-------------------------------------- | | | Biuletyn PTA nr 7 | | | -------------------------------------- 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. Strona WWW PTA znowu aktualna II. Ogloszenie: Stanowiska adiunkta w CA UMK III. Nowinki astronomiczne ======================================================================= I. Strona WWW PTA znowu aktualna: http://phobos.camk.edu.pl/pta/ ======================================================================= II. Ogloszenie Dziekan Wydzialu Fizyki I Astronomii Uniwersytetu M.Kopernika w Toruniu oglasza KONKURS NA DWA STANOWISKA ADIUNKTA w Centrum Astronomii UMK. W wypadku odpowiednio wysokich kwalifikacji kandydata, mozliwe bedzie zatrudnienie na wyzszym stanowisku. Centrum Astronomii oferuje szerokie mozliwosci prowadzenia badan astrofizycznych z Katedrze Astronomii i Astrofizyki oraz Radioastronomii zarowno przy pomocy posiadanych przez siebie instrumentow jak rowniez przez istniejace i planowane programy wspolpracy miedzynarodowej. W posiadaniu Centrum znajduje sie miedzy innymi niedawno oddany do uzytku, nowoczesnie wyposazony 32-metrowy radioteleskop, oraz intensywnie modernizowany 90-centymetrowy teleskop Schmidta. Centrum uczestniczy w miedzynarodowych programach interferometrii wielkobazowej (VLBI, VSOP), chronometrazu pulsarow i jest w trakcie staran o wlaczenie sie wraz z innymi osrodkami w kraju do projektu budowy 10-metrowego teleskopu optycznego SALT w Afryce Poludniowej. W Centrum prowadzone sa miedzy innymi badania poznych stadiow ewolucji gwiazd, materii miedzygwiazdowej, pulsarow oraz radiozrodel pozagalaktycznych. Kandydaci powinni legitymowac sie doktoratem z astronomii lub fizyki oraz udokumentowanymi osiagnieciami w dziedzinie astrofizyki. Obok podania z zyciorysem oraz listow referencyjnych wymagane jest opisowe przedstawienie planow dzialalnosci naukowej w Centrum. Kandydatury beda rozpatrywane do czasu obsadzenia wszystkich stanowisk, ktorymi dysponuje Centrum. Termin zgloszen uplywa 15 czerwca 1998r. From: Romuald Tylenda ======================================================================= III. Nowinki astronomiczne THE STRONGEST GRAVITATIONAL FIELDS EVER MEASURED, corresponding to a spacetime warping of 30%, have been recorded by scientists using the Rossi X-Ray Timing Explorer (RXTE) satellite. By comparison, the proportional curvature of space is 100% at a black hole, but only about one part in a million near the sun's surface and one part per billion near the Earth's surface. RXTE was designed to monitor (over microsecond time intervals) the x rays coming from binary star systems in which matter from a conventional star is siphoned off into an accretion disk surrounding a nearby neutron star or black hole. In about 16 binary-star systems that contain neutron stars, blobs of gas in the disk are thought to spiral in toward the neutron star, picking up speed before they make a final plunge onto the surface. The x rays produced in this process are regularly dimmed when the hot gas is on the far side of the star. This leads to quasi-periodic oscillations (QPOs) in the x-ray brightness of the star. Also notable is the fact that the brightness variations only occur at certain well-defined rates, "pure tones" corresponding to special orbital periods for the gas going around the star. The spacetime encountered by the gas is so highly warped because the gas is able to skim within a few km of the neutron star, which itself is only about 10 km in diameter. At this week's meeting of the American Physical Society in Columbus, Ohio, Frederick Lamb of the University of Illinois (217-333-6363, f-lamb@uiuc.edu) described how the observed variations in the x-ray brightness can be used to deduce properties of the neutron star, such as its mass and size. At a press conference, Lamb and William Zhang of NASA Goddard concentrated on the binary-star system 4U1820-30, about 20,000 light years from Earth. The neutron star has a mass of 2.3 solar masses and orbits its companion star in only 11 minutes. Close observations of this system confirm a prediction made by Lamb and his colleagues Coleman Miller and Dimitrios Psaltis that the gas blobs would continue to spiral inward until they reached an "innermost stable orbit," where they would orbit before making the dive for the surface. This is a purely general relativistic (GR) effect; in Newton's mechanics, by contrast, the blob could have gotten arbitrarily close to the surface, providing it were going fast enough. The observations by Zhang and his collaborators now confirm Lamb's prediction, thus opening up a new "strong-gravitational field" era in GR studies. The measurements of the gas motion even provide hints as to the nature of the strong nuclear force sustaining the neutron star against further gravitational collapse. The new evidence indicates that the nuclear force is stiffer and more repulsive than has generally been thought. PLANETARY SYSTEMS IN THE MAKING have been discovered in the form of tenuous dust disks surrounding several more stars. Astronomers believe that our own solar system evolved out of such a disk of material left over after the formation of the sun. Previously a disk like this had been found around the star Beta Pictoris. Now a report in Nature (23 April) reveals disks around two more stars, Formalhut and Vega. Yet another, around the star HR4796A, was announced at a NASA press conference on 21 April. Formalhut's disk even has a dust-free inner zone which one would have expected if rocky planets formed there had swept all such material for their own use. The observations are possible because of new infrared detectors sensitive to the radiation emitted by the relatively cool dust. THE MOST DISTANT GAMMA RAY BURST, at a red shift of 3.4, was discovered in December and observed at several wavelengths. Optical measurements (yielding a red shift) of the object made with the Keck Telescope and the Hubble Space Telescope were announced by Caltech astronomer Shrinivas Kulkarni at last week's APS/AAPT meeting. Optical astronomers were led to the burst's spot in the sky by x-ray observations made by the BeppoSax satellite. (Science, 24 April 1998.) THE BEST ARTIFICIAL VACUUM ever achieved is produced behind a 4-meter disk dragged through Earth orbit by the Space Shuttle. Called the Wake Shield, the deflector pushes atoms out of the way, producing a small region in which the typical distance between residual atoms is a millimeter. Judging tenuousness by this some convention, the best pumped vacuum on Earth attains a residual atom spacing ten times worse---a tenth of a mm. By comparison, the atoms between stars are spaced a centimeter apart; in the gaseous halo of our galaxy the spacing is about 10 cm; and for intergalactic voids, it's up to 10 m, the lowest density (or highest vacuum) ever measured. (New Scientist, 25 April.) CORRECTION: The best artificial vacuum was reported above as corresponding to a spacing between residual atoms of about 1 mm. Several labs have done better: Gerald Gabrielse, for example, achieves a vacuum of 5 x 10^-17 torr, corresponding to about 2 atoms per cm^3. From: physnews@aip.org (AIP listserver) =======================================================================