Our group topic is Quasars. We have focused thus far on finding articles and
discussing what we want our projects main focus points to be. At this point in time we
are still collecting articles, organizing material, and beginning to shape our web page. In
the following weeks we will be putting together a more concise report on Quasars,
formatting our web page and putting our poster together for the science fair.
     We have chose to split up the remainder of our research into the following:
Jeremy will work mainly with our web page, and will also be observing. Caylin is our
"information gatherer" and will be collecting more articles and observing. Julie will be
our "organizer" and will go through information Caylin has found and will put it into our
own words to begin forming our report. She will also be observing.
     We hope to focus our research of Quasars on ways in which the understanding of
Quasars can help us gain insight into how the universe began.
 
 
      In the 1950's radiation was detected in M31, in Andromeda, at high radio frequencies. A year later a stronger radio source was discovered in Cygnus A, in a faint galaxy, 700 million light years away (300 x the distance from Andromeda). The source of the radiation had to be enormously powerful to transmit so much energy over such a stupendous distance (Quasars and Pulsars) These radio sources became known as QUASARs or QUASi-stellAR radio sources because they are generally seen as point sources, like stars, and for their emission of radio waves (Bahcall 12-6-97).  Click for more history
    Quasars are thought to be the most energetic objects in the universe (Astronomy 3-97). Quasars give off 100-1000 times as much light as an entire galaxy containing a hundred billion stars (Bahcall 1-28-97). Quasars are so bright that they drowned out the light from the other stars in that galaxy. They also emit UV, IR, x-rays, and gamma rays (StarChild). The brightest quasar is 1.5-3.0 billion light years away from Earth and is called 3C273 (French and Maran). In February of 1998 a new discovery was made of Quasar PDS 456. This Quasar is 2.5 Billion light years away, much closer than most Quasars. It was difficult discern because it was hidden behind the Milky Way's dust. After the dimming due to dust is taken into consideration it was determined that PDS 456 is 1.3X more luminous than the nearest known quasar 3C273, making it the most luminous quasar within 4 billion light years. The discovery was made by a team of Brazilian scientists led by Carlos Torrer of the Laboratorio nacional de astrofisica (Astronomy 2-98).
    Quasars are thought to be not much bigger than our solar system (Bahcall 1-28-97). A quasar is about 1kpc in width (Starchild).
    The radiation from quasars is greatly redshifted suggesting that they are moving away from us at near fractions of the speed of light (some 90% of c) (Bahcall 1-28-97). The quasar 3C273 is speeding away from us at 16% of the speed of light. Some of the new quasars found by the HEAO-2 satellite are much further away, with recession velocities of 2/3 the speed of light (French and Maran). From their redshifts it is concluded that quasars are the most distant objects that we have detected in the universe. This gives us a look into the beginnings of the universe since we are seeing them how they were billions of years ago (Starchild).
    Shortly after they were discovered studies by Halton Arp at the Mt. Wilson and Palomar observatories found that some of the quasars are associated with "peculiar" galaxies that show evidence of having been subject to violent processes, releasing high amounts of energy. In many cases a pair of radio sources are located on opposite sides of the host galaxy, suggesting that they were ejected from it after an explosion (Quasars and Pulsars). Most quasars lie in the cores of luminous spiral or elliptical galaxies, even those quasars where no host galaxy could be found before. Most quasars are surrounded be a relatively faint nebulous patch. Astronomers are still trying to identify the nature of these patches (Dunlop 4-98). Observations with the HST have also confirmed that quasars are galaxies in which only the bright nucleus can be seen. Quasars have spectral properties similar to those of the central regions of active galaxies, galaxies that contain very bright, compact regions in the centers (Scientific America, 1997). Observations with the 2 largest optical telescopes in the world, the University of California Observatories/ Lick observatories used the twin 10-meter Keck I and Keck II telescopes in Hawaii to take spectra of the nebulous blobs surrounding 10 bright and nearby quasars, were the first to confirm that quasars lie in normal galaxies. This led astronomer Joseph Miller to believe that "quasars are natural features of massive galaxies and that they are direct consequences of how galaxies evolve." (Astronomy 7-97).
    The most plausible mechanism that could produce the vast energy output of quasars is the accretion of matter into a massive black hole (Scientific America, 1997). Only a super-massive black hole could liberate that much energy from such a small volume. Collisions or near encounters of such host galaxies with another galaxy perturb the motions of matter (stars, gas and dust) in the host galaxy and cause the matter, or some of it, to fall toward the central black hole (Bahcall 1-28-97). As gas falls into the black hole it forms a disk that grows extremely hot because of friction. This process releases energy in accordance with E=mc². This is the source of the quasar's brightness. This hypothesis is supported by evidence indicating the presence of massive dark objects in the nuclei of some active galaxies (Scientific America, 1997). Hubble images show that quasars exist in a striking diversity of galaxies, many of which are colliding violently (Astronomy 3-97). The black holes thought to constitute the engines of quasars may have a mass of a few million to a billion times that of our sun and sizes comparable to the orbits of the suns outer planets (Bahcall 1-28-97).
 We see quasars when they were very young. Quasars that are close are very rare, so it is believed that they must evolve into something else that is more common near our galaxy. The most likely objects are normal, quiescent galaxies. If this is true, normal galaxies should still have black holes in their nuclei but those black holes should now be starved of fuel. Observations of several normal galaxies, including the Milky Way, have provided evidence of black holes. Astronomers do not yet know what fraction of normal galaxies once passed through a quasar phase. Using the STIS spectrograph, a high-spatial resolution spectroscope installed by NASA on the HST, to observe a large sample of normal galaxies, might reveal the presence of a massive black hole (Scientific America, 1997).
 

A SURVEY OF QUASAR HOST GALAXIES

EMBARGOED UNTIL:  9:00 A.M. (EST) November 19, 1996

PHOTO RELEASE NO.: STScI-PRC96-35a
     normal galaxies                               colliding galaxies                                 peculiar galaxies
 

 
 Quasars reside in a variety of galaxies, from normal to highly disturbed. When
seen through ground-based telescopes, these compact, enigmatic light sources
resemble stars, yet they are billions of light-years away and several hundred
billion times brighter than normal stars. The following Hubble Space Telescope
images show examples of different home sites of all quasars. But all the sites
must provide the fuel to power these unique light beacons. Astronomers believe
that a quasar turns on when a massive black hole at the nucleus of a galaxy
feeds on gas and stars. As the matter falls into the black hole, intense
radiation is emitted. Eventually, the black hole will stop emitting radiation
once it consumes all nearby matter. Then it needs debris from a collision of
galaxies or another process to provide more fuel.
 
Top left: This image shows quasar PG 0052+251, which is 1.4 billion
light-years from Earth, at the core of a normal spiral galaxy.  Astronomers
are surprised to find host galaxies, such as this one, that appear undisturbed
by the strong quasar radiation.

Bottom left: Quasar PHL 909 is 1.5 billion light-years from Earth and lies at
the core of an apparently normal elliptical galaxy.
 
Top center: The photo reveals evidence of a catastrophic collision between two
galaxies traveling at about 1 million mph. The debris from this collision may
be fueling quasar IRAS04505-2958, which is 3 billion light-years from Earth.
Astronomers believe that a galaxy plunged vertically through the plane of a
spiral galaxy, ripping out its core and leaving the spiral ring (at the bottom
of the picture).  The core lies in front of the quasar, the bright object in
the center of the image.  Surrounding the core are star-forming regions.  The
distance between the quasar and spiral ring is 15,000 light-years, which is
one-seventh the diameter of our Milky Way.  A foreground star lies just above
the quasar.
 
Bottom center: Hubble has captured quasar PG 1012+008, located 1.6 billion
light-years from Earth, merging with a bright galaxy (the object just below
the quasar).  The two objects are 31,000 light-years apart.  The swirling
wisps of dust and gas surrounding the quasar and galaxy provide strong
evidence for an interaction between them.  The compact galaxy on the left of
the quasar also may be beginning to merge with the quasar.
 
Top right: Hubble has captured a tidal tail of dust and gas beneath quasar
0316-346, located 2.2 billion light-years from Earth.  The peculiar-shaped
tail suggests that the host galaxy has interacted with a passing galaxy that
is not in the image.
 
Bottom right: Hubble has captured evidence of a dance between two merging
galaxies.  The galaxies may have orbited each other several times before
merging, leaving distinct loops of glowing gas around quasar IRAS13218+0552.
The quasar is 2 billion light-years from Earth.  The elongated core in the
center of the image may comprise the two nuclei of the merging galaxies.
 
Credits: John Bahcall (Institute for Advanced Study, Princeton) Mike Disney
(University of Wales) and NASA
 

SUBTOPICS:

RADIO WAVES AND BLACK HOLES

REDSHIFTS

GALAXIES AND OBSERVATIONS

BIBLIOGRAPHY