Added 1/27/03, RAR

Dark Matter in the Universe

 

The following article has been abstracted from the February 2003 issue of National Geographic Magazine [1], entitled "Galaxy Hunters". Its main topic is the importance of dark matter in forming and maintaining structure in the universe. Dark matter turns out to have several almost magical properties! My comments are added in italics after the quoted paragraphs.

 

How Dark Matter Affects The Universe

"Our view of the universe is changing completely, says cosmologist Carlos Frenk of the University of Durham in England, and it's largely because of our new understanding of galaxy formation. Smaller and denser than today, the early universe was pitch-black and contained mostly hydrogen and helium with a smattering of lithium. During the past few years, one of the new cosmologists, Tom Abel of Pennsylvania State University, has created supercomputer simulations that show how stars were formed from these gases. The first step, according to the simulations, was when gravity gathered gases into diffuse clouds. As the gases cooled, they coalesced at the center of each cloud into a clump no larger than our sun. The clump collapsed further, while surrounding gas piled on top of it. In this way it grew into a behemoth about 100 times the mass of the sun. Finally, several million years after the entire process began, the intense compression forged a full-fledged star--and there was light."

These computer simulations are based upon an assumption that the Big Bang scenario is correct, because they draw their initial conditions from this model! In fact, the answers will change when the initial conditions are changed, so how does one judge that the answer is right? Are there quantitative criteria, or is it sufficient that the pictures just "look good"?

" The explosive demise of these stars may have left behind dense cinders, the first black holes in the universe. Moreover, the supernova explosions may have been accompanied by flashes of energetic radiation known as gamma-ray bursts that are billions of times brighter than the sun. If so, some of the gamma-ray bursts that have already been detected may actually have come from the first stars."

Here is an assertion that the mysteriously powerful gamma ray bursts come from early supernovae, even though the energy release mechanism for these bursts is unknown!

"The simulations are based on a mind-blowing concept. Some kind of mystery material, which couldn't be seen, and has come to be known as dark matter, outweighs all the visible material in the universe by at least nine to one. Galaxies are merely bright flecks on a sea of dark matter. Without the extra tug provided by dark matter, astronomers say, there wouldn't be enough gravity to pull material into galaxy-size clumps or even form the first star. That was the only way to explain why stars at the outer edge of the spiral galaxies moved no more slowly than stars at the core."

If all galaxies contain a central black hole like the one found inside the Milky Way, do these simulations produce black holes? Does the dark matter move in these simulations under the force of gravity, or does it remain aloof in some sort of initial pattern?

"Dark matter, moreover, answered a key riddle of galaxy formation: how the universe changed from a smooth, hot soup of particles into a jumble of galaxies and galaxy clusters. There had to be some lumps in the first place. By itself, ordinary matter--protons, electrons, and neutrons-couldn't provide those lumps. There wasn't enough of it, and it couldn't begin clumping until the universe had cooled. Dark matter, by contrast, was plentiful and all but impervious to every force but gravity. It could coalesce almost immediately after the universe's birth, giving ordinary matter a foothold to form galaxies, even as cosmic expansion tried to pull them apart." Tiny fluctuations in the Cosmic Microwave Background are thought to be the cause of the original inhomogeneity in the dark matter distribution that provided places for coalescence to take place.

The conclusion is that nothing could have formed in the first place without having dark matter!

"Decades later, resistance to Fritz Zwicky's early ideas about dark matter began to fade when astronomers found themselves invoking dark matter to explain a host of puzzles. In 1973 Princeton cosmologists Jim Peebles and Jerry Ostriker said the mystery material was necessary to keep spiral galaxies, including our own Milky Way, from falling apart. A few years later, Vera Rubin of the Carnegie Institution of Washington concluded that spiral galaxies she and her colleagues had examined had to be embedded in a halo of dark matter. The most popular version of the dark matter theory says that galaxies began small and grew over time through collisions and slow accumulation of material from their surroundings."

Here is a most interesting property of dark matter: Even though it is the major constituent of the universe, and once had clumped to allow galaxy formation to begin, it apparently doesn't gather in the center of galaxies like ordinary matter but is content to remain outside in a Halo!!! This implies that dark matter doesn't seem to attract other dark matter into tight structures, but rather remains fixed in space in a sort of early gelled existence!

"In September 30, 1995, Charles Steidel at Cal Tech hoped to accomplish what no one had ever done--detect in wholesale numbers galaxies so distant that the light they emitted more than 12 billion years ago was only now reaching Earth. Until then astronomers hunting distant galaxies hadn't made much progress. They recorded galaxies that showed up brightly in red and green filters but were absent when viewed through an ultraviolet filter. They called these galaxies Lyman-break galaxies, after Theodore Lyman, a physicist who pioneered studies of ultraviolet light in the early 20th century. According to the color criterion, the faint galaxies Steidel's team had found prior to coming to Mauna Kea ought to be remote. By 1997 Seidel's team had bagged another 250 Lyman-break galaxies, and an intriguing pattern emerged. To the surprise of the astronomers, those distant galaxies were strongly clustered in a way that revealed how dark matter is distributed."

Dark matter seems to clump in some cases but not in others!

"Just as important was another discovery made by Steidel and Kurt Adelberger in 2001: Powerful winds from supernovae were rushing out of the Lyman-break galaxies, proving that there was more to the story of galaxy formation than dark matter. Without such winds we can't easily explain the appearance of the visible universe today. At redshift one, corresponding to a time when the universe was little more than half its current age, the shapes of galaxies cataloged by Edwin Hubble were beginning to fall into place. In between is a mystery interval from 12 to 8 billion years ago in which galaxies are notoriously hard to detect. There's one saving grace, however. The normal emission lines are narrow, while those from distant galaxies are much broader."

Some people have claimed that the high redshift galaxies and quasars are not as far away as the Hubble relationship says they are. Here is an experimental difference that might support the idea of a gravitational redshift bias that both shifts and broadens those lines.

"So what does it all mean? Have astronomers finally solved the riddle of how galaxies were born and evolved? Not quite, says William C. Keel of the University of Alabama, but astronomers are likely to put pieces of the puzzle together over the next decade. Astronomers are pinning their hopes on NASA's James Webb Space Telescope, the proposed successor to the Hubble Space Telescope, scheduled for launch about 2010. Equipped with a mirror capable of collecting six times as much light as Hubble, the telescope, with its advanced infrared and visible light instruments, will be able to detect objects much dimmer and farther away than those observed by any other telescope. That should give scientists the power for the first time to peer into the Dark Ages and to record the faint, warm light from some of the very first stars and galaxies, objects that can now only be seen in computer simulations."

Hence, mathematical computations that give just the semblence of reality are taken to be fact! Once again, new data is expected to be the savior of the Conventional Big Bang. No one wants to face the inconsistencies already pointed out. And this very long article fails to even mention the Deep Redshift Pencil Surveys and their implications.

 

Reference

1) Ron Cowan, "Galaxy Hunters, the search for cosmic dawn", National Geographic, pp. 2- 29, February 2003.