2011/12/06 by Tod R. Lauer, R. Bender, Ralf Bender +3 · 53 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Blue straggler #Galaxies: Formation, Evolution, Phenomena #Galaxy #Gamma-ray bursts and supernovae #Milky Way #Physics #Population #Star cluster #Stars #Stellar collision #Stellar evolution #Surface brightness #astro-ph.CO
paper · pdf · doi:10.1088/0004-637x/745/2/121
published in The Astrophysical Journal 745(2), 121 (IOP Publishing) · 29 pages, 11 figures (3 color); Astrophysical Journal accepted
arxiv created 2011/12/06 · openalex publication_date 2012/01/06 · arxiv updated 2015/06/03 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We obtained U 330 - and B -band images of the M31 nucleus using the High Resolution Camera of the Advanced Camera for Surveys on board the Hubble Space Telescope ( HST ). The spatial resolution in the U 330 band, 0 03 FWHM, or 0.1 pc at M31, is sufficient to resolve the outskirts of the compact cluster (P3) of UV-bright stars surrounding the M31 black hole. The center of the cluster is marked by an extended source that is both brighter and redder than the other point sources within P3; it is likely to be a blend of several bright stars. We hypothesize that it marks the location of the M31 black hole. Both stellar photometry and a surface brightness fluctuation analysis show that the P3 stellar population is consistent with early-type main-sequence stars formed in a ∼100–200 Myr old starburst population. Evolutionary tracks of post early asymptotic giant branch (PEAGB) stars, associated with late-stage evolution of an old population, also traverse the U and U − B domain occupied by the P3 stars; but we argue that only a few stars could be accounted for that way. PEAGB evolution is very rapid, and there is no progenitor population of red giants associated with P3. The result that P3 comprises young stars is consistent with inferences from earlier HST observations of the integrated light of the cluster. Like the Milky Way, M31 harbors a black hole closely surrounded by apparently young stars.