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The M.A.S. Newsletter
Journal of the Mauritius Astronomical Society
May 2000
The Next Meeting:
The next meeting will be held on Friday 26th, weather permitting at 7:00 pm at the Saint Esprit College, Quatre Bornes, for a visit to Bras d'Eau Radio Telescope.
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The sky this month:
At dawn on the 17th, Venus and Jupiter are seperated by less than 1 minute of arc (1') and visible over the eastern horizon at 06:15.
The Boomerang:
An international team of astronomers said that images of the cosmic microwave background (CMB) taken from an instrument flown in a balloon over Antartica show that the universe is flat and not curved, a requirement for the "inflation" theory of the universe's formation. The BOOMERANG (Balloon Observations of Millimetric Extragalactic Radiation and Geophysics) experiment detected the radiation left behind by the Big Bang explosion some 12 billion years ago. The images from the data show what conditions were like about 500,000 years after the Big Bang, when the universe became transparent to radiation.
Chandra provides Cosmic Yardstick:
Astronomers using data from NASA's Chandra X-Ray Observatory have developed a new way to determine how far away distant x-ray sources are. The technique, which measures variations in the x-ray light diffused through a halo of gas and dust, allowed them to determine the distance to Cygnus X-3. The measurement was made by observing the periodic variation in the x-ray emitted by Cygnus X-3 (believed to be a neutron star or black hole orbiting a neighboring star) and how that variation propagated through the dust and gas halo surrounding the object that scatters and delays the x-ray. The halo, explained lead author Peter Predehl of Max Planck Institute, is similar to the halo that surrounds a traffic light on a foggy night. "When the light switches from red to green, or vice versa, the halo around the light is also slightly delayed," he explains. For a traffic light, Predehl said, that delay would be on the order of a billionth of a second: too small to measure. "But if the 'traffic light' is 30,000 ly away, the delay is of the order of 15minutes" and thus could be measured. Detecting even that degree of a delay requires very high quality data, which was not available until the launch of Chandra. The astronomers observed Cygnus X-3 for 3.5 hours using the Advanced CCD Imaging Spectograph on the HST, looking at variations and time relays in different parts of the object's halo. After an analysis of that data, the astronomers concluded that Cygnus X-3 must be about 30,000 ly from Earth. The uncertainty being about 20%, in part because the period of Cygnus X-3's variation is about 4.8 hours, about a third longer than the length of the observations. Tha astronomers hope to reduce the uncertainty with additional observations of the object later this year. Predehl and others believe that this technique can be applied not only to x-ray sources within our own galaxy, but also in neighboring galaxies such as SMC, LMC and M31. If so it could become an important tool for astronomers, as determining the distance to stars and galaxies has been one of the biggest challenges in astronomy. Direct measurement techniques such as parallax only work on nearby objects, forcing astronomers to rely on a series of other techniques, such as Cepheid variable stars to estimate how far away more distant objects lie.
Hubble Discovers "Missing" Hydrogen in Universe:
Using an innovative technique, astronomers announced Wednesday 3rd that they have detected the "missing" hydrogen that makes up half of the ordinary mass of the universe. The astronomers indirectly located the otherwise-invisible hydrogen by detecting a tracer, ionized oxygen, in clouds of gas in intergalactic space. Astronomers had long predicted that such clouds of gas had formed in the aftermath of the Big Bang, creating vast, intricate structures of gas. Clusters of galaxies had been predicted to form where those filaments intersected, heating up the gas. However, until now that gas had eluded detection even though it was believed to comprise up to half the mass of normal matter in the universe. Efforts to detect the extremely hot gas by looking for x-rays emitted by it had not been conclusive since astronomers had difficulty determining what x-rays came from the gas versus other sources. The data obtained from HST's ultraviolet spectrograph observing a quasar showed evidence of spectral absorption "fingerprints" caused by highly ionized oxygen atoms, created by stellar explosions, that are mixed with hydrogen. The hydrogen itself is too hot to be detected directly because at the high temperatures of the clouds - estimated to be at least 100,000 K - all the hydrogen atoms have been stripped of their sole electron, eliminating any spectral signature. Oxygen, with 8 electrons, is able to hold on to a few at even those high temperatures and thus can absorb specific wavelengths of ultraviolet light. While the discovery helps identify the ordinary, visible mass in the universe, it does not provide any information on the missing "dark" matter that makes up the vast majority of the universe's mass.
Serge Florens, Secretary
