-------------------------------------- | | | Biuletyn PTA nr 17 | | | -------------------------------------- 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. Europejski program ASTROVIRTEL II. Nowosci naukowe - LIGHT AT 1 mph - CANDIDATE DARK MATTER PARTICLES + UPDATE - STRANGE HALO ORBITS EXPECTED AT SATURN - BEST MEASUREMENT OF THE GRAVITATIONAL CONSTANT - MAGNETIC FIELDS ARE EVERYWHERE - GRAVITY HAS BEEN MEASURED AT THE SUB-MILLIMETER SCALE - 1997/98 PHYSICS DEMOGRAPHICS ======================================================================= I. Europejski program ASTROVIRTEL On behalf of ESA and ESO, we are glad to be able to announce the opening of the ASTROVIRTEL Programme. ASTROVIRTEL is an initiative financed by the European Commission under the scheme "Enhanced Access to Large Infrastructures" of the 5th Framework Plan and it is operated by the ST-ECF and ESO/DMD. The aim of ASTROVIRTEL is to give the opportunity to selected groups of European scientists (from EC Member and Associated States [for a list of these states, see http://www.stecf.org/astrovirtel/EUStates.html]) to access and use the ESO/ST-ECF Archive (which currently contains data obtained with the ESA/NASA HST, with the ESO NTT, VLT and with the Wide Field Imager on the ESO/MPI 2.2m Telescope) as if it would be a "virtual" Telescope. A description of the ASTROVIRTEL Programme, together with the details of the first Call for Proposals, can be found at http://www.stecf.org/astrovirtel . Please note that the deadline for the first Call is June 15th, 2000. Do not hesitate to contact us if you need further information. The ASTROVIRTEL email address is astrovirtel@eso.org Piero Benvenuti Head / ST-ECF Peter Quinn Head / DMD From: Piero Benvenuti (pbenvenu@eso.org) ======================================================================= II. Nowosci naukowe LIGHT AT 1 mph. A year ago Lene Verstergaard Hau used a Bose Einstein condensate (BEC) as a special nonlinear optical medium for slowing light from 3 x 10^8 m/sec to a mere 17 m/sec (38 mph; Update 415). This comes about when an incoming light pulse enters the BEC and experiences an extremely abrupt change in index of refraction (and as for absorption of the light, this is prevented by applying two laser beams which induce a transparency at the frequency of the incoming light). In a talk presented at this week's meeting of the American Association for the Advancement of Science (AAAS) in Washington, DC, Hau said that she and her Harvard colleagues had slowed the light further, to a speed of 1 mph. She said that if the velocity could be slowed still more, to a value of 1 cm/sec, then this would be comparable to the speed of sound in the condensate and it might be possible to get atoms to surf on the front of the light pulse. Hau believes that this approach to slowing light, if it can be simplified, would lead to highly sensitive light switches and to low-power nonlinear optics (right now high-power laser light is required to produce nonlinear effects). CANDIDATE DARK MATTER PARTICLES, specifically thought to be examples of "weakly interacting massive particles" (WIMPs), have been indirectly detected by a group operating in the Gran Sasso National Lab (INFN) in Italy, according to a paper to be delivered by Pierluigi Belli of the University of Rome (DAMA collaboration) at a dark matter detection meeting in Marina del Rey, California this week (a meeting sponsored by UCLA: information from dm20@physics.ucla.edu). Dark matter is a hypothetical non-luminous substance thought to be lurking in and around galaxies, influencing the way the galaxies rotate and interact. The dark matter might consist in part of baryons (particles such as the protons found in common atoms) or more novel forms such as WIMPs. Because of the way the Earth orbits the sun and the way our solar system moves through the galaxy (buffeting the presumed dark matter halo as it goes) there is reason to think that the flux of WIMP wind we encounter (and the rate at which WIMPs feebly interact in terrestrial detectors) would be higher in June than in December. The DAMA experiment reports having discovered just such an seasonal effect in the frequency of events in which a presumed incoming WIMP (with masses about 50 times that of the proton) strikes a shielded sodium-iodine scintillation material, causing tiny flashes of light deep within the detector (INFN preprint AE-00/01; www.lngs.infn.it). Dark matter interactions in detectors are expected to be rare and analysis difficult, so the DAMA interpretation will be subject to great scrutiny at the California meeting, where other groups searching for WIMPs will be reporting as well. DARK MATTER UPDATE. At the dark matter detection meeting in Marina del Rey, California last week (Update 473) a group form Gran Sasso, Italy reported detecting evidence for dark matter particles. The Cryogenic Dark Matter Search collaboration (10 US institutions), using a different detection scheme, reported finding no evidence for such particles, and asserted that their results were incompatible with the Gran Sasso finding. (Stanford press release, 2/24. see preprint at http://arXiv.org/abs/astro-ph/?0002471.) 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. 1997/98 PHYSICS DEMOGRAPHICS for US institutions from a recent AIP report: 1323 physics PhDs were granted, a 4% drop from the previous year. Of these 13% were to women and 46% to foreign citizens. Among first-year physics graduate students, foreign citizens now exceed their US counterparts. Physics PhDs were awarded to a total of 9 African-Americans and 9 Hispanic- Americans during the academic year. Over the three year period 1996-1998 the leading institutions for African-American physics bachelors were Xavier U (LA), Southern U & A&M Coll (LA), and Lincoln U (PA). In astronomy 116 PhDs were granted: 19% went to women and 30% to foreign citizens. (Enrollment and Degrees Report, AIP Education and Employment Statistics Div; www.aip.org/statistics/trends/undtrends.htm) =======================================================================