| |
 |
| Paper: |
Mass Segregation in the Galactic Centre |
| Volume: |
439, The Galactic Center: a Window to the Nuclear Environment of Disk Galaxies |
| Page: |
180 |
| Authors: |
Hopman, C.; Madigan, A. |
| Abstract: |
Two-body energy exchange between stars orbiting massive black holes (MBHs) leads to the formation of a power-law density distribution n(r) α r–α that diverges towards the MBH. For a single mass population, α =7/4 and the flow of stars is much less than N(< r)/ tr (enclosed number of stars per relaxation time). This “zero-flow” solution is maintained for a multi-mass system for moderate mass ratios or systems where there are many heavy stars, and slopes of 3/2 < α < 2 are reached, with steeper slopes for the more massive stars. If the heavy stars are rare and massive however, the zero-flow limit breaks down and much steeper distributions are obtained.
We discuss the physics driving mass-segregation with the use of Fokker-Planck calculations, and show that steady state is reached in 0.2–0.3 tr. Since the relaxation time in the Galactic centre (GC) is tr∼ 2–3 ×1010 yr, a cusp should form in less than a Hubble time. The absence of a visible cusp of old stars in the GC poses a challenge to these models, suggesting that processes other than two-body relaxation have played a role. We discuss astrophysical processes within the GC that depend crucially on the details of the stellar cusp. |
|
|
|
|
|
