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UCSD astronomers to target Hubble to Quasars, active galaxies and supernova remnants April 4, 1990 Contact: Yvonne Baskin, (619) 534-0362 UCSD ASTRONOMERS WILL TARGET SPACE TELESCOPE TO QUASARS, ACTIVE GALAXIES, SUPERNOVA REMNANTS The University of California, San Diego team will devote much of its observing time to quasars, the most distant and energetic objects in the universe. The goal is to try to understand the nature and evolution of these enigmatic objects that are as compact as our solar system yet as bright as 100 trillion stars. Other targets include potential black holes lurking in the centers of active galaxies. The key to interpreting the light picked up from these celestial objects by the Faint Object Spectrograph (FOS) is a phenomenon called redshift. Elements such as hydrogen and iron emit light at specific wavelengths or spectral lines when tested in the laboratory. Yet the light from objects such as galaxies and quasars is skewed from these laboratory values and shifted toward longer wavelengths--the red end of the spectrum--by the time it reaches the Earth. Since 1929, orthodox theory has attributed this "redshift" to the Doppler effect, the same effect that causes the sound of a passing train to drop in pitch as it moves farther away. Thus, the redshift in an object's spectral lines is used to calculate how fast it is receding from the Earth due to the expansion of the universe and how far away it is in space and time. Here is a list of the primary targets for the UCSD team's guaranteed observing time from the FOS: I. The ultraviolet spectra of low redshift quasars "Some quasars have such extremely high redshifts that lines in the ultraviolet end of the spectrum are actually pulled into the visible range," says Margaret Burbidge, University professor of physics at UCSD and leader of the UCSD team. "We've been able to study these with ground-based telescopes." The Earth's atmosphere, however, absorbs ultraviolet radiation and makes it impossible to study the UV spectrum of low redshift quasars from the ground. These objects are a key target for the FOS. Because of their low redshift, these quasars are presumed to be younger in time and nearer to the Earth than better-studied high redshift quasars. Burbidge's team wants to compare data on older and younger objects for clues to the evolution of quasars. 2. The ultraviolet spectra of very high redshift quasars "A redshift greater than 3.1 is just large enough that the spectral lines of both ionized and neutral helium are pulled from the far ultraviolet into the visible range of the Faint Object Spectrograph," Burbidge says. "Helium is a very important element for cosmologists. It was supposed to have been created in the Big Bang, and various theories about the Big Bang call for differing amounts of helium. "So we want to know, how much helium is left in intergalactic space? In quasars? What was the primordial amount?" Looking at a quasar with a redshift of four, for instance, corresponds to looking back 10 billion years in time to the period shortly after the Big Bang. 3. The spectra of intermediate redshift quasars Light emitted by hydrogen is the most prominent line in the spectra of quasars and is called the Lyman alpha emission line. A redshift of two or greater will pull this emission line from the ultraviolet into the visible range. A large number of weaker absorption lines produced by Lyman alpha from these quasars remain obscured in the UV range, however, at wavelengths just short of the transition to the visible range. These have been named the "Lyman alpha forest," and one goal of the UCSD FOS team is to measure just how far back into the blue end of the spectrum this forest of lines goes. The forest, Burbidge notes, may represent light not from the quasar itself but from diffuse gas clouds that lie along our line of sight to the quasar and absorb some of its spectrum. "These gas clouds may be in a primordial region, perhaps evolving into a cluster of galaxies around the quasar," Burbidge says. "Or perhaps it's an area of star formation and the quasar itself is the early stage of an evolving galaxy." 4. BL Lacertae (BL Lac) objects and gravitational lenses Einstein's General Theory of Relativity predicted that even rays of light can be bent by the gravitational pull of a massive object. Such an object acts like a lens--a gravitational lens--distorting passing light rays in such a way that a distant observer may see multiple objects where only one exists. Some astronomers have proposed that strange quasar-like phenomena called BL Lac objects may actually be the result of gravitational lensing by quasars. The UCSD team will use FOS along with the space telescope's Wide-Field Planetary Camera to study these objects and other suspected lensing phenomena. 5. Nuclei of active galaxies and radio galaxies The nuclei of some galaxies such as M51, the Whirlpool galaxy, actively emit radio waves or high-speed gas jets. Could black holes be creating this radiation? The UCSD team will use the FOS to resolve the spectral lines as close to the nuclei of such galaxies as possible. By using a blocking disk to filter out the emissions from the nuclei, they will also try to find out what's happening in the regions around the centers of these galaxies. 6. Globular clusters in the Milky Way The globular clusters are dense clusters of stars that form a halo around our own galaxy, the Milky Way. "These areas contain some of our oldest stars, the ones that are least rich in elements heavier than hydrogen," says Burbidge. "With FOS, we'll try to resolve the centers of these clusters and determine the source of their strong X-ray emissions. One theory is that these emissions come from hot gases turning into an accretion disk around a collapsing neutron star." 7. Other targets: supernova remnants to radiation jets "The Crab Nebula is our nearest and best-studied supernova remnant, but no one has gotten the ultraviolet spectrum of it," says Burbidge. "That's one of our goals." Another goal is the UV spectrum of the synchrotron radiation jet coming out of a radio galaxy called M87. And a final challenge is to get the optical and UV spectrum of a radiation jet coming from the quasar 3C273, one of the lowest redshift and brightest quasars known. "In 1963 this was the first quasar ever identified," Burbidge says. "But all attempts to separate out the spectrum of the jet from the quasar itself have failed. The FOS should resolve it." (April 4, 1990)