<p>Star S2 reaches maximum velocities of 5,000 km/s according to <a href="http://www.eso.org/public/news/eso0226/">this ESO page</a>.</p>

<p>The orbital period is given as a little over 15 years and <a href="https://arxiv.org/pdf/astro-ph/0306220v1.pdf">this paper</a> gives a peri-center (closest approach to the black hole) of 17 light hours.</p>

<p>There's another star in the area called <a href="https://en.wikipedia.org/wiki/S0%E2%80%93102">S0-102</a> which has a shorter period, but its orbit is less eccentric - so its closest approach to the black hole is further out at 36 light hours. Its maximum velocity will <em>probably</em> be less than S2 but I haven't been able to find a figure.</p>

CC BY-SA 3.0
2016-07-05T13:52:56.570Z
Am I right that our sun is orbiting at about **30** km/s, versus S2 at **5000** km/s - ?
Fattie
CC BY-SA 3.0
2016-07-05T14:09:18.820Z
@JoeBlow yup - and that's 5000 km/s at a distance of over 100 astronomical units. But the [black hole there](https://en.wikipedia.org/wiki/Sagittarius_A*#Central_black_hole) is probably millions of solar masses... :)
Andy
CC BY-SA 3.0
2016-07-05T14:13:37.340Z
thanks ... at 100 au!   the hole (joke :) ) situation is quite confusing physically: I'm only used to intuitively thinking about Kepplerian situations with all the mass at the middle.  it's very hard to intuitively grasp what happens at the middle of the galaxy, further confused by the SMBH. Say, no SMBH was there at all.  (So it's more like "the center of the Earth" type phsyics.)  What would happen to such stars?  would they even rotate the CG? or just kind  of mill around?  I don't know.)  thanks again!
Fattie
CC BY-SA 3.0
2016-07-05T14:24:54.140Z
The motion of the stars at the very centre is Keplerian.
ProfRob
CC BY-SA 3.0
2016-07-05T14:31:15.910Z
@JoeBlow yes I think it'd be standard Kepler-style orbits near the hole itself, as there's a concentrated center. The more spread out situation you describe might well be real; the centre of [globular clusters](http://www.astro.keele.ac.uk/workx/globulars/globulars.html) might be like that...
Andy
CC BY-SA 3.0
2016-07-05T14:35:51.970Z
Right.  So very near the SMBH, it's basically a simple Kepplerian system, with the SMBH as the "sun" and a central group of stars as "planets" to that "sun".  The fact that that Kepplerian-like system is sitting in the middle of a big-ass galaxy is overwhelmed by that Kepplerian picture, in that "central, SMBH dominated" area.
Fattie
CC BY-SA 3.0
2016-07-05T11:34:22.823Z
2016-07-05T11:34:22.823Z
Andy
<p>The Sun moves at the speed of 220km/s around the galactic center in a circular orbit. The sun is located at about 30,000 light years from the galactic center. The Sun orbits around the center of the Milky Way once every 225 million years. The period of time is called a cosmic year.</p>

<p>I am curious about the speed at which the star closest to galactic center revolves around galactic center. Has this been calculated or approximated. Also what is the time it takes to complete one revolution for the star around galactic center or what is the cosmic year length for the star that is closest to galactic Center .</p>

<p>I have taken reference from <a href="http://www.bibliotecapleyades.net/ciencia/ciencia_astrosciences07.htm" rel="nofollow">http://www.bibliotecapleyades.net/ciencia/ciencia_astrosciences07.htm</a></p>

CC BY-SA 3.0
2016-07-05T09:48:21.560Z
Due to dark matter, the speed is more or less constant throughout the disk, only decreasing in the very center. See [Galaxy rotation curve](https://en.wikipedia.org/wiki/Galaxy_rotation_curve).
pela
CC BY-SA 3.0
2016-07-05T12:29:38.833Z
OP, you may be interested in [this](http://astronomy.stackexchange.com/questions/16204/is-our-central-black-hole-actually-at-the-cg-of-the-galaxy) question
Fattie
<star><cosmology><galaxy-center>
What may be the period and speed of revolution of the star that is closes to galactic centre?
Anupam Rekha
# What may be the period and speed of revolution of the star that is closes to galactic centre?

(Asked by: username_0 on 2016-07-05)

The Sun moves at the speed of 220km/s around the galactic center in a circular orbit. The sun is located at about 30,000 light years from the galactic center. The Sun orbits around the center of the Milky Way once every 225 million years. The period of time is called a cosmic year.

I am curious about the speed at which the star closest to galactic center revolves around galactic center. Has this been calculated or approximated. Also what is the time it takes to complete one revolution for the star around galactic center or what is the cosmic year length for the star that is closest to galactic Center .

I have taken reference from <http://www.bibliotecapleyades.net/ciencia/ciencia_astrosciences07.htm>

**Tags:** star, cosmology, galaxy-center
> **Comments:**
> **username_1**: Due to dark matter, the speed is more or less constant throughout the disk, only decreasing in the very center. See [Galaxy rotation curve](https://en.wikipedia.org/wiki/Galaxy_rotation_curve).  
> **username_2**: OP, you may be interested in [this](http://astronomy.stackexchange.com/questions/16204/is-our-central-black-hole-actually-at-the-cg-of-the-galaxy) question  

---

## 1 answers

### Answer by username_3 on 2016-07-05. Score: 5 | Accepted answer

Star S2 reaches maximum velocities of 5,000 km/s according to [this ESO page](http://www.eso.org/public/news/eso0226/).

The orbital period is given as a little over 15 years and [this paper](https://arxiv.org/pdf/astro-ph/0306220v1.pdf) gives a peri-center (closest approach to the black hole) of 17 light hours.

There's another star in the area called [S0-102](https://en.wikipedia.org/wiki/S0%E2%80%93102) which has a shorter period, but its orbit is less eccentric - so its closest approach to the black hole is further out at 36 light hours. Its maximum velocity will *probably* be less than S2 but I haven't been able to find a figure.

> **Comments:**
> **username_2**: Am I right that our sun is orbiting at about **30** km/s, versus S2 at **5000** km/s - ?  
> **username_3**: @JoeBlow yup - and that's 5000 km/s at a distance of over 100 astronomical units. But the [black hole there](https://en.wikipedia.org/wiki/Sagittarius_A*#Central_black_hole) is probably millions of solar masses... :)  
> **username_2**: thanks ... at 100 au!   the hole (joke :) ) situation is quite confusing physically: I'm only used to intuitively thinking about Kepplerian situations with all the mass at the middle.  it's very hard to intuitively grasp what happens at the middle of the galaxy, further confused by the SMBH. Say, no SMBH was there at all.  (So it's more like "the center of the Earth" type phsyics.)  What would happen to such stars?  would they even rotate the CG? or just kind  of mill around?  I don't know.)  thanks again!  
> **username_4**: The motion of the stars at the very centre is Keplerian.  
> **username_3**: @JoeBlow yes I think it'd be standard Kepler-style orbits near the hole itself, as there's a concentrated center. The more spread out situation you describe might well be real; the centre of [globular clusters](http://www.astro.keele.ac.uk/workx/globulars/globulars.html) might be like that...  
> **username_2**: Right.  So very near the SMBH, it's basically a simple Kepplerian system, with the SMBH as the "sun" and a central group of stars as "planets" to that "sun".  The fact that that Kepplerian-like system is sitting in the middle of a big-ass galaxy is overwhelmed by that Kepplerian picture, in that "central, SMBH dominated" area.  

---

