Retrograde star orbits in the Milky Way

In summary, there are no known stars in the solar neighborhood that orbit the galactic center in the opposite direction. However, there are a few globular clusters with retrograde motion and a sub-dwarf Halo star, Kapteyn's star, that could possibly be considered a nearby star. Retrograde rotation, like that of Venus and Uranus, is not the same as retrograde orbit. It is also unlikely for a star to be tidally locked with the galactic center. The majority of stars with retrograde motion are found in the galactic halo, which formed through a different process than the galactic disk.
  • #1
lifeonmercury
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Are there any stars in the solar neighborhood that orbit the galactic center in the opposite direction?
 
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  • #2
lifeonmercury said:
Are there any stars in the solar neighborhood that orbit the galactic center in the opposite direction?
Not sure if this counts, it's a fun video with some corny music:

 
  • #3
lifeonmercury said:
Are there any stars in the solar neighborhood that orbit the galactic center in the opposite direction?
None known, and no reason (that I know of) to expect that there might be.
 
  • #4
What about stars with retrograde rotation (like Venus and Uranus)?
 
  • #5
lifeonmercury said:
What about stars with retrograde rotation (like Venus and Uranus)?
These are 'wandering stars', which in greek is asteria planetes, from which the English word 'planets' derives.
That is, these are not actual stars. :)

Furthermore, retrograde rotation is not the same as retrograde orbit. The difference is the same as between a day and a year.

So, perhaps you can tell us exactly what you're looking for - it might be easier to get you an answer.
 
  • #6
All planets orbit the Sun in the same direction,
Note that is the SUN, and has nothing to do with the galactic center.
Sometimes a planet as seen from Earth appears to reverse then go forward again.
However it isn't really doing that, this is an illusion due to the different speed of planet orbits.
Rather like if you have a fast car and overtake a slower one, it look similar to as if the slow car moved backwards.
 
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  • #7
Sorry for the confusion. I understand the difference between retrograde orbit and retrograde rotation. After my original question was answered that there are no known stars in the Milky Way with a retrograde orbit, I then asked if any stars have a retrograde rotation. "Like Venus and Uranus" was intended to solely point out their retrograde rotation with regard to our sun. I wasn't implying that these are stars.
Does the black hole at the galactic center spin in a certain direction that we can detect?
 
  • #8
Ah, as for actual stars rather than planets.
While they all appear to be rotating around the galactic center in the same direction, (more or less),
that direction is is not correlated with their spin around their own axis.
As far as I know the spin on their own axis, as far as can be determined. which can be hard, it can be just about anything.
Certainly it is not correlated with the spin of our Sun on it's axis, or with the orbits of solar planets.
 
  • #9
lifeonmercury said:
Sorry for the confusion. I understand the difference between retrograde orbit and retrograde rotation. After my original question was answered that there are no known stars in the Milky Way with a retrograde orbit, I then asked if any stars have a retrograde rotation.

No, people answered you question: Are there any nearby stars in retrograde orbit?

The answer to that depends a lot if your definition of nearby (I would consider within 10 ly, 100 ly, 1000 ly, 10000 ly all to be resonable definitions of nearby depending on you purpose). There are however billions of stars in retrograde galactic orbits in the milky way, most of them are in the halo, in-falling star streams from dwarf galaxies being absorbed or in the galactic bulge. They are mostly tens or hundreds of thousand light years away from Earth but at just 12 ly one star that is hard to exclude is the M1 sub-dwarf Halo star known as Kapteyn's Star (A&A paper).
 
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  • #10
glappkaeft said:
There are however billions of stars in retrograde galactic orbits in the milky way, most of them are in the halo, in-falling star streams from dwarf galaxies being absorbed or in the galactic bulge. They are mostly tens or hundreds of thousand light years away from Earth but at just 12 ly one star that is hard to exclude is the M1 sub-dwarf Halo star known as Kapteyn's Star (A&A paper).
Interesting! From Wikipedia's article Retrograde and prograde motion:

Stars with a retrograde orbit are more likely to be found in the galactic halo than in the galactic disk. The Milky Way's outer halo has many globular clusters with a retrograde orbit and with a retrograde or zero rotation.
 
  • #11
So, stars with retrograde orbit exist, and the nearest of them is Kapteyn's star.
No objects qualifying as planets orbit Sun in a retrograde direction. However, a number of bodies do orbit Sun in retrograde directions, but are classified as minor planets or comets rather than planets. Most conspicuously Halley Comet.
 
  • #12
A star that is tidally locked with the galactic center is also possible I suppose.
 
  • #13
lifeonmercury said:
Are there any stars in the solar neighborhood that orbit the galactic center in the opposite direction?
I'm merely speculating here, but I guess a galactic collision between a big galaxy like ours and a much smaller galaxy (so that the big galaxy does not lose it's individuality) could produce retrograde motions of stars.
 
  • #14
lifeonmercury said:
A star that is tidally locked with the galactic center is also possible I suppose.

No, I don't think so and I have never heard about it before. How would it even work?
 
  • #15
I guess this means, could a star be tidally locked with Sag A*, the SMBH embedded in the core.
If it is possible at all it would have to be very close to the SMBH.
Stars further out would be overwhelming more subject to gravitational influence of nearby stars in the own region.
 
  • #16
Stars with a retrograde orbit are more likely to be found in the galactic halo than in the galactic disk.
While technically correct, it hides the causal order. The Milky Way started with gas clouds with a random total angular momentum, which then assembled to a disk over time based on collisions between gas clouds. Those clouds then formed the stars in the disk with prograde motion. Stars with retrograde motion were captured from outside or got their motion from violent events in binary systems (e. g. their partner star exploded in a supernova) or similar events.
 
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1. How common are retrograde star orbits in the Milky Way?

Retrograde star orbits, where the star moves in the opposite direction of the majority of stars in the galaxy, are relatively rare in the Milky Way. Only about 5% of stars in our galaxy have a retrograde orbit.

2. What causes a star to have a retrograde orbit?

There are a few different factors that can contribute to a star having a retrograde orbit. One possibility is that the star was captured by the gravitational pull of a larger object, such as a black hole or a passing galaxy, causing it to change its orbit. Another possibility is that the star formed from a collision between two smaller stars, resulting in a retrograde orbit.

3. Do all retrograde stars have the same orbit patterns?

No, retrograde stars can have a variety of orbit patterns. Some may have highly eccentric orbits, while others may have a more circular orbit. The specific orbit pattern depends on the initial conditions and any interactions with other objects in the galaxy.

4. Are retrograde star orbits stable?

It is possible for retrograde star orbits to be stable, but it depends on a variety of factors. If the star is in a binary system, its orbit may be more stable due to the gravitational influence of its companion star. However, if the star is in a crowded region of the galaxy, interactions with other objects may disrupt its orbit over time.

5. Can we observe retrograde star orbits in other galaxies?

Yes, retrograde star orbits have been observed in other galaxies as well. In fact, some galaxies have a higher percentage of retrograde stars compared to our Milky Way. This can provide valuable insights into the formation and evolution of galaxies and their stars.

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