the name "QSO" (quasi-stellar object) is used (in addition to "quasar") to refer to these objects, further categorised into the "radio-loud" and the "radio-quiet" classes. The discovery of the quasar had large implications for the field of astronomy in the 1960s, including drawing physics and astronomy closer together. In 1979 the gravitational lens effect predicted by Albert Einstein's general theory of relativity was confirmed observationally for the first time with images of the double quasar 0957+561. A study published in February 2021 showed that there are more quasars in one direction (towards Hydra) than in the opposite direction, seemingly indicating that the Earth is moving in that direction. But the direction of this dipole is about 28° away from the direction of the Earth's motion relative to the cosmic microwave background radiation. In March 2021, a collaboration of scientists, related to the Event Horizon Telescope, presented, for the first time, a polarized-based image of a black hole, particularly the black hole at the center of Messier 87, an elliptical galaxy approximately 55 million light-years away in the constellation Virgo, revealing the forces giving rise to quasars. Current understanding It is now known that quasars are distant but extremely luminous objects, so any light that reaches the Earth is redshifted due to the metric expansion of space. Quasars inhabit the centers of active galaxies and are among the most luminous, powerful, and energetic objects known in the universe, emitting up to a thousand times the energy output of the Milky Way, which contains 200–400 billion stars. This radiation is emitted across the electromagnetic spectrum, almost uniformly, from X-rays to the far infrared with a peak in the ultraviolet optical bands, with some quasars also being strong sources of radio emission and of gamma-rays. With high-resolution imaging from ground-based telescopes and the Hubble Space Telescope, the "host galaxies" surrounding the quasars have been detected in some cases. These galaxies are normally too dim to be seen against the glare of the quasar, except with special techniques. Most quasars, with the exception of 3C 273, whose average apparent magnitude is 12.9, cannot be seen with small telescopes. Quasars are believed—and in many cases confirmed—to be powered by accretion of material into supermassive black holes in the nuclei of distant galaxies, as suggested in 1964 by Edwin Salpeter and Yakov Zeldovich. Light and other radiation cannot escape from within the event horizon of a