53 results found.
... Science Frontiers ONLINE No. 122: Mar-Apr 1999 Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects Ghost Galaxies "Small ghost galaxies, devoid of stars but harboring dense clumps of invisible matter, may outnumber the entire population of luminous galaxies in the universe." If ghost galaxies contain no stars at all, how do we know they are there? By extrapolation! In recent years, astronomers have been able to detect dwarf galaxies lit by just a few luminous stars. These faint, miniscule galaxies are kept from flying apart by the gravitational pull of invisible dark matter. In fact, the density of dark matter in dwarf galaxies is a hundred times that in our bright, normal-size Milky Way. Further, the more dwarfish and dimmer a galaxy, the denser its dark matter and the more of them there are in the universe. Now for the promised extrapolation. J. Kormendy and K.C . Freeman take things one step further, concluding that the universe is flooded with sub-dwarf galaxies that are thick with dark matter, and without enough luminous stars for us to see them in our telescopes. These ghost galaxies are only 1/10,000 as massive as the bright galaxies like the Milky Way but much more common. (Cowen, R.; "Tiny Galaxies Have Hearts of Darkness," Science News, 155:38, 1999.) Comments. If the universe if awash in ghost galaxies, why don't we bump into them occasionally? Maybe we have! Another ...
Terms matched: 1 - Score: 15 - 15 May 2017 - URL: /sf122/sf122p04.htm
... )+ 1 (first anomaly in Chapter BHB). Some anomalies and curiosities that are listed below have not yet been cataloged and published in catalog format. These do not have the alphanumerical labels. AA ASTEROIDS AAB CELESTIAL MECHANICS PROBLEMS WITH ASTEROIDS AAB1 Anomalous Asteroid Orbits AAB2 Asteroid Distribution Anomalies AAB3 The High "Internal Energy" of the Asteroid Population AAB4 Peculiar Distribution of Asteroid Spin Rates AAB5 Unexplained Residual Precession of Icarus AAB6 Evidence against an Explosive Origin for Asteroids AB SOLAR SYSTEM "LAWS" AND INTERRELATIONSHIPS ABB DYNAMICS OF THE SOLAR SYSTEM AS-A -WHOLE ABB1 Solar-System Instability ABB2 Circularity of Planetary Orbits ABB3 Anomalous Split of Angular Momentum between Sun and Planets ABB4 Ubiquity of Resonances in the Solar System ABS REMARKABLE RELATIONSHIPS AMONG PLANETARY AND SATELLITE PARAMETERS ABS1 Solar System Laws of Distance ABS2 Similarity of Densities of Composite Terrestrial Planets ABS3 Multiple Primaries in the Solar System ABS4 Supposed Quantization of Planetary Orbital Periods ABS5 Solar System Mass Laws ABS6 The Quantized Nature of Orbital Systems AC COMETS ACB ORBITAL ANOMALIES OF COMETS ACB1 The Appearance of Comets in Cycles ACB2 Nonrandom Direction-of-Approach of Comets to the Sun ACB3 New Comets Have Almost Critical Velocity ACB4 Sun-Grazing Comets: The Kreutz Group ACB5 Changing Cometary Periods ACB6 Jupiter's Family of Comets ACB7 Low-Eccentricity Cometary Orbits ACB8 The Scarcity of Hyperbolic Orbits ACB9 Cometary Groups ACB10 Orbits of New Comets Diverge from Common Point ACB11 Excess of Retrograde Long Period Comets ACB12 Uranus-Neptune Region Favored as Comet Source ACB13 Cometary Perturbations Suggestive of Planet X ACB14 Rapid Attrition of the Oort Cloud by Molecular Clouds ACB15 Dynamical Improbability of the Oort Cloud ACO OBSERVATIONAL ...
Terms matched: 1 - Score: 31 - 15 May 2017 - URL: /cat-astr.htm
... 100-kilometer craters on a regular basis. And scientists are casting worried looks at those near-earth asteroids, knowing that one day one will be on a collision course. Not to worry, say the modern-day Technocrats, we will launch nucleararmed rockets that will nudge such cosmic threats into harmless trajectories. These Pollyannas are presumptious. They assume that asteroids are hard, cohesive objects that will be shoved aside by a few megatons of explosive energy. There are two things wrong with this idea, and these reveal how radically our ideas about the nature of asteroids have changed in just 10 years. First, most astronomers will now agree that asteroids are orbiting rubble piles rather than monolithic objects. For example, the near-earth asteroid Mathilde, 53 kilometers in diameter, has a density of only 1.3 grams/cubic centimeter. Its porosity must be greater than 50%. It is not a hard, coherent object. Instead of a bullet, it is more like a cloud of shotgun pellets. It would be hard to divert all this debris with a nuclear blast. To make matters worse, asteroids like Mathilde are stickier than a cloud of buckshot. This fact is deduced from photos of asteroids showing many to be marked by huge craters. (Mathilde has one 33 kilometers wide.) K.R . Housen et al, using laboratory tests and scaling data, argue that asteroid craters were not blasted out by collision. (Mathilde is not "shattered" as one would expect given such a huge crater.) Rather, the craters are " ...
Terms matched: 1 - Score: 14 - 15 May 2017 - URL: /sf127/sf127p03.htm
