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By Daniel Fischer Every page present in Europe & the U.S.!
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The latest issue!
| A German companion! (SuW version) Current mission news: MGS (latest pictures!) + Cassini + Galileo + NEAR |
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"Low density galaxies" - how can they survive?A number of extremely faint galaxies discovered among other, more normal ones is raising the question how they can survive at all, since their density of stars is 10 times lower than in any previously known galaxy. Not only do these "flimsy" galaxies survive, but they are found only in an area of space already crowded by other more robust galaxies. In our Galaxy there is one star like the Sun in 25 cubic light years, while in the flimsy galaxies there is only one star for every 6000 cubic light years - the density is 250 times lower, and these galaxies only contain a few hundred thousand stars in total.
Because these galaxies are small and have very few stars to provide
the gravitational glue to to keep them intact, one would expect them
to be disrupted by the surroundig big galaxies, but they are not:
Dark Matter must thus be present and play a key role in their survival.
The flimsy galaxies were discovered with the 4-meter telescope on
Kitt Peak during a survey of the Virgo galaxy cluster.
(Caldwell & Armandroff, Press Release of Jan. 9)
But since SBS 1453+593 turned out to be so hydrogen-rich, it is well possible that LSB galaxies contribute significantly to the population of interstellar clouds sampled in the early Universe. And if that is the case, the derivation of the abundance of heavier elements in that era would be way off: Astronomers had always assumed that the same ratio of heavy to light elements applied to the ancient clouds that is common in today's normal galaxies - but LSB galaxies are much poorer in heavy elements. (Princeton Press Release of Jan. 8) |
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A mysterious source of galactic heatingbeyond that supplied by starlight has been found in two galaxies similar to the Milky Way: There seems to be an unrecognized process in the thin gaseous haloes that surround galaxies. The clue comes from faint light emitted by singly ionized oxygen in the interstellar gas which holds important clues about the temperature and excitation of the gas in galaxies: There had already been clues that this diffuse interstellar gas might be varying significantly from one location to another in some galaxies (including our own). If starlight were the only energy source, the temperatures should have been more uniform.The two galaxies investigated now by the WIYN telescope, NGC 3079 in UMa and NGC 4631 in CVn, were chosen because we see them almost edge-on: The intensity of the emission by oxygen and other ions as a function of distance from the galaxies' midplane could be measured. The farther the astronomers looked from the midplane, the brighter the oxygen emission became, relative to other ions such as hydrogen, nitrogen and sulfur: The temperature went up, instead of down, with greater distance. What is heating the haloes is unclear at present: Candidates are the dissipation of turbulent motions caused by supernovae or magnetic fields. (Otte & al., Press Release of Jan. 8) |
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A globular cluster born recently in normal spiral galaxy?Could it be that "the traditional distinction between open and globular (star) clusters may turn out to be rather artificial"? That's what astronomers are wondering after they've discovered a young star cluster with a million solar masses in the nearby spiral galaxy NGC 6946 - it contains 100 times as many stars as the largest young stellar cluster known in our galaxy and resembles much more the biggest globular clusters such as Omega Centauri or 47 Tucanae. Those are many billions of years old, however, while the giant open cluster in NGC 6946 was born only 15 million years ago. It's high mass was determined both from the brightness and from the velocity dispersion of its stars.Similar luminous young clusters have previously been found in colliding galaxies and other starburst galaxies with strongly enhanced levels of star forming activity. But this is the first time such an object has been detected in an otherwise normal spiral galaxy - it is actually visible in a small telescope, though its extraordinary nature has been noted only now. The cluster, which is accompanied by many others (not nearly as massive but still very bright) and resides in a peculiar star forming complex, clearly illustrates that many aspects of star forming processes even in "normal" galaxies still remain to be understood. (Larsen & al., Press Release of Jan. 9) |
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Winds from other Sun-like stars detectedFor the first time astronomers have succeeded in detecting the hot ionized gas blown out by stars like the Sun - the exact equivalent of the latter's solar wind. So far stellar winds had only been observed from very different stars, where other mechanisms are driving the mass outflow. The breakthrough was possible with Hubble spectroscopy: The winds leave small but characteristic absorption features in the Lyman-Alpha hydrogen emission lines of stars. A clear detection has been made at the double star Alpha Centauri, showing a wind similar to the Sun's, while Proxima Centauri's wind was not seen: The mass loss of this M dwarf is less than 20% of the Sun's. (Wood & al., Press Release of Jan. 8) |
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Famous X-ray transient the remnant of a hypernova?Strange elemental abundances of the star component of the X-ray binary V4641 Sagittarii have led to the speculation that the other partner, a compact object suspected of being a black hole, is not the result of a supernova but actually of a hypernova - a popular but nonetheless speculative stellar explosion proposed as the origin of gamma ray bursts. V4641 Sgr became famous in September 1999 when it underwent a very bright X-ray flare, after which matter was seen shooting away from the source at 99% of the speed of light. Later the mass of the compact partner was determined as 9 to 12 solar masses, which made it a black hole candidate (though a neutron star with a heavy disk would also fit).V4641 Sagittarii is one of 11 known X-ray transients with bhcs, but what sets it apart is the companion star: It appears to be in an unusual evolutionary state, as inferred from its measured surface temperature, mass and diameter. And especially thrilling is its unusual chemical composition: Nitrogen, oxygen, calcium, magnesium and titanium are overabundant by factors of 2 to 10 - all elements produced in supernova explosions. Such an abundance anomaly had been noted in another X-ray transient with a bhc, V1033 Scorpii, and there was the proposal that it was the result of a hypernova (with the debris of the explosion being implanted into the companion star). Perhaps V4641 Sagittarii is the 2nd such case. (Orosz & Kuulkers, Press Release of Jan. 10) |
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Clouds can improve visual observations, Leonids 2000 experience showsA most bizarre effect has been discovered in the course of the analysis of the worldwide visual observations of the Leonid meteors in November 2000 (see Updates # 210 and 211 for early results). The meteors had been numerous, but there was also a bright Moon in the sky. And staring at the brightened sky for hours on end has apparently fatigued the eyes of those observers blessed with clear skies much more than they realized - while the majority which had to wait for occasional holes in the clouds obtained more reliable results!This sounds incredible, but a forthcoming paper in WGN, the journal of the International Meteor Organization, will present convincing proof: The "all-nighters" tended to see fewer and fewer of the ubiquitous sporadic meteors as the night progressed (while their number in fact rises all the time, as the observer rotates more and more into the direction in which the Earth travels around the Sun). And they also saw fewer and fewer of the fainter Leonid meteors. The "cloud-gappers," in contrast, saw the rise in sporadics and did not suffer from the loss of faint meteors. The lesson from this experience, according to IMO: "The influence of the Moon - although disturbing the joy of a nice meteor display - did not ruin the actual results. [...] An in depth-study of the considerations made above about the possible influence of fatigue in long observations under poor circumstances may result in even more refined instructions for optimal observation of major showers under poor Moon conditions. From this perspective, we are confident to be able to present meaningful results also for the 2002 Leonid meteor shower which will suffer from an almost Full Moon" - and promises the greatest storm of all. (Arlt & Gyssens, WGN 28, 191-204, in press) |
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Final Progress launch delayed to Jan. 24There will be another attempt to launch the Progress M1-5 cargo ship toward Mir on January 24 (for a docking on the 27th), but only if the main computer onboard the station can be re-booted in time: ground controllers plan to change the circuitry to bypass the faulty pieces of equipment and dead batteries. The Salyut 5B computer inside Mir's core module provides commands to the station's working gyrodines, which orient the outpost in space (before the latest control system shutdown earlier this week, 10 out of 12 gyrodines were online).After initial testing of the computer on Jan. 18, the ground controllers were convinced that the computer is in healthy condition and the new set of instructions could be uploaded into the machine on Jan. 19 and 20. It's now believed that high temperatures inside Kvant-2 module most likely caused the energy supply failure onboard Mir early on Jan 17, which had caused renewed worries: In the current phase of its orbit, Mir receives more than average exposure to the Sun, while thermal control system onboard Kvant-2 experiences problems.
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Stardust flies by Earth, gets sighted, shoots the MoonStardust is now on course to Comet Wild 2, where it will collect dust samples for return to Earth: that word comes after a close encounter with Earth early on Dec. 15, marking the completion of the craft's first solar orbit since its launch in 1999: Status, SC, SN, SPIEGEL. The s/c was imaged by amateurs before C/A: Special Page.After the Earth Gravity Assist Stardust also observed the Moon for calibration purposes: Special Page, CNN. Rosetta flight structure arrives from Finland at Alenia Spazio in Turin - now work can begin on assembly, integration and testing of ESA's comet chaser: ESA Science News. Cassini fails to find evidence of lightning on VenusObservations during the 2 flybys ins 1998 and 1999 confirm suspicions that earlier measurements of lightning activity were erroneous: U Iowa Press Release [SN].Cassini was inside the magnetosphere of Jupiter for a few hours: JPL Release. Monitoring Io with Adaptive Optics: Berkeley page. Europa in rotation in a computer animation based on Voyager data: APOD. Some channels on Mars carved by ice? Rather than by catastrophic flooding, as is generally believed, but the suspected ice flows could not account for all of the channels seen on Mars: AGU Press Release [SD], BBC, CNN, SC, SPIEGEL. Molecular clouds are extremely drytwo years of observations by the SWAS satellite show - water seems to be 10,000 times less abundant in these stellar nurseries than previously thought and so scarce that it is found in the ratio of only one part in a hundred million compared with hydrogen molecules, which are the most common component: Cornell Press Release [SN].Stunning IR views of the Orion nebula have been obtained with the Very Large Telescope - including the famous proplyds: ESO Press Release, SC, SPIEGEL. Claim of Earth-like planets at CM Dra is premature, says the very scientist who was said to have made it: SC. What is a planet anyway? NYT. Star formation is affected by other nearby stars, extensive millimeter-wave observations show: Press Release. Dissociating stars tracked down: NRC Press Release. Supernova may control the center of our galaxyAn apparent supernova remnant in the center of our galaxy might help regulate its Central Engine, and such relationships between supernova remnants and galactic centers might be common throughout the Universe: PSU News Release [SN], pictures.High Proper Motion stars found towards the center of our galaxy and the LMC: LLNL Press Release [SN]. British and Chinese satellites head for space rendezvousA tiny British-built spacecraft is achieving a variety of firsts in the nanosatellite technology field - SNAP-1 will finish off this series of ground-breaking accomplishments in the next few months as it approaches a rendezvous with another satellite: SN.Canada to invest big in the VLA and ALMA radio telescopes, while Canadian astronomers get more access to U.S. facilities: NRC Press Release. |
Solar power farm turned into gamma ray observatorySolar Two, once the largest solar power farms in the world, has been given a second life as a gamma ray observatory - the Californian facility consists of an array of 1,800 mirrors and is the only one capable of containing the entire Cherenkov light pool: Homepage, UCR Press Release, BBC."CONtinuous CAMera" watches the skies over KPNOCONCAM, a fish-eye system, is creating a continuous record of the night sky, and many more such systems (with better resolution, one should hope) are planned: Homepage.Yet another cosmology ballonhasn't gotten very far: Archeops was launched from Kiruna, but the flight has been aborted: Reuters, Updates. TopHat's flight is successful: Discovery. Preliminary Results from the Cosmic Background Imager (see Update # 212 story 4): paper by Mason & al."Cosmic shear" now also detected by the HST in the Hubble Space Telescope (HST) Survey Strip: paper by Rhodes & al. Measuring Ho with the Sunyaev-Zeldovich Effect - it's 66 +/- 20 km/s/Mpc: paper by Mason & al. Search for Dark Matter particles sets new limits - the "Edelweiss Experiment" has begun to exclude the upper part of the DAMA region: paper by Chapellier & al. Antarctic balloon flight checks Cosmic Ray theoryAre supernova explosions a major source or not? Science@NASA.Next test flight for NASA's Ultra-Long Duration Balloon to begin in Australia: GSFC Release. Cluster satellites start simultaneous measurementsFor the first time in the history of space exploration, identical instruments on four spacecraft have begun to return simultaneous measurements of the bow shock - by comparing these unique sets of data, scientists are obtaining their first three-dimensional view of this turbulent "barrier" that separates the realms of the Sun and the Earth: ESA Science News, SPIEGEL.Short glitch in SOHO operations - the spacecraft has entered and emerged from an emergency sun reacquisition: SR. ESA switches Artemis from Japanese rocket to Ariane 5 - that's now official: Press Release, SC, SN.
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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
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Compiled and written by Daniel Fischer
(send me a mail to [email protected]!), Skyweek
