Impressive images from the Hubble Space Telescope have revealed long-sought information about the space environments where quasars live. Quasars are faint blue celestial objects, starlike in appearance, believed to be the most distant objects in the universe. Dr. Bruce Margon, an astrophysicist at the University of Washington said: "What we are seeing now is the conclusive proof. The homes of quasars are now evident without any ambiguity." The new data indicates that quasars always exist within galaxies, an assertion unproved until now because, while quasars are extremely distant, they are considered the most luminous objects in the universe; this overwhelming brightness has masked their immediate environment and made close observation difficult. The Hubble images also reveal the surprising finding that quasars exist in different kinds of galaxies, some in collision or near-collision with each other, and some at rest.

The findings further indicate that most quasars exist in different kinds of galaxies: some spiral, and some elliptical. A spiral galaxy resembles a flat disk with rounded, swirling arms and a central bulge. An elliptical galaxy has no arms and simply looks like the center of a spiral galaxy. Most galaxies are either spiral or elliptical; a few are known as "irregular".

The leaders of the two teams reporting the new information are Mike Disney of the University of Wales College, Cardiff, U.K., who is the leader of the European team, and Dr. John Bahcall of the Institute for Advanced Study in Princeton, N.J., the leader of the American team. Their findings have not yet been formally published.

Quasars

Quasar is an abbreviation for quasi-stellar, so-named because of the starlike appearance of quasars. Scientists believe that as the universe expands, quasars recede from the galaxy with tremendous speed, perhaps as great as 95% of the speed of light. According to Einstein's theory of relativity, light moves at a speed of 299,792.458 kilometers per second (186,282 miles per second). In 1963, the unknown space object called 3C 273 in the constellation Virgo, led astronomers to realize they had identified a new, previously undiscovered type of celestial body, a quasar; this quasar was calculated to be moving away from Earth at almost 30,000 miles per second.

Quasars were positively identified as new, previously undiscovered space objects only 33 years ago, in 1963. Until the introduction of the Hubble Space Telescope, or "HST," it was extremely difficult to study quasars because of their distant location at the outer edges of the universe. They remain among the most baffling objects in the universe, relatively small in size--not much larger than our own solar system--but of staggering luminosity. A quasar produces 100 to 1000 times more light than an entire galaxy composed of a hundred billion stars. This overwhelming brightness masks the environment where quasars reside and has created difficulty for scientists who are trying to adequately observe and study them.

The Hubble findings paint a new, more complicated picture for astronomers, since their general suspicion was that violent activity between galaxies, such as collisions or near-collisions, was necessary for quasars to exist. The discovery of quasars in seemingly peaceful galaxies now contradicts this belief. Astronomers also thought that some quasars, known as "naked quasars," might exist on their own outside of any galaxy, but the new findings also prove this false. Since the new images show that some quasars reside in peaceful galaxies, scientists are hypothesizing that the forces that activate a quasar may sometimes be more subtle than expected. Or, it is possible that a second galaxy is indeed present during a collision with a galaxy that is visible, but is too close to the nucleus of the visible galaxy to be observed by Hubble.

"If we thought we had a complete theory of quasars before, now we know we don't," Bahcall said. "No coherent, single pattern of quasar behavior emerges. The basic assumption was that there was only one kind of host galaxy, or catastrophic event, which feeds a quasar. In reality, we do not have a simple picture -- we have a mess."

Both teams of researchers do agree on certain findings from Hubble. They both agree that quasars reside at the core, or nucleus, of galaxies, and these galaxies can be either spiral or elliptical. They also agree that interactions between galaxies, either in the form of collisions or near-collisions, can cause a quasar to become active. This is because a galactic collision, that is, a collision between galaxies, feeds gas and stars to the black hole that exists at a galaxy's core. As these materials fall into the black hole, intense nuclear energy is emitted, which activates and sustains the quasar. In determining the energy source for quasars, Russian scientist Yakov Zeldovich is credited with proposing the theory that black holes are the "engines" that power a quasar. Today, Zeldovich's theory is widely held.

Lastly, the Hubble findings have spurred agreement between both research teams on the question of "radio quiet" quasars; these do not emit any radio waves, and were thought to exist only in spiral galaxies. Now, however, astronomers know that radio quiet quasars can exist in elliptical galaxies, also. Thousands of quasars have so far been identified, and most are "radio quiet." The first quasars discovered by astronomers emitted radio waves, and so were not radio quiet.

Black holes, the celestial phenomena that are believed to be the energy source for quasars, are formed by the remains of certain dying stars. When the radius of a dying star decreases below a certain limit, the extreme curvature of space seals off contact with the outside world, and the former star becomes a black hole. In other words, a black hole is created when a giant star collapses to a tiny point. These tiny points, or black holes, always have an irresistable gravitional pull. Because light and other forms of energy and matter are permanently trapped inside a black hole by this enormous pull, the black hole can be observed only indirectly; it is, in effect, "invisible."

The Hubble Space Telescope itself owes its existence in large part to the mysteries of the quasar. Finding answers to the questions posed by these elusive space objects was a major reason for the effort to fund and construct the space telescope. Researcher Bahcall was a principal advocate for the telescope, telling the U.S. Congress in 1978 that "one needs to observe quasars with the space telescope to find out whether or not these bright point-objects, quasars, are surrounded by fainter, more diffuse light of galaxies." The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency.

More Quasar Questions

In science, as in all disciplines, finding new answers often creates further questions. Now that scientists know where quasars reside, for example, they wish to determine whether most quasars exist for only a brief period of a galaxy's life (100 million years or less), or if they are long-lived. If their lives are short, then most galaxies, including our Milky Way, might actually be "burned out" quasars. If quasars possess long lives, it implies they are more rare. "This means a few extremely massive black holes formed very early in the universe," says Disney. Scientists now possess only the first hints of answers to this question. Researchers also need to address a so-called "chicken and egg" problem regarding the birth of quasars: did the massive black holes that feed quasars form first, with galaxies later forming around them? Or, did galaxies precede black holes, which then quickly grew in the cores of galaxies? Additionally, those working in this area also wish to determine if quasars are pointing their energy only in the direction of Earth, or radiating it in all directions.

Astronomy has its dissenting voices. German astronomer Halton Arp of the Max Planck Institute for Astrophysics has countered the common understanding that quasars are extremely distant galactic objects, living at the center of galaxies. He theorizes that quasars are ejected from relatively nearby active galaxies. This assertion also challenges the usual understanding of "redshift," which is the main calculation used to measure the distance of a celestial object. Astronomers have largely rejected Arp's claims, though he is currently preparing to present his most systematic study yet.

Further research on quasars will continue to challenge scientists because of the long distances involved, and accordingly, the length of time it takes light to reach Earth. However, this work will be aided by new space observation and photographic technologies to be installed inside the Hubble telescope in coming years. Anticipated installations include the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), in 1997, and the Advanced Camera, in 1999. These new devices will have "coronagraphic" abilities, which will block out the glare of a quasar and allow astronomers to see more closely into a galaxy's nucleus. By viewing galactic structures in infrared light, the NICMOS device should be able to provide a new level of detail. This will deepen understanding about the galaxies that quasars call home.