The Mystery of Quasars

The Mystery of Quasars[1]

At left is a Hubble Space Telescope image of quasar 3C 273, showing the incredibly powerful, distant galaxy blazing as the central “star” in the frame. Material shot outward from the supermassive black hole in the quasar’s center is visible as a faint jet to the upper left of 3C 273

In the early 1960s, astronomer Maarten Schmidt had a problem. Along with other researchers, this fixture of the California Institute of Technology had been studying mysterious radio sources discovered in the 1950s.

These strange objects, the two most notable designated 3C 48 and 3C 273, appeared tiny on the sky but were extremely energetic sources of radio waves. They didn’t fit any logical explanation of what astronomers understood at the time. (The designation 3C came from the Third Cambridge Catalog of Radio Sources, produced at Cambridge University.)

A precise position of 3C 273, using the 200-inch Hale Telescope on Palomar Mountain in California, finally allowed Schmidt to record the object’s spectrum, the signature of its light, for the first time. This, in turn, produced a 1963 paper declaring that the strange radio object lay at the impressive distance of 2.4 billion light-years. Yet in Earth’s sky, the object appeared merely as a faint star, leading Schmidt to name this new thing a “quasi-stellar object,” or quasar.

How could something so far away be so incredibly energetic? At first, the notion completely baffled astronomers.

And then the mystery deepened. Over the years to come, astronomers found a series of strange, distant, highly energetic objects far beyond the Milky Way. Using a wide range of the electromagnetic spectrum, a rogues’ gallery of super-energetic, distant object emerged. They came to include quasars, Seyfert galaxies, BL Lacertae objects (or “blazars”), and radio galaxies. For nearly a whole generation, this array of weird objects seemed to represent a complex puzzle of the unrelated oddities in the astrophysical zoo.

Eventually, astronomers learned that these strange high-energy objects were similar beasts viewed from different angles. They were all some form of high-energy galaxy, called active galactic nuclei, with centers harboring supermassive black holes. Material cascaded around the black hole—but not swallowed—was slingshot outward for astronomers to see.

And the first step in resolving the mystery of quasars was complete.

[1] See David J. Eicher, “The Mystery of Quasars”, Astronomy (45, 5, May, 2017, p. 8).


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