-------------------------------------- | | | Biuletyn PTA nr 18 | | | -------------------------------------- Biuletyn informacyjny Zarzadu Glownego Polskiego Towarzystwa Astro- nomicznego (Adres kontaktowy: M. Ostrowski, pta@oa.uj.edu.pl , a w bardzo pilnych sprawach: mio@oa.uj.edu.pl ) ======================================================================= Spis tresci: I. Wstepny program Zjazdu PTA we wrzesniu 2001 II. Nowosci naukowe - nie wszystkie calkiem nowe ======================================================================= I. Wstepna informacja o Zjezdzie PTA w Krakowie Najblizszy zjazd PTA odbedzie sie w Krakowie, w Instytucie Badan Polonijnych UJ^*, w okresie 10 - 12 (13) wrzesnia 2001. Ponizej przedstawiono wstepna przymiarke do "rozkladu zajec" w trakcie Zjazdu. Wszyscy wykladowcy wyrazili zgode na wygloszenie wykladu, ale ich tytuly i czas moga w niektorych przypadkach ulec zmianie. Zarzad PTA bardzo prosi wszystkich czlonkow o wlaczenie udzialu w Zjezdzie w swoj kalendarz konferencji. Na Walnym Zgromadzeniu pragniemy w koncu doprowadzic do przeglosowania nowego statutu PTA. ---------------------------------------------------------------------- Poniedzialek 10.09 10:00-13:00 LKO Rejestracja, kwaterowanie 15:00 Otwarcie Zjazdu 15:30 B. Paczynski Monitorowanie zmiennosci calego nieba 16:30 Przerwa 17:00 T. Kwiatkowski Badania fizyczne planetoid 200 lat po ich odkryciu 18:00 K. Stepien Spotkanie z reprezentantem w KBN 20:00 Spotkanie powitalne ------------------------------------------------------------------------- Wtorek 11.09 09:00 R. Wielebinski Radiowe mapy nieba 10:00 J. Kaluzny Stare oraz m³ode gromady kuliste 11:00 Przerwa 11:30 G. Madejski Zrodla rentgenowskie 12:30 15:00 J. Gil Zagadka promieniowania radiowego pulsarow 16:00 Przerwa 16:15 ------ Walne Zebranie 18:15 18:30 ------ Spotkanie dyr. inst i przedst. w KBN 20:00 ------ Przyjecie konferencyjne -------------------------------------------------------------------------- Sroda 12.09 09:00 M. Tomczak Promieniowanie rentgenowskie rozblyskow slonecznych 10:00 R. Juszkiewicz Kosmologia 11:00 Przerwa 11:30 J. Kreiner Sesja dydaktyczna 13:00 14:30 M. Abramowicz Klasyczna i kwantowa fizyka czarnych dziur 15:30 A. Zdziarski Sesja instrumentalna 17:30 19:00 Teatr, koncert (?) -------------------------------------------------------------------------- Czwartek 13.09 - Wycieczka szlakiem zegarow slonecznych (J. Kreiner) --------------------------------------------------------------------------- ^* Miejsce Zjazdu znajduje sie na lesistych wzgorzach nad Wisla, niedaleko krakowskiego ZOO i Obserwatorium Astronomicznego UJ. Zakwaterowanie mamy zapewnione w hotelu Instytutu Badan Polonijnych, a wyzywienie w restauracji "U Zijada" 150 m obok. Zarzad PTA i LOK (przewodniczacy M. Urbanik) czynia starania, aby uzyskac fundusze na dofinansowanie kosztow konferencji dla wszystkich, ktorzy bede tego potrzebowali. From: Marek Urbanik Informacja od M. Urbanika rozbudowana przez M. Ostrowskiego. ======================================================================= II. Nowosci naukowe - nie wszystkie calkiem nowe STRANGE HALO ORBITS EXPECTED AT SATURN. Consider particles in orbit above a planet. If the particles are uncharged or have a very low charge-to-mass ratio, they will follow a conventional ("Keplerian") trajectory centered about the axis of the planet at the equator (Saturn's rings are an example of such particles). If, however, the particles are highly charged, their motions are dominated by an electromagnetic interaction with the planet's magnetic dipole (Earth's van Allen belts are an example). If the charge is somewhere in between these two cases, and gravity and electromagnetic forces are comparable, then strange orbits are possible. Scientists at the University of Colorado (Mihaly Horanyi and Jim Howard, 303-492-6903) and Loughborough University (Holger Dullin) in the UK estimate that if conditions are just right some particles could race around a planet in orbits (stable for as long as 10 years) that never cross the planet's equatorial plane (see figure at www.aip.org/physnews/graphics). The dust analyzer on the Cassini craft now gliding toward Saturn might be able to detect particles in these novel orbits. (Howard et al., upcoming article in Physical Review Letters; Select Article.) BEST MEASUREMENT OF THE GRAVITATIONAL CONSTANT. At this week's American Physical Society Meeting in Long Beach, Jens H. Gundlach of the University of Washington (paper P11.3) reported a long-awaited higher precision measurement of the gravitational constant, usually denoted by the letter G. Although G has been of fundamental importance to physics and astronomy ever since it was introduced by Isaac Newton in the seventeenth century (the gravitational force between two objects equals G times the masses of the two objects and divided by their distance apart squared), it has been relatively hard to measure, owing to the weakness of gravity. Now a group at the University of Washington has reduced the uncertainty in the value of G by almost a factor of ten. Their preliminary value is G=6.67390 x 10^-11 m^3/kg/s^2 with an uncertainty of 0.0014%. Combining this new value of G with measurements made with the Lageos satellite (which uses laser ranging to keep track of its orbital position to within a millimeter) permits the calculation of a brand new, highest precision mass for the earth: 5.97223 (+/- .00008) x 10^24 kg. Similarly the new mass of the sun becomes 1.98843 (+/- .00003) x 10^30 kg. Gundlach's (206-543-4080, jens@phys.washington.edu) setup is not unlike Cavendish's venerable torsion balance of two hundred years ago: a hanging pendulum is obliged to twist under the influence of some nearby test weights. But in the Washington experiment measurement uncertainties are greatly reduced by using a feedback mechanism to move the test weights, keeping pendulum twisting to a minimum. (See Gundlach's written summary at http://www.aps.org/meet/APR00/baps/vpr/layp11-03.html; figures at www.aip.org/physnews/graphics.) MAGNETIC FIELDS ARE EVERYWHERE. The history of the universe is usually described in terms of the distribution of matter: first primordial knots, then clouds, galaxies, stars, and clusters. A parallel, and perhaps not unrelated, saga can be written for magnetic fields. Basically, Philipp Kronberg (416-978-4971) of the University of Toronto finds magnetic fields every place he has looked in the cosmos: within the Milky Way (where the fields are typically about 5 microgauss), in intergalactic areas within galaxy clusters (1-2 microgauss for the Coma cluster, 350 million light years away), and even outside clusters. The latter observations are brand new and were reported by Kronberg at the APS meeting (http://www.aps.org/meet/APR00/baps/vpr/layb7-02.html). Detecting weak magnetic fields outside clusters was difficult and required the use of new low-frequency receivers mounted on the Very Large Array (VLA) radio telescope. The radio range employed, around 75 MHZ, is normally problematic owing to scattering in the Earth's ionosphere, but new image processing techniques have allowed a sharp VLA "deep field" image to be formed. From the intensity of the radio glow, Kronberg deduced a magnetic field of about 10^-8 to 10^-7 gauss for a distant region outside any galaxy cluster, a place (near the "Great Wall") where fields had not been mapped before. Where did such fields come from? Kronberg suggests that huge shock waves, formed where two large streams of weakly magnetized gas come together, could amplify existing fields to much higher levels, as well as playing a part in the acceleration of cosmic rays. Angela Olinto (paper B7.1) of the University of Chicago (773-702-8206) discussed the idea of primordial magnetism, fields that might have existed at or shortly after the time of the big bang. Such fields, she speculated, might have come about through the development of some asymmetry (just as matter came to predominate over antimatter) in the infant universe. Early magnetism might then have influenced subsequent galaxy formation or even the distribution of matter now seen imprinted in the cosmic microwave background (CMB). She said that the surprising absence of subsidiary peaks in the CMB spectrum (see Update 481) might be attributable to magnetic effects. This hypothesis could be addressed, Olinto said, by the Planck satellite (launch date several years from now; see Update 342), dedicated to mapping the CMB with unprecedented precision. GRAVITY HAS BEEN MEASURED AT THE SUB- MILLIMETER SCALE for the first time. Gravity has of course long been studied over planetary distances but is more difficult to gauge at the terrestrial scale, where intrusive electric and magnetic fields, many orders of magnitude stronger than gravity fields, can be overwhelming. Nevertheless, Eric Adelberger and his colleagues at the University of Washington have managed to measure the force of gravity over distances as small as 150 microns using a disk-shaped pendulum carefully suspended above another disk, with a copper membrane stretched between them to help isolate electrical forces. (This experiment should not be confused with another University of Washington effort in which the gravitational constant is measured with higher precision see Update 482). Adelberger (206-543- 4294, eric@gluon.npl.washington.edu) presented one of several talks at this week's APS meeting in Long Beach, California devoted to short-range gravity, a subject which has suddenly attracted much theoretical and experimental interest owing to a relatively new model which supposes the existence of extra spatial dimensions in which gravity, but not other forces, might be operating. According to Nima Arkani-Hamed of LBL (arkani@thsrv.lbl.gov, 510-486- 4665) this is why gravity is so weak: it dilutes itself in the extra dimensions. In other words, ordinary particles are tethered to our conventional spacetime, or "brane," while gravitons are free to roam into otherwise unseeable dimensions. One implication of the model, testable with tabletop experiments such as Adelberger's, is that the gravitational force might depart from Newton's inverse square law (gravity inversely proportional to the square of the distance between two objects) at close range. Adelberger did not observe such a departure at distances down to tenths of a millimeter and will continue to explore even shorter distances. For a list of tabletop experiments underway, see http://gravity.phys.psu.edu/mog/mog15/node12.html. Another interesting implication of the model introduced by Arkani-Hamed (and others; see preprint hep-th 9803315) two years ago is that the unification of the four known forces would not necessarily occur at energies as high as 10^19 GeV but possibly at energies as low as 10^4 GeV, an energy scale within reach of the Large Hadron Collider under construction at CERN. Extra dimensions could, for example, manifest themselves in proton- proton smashups as an apparent disappearance of energy, implying that some of the collision energy had been converted into gravitons (the particle form of gravity) which then disappear into the extra dimensions. The gravitons produced in this way might come back into our conventional world of 3 spatial dimensions and decay into two photons. Physicists have already looked for this kind of event. Gregory Landsberg of Brown University (401-863-1464; landsberg@hep.brown.edu) reported that at the D0 experiment at Fermilab some energetic two-photon events have been observed (including one in which the energy of the photons added up to 574 GeV, representing the highest composite mass ever seen in the D0 experiment) but not often enough to constitute evidence for extra dimensions. In fact this shortage of events has been translated into a lower limit of 1300 GeV for the energy at which a prospective unification of the forces could take place. THE FIRST GLOBAL IMAGE OF THE EARTH'S PLASMASPHERE, the shell of positively charged ions and negatively charged electrons lying at the top of our atmosphere and extending far out into space, has been recorded by the Imager for Magnetosphere to Aurora Global Exploration (IMAGE) satellite. The ability to view the Earth and its environs through plasma- colored glasses is important for understanding basic geophysics properties of the Earth and for monitoring "space weather," the general name for disturbances in our planet's vicinity caused by fields and particles coming from the sun. A violent storm on the sun can, a few days later, pose hazards for satellites and even ground-based power grids. IMAGE performs its sentry duty by photographing the glow caused when light or particles coming directly from the sun or nearby particles whipped up to high energies smash into atoms in our upper atmosphere. Launched in March 2000, the IMAGE spacecraft follows a highly eccentric orbit which takes it far enough from the Earth that at times the whole planet, and its fluorescing plasma, can be captured within the photographic frame. First data from the IMAGE mission were reported this week by James Burch, Southwest Research Institute (210-522-2526) and several colleagues at the American Geophysical Union meeting in Washington, DC. One surprise: a picture of the helium glow around the Earth at extreme ultraviolet (EUV) wavelengths (see figure at www.aip.org/physnews/graphics) exhibited unexplained lobe structures. Another first: separate ultraviolet movies of electron and proton auroras were shot simultaneously by using filters that discriminate among fluorescence at different wavelengths coming from hydrogen, oxygen, and nitrogen atoms in the atmosphere; EUV at 121 nm, for instance, comes from energetic protons resonantly scattering from hydrogen atoms. To locate more precisely the position and velocity of the plasma clouds being viewed, IMAGE uses an immense cross-shaped radio antenna (mission scientist James Green of Goddard Space Flight Center called it a "radar cop in the sky") measuring 500 meters from tip to tip (longer than the Empire State Building is tall, or equivalent to three Washington Monuments laid end to end), making it the longest manmade structure in space. (See also the IMAGE website: http://image.gsfc.nasa.gov/press_release/2000_05_31/.) JUPITER'S MOON IO BEARS WATCHING. The most volcanically active object in the solar system, Io has recently been visited again (in Feb 2000) by the Galileo spacecraft, and the surface shows noticeable changes from a flyby made in Oct 1999. Results reported at last week's American Geophysical Union meeting in Washington, DC include the following: John Spencer of the Lowell Observatory summarized infrared observations of Loki, Io's (and the solar system's) greatest volcano, whose immense lava flow, the size of Connecticut, is unequaled on Earth in historic times. In the past few months the flow has warmed by 40 K and greatly grown. Rosaly Lopes-Gautier of JPL showed several new hot spots (potential volcanos) discovered with a high-resolution infrared spectrometer. One might extrapolate from the density of sources, she said, that Io might have more than 300 volcanos, representing a colossal energy loss. Meanwhile, Alfred McEwen of the University of Arizona described the Chaac canyon which, with a depth of 2.8 km and an average steepness of 70 degrees, is much more dramatic than the Grand Canyon in Arizona (1.5 km deep and 30 degrees in steepness). See also Science, 19 May 2000. THE NEXT GENERATION SPACE TELESCOPE (NGST), 100 times more sensitive than the Hubble Space Telescope, sits at the top of the list of desirable future observatories, a list formulated by the National Academy of Sciences. The billion-dollar NGST should possess an 8-m mirror, an orbit 1 million miles from Earth, and an ability to view the most distant (and earliest) stellar objects in the universe at infrared wavelengths. Next in order of priority is the Giant Segmented Mirror Telescope (GSMT), a 30-m ground based telescope for complementing with superb spectroscopy the sharp imaging of the NGST; the $800 million Constellation-X Observatory, specializing in x rays; an Expanded Very Large Array (EVLA) radio telescope; the Large-aperture Synoptic Survey Telescope (LSST), which would scan the whole sky, every week for faint objects; and the Terrestrial Planet Finder (TPF), "the most ambitious science mission ever attempted by NASA," whose goal is to search for planets around nearby stars. (NAS website: http://www.nationalacademies.org/topnews/.) NEW MEASUREMENTS OF DEUTERIUM at the center of our Milky Way galaxy confirm theoretical models that most deuterium, the heavy isotope of hydrogen containing one proton and one neutron, is primordial (made at the time of the big bang) and not subsequently created in galaxies or stars. A Hofstra-Williams-Colgate-Manchester (UK) team of astronomers have used the National Radio Astronomy Observatory 12-m radio telescope to scan a huge molecular cloud only 30 light years from the galactic center. In particular they look at the spectra of hydrogen cyanide (HCN) and its deuterium counterpart DCN. In general stars are expected to be net consumers (not producers) of deuterium: they burn it into helium. But the galactic center is the Times Square of the Milky Way; it is the scene of jets, bursts, x-ray and gamma sources, a massive black hole, filaments, arcs, and other material-processing objects. From their observed ratio of deuterium-to-hydrogen D/H, the researchers (Don Lubowich, Jay Pasachoff, Tom Balonek, and Tom Millar) deduce three things: (1) The D/H ratio is higher than you would expect in the absence of a source of virginal unprocessed material (high in D, low in heavier elements). This demonstrates that matter comparatively rich in D is indeed raining down with the cloud onto the plane of our galaxy (see figure at www.aip.org/physnews/graphics). In other words, the infalling matter is to the galaxy what comets are to our solar system: specimens of relatively unprocessed, primitive material. (2) For all that, the D/H ratio at the galactic center is lower than in all other places in the galaxy. This is important evidence confirming that D is not made in stars and that what D we see is made by the big bang. (3) >From models of D production in quasars, the observed D/H ratio suggests that the Milky Way could not have harbored a quasar for at least a billion years and probably not for four billion years. (Lubowich et al., Nature, 29 June 2000.) MARTIAN GULLIES, perhaps as young as thousands of years old or even newer, have been photographed by the orbiting Mars Global Surveyor. Evidence of ancient water action on the Martian surface had been noted before, but the sharper resolving power of the Global Surveyor shows that the water-cut features lie on top of older rockforms. The presence of recent, not just ancient, water flows will certainly enter into discussions of the hypothetical existence and nature of Martian life. (NASA press release, 22 June; also Science, 29 June 2000.) Meanwhile, the density of tiny water crystals in a Martian meteorite recovered in Antarctica (a rock jarred loose from Mars perhaps 3 million years ago) indicates that Mars might have a below-surface reservoir of water two to three times higher than previously thought. (Laurie Leshin of Arizona State, reporting in the 15 July Geophysical Research Letters.) A PLANETESIMAL AGGREGATION EXPERIMENT has been carried out in the low gravity environment of the Space Shuttle to test notions of how our solar system developed from a primordial cloud of micron sized dust particles. The experiment is the first direct re- creation, under realistic solar-nebula conditions, of the proposition that protoplanetary dust accumulates through sticky collisions amid the random Brownian motion of the particles. A consortium of German and US scientists (contact Jurgen Blum, University of Jena, Germany, 011-49-364-194-7515, blum@astro.uni-jena.de) observed that the dust quickly aggregates. The data bears out the main theory of planetesimal formation, but there was one surprise: the structures were expected to be somewhat fractal in nature, with a fractal dimension d of about 1.8, meaning that the mass of the cluster should be proportional to the cluster size raised to the d power. Instead the dimensionality turned out to be about 1.3, meaning the structures were observed to be more linear and less sheetlike (see figure at www.aip.org/physnews/graphics). (Blum et al., Physical Review Letters, 18 September 2000; Select Article.) =======================================================================