• 7/21/2000 - Scientists find first direct evidence of subatomic particle tau neutrino - Discovery supports standard model theorized in 1978 - by Joseph B. Verrengia, The Associated Press.
      After a two-decade search, scientists have found the first direct evidence of one of the most elusive subatomic particles in nature -- the tau neutrino.    The discovery announced by the scientists from the United States, Japan, Korea and Greece at the Fermi National Accelerator Laboratory outside of Chicago after searching since 1997.    The tau is one of the fundamental building blocks of all matter.    It is the last of the tiny particles described in the Standard Model of Particle Physics to be confirmed in experiments.
      The standard model seeks to encapsulate all elementary particles and forces in a single explanation.    Now the bits have been identified, though the many forces that guide their interplay remain a mystery.
      "It's a tremendous milestone," said Stanford University physicist and Nobel Prize winner Martin perl, who theorized the existence of the tau neutrino in 1978.    "Now it has been seen and it behaves in the way we expected."
      Neutrinos are hurtling everywhere at the speed of light.    Trillions pass through each of us every second.    Yet they are among the hardest to detect of all subatomic particles, carrying no electrical charge and virtually no mass -- perhaps one-millionth that of an electron.
      The tau neutrino is the third and perhaps final type of neutrino to be found.    The first two types -- electron neutrinos and muon neutrinos -- were discovered in 1956 and 1962.    In 1978, tests by Perl and others at Stanford discovered the existence of another class of subatomic particle, the tau lepton.    This suggested there would be a tau neutrino, too, because neutrinos are precursors to leptons.
      In 1997, scientists using the ring-shaped particle accelerator at Fermilab fired an intense neutrino beam into a 50-foot detector composed of iron plates coated with an emulsion.    Then they analyzed the 6 million impressions left on the coating, and with computer assisted video camera to create 3-D images of the particle tracks.    After narrowing it down they found four clear tracks of a tau lepton that were caused by tau neutrino collisions.    They can never be detected directly, since they have no charge, only their signature is detected.
  
  
• 3/14/2001 - Black holes once were much more active by Paul Recer, The Associated Press.
      Washington -- The early universe teemed with supermassive black holes spewing X-rays across the heavens, according to data from an orbiting telescope that picked up images from far, far away and long, long ago.    The Chandra X-ray telescope, in a study focused on small sections of the sky for days-long exposures, has captured faint X-rays straming from black holes up to 12 billion light-years away, astronomers said.    "The Chandra data show us that giant black holes were much more active in the past than at present," said Riccardo Giacconi, a Johns Hopkins University astronomer.    "If you look at the sky with X-ray eyes, you see almost nothing but black holes," said Bruce Margon, a professor of astronomy at the University of Washington, Seattle.
      Black holes are single points of extreme density forming gravitational fields so strong that nothing, not even light, can escape.    Extremely powerful black holes at the center of galaxies can have a mass one million to 100 billion times that of the sun concentrated at a point not much bigger than the Earth.    Stellar black holes, formed from collapsed stars, are much smaller, down to three solar masses, and can have a core only a few miles across.    Since they allow no light to escape their centers, black holes are detected by the effect that they have on surrounding gas, dust and stars.    Before matter is pulled into the center of a black hole, it is accelerated to near the speed of light, resulting in streams of X-rays.
• 3/19/2001 - Unusual States of Matter by Earl Lane, Times-Post News Service.
      Reinhard Stock remembers the days in the late 1970s when a small band of physicists speculated that ordinary matter, if compressed enough, might transform into a new state that would mimic some of the conditions at the birth of the cosmos.    Theorists argued that the protons and neutrons at the core of the atom, under extreme conditions, would "melt."    That could allow the constituent building blocks, called quarks, to briefly roam free (along with particles called gluons that bind the quarks tightly together) in a state called the quark-gluon plasma.    Physicists figured they might get a glimpse of it by accelerating heavy ions -- atoms stripped of their outer electrons -- to nearly the speed of light.    The ions would then be sent crashing into each other or against stationary targets.
      Last year, officials at CERN, the European physics research center near Geneva, Switzerland, announced that heavy ion experiments at that lab had produced circumstantial evidence for a new state of matter in which quarks had been briefly "deconfined."    Many physicists were skeptical, since the current heavy ion program at CERN winds down, for the researchers to make their best case for having found a hint of the quark-gluon plasma.    Evidence from other colliders may take two or three years.    The goal is to explain why the universe turned out the way it looks today, physicists say.    Quarks combine in trios or pairs to form the bulk of the matter we see today in the cosmos, and they are tightly bound through the strong nuclear force transmitted by uncharged particles called gluons.    The experiment suggest that force gets only stronger as efforts are made to separate pairs of quarks.
• 4/2/2001 - Antarctic telescope detects neutrinos by The Washington Post.
      A telescope 164 stories tall and 400 feet across, buried a mile deep in Antarctic ice, has detected some of the most exotic particles known.    Neutrinos are invisible particles that have no electrical charge or mass.    They are devilishly difficult to catch, but considered worth the bother, because they carry information about the most distant and violent events in the universe.    The telescope has for the first time observed high-energy neutrinos, according to a team of scientists reporting in a recent issue of Nature.    The ability to find high-energy neutrinos promises new insights into such phenomena as colliding black holes, gamma-ray bursters and the wreckage of exploded stars, the researchers said.
• 4/2/2001 - Dark Matter detected by its influences by Gannett News Service.
      Scientists from the United States and the United Kingdom have for the first time detected the presence of dark matter in our galaxy.    Scientists say that to account for the galaxy's rotation, unseen dark matter must exist.    They can detect its presence by its influence on the motion of stars and other galaxies.
      The researchers, who published their work in the journal Science, studied ancient white dwarf stars -- dense, cool, faded stars that no longer produce energy through nuclear fusion.    They found a population of dwarf stars that may account for at least 3 percent of the halo dark matter.    Since these degenerated stars are also very ancient, they could give astronomers a glimpse of the earliest history of our galaxy as well.
• 5/14/2001 - Finding Sheds Light On Spinning Black Holes by Kathy Sawyer, The Washington Post.
      For the first time, astronomers have evidence that a black hole can spin like a top.    In this case, a black hole 10,000 light-years from Earth appears to be whipping matter around itself at 27,000 revolutions per minute, flashing X-rays in unsteady spasms and twisting the fabric of space-time.    "We can see the light emitted from matter plunging into the black hole, said Todd Strohmayer, of NASA's Goddard Space Flight Center in Greenbelt, Md.    This material "whips frantically around the black hole before it is lost forever."    The study of black holes is suppose to move science closer to a theory that explains how all the forces of nature work together, so called "theory of everything."    This would represent the workings of gravity to fit harmoniously with the other forces of nature, said Virginia Trimble, of the University of Maryland and the University of California, Irvine.    Albert Einstein's theory of gravity has passed a series of observational tests, but nobody has figured out how to make it compatible with the laws of quantum physics that govern the subatomic world.    Black holes, where all these forces reach extremes, make ideal -- if difficult -- laboratories.    What Strohmayer found were unique patterns in the X-ray radiation emitted around the black hole as it pulls material at almost the speed of light from a companion star orbiting around it.    At the same time, the maelstrom around the hole ejects particles in jets from its north and south poles, also at incredibly high velocities.    "Black holes are one of the greatest energy sources in the universe," Strohmayer noted.    They surmised that the black hole inherited the rotation properties, or angular momentum, of the star that formed it.
• Scientific American, August, 2002 issue, pg. 42-52 - Does Dark Matter Really Exist? - Ninety-five percent of the universe has gone missing. Or has it? - by Mordehai Milgrom, author.
      The need for extra matter arises not only in well-formed galatic systems but also through the universe at large.    Long before galaxies even formed, the universe was filled with a plasma of atomic nuclei and subatomic particles.    Radiation suffused the plasma and kept it extremely smooth.    Fluctuations in the density of this plasma did not have a chance to grow and develop into galaxies until after the plasma had turned into a neutral gas, which does not interact with radiation as strongly.
      The problem is that there just wasn't enough time for those flucuations to become galaxies we observe.    Dark matter would help in that, being neutral by definition, it would not be homogenized by radiation.    Therefore, it would have been contracting all along.    Dark matter would have had enough time to form galaxy-mass bodies.
      Common knowledge has it that part of this extra mass consists of ordinary matter that gives off too little radiation for present technology to detect: planets, dwarf stars, warm gas.    Such material is more precisely called dim matter.    It could represent up to 10 times as much matter as astronomers see, but even so it could account for only a small fraction of the missing mass.    When researchers refer to dark matter, they usually mean an exotic breed of matter that makes up the difference.    To add to the confusion, they also suspect the existence of dark energy, a distinct type of energy that would produce the observed accelerated expansion of the universe.
      In sum, astronomers widely believe the current energy content of the universe to be roughly 4 percent ordinary (or "baryonic") matter, about a tenth of which is seen as stars and gas; a third dark matter in some unknown form; and two-thirds dark energy, the nature of which is even less understood.
      If we accept a departure from these standard laws, we might do away with dark matter.
      The formula in Newtonian physics combines two basic laws: Newton's law of gravity (which relates the force of gravity between bodies to the bodies' masses and separation) and Newtonian's second law (which relates force to acceleration).    These laws accurately explain the flight of a ballistic missile and the motions of the planets.    But their extrapolation to galaxies has never been directly tested.
      This article suggest that if the laws break down, then modifying them might obviate dark matter.    Two drastic changes to Newtonian physics have already proved necessary.    The first upgraded Newtonian dynamics to the theory of relativity -- both the special theory (which changed Newton's second law) and the general theory (which altered the law of gravity).    The second led to quantum theory.
      Overview/Alternative to Dark Matter
  
  • Astronomers have two ways to determine how much matter fills the universe, the total of what is seen, and the measure of how fast the visible objects move, apply the law of physics and deduce how much mass is needed to generate the gravity that restrains those objects.    So the conclusion was dark matter.
  • Perhaps the fault lies not in the matter but in the laws of physics.    The author has proposed a modification to Newton's laws of motion or gravity to explain away the discrepancy.
  • The modification, known as MOND, does a good job of reproducing observations, than dark matter does.
  
      The author zeroed in on accleleration, propossing a modification 20 years ago to Newton's second law that changed the relation between force and acceleration when accleration is low.    This was the beginning of the idea called MOND, for Modified Newtonian Dynamics.    MOND introduces a new constant of nature with the dimensions of acceleration, called a₀.
      When the acceleration is much larger than a₀, Newton's second law applies as usual: force is proportional to acceleration.
      But when acceleration is small compared with a₀, Newton's second law is altered: force becomes proportional to the square of the acceleration.
      To account for the observed accelerations in galaxies, MOND predicts a smaller force -- hence, less gravity-producing mass--than Newtonian dynamics does, allowing for the elimination of dark matter.
      In the outskirts of galaxies, the acceleration produced by gravity decreases with distance and eventually goes below a₀.
      Exactly where this happens depends on the value of a₀ and on the mass.    The higher the mass, the farther out the effects of MOND set in.
      The bulk of the solar system's mass is contained in the sun, and the orbital velocity of the planets decreases with distance.    Mercury has a faster orbit than Earth does, the effects of MOND falling below a₀ would be 10,000 times as far from the sun as Earth is, far beyond the orbit of Pluto.
      At large distances from the center of a galaxy, the orbital velocity should stop decreasing and reach a constant value.    This constant velocity should be proportional to the fourth root of the galaxy's mass.    So far MOND's main failure has occurred in the observations in the cores of large rich galaxy clusters, but fits well with Globular clusters, Spiral galaxies, Galaxy clusters, Dwarf spiral galaxies, Dwarf spheroidal galaxies, and small galaxy groups.
  
      Commentary Not a Bad Idea, MOND is out of the mainstream, but it is far from wacky, by Anthony Aguirre, a theoretical cosmologist at the Institute for Advanced Study in Princeton, N.J.
      As an alternative hypothesis -- a modification of Newtonian gravitational dynamics (MOND) -- has quitely endured since its proposal in 1983.    As Mordehai Milgrom discusses in the above article, MOND can claim an impressive number of correct predictions regarding the dynamics of galaxies.    The reactions of most astronomers fall into three categories:
  • 1. MOND is a tautology, that explains only what it was designed to explain.    Its few predictions have been exaggerated by its proponents.
    • Since MOND has been released many have reproduced the statistics of galaxy properties at least as well as dark matter models do, even though these models describe crucial aspects of galaxy formation in an ad hoc way.    MOND can predict the details of galaxy rotation using only the distribution of visible matter and assumed (fixed) ratio of mass to luminosity - a feat beyond the ability of dark matter models.    This statement helps to refute the claim of it being a tautology.
  • 2. MOND describes a mysterious regularity in the formation and evolution of galaxies.    The standard theory of gravity still applies and dark matter still exists, but somehow the dark matter emulates MOND.    When applied to unusual galaxies or systems other than galaxies, MOND will eventually be shown to fail.
    • Standard dark matter theory has run into difficulty when applied to galaxies.    It predicts that the dark matter cores of galaxies should be far denser than observations indicate.    Some claim this is because of computational limitations.    Some theorists have converted from the first view to the second view in recent years.
  • 3. MOND replaces Newtonian dynamics under certain conditions.    It is one aspect of a theory of gravitational dynamics that will supplant Einstein's general theory of relativity.
    • Few theorists have gone to the third view yet.    MOND's proponents have yet to formulate it in a way that can be applied to post-Newtonian phenomena such as gravitational lensing and cosmic expansion.    Its predictions about the temperature of hot gas in clusters of galaxies disagree starkly with observations, unless clusters are dominated by -- what else? -- undetected matter.    The standard dark matter theory has scored some impressive triumphs in recent years.

Last updated April 1, 2005, August 30, 2006, February 3, 2007, August 1, 2007, August 17, 2007, and January 12, 2012.