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By Daniel Fischer Every page present in Europe & the U.S.!
| Ahead | Awards 
The latest issue!
| A German companion - only available here! Current mission news: MGS (latest pictures!) + Cassini + Stardust |
Coverage by AFP, USA Today. Watch the moons: S&T. Mars met the Moon on July 17 - spectacular pictures from the U.S.: S&T, Science@NASA (scroll down!), SC, Parker & Beish (earlier). Previews: NSU, APOD, Ast. Mars Express views Earth, Moon for a camera test while OMEGA & SPICAM scan Earth's atmosphere: ESA Science News, DLR page, more tests, SC. Opportunity trajectory correction: JPL Release. The MER batteries: AF PR. Scout selection coming up: Machine. ExoMars progress: ESA News. How active is Mars? SciAm. More evidence for ancient seas? PSRD. A fresh crater: SN. A strange mound: MSSS Release.
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New physical evidence for Dark Energy emerges: the ISW effectHave you ever thought about the Integrated Sachs-Wolfe (ISW) effect? Now you should: This complex physical phenomenon has apparently been detected thanks to the SDSS optical sky survey and the WMAP cosmology satellite (see Update # 249 story 2) - and it presents independent evidence for the mysterious Dark Energy dominating the Universe! As photons from the cosmic microwave background (CMB) travel to us from 380,000 years after the Big Bang, they can experience a number of physical processes, including the Integrated Sachs-Wolfe effect. This effect is an imprint or shadow of dark energy on microwaves and also measures the changes in temperature of cosmic microwave background due to the effects of gravity on the energy of photons. Technically speaking, the ISW effect is the integrated differential gravitational redshift caused by the evolution of gravitational potentials along the path traveled by the photons.Photons streaming from the cosmic microwave background pass through many concentrations of galaxies and dark matter. As they fall into a gravitational well they gain energy (just like a ball rolling down a hill). As they come out they lose energy (again like a ball rolling up a hill). Photographic images of the microwaves become more blue (i.e. more energetic) as they fall in toward these supercluster concentrations and then become more red (i.e. less energetic) as they climb away from them. In a universe consisting mostly of normal matter one would expect that the net effect of the red and blue shifts would cancel - but not in the presence of repulsive Dark Energy: If the depth of the gravitational well decreases while the photon travels through it then the photon would exit with slightly more energy. One thus would expect to see that the cosmic microwave background temperature is slightly hotter in regions with more galaxies - and that is exactly what has been found. The net energy change expected from a single concentration of mass is less than one part in a million: Researchers had to look at a large number of galaxies before they could expect to see the effect. But now the results confirm that dark energy exists in relatively small mass concentrations: only 100 million light years across where the previously observed effects dark energy were on a scale of 10 billion light years across. A unique aspect of the SDSS data is its ability to accurately measure the distances to all galaxies from photographic analysis of their photometric redshifts: Therefore one can watch the imprint of this effect on the CMB grow as a function of the age of the universe. And eventually one might be able to determine the nature of the dark energy (the equation of state) from measurements like these, though that is a bit in the future. To make the conclusion that dark energy exists from the SDSS/WMAP data set one had to assume that the universe is not curved - but given the WMAP data themselves, that is a well-accepted assumption. |
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Stony asteroids more likely to explode in mid-airSignificantly fewer asteroids could hit the Earth's surface than previously reckoned, according to new computer simulations of their behaviour in the atmosphere: The results indicate that asteroids with a diameter greater than 200 meters will hit the surface approximately once every 160,000 years, way down on previous estimates of impacts every 2,500 years. When small asteroids hit the atmosphere the two forces collide like two objects smashing together, which often breaks the asteroid into fragments. Until now, scientists have relied on the 'pancake' model of asteroid impact to calculate whether the asteroid will explode in the atmosphere: This treats the cascade of fragments as a single continuous liquid that spreads out over a larger area - to form a 'pancake'. But a new model known as the 'separate fragment' (SF) model yields very different results when it comes to smaller asteroids.More than 1000 simulations were run using both models. Objects made of either iron or stone, known as 'impactors', were used to reflect the composition of asteroids and experiments were run with varying diameters up to 1 km. The researchers found the number of impacts for iron impactors were comparable using both models. For stone the pancake model significantly overestimated the survivability rate across the range used. Over most of the size range stony asteroids need to be 1000 times bigger than the iron ones to make a similar sized crater. Much larger objects are disrupted in the atmosphere than previously thought. That's no big relief for mankind, though: Asteroids that fragment in the atmosphere still pose a significant threat to human life, as they cause airbursts with explosion energies approaching hundreds of megatons of TNT. |
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Antarctic telescope delivers first neutrino sky mapAMANDA, a novel telescope that uses the Antarctic ice sheet as its window to the cosmos, has produced the first map of the high-energy neutrino sky - while there is not yet a truly significant signal present, the map nonetheless gives a first tantalizing glimpse of very high-energy neutrinos, ghostly particles that are believed to emanate from some of the most violent events in the universe such as crashing black holes, gamma ray bursts and the violent cores of distant galaxies. The map produced by AMANDA II is preliminary and represents only one year of data gathered. Using two more years of data already harvested with AMANDA II potential signals from statistical fluctuations in the present map may soon be either confirmed or not. The significance of the present map is that it proves the detector works - it establishes the performance of the technology.Sunk deep into the Antarctic ice, the AMANDA II (Antarctic Muon and Neutrino Detector Array) Telescope is designed to look not up, but down, through the Earth to the sky in the Northern Hemisphere. The telescope consists of 677 glass optical modules, each the size of a bowling ball, arrayed on 19 cables set deep in the ice with the help of high-pressure hot-water drills. The array transforms a cylinder of ice 500 meters in height and 120 meters in diameter into a particle detector. The glass modules work like light bulbs in reverse: They detect and capture faint and fleeting streaks of light created when, on occasion, neutrinos crash into ice atoms inside or near the detector. The subatomic wrecks create muons, another species of subatomic particle that, conveniently, leaves an ephemeral wake of blue light in the deep Antarctic ice. |
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STS-107/ISS UpdateA NASA Press Release on a new independent Engineering and Safety Center (NESC), a transcript of a PC w/Linda Ham on July 22 and coverage of July 23: WP, FT, AP, ARRL. July 22: SN 2, 1, WP, FT, AP, AFP, Rtr. |
July 21:
FT,
SpaceRev,
AFP,
AP.
July 20:
ST,
FT.
July 19:
ST,
AFP.
July 18:
Newsweek,
BBC,
AP,
Welt,
RP.
July 17:
FT,
ST,
Indep.,
SC.
July 16:
FT,
WP,
CBS,
ST 2,
1,
AP 3,
2,
1,
NZ.
July 15:
SN,
FT,
SD,
SC.
July 14:
ST 2,
1.
OSP schedule accelerated by 2 years: SC. Will have escape pod: WP, FT. |
Almost empty galaxiesconsisting mainly of big hydrogen disks have been identified: ANU Press Release, Ast., BBC.The inner workings of the active galaxy NGC 1068 as revealed by Chandra: MSFC PR, Ast. The internal dynamics of M 83 and its central bar: Cambridge PR. More metal-rich stars more likely to have planetsThis trend is now very clear, based on hundreds of cases: Berkeley Press Release [SR], histogram, NSU, S&T, Ast., BBC, SC, BdW.SOHO resumes full operationSOHO is back to full operation after its predicted 9-day-long high-gain antenna blackout: ESA Science News, SC, ST."Brain transplant" for FUSE satellite - in response to hints of the potential for future new difficulties with FUSE's gyroscopes, researchers have uplinked new software: NASA, JHU Press Releases, ST, SC. 1000th ISO paper published: ESA News. ESA builds news ground station in Cebreros (Spain) - it becomes operational in September 2005: ESA News. China's lunar orbiter outlinedat IAU GA - little was said about the spacecraft itself, but the payload is now clear: SD.A newsletter about the Deep Impact mission has been launched: find the latest issue here and the first one here! Mt. Stromlo comeback plans get clearerThe burned-down observatory will resume its mantle as the home of Australian astronomy through the planned redevelopment, which includes the placement of two telescopes on Mount Stromlo and one at the ANU Siding Spring Observatory: ANU Press Release [SR], Ast.New roadblock for Mauna Kea upgrade - a federal judge has ruled that NASA must redo its environmental assessment to erect more telescopes around the two existing Keck telescopes: Star Bulletin, Honolulu Adv., Pacific Biz, S&T, AP, ST. |
Lots of dust in a supernova remnant(Cas A) have been detected by the JCMT - the probable source of the first solid particles in the Universe may thus have been the supernovae of the first massive stars: a paper by Dunne & al., JACH, PPARC and Cardiff Univ. Press Releases and coverage by New Sci., SciAm, Guardian, Rtr, BBC, ORF.Why supernovae explode is still not really understood: MPA Note. A whole new population of very massive newborn stars has been detected in the Giant Molecular Cloud W 49, stars as massive as 120 solar masses: ESO Press Release, SC. Orphaned globular clustersdo really exist in intergalactic space - they were torn from their galaxies long ago and present a unique window into the past: IAU release, S&T, BBC, AstroBio, SC.Galaxies and their SMBHs grow simultaneously, SDSS data indicate - the same gas that feeds the central Black Hole is also good for making stars at the same time: SDSS and MPG Press Releases, NSU, Ast., RP. A "pancake" of gas and dust at the center of the Circinus galaxy instead of the expected dust torus: CfA Release. Gravity Probe B arrives at launch siteThe controversial NASA satellite is now at Vandenberg AFB, so it'll fly after all: KSC Release.The mirror concepts for the JWST get tested in a tucked-away workspace at Marshall Space Flight Center: AP. GRACE delivers best gravity map of Earth yet - the newest tool for scientists working to unlock secrets of ocean circulation and its effects on climate: NASA Release, APOD. Cause of X-43A Hyper-X crash in 2001 identifiedThe failure of the NASA X-43A hypersonic aircraft in June 2001 (see Update # 224 story 2) was the result of inaccuracies in computer and wind-tunnel tests that were based on insufficient design information about the vehicle itself: NASA Release. Earlier: SC, ST.
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All other historical issues can be found in the Archive.
The U.S. site of this Cosmic Mirror has been visited
since it was issued (the German site has no counter).
Compiled and written by Daniel Fischer
(send me a mail to dfischer@astro.uni-bonn.de!), Skyweek