The road to quasars

Abstract

Abstract. Although the extragalactic nature of 3C 48 and other quasi stellar radio sources was discussed as early as 1960 by John Bolton and others, it was rejected largely because of preconceived ideas about what appeared to be unrealistically high radio and optical luminosities. Not until the 1962 occultations of the strong radio source 3C 273 at Parkes, which led Maarten Schmidt to identify 3C 273 with an apparent stellar object at a redshift of 0.16, was the true nature understood. Successive radio and optical measurements quickly led to the identification of other quasars with increasingly large redshifts and the general, although for some decades not universal, acceptance of quasars as the very luminous nuclei of galaxies.Curiously, 3C 273, which is one of the strongest extragalactic sources in the sky, was first cataloged in 1959 and the magnitude 13 optical counterpart was observed at least as early as 1887. Since 1960, much fainter optical counterparts were being routinely identified using accurate radio interferometer positions which were measured primarily at the Caltech Owens Valley Radio Observatory. However, 3C 273 eluded identification until the series of lunar occultation observations led by Cyril Hazard. Although an accurate radio position had been obtained earlier with the OVRO interferometer, inexplicably 3C 273 was initially misidentified with a faint galaxy located about an arc minute away from the true quasar position.

The faint radio sky: radio astronomy becomes mainstream

“…They also correctly identified the other two sources with M 87 and NGC 5128 (both FR Is) but, realizing that, were they extragalactic their radio power would be enormous (for the time), they concluded that if the identifications were correct it would imply that M 87 and NGC 5128 had to be within our own Galaxy. Bolton later explained that he understood the true nature of the two sources "but that he was concerned that a conservative Nature referee might hold up publication" (Kellermann, 2015)! By the mid 1950s, however, many RGs were identified with optical counterparts and most high Galactic latitude sources were recognized to be extragalactic with radio powers ≈ 10 7 − 10 10 times larger than that of the Crab Nebula (e.g., 8 × 10 42 erg s −1 , i.e., ≈ 10 27 W Hz −1 at 100 MHz in the case of Cygnus A: Baade & Minkowski, 1954).…”

“…The two classes represent intrinsically different objects, with RL AGN emitting a large fraction of their energy non-thermally and in association with powerful relativistic jets, while the multi-wavelength emission of RQ AGN is dominated by thermal emission, directly or indirectly related to the accretion disk 6 . 5 Most of the so-called "quasi-stellar galaxies" described by Sandage (1965) actually turned out to be stars (e.g., Kellermann, 2015); but the concept of radio-quiet quasars (i.e., the existence of quasars with much weaker radio emission) proved to be correct. 6 The words in italics highlight the presence of a thermal component (the UV bump, due to the accretion disk) in RL quasars and of a hot corona (producing the hard X-ray power law, due to inverse Compton One of the strongest arguments in support of this statement comes from the hard X-rayγ-ray bands.…”

What Causes the Active Galactic Nuclei of Quasars During the Quasar Epoch to be so Luminous?

“…Supermassive black holes are still largely a mystery to astrophysicists. For a long time, people only theorized their existence, until it was proved by Maarten Schmidt in 1963 (11). In modern times, there is direct evidence for the existence of SMBH by observing objects orbiting the SMBH.…”