Normal and Active Galaxies: Building...
Chapter 15 Image Archive
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NEW: February 2004
Distant X-ray Jets May Provide Clues to the Universe's Beginning
Quasars are thought to be galaxies with active central supermassive black holes that are being fueled by infalling gas and stars. The inward fall of material is often accompanied by the generation of high-energy jets that emit in X-rays. The most distant X-ray jet ever to be seen was discovered by by NASA's Chandra X-ray Observatory. Electrons from the jet fly away from the quasar at near the speed of light. These fast-moving electron occasionally collides with a photon that was left over from the hot, early phase of the universe. These collisions can boost the photon's energy up into the X-ray band allowing astronomers to determine the intensity of the left over photons which constitute the background radiation of the universe. This distant jet from the quasar GB1508+5714 is so far away that it is allowing astronomers to probe the cosmic background radiation 1.4 billion years after the universe was formed.
Chandra Photo Album,
Image ID: gb1508_xray_illustration.jpg
- Turbulent Cauldron of Starbirth in Nearby Active Galaxy
NASA's Hubble Space Telescope offers a stunning unprecedented close-up view of a turbulent firestorm of starbirth along a nearly edge-on dust disk girdling Centaurus A, the nearest active galaxy to Earth. A ground-based telescopic view (upper left insert) shows that the dust lane girdles the entire elliptical galaxy. This lane has long been considered the dust remnant of a smaller spiral galaxy that merged with the large elliptical galaxy. The spiral galaxy deposited its gas and dust into the elliptical galaxy, and the shock of the collision compressed interstellar gas, precipitating a flurry of star formation. Resembling looming storm clouds, dark filaments of dust mixed with cold hydrogen gas are silhouetted against the incandescent yellow-orange glow from hot gas and stars behind it.
- Hubble Goes to the Limit in Search of Farthest Galaxies in 1998
The NASA Hubble Space Telescope has achieved a view of the faintest galaxies ever seen in the universe. The view was taken in infrared light with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS). In the left frame of the picture there are over 300 galaxies having spiral, elliptical, and irregular shapes. Though most of these galaxies were first seen in 1995 when Hubble was used to take a visible-light deep exposure of the same field, NICMOS uncovers many new objects. Most of these objects are too small and faint to be apparent in the full field NICMOS view. Astronomers believe that some of these galaxies could be more than 12 billion light-years away (depending on cosmological models), making them the farthest objects ever seen. A powerful new generation of telescopes will be needed to confirm the suspected distances.
Antimatter Annihilation Above Milky Way
This map of gamma rays from NASA's Compton Gamma Ray Observatory shows evidence announced in 1997 of a previously unknown and unexpected cloud of positrons, a form of antimatter, extending 3000 light-years above the center of our galaxy. These gamma rays have an energy of 511,000 electron volts, or about 250,000 times the energy of normal visible light. They are produced when positrons (antimatter) and electrons (matter) collide and annihilate, converting all of their mass into energy according to Einstein's famous equation E=mc2. Oddly, there appears to be a cloud or jet of positron annihilation that extends north of the galactic plane, but not to the south.
Large-Scale Structure of Galaxy Distributions
Data from the survey of galaxies show the universe to be clumpy and uneven. The voids and "walls" that form the large-scale structure are mapped here by 11,000 galaxies. Our galaxy, the Milky Way, is at the center of the figure. The outer radius is at a distance of approximately 450 million light-years. Obscuration by the plane of the Milky Way is responsible for the missing pie-shaped sectors.
North is at the top. (Original image courtesy Smithsonian Astrophysical Observatory, 1993.)
Model of Interacting Galaxies
In this computer model of "galactic cannibalism," large galaxies are created through the merger of smaller ones. Two spiral galaxies are shown here colliding, pulled together by their mutual gravitational attraction. Gas density, nuclear bulges, and supernovae explosions are represented.
Distant Sub-Galactic Clusters
These 18 small blue objects--each about 11 billion light-years from Earth--could be similar to the seeds of some of today's galaxies. Each object is 2000 to 3000 light-years across, contains several billion stars, and was found in an area about 2 million light-years wide (see image key below). Astronomers believe that many of these objects have collided and merged with each other over time to grow into the giant and luminous galaxies seen around us today.
Embedded in this Hubble Space Telescope image of nearby and distant galaxies are the 18 young galaxies or galactic building blocks shown here, each containing dust, gas, and a few billion stars. At this distance, the universe was only about 16 percent of its current age. The 18 young galaxies were found within an area about 2 million light-years across, which is about the distance between our Milky Way and the Andromeda Galaxy. Since this distance is comparatively small, it is possible that these clusters may merge into a larger, full-blown
galaxy approximately 30,000 to 100,000 light-years wide.
Source: NASA Space Telescope Science Institute,
HubbleSite News Center, Image ID: PR96-29_KeyColor.jpg;
The Hubble Deep Field
Several hundred never-before-seen galaxies are visible in this
"deepest-ever" view of the universe, called the Hubble Deep Field
(HDF), made with NASA's Hubble Space Telescope. Besides the classical
spiral and elliptical shaped galaxies, there is a bewildering variety
of other galaxy shapes and colors that are important clues to understanding the evolution of the universe. Some of the galaxies may
have formed less than 1 billion years after the Big Bang. A full set of high-resolution images that comprise the entire HDF is available
at the source site given below.
Peculiar Galaxies in the Hubble Deep Field
This image shows some examples of morphologically peculiar galaxies in the HDF, arranged according to their position on an asymmetry vs. central concentration diagram. According to researchers, below an intensity of about 25 magnitutdes, roughly 35 percent of the faint galaxy population appears to be morphologically peculiar relative to a control sample of artificially redshifted local galaxies. Study of the Hubble Deep Field image continues to yield new information about
the formation and evolution of galaxies and pre-galactic clusters.