Messier 87 - Components

Components

At the core of this galaxy is a supermassive black hole (SMBH) with an estimated (6.6 ± 0.4) × 109 times the mass of the Sun and a diameter larger than the orbit of Pluto. This is one of the highest masses known for such an object. Surrounding the black hole is a rotating disk of ionized gas that is oriented roughly perpendicular to a relativistic jet. This disk is rotating at velocities of up to roughly 1,000 km/s, and spans a maximum diameter of 0.12 pc (0.39 ly). Gas is accreting onto the black hole at an estimated rate equal to the mass of the Sun every ten years.

Observations suggest that the black hole in M87 may be displaced from the galaxy center by a distance of about 25 pc (82 ly). The displacement is in the opposite direction from the one-sided jet, which may indicate that the black hole has been accelerated away from the center by the jet. Another possibility is that the displacement occurred during the merger of two SMBH. However care has to be taken with these findings. The study does not include any spectroscopic discrimination between the stellar and active galactic nucleus component. It is therefore possible that the seeming position of the galaxy center with respect to the black hole is misinterpreted by an optical flare of the jet itself. In 2011, an analysis of M87 did not find any statistically significant displacement.

Active elliptical galaxies of a form similar to Messier 87 are believed to form as a result of one or more mergers between smaller galaxies. There is now little dust remaining to form the diffuse nebulae where new stars are created, so the stellar population is dominated by old, population II stars that contain relatively low abundances of elements other than hydrogen and helium. The elliptical shape of this galaxy is maintained by random orbital motions of its member stars, in contrast to the more orderly rotational motions found in a spiral galaxy such as the Milky Way.

The space between the stars in the Messier 87 galaxy is filled with a diffuse interstellar medium of gas, which has been chemically enriched by the elements ejected from stars as they passed beyond the end of their main sequence lifetime. Carbon and nitrogen is being continuously supplied by intermediate mass stars as they pass through the asymptotic giant branch. The heavier elements from oxygen to iron are primarily produced by supernova explosions within the galaxy. About 60% of the abundance of these heavy elements was produced by core-collapse supernovae, while the remainder came from Type Ia supernovae. The distribution of these elements suggests that early enrichment was from core-collapse supernovae. However, the contribution from this source was much lower in abundance than in the Milky Way. Type Ia supernovae have provided a continuous contribution to the interstellar medium of Messier 87 throughout the history of the galaxy.

Examination of Messier 87 at far infrared wavelengths shows an excess emission at wavelengths longer than 25 μm. Normally such emission may be an indication of thermal emission by warm dust. However, in the case of Messier 87, the emission appears to be fully explained by synchrotron radiation from the jet. Within the galaxy, silicate grains are expected to survive for no more than 46 million years because of the X-ray emission from the core. This dust may be destroyed by the hostile environment or expelled from the galaxy. The combined mass of dust in this galaxy is no more than 70,000 times the mass of the Sun. By comparison, the Milky Way contains about a hundred million (108) solar masses worth of dust.

Within a 4 kpc (13 kly) radius of the core, the abundance of elements other than hydrogen and helium—what astronomers term the metallicity—is about half the abundance in the Sun. Outside this radius, the abundance of metals steadily decreases with increasing distance from the core. Although this is classified as an elliptical galaxy and therefore lacks the dust lanes of a spiral galaxy, optical filaments have been observed in Messier 87. These filaments have an estimated mass of about 10,000 times the mass of the Sun. Surrounding the galaxy is an extended corona with hot, low density gas.

Messier 87 has an abnormally large population of globular clusters. A 2006 survey out to an angular distance of 25′ from its core estimates that there are 12,000 ± 800 globular clusters in orbit around Messier 87, as compared to the Milky Way's 150–200. These clusters are similar in size distribution to the globular clusters of the Milky Way, with most having an effective radius between 1 and 6 parsecs. The size of the Messier 87 clusters shows a gradual increase with distance from the galactic center.