The Cosmic Mirrorof News events across the Universe |
Compiled and written by Daniel Fischer, Skyweek - older "Mirrors" in the Archive - and find out what the future might bring! The latest issue! |
Current mission news: MGS (science!) + Cassini + Galileo + Prospector |
New cosmological trouble brewing?How reliable are the results from supernova Ia studies that show the Universe's expansion accelerating (see Updates # 68 and 115)? The discovery that very distant supernovae are 'too faint' is independent of the actual value of the Hubble constant as well as of the absolute calibration of the supernova luminosities. But what the studies (by two competing groups) implicitly assume is that the expansion of space is the same in the Universe on large scales as in our cosmic neighborhood. Now a - purely speculative - mathematical study has shown that if the local Universe is atypical and we live in an underdense region, the strong conclusions from the supernova studies (i.e. that the density of the Universe is subcritical and that there is a 'dark energy' with negative pressure) can vanish.For example, if the 'local' Hubble constant should turn out to be 10% higher than the global value, the best fit to the supernova observations would be an open model (Omega M = 0.3, Omega Lambda = 0). And if the local "Ho" would be 20% higher then even the old "standard cosmological" model (Omega M = 1, Omega Lambda = 0) could in principle be true again. So - is there any evidence for a local underdensity of space? "Numerous authors" have claimed it, but "these claims are not without their detractors". The ongoing major sky surveys as well as future work of the supernove teams (that haven't seen a major effect so far) will test the bold hypothesis in the foreseeable future, and firmer statements on the state of our Universe will then be possible. But until then this potential caveat should be kept in the back of one's mind. (Goodwin & al., Preprint astro-ph/9906187 of June 10th) |
The paper by Goodwin & al. This paper casts a shadow of doubt on a nice new review of the state of cosmology by Bahcall & al. in Science of May 28, 1999, p. 1481-8 (summarized in this press release): There it was concluded that What all this means for the age of the Universe is discussed in a paper by Lineweaver in Science of May 28, 1503-7: Accepting the supernova (and other recent) results on the cosmic density and accelerated expansion plus using a Hubble constant of 68, he gets a world age of 12 to 15 Gyr, compatible with the age of the oldest stars. Only of Ho would be significantly larger than 80, there would be trouble.
| U.S.-European collaboration on big radio array confirmedThe Atacama Large Millimeter Array (ALMA) is now a Europe-U.S. collaboration and may soon include Japan, the National Science Foundation and the European Southern Observatory have announced jointly. Representatives from the United States and Europe signed an agreement on June 10th to continue collaboration on the first phase of a giant new telescope project. It will image the universe with unprecedented sensitivity and sharpness at millimeter wavelengths (between the radio and infrared spectral regions). ALMA will be a major step for astronomy, making it possible to study the origins of galaxies, stars and planets. The Europe-U.S. agreement signed today may be formally extended in the very near future to include Japan, following an already existing tripartite declaration of intent.
| ESO Press Release NSF Press Release. ALMA Homepages at NRAO and ESO, plus Japan's LMSA project. ABQ Journal story.
| The Sun's coronal magnetic field has doubledduring the past 100 years, an analysis of geophysical measurements and has shown: They can be used as "surrogates" for the state of the interplanetary field and calibrated by satellite measurements. The surprising result: Since 1964 the total magnetic flux leaving the Sun has risen by 40%, and since 1901 the increase was about 130%. This longterm trend seems to be not affected by the 11-year solar activity cycle. It may have something to do with chaotic changes in the dynamo that generates the Sun's field - and it raises the question whether the luminosity of the Sun (that varies a bit during the activity cycle) has risen on average, too. And if so, one wonders whether part of the global warming throughout the 20th century might have been due to that effect and not to the increase in atmospheric greenhouse gases. (Lockwood & al., Nature of June 3rd, 1999, p. 437-9)
| BBC story on the Nature piece. The role of the Ulysses spacecraft in this discovery. The change in climate cannot be attributed to natural effects, including the Sun: Nature Science Update!
| Big magnet in space finds particle mysteriesResearchers had expected the magnetic field to repel less energetic particles arriving around the equator. This terrestrial magnetic field repulsion becomes weaker at higher latitudes, so researchers expected to see more particles of lower energy nearer the North and South Poles. Instead, AMS found high levels of lower energy protons at almost all latitudes, particularly over the equator. For protons below 6 GeV the AMS counted as many particles moving upwards (away from Earth) as moving downwards. Researchers saw a similar effect with cosmic electrons having energies of about 3 GeV. How all this fits into the big picture of the Earth's magnetosphere is unclear. (Talk by AMS' S. Ting)
| Press Release on the AMS data (from another presentation) One AMS Homepage with links to several others. The cosmic ray discoveries were a mere 'accident' of the test flight of the detector that has the main task of looking for antiatoms of Helium and Carbon and to search for decay products of hypothetical dark matter particles. No results regarding those questions came from the STS-91 mission: They require many months of data-taking, possible only on the ISS. An upgraded AMS - probably with a superconducting magnet - will be installed on the International Space Station, probably in mid-2003. S. Ting.
| Clocks with ultra-cool atomsMicrogravity makes for better clocks! Atomic clocks, that is: Their precision goes up when the speed of the atoms (whose resonances are used) goes down - but you can't slow an atomic beam below a certain speed on Earth, or the atoms are simply pulled to the ground by gravity. French scientists have therefore built a special experiment ("PHARAO") for use in parabolic flights - and they plan to have an "Atomic Clock Ensemble in Space" (ACES) on the International Space Station. This promises to become the most precise atomic clock ever, and it could be used to synchronize atomic clocks on Earth on a global scale. (Talk by C. Cohen-Tannoudji)
| PHARAO Homepage. C. Cohen-Tannoudji.
| The Origin of Life? Easy!Most biologists (and even most exobiologists) consider the origin of life on Earth one of the hardest questions of all - not so Christian de Duve: For this biochemist it just had to happen. The key argument: Chemistry is deterministic, and chance plays hardly a role (as opposed to physics, e.g.). So since there is life on Earth, it had to arise there, and do so quickly. For de Duve that was a natural chemical process by a very large number of successive steps that were highly probable under the prevailing conditions of the young Earth. And since the conditions on planets of other suns shouldn't be too different, he firmly expects the galaxy to abound with at least primitive life forms. (Talk by de Duve)
| C. de Duve.
| The biggest molecule in interstellar space
| List of molecules at the NRAO. Another ISM story: J. P. Maier of Basel University has shown by lab experiments that the negative ion of carbon 7 is a good candidate for explaining Diffuse Interstellar Band (DIB) absorptions in stellar spectra - one of the enduring mysteries of astrophysics.
| Hubble captures key phases of stellar life cycle - in one striking pictureEverything is there. A gas nebula. Dark Bok globules where stars first form. Proplyds, where young stars are surrounded by disks. A cluster of bright stars (whose radiation is eating away both the proplyds and the nebula gas). And a dying massive star ("Sher 25") that will soon go supernova and that has already ejected matter - in a fashion reminiscent of the circumstellar gas that surrounded the progenitor star of famous supernova 1987A, including a beautiful narrow ring of gas. All this action was captured in just one WFPC2 view of the Southern object NGC 3603 that is both visually striking and full of information. The proplyds, e.g., are much bigger than the famous proplyds in the Orion nebula - but they're being destroyed by the radiation from the star cluster at such a rate that they'll probably never have the time to form planets. (News conference on June 1st)
| Press Releases from the Univ. of WA (alternative version) and the STScI. Astromomy Magazine coverage. Somewhat related stories: The role of magnetic fields in triggering star formation has been clarified by ISO observations of dark globules. In the star-forming globule GF9 the field is uniform and parallel, in a star-less globule the field is disordered: ESA Science News. And the VLBA has studied the birth of sunlike stars with complicated outflows: NRAO Press Release.
| Earth's Motion around the center of the Galaxycan be detected by the Very Long Baseline Array in just 10 days - by comparing the positions of the central object Sgr A* relative to distant quasars! It moves by 6 milliarcseconds per year, and one can conclude that a) the mass of Sgr A* is at least 1000 solar masses, b) that the Sun goes around it with 220 km/s (assuming a distance of 8 kpc) and c) that it takes us about 226 million years for one orbit (a "galactic year"). The lower limit for Sgr A*'s mass, however, which follows from the source's immobility in space (residual proper motions < 20 km/s). Further improvement of this value will raise the limit and thus the density of the object that many believe to be an (under-nourished) black hole. (News conference on June 1st)
| NRAO Press Release. The Paper by Reid & al., and another paper on Sgr A*'s proper motion, measured with the VLA. Florida Today story.
| The most bizarre young Planetary Nebulaehave been imaged by the HST - the wealth of structure is astounding and challenges current models of how these nebulae around dying stars form. PNe are generally thought to form as a result if the expansion of a fast stellar wind inside a slowly expanding cloud ejected earlier when the star was still a red giant. If this cloud is more dense near its equator than near its poles, the resulting nebula is bipolar. However, the complex structure and notable point symmetry hints at jet-like outflows - which in turn imply a close binary star system 'at work.' Multiple sub-stellar companions such as Brown Dwarfs or massive Jupiters may also be involved in creating and/or influencing the jets.
| Planetary Nebula Gallery from the WFPC2 - enjoy! Moderately related: The role of novae in changing the chemistry of the galaxy has been highlighted by other Hubble research. Clumps enriched in many heavy elements have been spotted in nova ejecta - the amount of matter released into the ISM this way seems to have been underestimated. And even important ingredients for planet-making seem to be created by novae: Press Releases from ASU and UMN, and the Hubble images.
| The Ten Greatest Discoveries...of the past 1000 and 100 years - and of the next (!) 100 years - have been tabulated by noted astronomy historian Virgina Trimble for a news conference at the Meeting. According to her the Astronomical Triumphs of the Millennium were
| Virginia Trimble's Homepage at the Univ. of CA in Irvine. The Brief History of Astronomy (very brief indeed :-). History of Astronomy Homepage. Astronomy Unbound (a virtual astronomy text). |
Long delay for Lunar A!Instead of this summer, the Japanese lunar mission won't fly until 2002, as technical problems abound and the penetrators failed during tests: ABC, Florida Today, SpaceViews (with various 'official' links).ESA's "Living Planet" programhas been launched on June 7th - and the first mission of that new Earth science enterprise will be British "Cryosat" satellite. Press Release from ESA, BBC story.The heaviest element ever createdhas 118 protons but a lifetime of less than 1 msec, after which it decays to an isotope with 116 protons (also new and also unstable). Three such decay-chains have been observed in a U.S. lab: LBL Press Release and coverage from the BBC and ABC.Shadow of the Moon detected undergroundA cosmic ray detector in the U.S. has seen a - fuzzy - negative image of the Moon which is blocking the arrival of muons. 10 years of data had to be added up: BBC story, the detector, Soudan 2 publications.Gamma ray bursts from thunderstormsare now and then detected by the BATSE instrument on CGRO: About 70 such "terrestrial gamma-ray flashes" (TGFs) have been seen in the past 8 years. NASA Science News.
| The fate of the solar systemwill be sealed - probably billions of years in the future - by a close passage of another star: It will either hurl our planet into the Sun or eject if from the solar system... Univ. of Michigan Press Release.A close star cluster over the South Polehas been identified thanks to the X-rays of the stars - the brightest three can even be seen in binoculars: Homepage of the star cluster Eta Cha, 97 parsecs distant.A new galaxy in the local grouphas been discovered in the constellation Cetus - a faint and fuzzy blob. It is unusual, though, in that it is rather isolated: Announcement page.Rare celestial objects found in POSS-IIThe initial scientific exploration of the Digital Palomar Obs. Sky Survey (DPOSS) has led to the discovery of distant quasars as well as rare, sometimes rather mysterious objects: CalTech Press Release and data.Supernova instabilities in the labCertain important hydrodynamic instabilities predicted by supernova models (and indicated by the shape of SN remnants) have been simulated in miniature laser experiments: LLNL Press Release.
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Compiled and written by Daniel Fischer
