Guest Author - Lea Terry
From Earth, quasars look like nearby, faintly shining stars. Only since the 1960s have we known their true identity: rare, distant objects with a glow more intense than that of 100 galaxies.
Quasars are galaxies located billions of years away, at the edge of our visible universe. They are the most distant objects known, and seem to be uncommon, as only about 6,000 have been catalogued. Astronomers believe there are less than 100,000 quasars, a small portion of the estimated 100 billion or more galaxies in the universe. Quasars probably form from a collision between two galaxies, during which one galaxy forms a black hole in the other. This black hole is thought to have the mass of 100 million Suns. The black hole draws in gas, dust, and stars, the temperature reaches hundreds of millions of degrees, and massive amounts of radiation are emitted. Astronomers believe this occurs only in the most massive galaxies. They also believe galaxies only behave as quasars during the early stages of their lives; however, this phase would still last billions of years.
Astronomer Alan Sandage discovered quasars in the 1960s while photographing the sky. He noticed that one star behaved strangely: it emitted radiation at wavelengths toward the red-end of the visible light spectrum. This effect is called a red-shift, and occurs when an object is moving away from the observer. The mystery was explained in 1962, by Dutch astronomer Maarten Schmidt. After observing a quasar, Schmidt determined that the object’s unusual spectrum was the same as that of a normal star with a high red-shift; however, he also determined that the object was 2 billion light-years away. In order to be observable from that distance, the object would have to be larger than a star, and closer to the size of a galaxy. Schmidt measured the object’s diameter, and determined it was emitting as much energy as 1 trillion Suns, even though it was only about the size of our Solar System.
Quasars were originally called “quasi-stellar radio sources,” because some had been observed with radio telescopes. However, only a small percentage of quasars emit radio waves; they can also emit visible light, X-rays, infrared and ultraviolet radiation, and may emit gamma rays. Quasars aren’t just a source of fascination; they also provide a glimpse into the universe’s beginnings. The light from a quasar takes billions of years to reach us, and so when we look at one, we are seeing it as it existed in the distant past. Some quasars are so far away that the image we see from them is nearly from the beginning of time. In fact, Schmidt determined that quasars were more common when the universe was young, which means the deeper we can look into space, the more quasars we can see. All quasars are far away, indicating they all formed during the early stages of the universe. Many of these quasars may now behave like normal galaxies, and it is possible that our own Milky Way galaxy once behaved as a quasar.
