M104 (NGC 4594) (The Sombrero Galaxy)
Distance: 31 Million Light Years

Right Ascension: 12 : 40.0 (hours : minutes)
Declination: -11 : 37 (degrees : minutes)

M104 is truly a remarkable site with its prominent glowing bulge transected by a thick dusty disk. In the realm of galaxies its haunting form is nearly an icon. M104 is a luminous and truly massive galaxy with an equivalent total mass of 800 billion suns. If it were located within the Virgo cluster it would be the third brightest member. Its edge on view has provided astronomers with insight into the organization of matter within spiral galaxies.

M104 has a rich population of globular clusters with several of the more impressive ones easily visible in the image. Some estimates say it may contain some 1100 globular clusters, far more than the 150 or so we know of in the Milky Way. M104's globular cluster population exhibits a bimodal distribution of younger metal rich clusters and older metal poor clusters. The older metal poor population of globulars are presumed to have formed from the collapsing protogalactic gas cloud early in the formative years of the galaxy. The origin of the younger metal rich population is somewhat of a mystery. The most popular explanation is that the younger population came about through mergers and encounters with smaller galaxies. Tidally acquired clusters of stars became incorporated into the galactic halo forming a new population of globular clusters with distinct chemical abundances. Alternatively the origin of a second population of GC's could be explained by a more recent phase of star formation occurring more recently and long after generations of stars and supernovae enriched the galactic medium with heavier elements.

M104 is one of a growing list of galaxies known to possess a super massive black hole within its nucleus. M104's black hole contains a monstrous one billion solar masses. Super massive black holes of that size are usually found in very luminous galaxies possessing an active galactic nucleus. An accretion disk feeds matter to the black hole provoking the release of prodigious amounts of energy in the form of light, radiation, and jets of superheated gas which are characteristic of AGN's. M104's central energy output is 200 times less than expected, barely qualifying it as a low luminosity AGN which raises the question of why the energy outflow from its nucleus is so restrained. M104 seems to suffer from inefficient accretion. Its super massive nuclear black hole is starved for matter. One explanation may be the "feedback modulated accretion model" where energy released by an accreting black hole feeds back to the accretion disk, shutting it down temporarily. This is predicted to give rise to cycles of activity where short bright phases are followed by prolonged periods of quiescence for the AGN. Perhaps M104 is in a quiescent period at the moment.