This Chandra image shows important new details in the powerful jet shooting from the quasar 3C273, providing an X-ray view into the area between 3C273's core and the beginning of the jet. [More...]

In the 1950s, astronomers began noticing a peculiar class of objects. In conventional telescopes they looked like ordinary stars. But they were extremely "bright" when observed with radio telescopes. Astronomers later started calling them quasars, short for "quasi-stellar radio sources."

In 1963, Caltech astronomer Maarten Schmidt aimed the 200-inch Hale Telescope on Palomar Mountain, California, at one of these quasars, known by its catalog number 3C 273. To his astonishment, he found that the object's spectral lines were significantly shifted toward the red end of the spectrum, a result of the universe’s expansion. The high redshift implied that 3C 273 lies at an immense distance from Earth, about 2 billion light-years. But to be so bright at that large distance, the object had to be extraordinarily luminous, pumping out an incredible amount of light from just a small volume of space. Alarmed by the implications of his discovery, Schmidt reportedly went home that night and told his wife "Something terrible happened at the office today."

Although he had no way of knowing it at the time, Schmidt had uncovered a crucial piece of evidence for the existence of supermassive black holes. These monsters contain millions or even billions of times the mass of the Sun, and they reside in the centers of every large galaxy. The monster black hole itself is dark, but if it has an abundant food supply in the form of nearby gas, the material will settle into a disk around the black hole. As the gas spirals in, it heats up and emits a torrent of radiation, sometimes packing the luminosity of a trillion stars into a volume of space the size of our solar system.

Since the 1960s, astronomers have found thousands of quasars, most of which, ironically enough, are not particularly bright radio sources. Quasars are seen in all directions, and in epochs dating back just a billion years after the Big Bang. Astronomers have also found other objects that are similar to quasars, but viewed from a different angle. These objects include blazars, Seyfert galaxies, and radio galaxies, and are collectively known as active galactic nuclei (AGN). NASA's Chandra X-ray Observatory has detected huge numbers of dust-enshrouded AGN at all epochs of cosmic history dating back to only about a billion years after the Big Bang.

This composite X-ray (blue), radio (pink and green), and optical (orange and yellow) image of the active galaxy Centaurus A presents a stunning tableau of a galaxy in turmoil.[More...]

A significant fraction of AGN appear to reside in galaxies that have undergone a recent merger, with the collision being the event that funneled gas into the galactic center, where it winds up being caught in the black hole's gravitational clutches. Given that all large galaxies appear to have monster black holes in their cores, astronomers now think that many large galaxies—possibly even our Milky Way—went through an active phase sometime in their lifetime. Since the vast majority of galaxies do not exhibit quasar-like activity, however, the quasar phase is probably comparatively short-lived, perhaps comprising just 1% of a galaxy's lifetime.

The Constellation-X mission, part of NASA's Beyond Einstein program, will take these observations to a higher level, mapping out details of AGN activity at different times in cosmic history. Such studies will give astronomers a clear picture of how monster black holes grew over time and influenced their host galaxies.