# What may be the period and speed of revolution of the star that is closes to galactic centre?

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

• Due to dark matter, the speed is more or less constant throughout the disk, only decreasing in the very center. See Galaxy rotation curve.
– pela
Jul 5, 2016 at 9:48
• OP, you may be interested in this question Jul 5, 2016 at 12:29

Star S2 reaches maximum velocities of 5,000 km/s according to this ESO page.

The orbital period is given as a little over 15 years and this paper gives a peri-center (closest approach to the black hole) of 17 light hours.

There's another star in the area called S0-102 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.

• Am I right that our sun is orbiting at about 30 km/s, versus S2 at 5000 km/s - ? Jul 5, 2016 at 13:52
• @JoeBlow yup - and that's 5000 km/s at a distance of over 100 astronomical units. But the black hole there is probably millions of solar masses... :)
– Andy
Jul 5, 2016 at 14:09
• 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! Jul 5, 2016 at 14:13
• The motion of the stars at the very centre is Keplerian. Jul 5, 2016 at 14:24
• @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 might be like that...
– Andy
Jul 5, 2016 at 14:31