Voyages of Discovery: Copernicus to the Big Bang                  

  Telescope: Hunting the Edge of Space

  Runaway Universe
  Type Ia Supernovae


  Adaptive Optics

  SN 1987A in the Large Magellanic Cloud

    Supernova 1987A exploded on 1987 February 23, in the Large
    Magellanic Cloud. Because of its relative proximity to us (a mere
    168,000 light years) SN 1987A is by far the best-studied supernova
    of all time. Immediately after the discovery was announced,
    literally every telescope in the southern hemisphere started
    observing this exciting new object.

    In addition to light, particle emission was detected from the
    supernova. "Kamiokande II" is a neutrino telescope whose heart is a
    huge cylindrical tub, 52 feet in diameter and 53 feet high,
    containing about 3000 metric tons of water; it is located in the
    Kamioka mine in Japan, 3,300 feet underground. On February 23,
    around 7:36 am Greenwich time, the Kamiokande II recorded the
    arrival of 9 neutrinos within an interval of 2 seconds, followed by
    3 more neutrinos 9 to 13 seconds later. Simultaneously, the same
    event was revealed by the IMB detector (located in the
    Morton-Thiokol salt mine near Faiport, Ohio), counted 8 neutrinos
    within about 6 seconds. 

    A third neutrino telescope (the "Baksan" telescope, located in the
    North Caucasus Mountains of Russia, under Mount Andyrchi) also
    recorded the arrival of 5 neutrinos within 5 seconds from each
    other. This makes a total of 25 neutrinos detected on Earth, out of
    the 10^54 of them produced in the explosion! 

  Neutron Stars & Black Holes

  Black Holes


  What is the dark matter? 

    21 Aug 2006 - NASA announced updated information about the
    "bullet cluster" 1E0657-56 today. Two clusters of galaxies have
    recently collided in this X-ray source. This cluster is filled
    with hot gas so X-ray observations by the Chandra X-ray
    Observatory show where the ordinary matter is located. 90% of
    the ordinary matter (the "baryonic" matter) is hot gas. The new
    results [Clowe et al., Bradac et al.] use gravitational lensing
    of background galaxies to show where the sources of gravity are
    located. The sources of gravity in the cluster are not located
    where the ordinary matter is located, so this cluster is a
    counter-example to MOND. All of this was known in 2003  but
    with less precision. 
    A direct empirical proof of the existence of dark matter

    From: Marusa Bradac [view email]
    Date: Sat, 19 Aug 2006 17:51:03 GMT   (119kb)

    Authors: Douglas Clowe (1), Marusa Bradac (2), Anthony H. Gonzalez
    (3), Maxim Markevitch (4), Scott W. Randall (4), Christine Jones
    (4), Dennis Zaritsky (1) ((1) Steward Observatory, Tucson, (2)
    KIPAC, Stanford, (3) Department of Astronomy, Gainesville, (4) CfA,

    Comments: Accepted for publication in ApJL

    We present new weak lensing observations of 1E0657-558 (z=0.296), a
    unique cluster merger, that enable a direct detection of dark
    matter, independent of assumptions regarding the nature of the
    gravitational force law. Due to the collision of two clusters, the
    dissipationless stellar component and the fluid-like X-ray emitting
    plasma are spatially segregated. By using both wide-field ground
    based images and HST/ACS images of the cluster cores, we create
    gravitational lensing maps which show that the gravitational
    potential does not trace the plasma distribution, the dominant
    baryonic mass component, but rather approximately traces the
    distribution of galaxies. An 8-sigma significance spatial offset of
    the center of the total mass from the center of the baryonic mass
    peaks cannot be explained with an alteration of the gravitational
    force law, and thus proves that the majority of the matter in the
    system is unseen.

    Strong and weak lensing united III: Measuring the mass distribution
    of the merging galaxy cluster 1E0657-56

    From: Marusa Bradac [view email]
    Date: Fri, 18 Aug 2006 20:06:48 GMT   (373kb)

    Authors: Marusa Bradac (1,2), Douglas Clowe (3), Anthony H.
    Gonzalez (4), Phil Marshall (1), William Forman (5), Christine
    Jones (5), Maxim Markevitch (5), Scott Randall (5), Tim Schrabback
    (2), Dennis Zaritsky (3) ((1) KIPAC, Stanford, (2) AIfA, Bonn, (3)
    Steward Observatory, Tucson, (4) Department of Astronomy,
    Gainesville, (5) CfA, Cambridge)

    Comments: Accepted for publication in ApJ; Version with
    full-resolution figures available at this http URL

    The galaxy cluster 1E0657-56 (z = 0.296) is remarkably well-suited
    for addressing outstanding issues in both galaxy evolution and
    fundamental physics. We present a reconstruction of the mass
    distribution from both strong and weak gravitational lensing data.
    Multi-color, high-resolution HST ACS images allow detection of many
    more arc candidates than were previously known, especially around
    the subcluster. Using the known redshift of one of the multiply
    imaged systems, we determine the remaining source redshifts using
    the predictive power of the strong lens model. Combining this
    information with shape measurements of "weakly" lensed sources, we
    derive a high-resolution, absolutely-calibrated mass map, using no
    assumptions regarding the physical properties of the underlying
    cluster potential. This map provides the best available
    quantification of the total mass of the central part of the
    cluster. We also confirm the result from Clowe et al.