists couldn't consider that the 0.8Sec/year under those variants is clearly not good enough.
Actually, if I recall it correctly, our scientists have discovered that the moon is drifting away just after setting at the moon a special reflector for a laser beam.
Therefore, in order to get a clear indication we need to set one probe on Mars and the other on Phobos.
There is no short cut.

As stated above, the overall accuracy of the laser altimeter is in the range of +30 milliseconds (+0.03 seconds). That uncertainty is significantly smaller than the measured value of 0.8 seconds per year, so you can't blame the measured decrease in orbital time of Phobos on uncertainty.

Sorry, I totally reject this unrealistic measurement.

Please remember - All objects at long rang MUST drift outwards due to gravity.
Moons and planets are considered as located at long rang.
Therefore, all the Moons and planets in the solar system must drift outwards without any exception!