Quasars in the Early Universe

Up until the year 2002, astronomers were puzzled by the presence of extremely deep space objects known as Quasars. These quasi-stellar objects (QSOs) were emitting energy in amounts rivaling that of the entire known visible Universe's normal material. The puzzling question was why quasars exist only in the deepest regions of space. Since it is known that the farther distant an object is, the more distant in the past its light is, and thus the younger the age of the object is at the time we are seeing its light. Quasars must be objects that existed early in the evolution of the Universe, but must no longer be active in the more recent Universe objects represented by stars and galaxies closer to the Milky Way. If quasars are relics of an earlier time frame, then how did they form and why did they stop emitting such prodigious energies?

For the answer to the question, and perhaps a better and more complete understanding of the process which brings about the formation of galaxies, we turn to a recent set of articles that appeared in Astronomy and also in Sky & Telescope during the year 2002. The articles discussed the presence of supermassive Black Holes that reside in the core region of spiral galaxies. In most cases, these gigantic objects are quiet because they are not in the action of swallowing stars. However, when a star happens to stray too close to the event horizon of the galactic black hole, the star is accelerated within an accretion disk to exceedingly high velocities, ripped apart, and engulfed by the black hole with a sudden outbursting beam of radiation perpendicular to the galactic disk. These beams of radiation are surprisingly similar to the type of radiation observed from quasars, and therein lies the relationship.

It is now believed that the early Universe was dominated by collapsing clouds of cooling matter arising from the Big Bang expansion. As the matter coalesced into smaller and smaller clouds, some began spinning and forming stars ... the rise of spiral galaxies. Centripetal forces slung material away from the collapsing core, but gravity forced much material toward the center of the core. Stars burst into existence from the collapse of protostellar gas and first light revealed collections of stars called galaxies. The large amount of mass centered in the core cause the high mass stars that evolved there to live and die quickly. Since high mass stars evolved into Neutron Stars and Black Holes, the center of these early galaxies were occupied by a high percentage of such exotic stars ... very small in size, but high in mass. The swirling nature of the collapsing galactic cloud forced more material toward the center where the neutron stars and black holes were lurking. The infalling mass accreted onto the neutron stars, causing violent eruptions and collapse into more black holes. Owing to the electromagnetic nature of the spinning disk of galactic gas, the energies from the infalling matter and explosions were funneled into beams perpendicular to the galactic plane. Since so much matter was accreting into the galactic core, the energy beams were of very enormous levels ... observable as quasars. With the slow passage of time, the galaxy would stabilize its balance between infalling material under the influence of gravity and outflowing matter under the influence of centripetal force. With less material to feed the central black hole, there would be less outflow of radiation, and the quasar beams would cease to shine. To be sure, the galactic core might hold a black hole of well over 1 million to 1 billion solar masses, but the very spin of the galaxy would not allow orbiting stars to cross the core's event horizon and light up the quasar beam. Only if a rogue star, moving in a path independent of the majority of orbiting stars, would wander close to the event horizon would the beam of energy reappear, and this event would not last very long while the star was being absorbed. Just such a giant black hole in a distant quasar was discovered in 2003. It is said to hold the mass of 3,000,000,000 Suns! An artistic impression of this object (estimated to be 13 billion lights years away, and thus from a time early in the Universe) is seen below:

The fact that we do not find these objects nearby lends credence to the theory that quasars were ruling the Universe at a very young age and represent an important part of galaxy formation. The fact that they are so exceedingly bright makes them ideal tools for looking at very distant regions of the Universe. More information on the nearby Quasar 3C 273 is available at the click of your mouse. It is the most distant object you can see with a reasonably-sized telescope. For additional general information on quasars, click on the External Quasar site.

Back to Galaxy Formation, or go to the Syllabus .


| Home | Course Information | Assignments | Teacher Bio | Course Units | Syllabus | Links |