Reproduce it in class. 1. One of the most perplexing and intriguing questions in astronomy is just how all the stars and galaxies visible in the night sky came to be there

1. One of the most perplexing and intriguing questions in astronomy is just how all the stars and galaxies visible in the night sky came to be there. Theories explaining this mysterious process abound, each more exotic than the next. But not long ago, many of them collapsed as astrophysicist flashed one simple graph summarizing the first results from NASA's Cosmic Background Explorer () satellite, launched in November 18, 1989.

2. COBE's instruments show that the primordial fireball that spawned the universe popularly known as the big bang apparently was a completely smooth explosion, sending radiation evenly into the nascent universe. This is not what most cosmological theorists expected to find. They anticipated perturbations, disturbances and "lumps" that would somehow metastasize later into galaxies and other great heavenly structures. "The important conclusion is, there isn't anything else there," said astronomers."Nothing."

3. "Zone of Mystery." That fundamental finding, along with other new discoveries, poses an enormous conundrum for cosmologists studying the origin, evolution and structure of the universe. COBE's remarkable instrument looked back to within a year after the big bang, farther back in time than any astronomical instrument has ever gazed before, and found nothing but smoothness ( looks back in time by measuring faint radiation from the big bang that pervades the universe). Yet in November, California Institute of Technology astronomers reported that they had discovered the oldest quasar an extremely bright object in a distant galaxy ever seen, dating from a mere one billion years after the big bang. Something obviously happened during that time a mere blink of the eye in cosmological terms to cause the formation of the enormous celestial structures detectable from Earth. Theoreticians at this point simply cannot explain what occurred. "It's a zone of mystery," they claimed.

4. Previous models of the universe' evolution assumed the existence of several so-far-unseen phenomena: ancient black holes, "cosmic strings," "dark matter" and pregalactic explosions. But these phenomena require some lumpiness in the earliest radiation, which failed to detect. "We're careering toward an absolutely contradictory situation," says Harvard cosmologists. Observations show that the universe is more lumpy than believed before, but the surprising smoothness of the early radiation does not lead logically to such observations. Five years ago, theoretical cosmologists had a lot of theories and no way to prove them right or wrong. Now, there are lots and lots of data and no viable theories.

5. Significantly, however, did not knock out the big-bang theory itself; indeed, it confirmed it in its simplest formulation. The big-bang theory holds that the universe began 10 to 20 billion years ago as a superhot, dense fireball that rapidly expanded and then cooled to form the complex heavenly structures now seen. In 1965, this idea advanced by detecting the first direct evidence. They found weak background radiation that pervades the universe in all directions radiation, that must have come from the original explosion has since cooled to about 3 degrees above absolute zero, and, like a fossil, it can reveal processes that shaped the explosion and its after math. Since the radiation is disturbed by the Earth's atmosphere, was designed to fly above the atmosphere and measure the cosmic background radiation far more precisely than ever before.

6. The experiment is straightforward. A major instrument aboard , called the Far Infrared Absolute Spectrophotometer, looks to see how the cosmic background radiation compares with that of a "black body", a hypothetically perfect radiator that emits a completely smooth spectrum of energy. Before the satellite flew, Space Flight Center said that if deviations from a perfect black-body spectrum were found, that would indicate explosions or other phenomena took place in the early universe. Last year, in fact, a team of scientists from the University of California at Berkeley and Japan reported that they had seen substantial deviations using another instrument, touching off a flurry of scientific papers that attempted to account for it.

7. No Missing Link. Surprisingly, the data received so far from "tell you the universe didn't even burp after it exploded", says John Bachall, a theoretical astrophysicist at the Institute for Advanced Study in Princeton, who found the results so "clear and beautiful that I had chills going up and down the back of my neck".

8. A second experiment, mapping minute differences in the brightness of the background radiation across the sky, failed to detect any hint of galactic progenitors or other stellar objects even 300,000 years further on in the universe's evolution. The scientists were looking for "the missing link" that might explain what we know appeared later. But again nothing. Project scientists concede now that even if reveals some cosmic ripple in the next year and a half, it will probably not be significant enough to explain the existing universe.

9. More Mysteries. COBE's remarkable new findings are not the only ones causing cosmologists theoretical difficulty. They have to contend also with recent discoveries of bigger, more massive structure than any previously known. These, too, are important to the understanding of the evolution of the universe. Most galaxies, it now appears, are on the walls of enormous bubble-like voids. Scientists have identified a sheet of galaxies 500-million-light years long, dubbed the "Great Wall", which is too big to fit into some theories of the universe's evolution. Astronomers confirmed the existence of an enormous gravitation source only 150 million light years from the Earth, called the "Great Attractor". With a mass equivalent to tens of thousands of galaxies, it appears to be pulling other galaxies, including the Milky Way, toward it. They suggest that the existence of such large structures others are likely to be found could be fatal to the notions of how matter clustered during the universe's development.

10. Ironically, the spectacular COBE's mission that promises to keep cosmologists busy for years to come almost didn't take place. It was conceived in 1974 as NASA's first probe of the dawn of the universe and designed to fly into orbit aboard the space shuttle. But the Challenger tragedy scratched from the shuttle schedule, even though the satellite had already been constructed. Scientists and engineers at Goddard persuaded NASA headquarters that they could change its design so it could fly on an expendable rocket. They managed the neat technical trick of preserving COBE's scientific capabilities while sweating the satellite's weight from 10,000 pounds to half of that. Then a series of nagging technical glitches delayed the launch. Now is safely in orbit 560 miles above the Earth. But the data all may be sucked into a terrestrial black hole.



: 2015-09-15; : 212.


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