Quasar
Among the most unusual objects in the universe, quasars (quasi-stellar radio sources) are strong radio sources with unusual properties. In the early 1960s, a number of powerful radio sources were pinpointed in space which did not correspond with the locations of known objects such as galaxies or nebulae. Astronomer Alan Sandage, studying photographs of an area in the sky where one such object seemed to be, could see only a tiny star with an adjoining smudge. Though the star was compact and not fuzzy like a galaxy or nebula, the star's spectrum was unlike any other seen before, revealing none of the elements known to exist in stars.
Maarten Schmidt (1929-), examining a similar object called 3C273 with the Palomar telescope in 1963, realized that its strange spectrum was actually a normal spectrum with a high red shift. This meant that the object was probably not a star at all, but an incredibly distant object like a galaxy. Schmidt's calculations placed it at an astonishing 2 billion light years away. While its diameter was much smaller than that of a galaxy, it emitted much more energy than even an entire galaxy should emit, including streams of x-rays.
The paradoxical properties of quasars made their explanation difficult, and their nature was hotly debated. But over the next twenty years, data for thousands of quasars was analyzed, yielding a characteristic profile: an incredibly distant object, about the size of the solar system, was emitting as much energy as one trillion suns might release.
Bringing together an understanding of the early evolution of the universe with black hole theory, astronomers concluded that a quasar is a massive black hole located at the center of a galaxy. Such black holes can be produced when two galaxies collide, thrusting large amounts of matter from one of the galaxies into the center of the other. As matter spins into the black hole, it gives off a tremendous quantity of radiation, including x-rays, which is detected by our radio telescopes. The conditions that produce galactic collisions are characteristic of the early universe, when matter was densely packed into a smaller space. Since quasars are the most distant objects yet detected, they are also the oldest, because their light has taken several billion years to reach us. Therefore when astronomers view quasars, they are not seeing the universe as it is now, but as it was billions of years ago.
Because of their brightness, quasars are used as measuring sticks to probe the farthest reaches of the universe, giving us estimates of its size and age. In 1998, the discovery of the most distant galaxy yet known was announced; it is a staggering 13 billion light-years away. Because we see this galaxy as it existed 13 billion years ago, it represents an extremely early epoch in the history of the Universe, when galaxies were still forming. This object is close to the observable limit of the Universe: we have now seen almost as far as we possibly can.
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