A new study using the Sloan Digital Sky Survey provides the most direct evidence yet that galaxies reside at the center of giant, dark matter concentrations that may be 50 times larger than the visible galaxy itself.For more background see my Dark Matters post back in January in which I cite the MOND theory as a possible alternative explanation to dark matter.
The study very directly supports the generally accepted astronomical theories on dark matter and contradicts an alternative theory of gravity known as Modified Newtonian Dynamics (MOND).
Lead investigator, Francisco Prada, of the Max Planck Institute for Astronomy in Germany and the Instituto de Astrofisica de Canarias in Spain, and a team of colleagues from New Mexico State University at Las Cruces and at other Sloan Digital Sky Survey (SDSS) institutions, will present the results of the team's research at a joint conference of the Isaac Newton Group of Telescopes and the Instituto de Astrofisica de Canarias, May 26-30 in La Palma, Canary Islands, Spain.
Prada and his colleagues studied the motion of about 3,000 satellites orbiting isolated bright galaxies and found strong evidence of dark matter gravitational effects.
The study "is important because it is a direct measurement of some of the properties predicted for dark matter," said Anatoly Klypin of New Mexico State University.
Although it cannot be observed directly, dark matter is believed to account for about 27 percent of the total mass of the universe, compared with only about 3 percent for normal, observable matter. The rest, according to standard models of the structure and evolution of the universe, consists of dark energy and radiation.
Prada and his colleagues observed 250,000 galaxies from the Sloan Digital Sky Survey (SDSS) telescope to find good candidates for a study of the gravitational effects of dark matter. From the SDDS data, they identified about 3,000 satellites -- generally small galaxies orbiting large ones ? for which they could measure velocities.
The velocity of a satellite declines predictably as the satellite moves away from the object it is orbiting, due to the effects of gravity. In the case of planets in our solar system, where there is too little dark matter to have a gravitational effect, the decline is rapid because there is no mass between the planets and the sun, he said. But in the outer reaches of galaxies, where dark matter is believed to be clustered, the decline in velocity would be much more gradual if standard cosmological models are correct.
"Our results imply the presence of dark matter," Prada said. The findings provide strong evidence against the MOND alternative theory of gravity, he said. MOND, controversial since it was proposed in 1983, eliminates the need for dark matter in explaining the nature of the universe, by changing the law of gravity in areas such as the outskirts of galaxies. [more]
Blast a crack in Earth's crust, pour in a few thousand tons of rock-busting molten iron, and then toss in a grapefruit-size instrument designed to ride the plunging elevator of liquid metal to the planet's core.Update
That scenario sounds like science fiction. Even its author, geophysicist David J. Stevenson of the California Institute of Technology in Pasadena, calls the proposal "highly speculative." However, in the May 15 Nature, he contends that such a mission to explore Earth's interior is technically feasible.
People have drilled into our planet's crust to investigate conditions there, but even the deepest borehole penetrates only about 10 kilometers, says Stevenson. Seismic analyses suggest that the continents, the thickest portions of Earth's outer layer, are between 200 and 250 km thick. Below that hardened crust lies the viscous mantle, which surrounds a liquid outer core and a solid inner core that are both made predominantly of iron.
All that iron sank to Earth's core because it's so dense, and Stevenson's plan would exploit that property. If scientists pour molten iron into a narrow crack at least 300 meters deep, the pressure at the bottom of the fissure would be enough to fracture the rock there, Stephenson says. As the crack grows deeper, the molten iron would flow downward and maintain pressure at the crack tip. The self-propagating crack—which high pressure in deep rocks would seal after the iron passed by—would progress at about 5 m per second and reach Earth's outer core in about a week.
Planetary missions have greatly enhanced our understanding of the solar system and how planets work. There is no correspondingly ambitious effort for Earth’s interior, where there are some equally fascinating scientific issues. I describe here a mission to Earth’s core in which a probe is imbedded in a large volume of liquid iron alloy that migrates to the core along a crack propagating under the action of gravity. The time to reach the core is ~ a week and the minimal required volume of iron ~ 108 kg, or about one hour of Earth’s iron production. The probe communicates its scientific results using high frequency seismic waves sensed by a ground-coupled LIGO.
Long before the invention of agriculture or the domestication of cattle, sheep, pigs, chickens and dogs, even before the ancestors of the American Indians crossed the Bering Strait into North America, the Japanese were already living in villages and cooking their meals in ceramic pots.
By 10500 BC (and possibly much earlier), the Japanese had developed the art of making ceramics. It's not clear whether this knowledge then spread to other regions or was independently rediscovered but it's worth noting that pottery does not appear in the "Cradle of Civilization" of West Asia any earlier than 7000 BC.
Archaeologists usually describe the appearance of pottery as the transition of a society from "paleolithic" to "neolithic", that is the change from a hunter gathering existence to a settled one based on food production with agriculture and animal husbandry. The extremely early date for the appearance of pottery in Japan, however, creates problems for such a simple and neat categorization. The Japanese "neolithic" period is notable for its essential lack of agriculture. Despite having abandoned nomadism in favour of the sedentary life of the village, the Japanese of this period could not in any way be described as farmers, "intensive foragers" would be a far more accurate description.
The richness of Japan's environment at the end of the last Ice Age was the principle reason for the emergence of this unique way of life. The first modern humans had walked to Japan from the Asian mainland some 30,000 years ago. At the time, Japan was a narrow isthmus that was connected both to Korea and to Siberia in an arc land that enclosed within it an enormous freshwater lake (now the Sea of Japan). When global temperatures began to rise, and with it sea levels, the islands became cut off and the big game that these paleolithic hunter gathers had relied upon started to become scarce due to increased hunting pressure. Fortunately at the same time, the warmer climate made the islands much more favourable to alternative food sources and the early Japanese switched from their meat-oriented diet to one based on a bountiful harvest of fruits and nuts produced by forests of deciduous trees. The rising sea-level flooded shorelines and made fishing much easier by creating countless shallow, silt-bottomed and nutrient-rich inlets.
With these resources at their disposal and the need to manage them the transition was made to living in permanent dwellings. This is not to say that life wasn't hard, the average life expectancy was only thirty years and periods of famine were not uncommon, but when compared to their contemporaries elsewhere in the world, the neolithic Japanese had many advantages and were able to collect enough to feed themselves. They achieved this without having to resort to the drudgery and back-breaking labour of subsistence farming (or indeed create the kind of rigid hierarchical class society that became such a trademark of Japan in later times).
The culture of the Japanese neolithic period has been aptly named after the style of its pottery, Jomon which literally means "cord motif" style. The Jomon made pots for storage, cooking and carrying. On the coasts, they used them to evaporate seawater to make salt for trading with forest communities further inland. The pots was generally made by women who built them up by pinching together coils of clay. Then they were elaborately decorated and hardened in open fires. It's interesting that in a culture with no precursors or preconceived notions of what "pottery" should look like, often turned instead to the designs of their reed baskets for models. To simulate the effect of weaving, the pots were often impressed with strands of twisted fibres.
By the time of the Middle Jomon period (about 4500 years ago), the designs had become extremely ornate and, at times, quite spectacular. This is not the kind of exquisitely minimalist art that we have come to associate with Japan. On the contrary, Middle Jomon art is brash, vibrant and flamboyant.
Flame pattern vessel
Coil-formed pottery, Japan, Jomon period, about 2500 BC.
The earliest known Japanese ceramics, made between the 11th and 5th centuries BC, are known as Jomon wares. The entire prehistoric Jomon culture derives its name from the method by which these ceramics were made: Jomon means, literally, "cord motif." In an age before potters wheels or kilns, artisans made vessels by building up basic forms with coils of clay, manipulating the soft surface to create the desired designs, sun-baking pots until dry, then firing them in above-ground bonfires of piled brushwood. The Jomon people lived in tribal units along rivers and coasts of Japan, and each area is identified with unique variants in its ceramics. The northeast Nigata region, for example, produced distinctive "flame pattern" vessels exemplified by this exuberant pot from about 2500 BC, one of the largest and best-preserved examples of its type known to exist. The hunting-gathering Jomon people used vessels--even spectacular creations like this one--mainly for cooking and for other, highly utilitarian purposes.
Jomon Women's PotteryDespite this remarkable head start along the road to "Civilization" that was attained by the Jomon, the advantages of having such a rich biological environment after a while led to a kind of backwardness and ultimately to stagnation. By the late Jomon (1000 BC), foods obtained from natural sources were becoming increasingly harder to get. It was only around this time that agriculture and metallurgy and many of the other trappings of civilization entered Japan, several millennia behind developments on the mainland.
The Jomon Period (c. 12, 000 - 300 BCE) is named for the cord-marked patterns found on much of the pottery produced during this time.
Jomon people were able to develop an unusually sophisticated hunting-gathering culture in part because they were protected from large-scale invasions by their island setting and also because of their abundant food supply... Its people lived in small communities, in the early Jomon period there were seldom more than ten or twelve dwellings together. All in all, the Jomon people seem to have enjoyed a peaceful life, giving them the opportunity to develop their artistry for even such practical endeavors as ceramics.
Jomon ceramics may have begun in imitation of reed baskets, as many early examples suggest. Other early Jomon pots have pointed bottoms. Judging from the burn marks along the sides, they must have been planted firmly into soft earth or sand, then used for cooking...still other early vessels were crafted with straight sides and flat bottoms, a shape that was useful for storage as well as cooking and eventually became the norm. Often vessels were decorated with patterns made by pressing cord onto the damp clay (jomon means "cord markings"). Jomon usually crafted their vessels by building them up with coils of clay, then firing them in bonfires at relatively low temperatures. It is thought that Jomon pottery was made by women, as was the practice in most early societies, especially before the use of the potter's wheel.
During the middle Jomon period (2500-1500 BCE), pottery reached a high degree of creativity. By this time communities were somewhat larger, and each community may have wanted its ceramic vessels to have a unique design. The basic form remained the straight-sided cooking or storage jar, but the rim now took on spectacular, flamboyant shapes... Middle Jomon potters made full use of the tactile quality of clay, bending and twisting it as well as incising and applying designs. They favored asymmetrical shapes, although certain elements in the geometric patterns are repeated. Some designs may have had specific meanings, but the lavishly creative vessels also display a playful artistic spirit. Rather than working toward practical goals (such as better firing techniques or more useful shapes), the Jomon potters seem to have been simply enjoying to the full their imaginative vision.
excerpts from ART HISTORY, edited by Marilyn Stokstad (Abrams, 1996)
Jomon PotterySee also:
The Jomon pottery culture not only begins early, but it continues till well down into the first millennium BC, for the Bronze Age did not begin till very late in Japan. Thus the majority of Jomon pottery is of the third and second millennia BC, when it achieved numerous exotic forms. Jomon means twisted cord in Japanese, and the main characteristic is the twisted cord decoration.