Messier 87 - Properties

Properties

Messier 87 is located near the high declination border of the Virgo, next to the constellation of Coma Berenices. It lies along a line between the stars Epsilon Virginis and Denebola. At an apparent magnitude of 9.59, this galaxy can be readily observed using a small telescope with a 6 cm (2.4 in) aperture. Visually, the galaxy extends across an angular area of 7′.2 × 6′.8, with a bright, 45″ core. Viewing the jet feature is a challenge without the aid of photography. Up through 1990, the only known visual observation of the jet had been by Russian-American astronomer Otto Struve using the 254 cm (100 in) Hooker telescope. In recent years, however, it has been observed in larger amateur telescopes under excellent conditions.

In the modified Hubble sequence galaxy morphological classification scheme of French astronomer Gérard de Vaucouleurs, Messier 87 is categorized as an E0p galaxy. The E0 designation is used for an elliptical galaxy that displays no flattening—that is, it appears spherical in profile. A 'p' suffix indicates a peculiar galaxy that does not fit cleanly into the classification scheme; in this case, the peculiarity is caused by the presence of a relativistic jet emerging from the core. Messier 87 is considered a type-cD galaxy, which is a supergiant D class galaxy. The latter category, first proposed by American astronomer William W. Morgan in 1958, is a galaxy that has an elliptical-like nucleus surrounded by an extensive, dustless, diffuse envelope.

The distance to Messier 87 has been estimated using several independent techniques. These include measuring the luminosity of planetary nebulae, comparison with nearby galaxies whose distance has been estimated using standard candles such as cepheid variables, the linear size distribution of globular clusters, and the tip of the red giant branch method using individually resolved red giant stars. These measurements are consistent with each other, and their weighted average yields a distance estimate of 16.4 ± 0.5 Mpc (53.5 ± 1.63 Mly).

This galaxy is one of the most massive in the local Universe. The mass of Messier 87 within a radius of 9–40 kpc (29–130 kly) from the core steadily increases roughly in proportion to r1.7, where r is the radius from the core. Within a radius of 32 kpc (100 kly), the mass is (2.4 ± 0.6) × 1012 times the mass of the Sun, which is double the mass of the Milky Way galaxy. However, only a fraction of this mass is in the form of stars, as Messier 87 has an estimated mass to luminosity ratio of 6.3 ± 0.8. That is, about one part in six of the galaxy's mass is in the form of stars that are radiating energy. The total mass of Messier 87 may be 200 times that of the Milky Way.

Gas is infalling into the galaxy at the rate of two to three solar masses per year, most of which may be accreted onto the core region. The extended stellar envelope of this galaxy reaches a radius of about 150 kpc (490 kly), compared to about 100 kpc (330 kly) for the Milky Way. Beyond that distance the outer edge of the galaxy has been truncated by some means; possibly by an earlier encounter with another galaxy. There is some evidence of linear streams of stars to the northwest of the galaxy, which may have been created by tidal stripping of orbiting galaxies, or by small satellite galaxies falling in toward Messier 87.