Quasars shine bright as Stars of Universe
By Amanda Jermyn



Reach for the Stars… Amanda Jermyn
October 2010
When you look up at the night sky, the objects that appear brightest are generally not the ones that give off the most light but rather those closest to us, such as nearby stars. The real powerhouses, however, are not stars but quasars, the most luminous, powerful and energetic objects we know of in the universe. A quasar is a compact region near the center of a massive galaxy surrounding the galaxy’s super-massive black hole. The black hole’s powerful gravity attracts nearby dust, gas and stars which form an accretion disk that swirls around it and spirals inwards towards the center of the black hole. This process generates tremendous friction, heat and gravitational stresses as the material is compressed by gravity, resulting in the emission of powerful radiation in the form of rotating beams of energy, some of which we view as light. This radiation is generated in the accretion disk, outside the event horizon, the spherical boundary of the black hole beyond which nothing can escape. It is thought that all large galaxies have black holes at their centers, but only a small fraction of these emit such powerful radiation that they are seen as quasars.
Today more than 200,000 quasars are known, most thanks to the Sloan Digital Sky Survey which created the most detailed sky map ever. Most are between three billion and 13 billion light-years away. Because light travels at the finite speed of 186,282 miles per second, it takes billions of years for light from the distant universe to arrive here on Earth. We therefore see the most distant quasars the way they looked 13 billion years ago, or just several million years after the Big Bang. In fact, quasars were much more common in young, active galaxies in the early universe. Their light only appears faint to us because they are so far away, yet these quasars are the most powerful and luminous objects in the universe. The light from a bright quasar is about two trillion times that of our sun, or about 100 times that of all the light from a large galaxy like our Milky Way.
To find out more about these enigmatic, distant denizens of the universe, join the Springfield STARS Club for a talk on Quasars by Dr. David Wexler. An amateur astronomer, Dr. Wexler studied neuroscience and engineering at Case Western Reserve University, and completed medical studies at Stanford University. He is an Ear, Nose and Throat specialist at Wing Memorial Hospital in Palmer. Dr. Wexler is currently pursuing a Masters degree in astronomy online through James Cook University. His areas of interest include galactic and radio astronomy, and astrochemistry, the study of chemical elements and compounds in the universe. Dr. Wexler’s talk for the Springfield STARS Club will take place on Tuesday, October 26th at 7:30pm at the Springfield Science Museum at the Quadrangle. Refreshments will be served, and the public is welcome free of charge.