Messier 87 - Observation History

Observation History

In 1781, French astronomer Charles Messier published a catalogue of 103 objects that had a nebulous appearance. This list was intended to identify objects that might be confused with comets. In subsequent use, each item in the catalogue was prefixed with an 'M'. Thus, M87 was the eighty seventh member of Messier's catalogue. During the 1880s, this nebula was included in the New General Catalogue as NGC 4486. This compilation of nebulae and star clusters was assembled by the Danish-Irish astronomer John Dreyer based primarily on the observations of English astronomer John Herschel.

In 1918, American astronomer Heber Curtis of Lick Observatory observed that there was no spiral structure in Messier 87 and he noticed a "curious straight ray ... apparently connected with the nucleus by a thin line of matter." The ray appeared brightest at the inner end. The following year, a supernova within Messier 87 reached a peak photographic magnitude of 21.5, although this event was not reported until photographic plates were examined by the Russian astronomer Innokentii A. Balanowski in 1922.

American astronomer Edwin Hubble categorized Messier 87 as one of the brighter globular nebulae, as it lacked any spiral structure but appeared to belong to the same family of non-galactic nebulae as spiral nebulae. In 1926 he produced a new categorization of nebulae, with Messier 87 being classified as a type of elliptical extra-galactic nebula with no apparent elongation (class E0). By 1931, Hubble had identified Messier 87 as a member of the Virgo cluster, for which he gave a provisional estimate of 1.8 million parsecs from Earth. At the time it was the only known example of an elliptical nebula for which individual stars could be resolved. Messier 87 continued to be called an extragalactic nebula for many years thereafter, but by 1956 it had been identified as an E0-type galaxy.

In 1947, a prominent radio source was identified overlapping the location of Messier 87, and this was labeled Virgo-A. This source was confirmed to be Messier 87 by 1953, and the linear jet emerging from the core of this extragalactic nebula was suggested as the cause. This jet extended from the core at a position angle of 260° to an angular distance of 20″ with an angular width of 2″. German-American astronomer Walter Baade found that the light from this jet is plane polarized, which suggested that the energy was being generated by the acceleration of electrons moving at relativistic velocities in a magnetic field. The total energy output of these electrons was estimated as 5 × 1056 eV. In 1969-70, a strong component of the radio emission was found to closely align with the optical source of the jet.

The US Naval Research Laboratory group launched an Aerobee 150 during April, 1965 that was equipped with a pair of geiger counters. This flight discovered seven candidate X-ray sources, including the first extragalactic X-ray source; designated Virgo X-1 as the first X-ray source detected in Virgo. A later Aerobee rocket launched from White Sands Missile Range on July 7, 1967, yielded further evidence that the source Virgo X-1 was the radio galaxy Messier 87. Subsequent X-ray observations by the HEAO 1 and Einstein Observatory showed a complex source that included the active galactic nucleus of Messier 87. However, there is little central concentration of the X-ray emission.