Stellar Evolution:
NASA site for images, spectra, and explanation of the life cycle of stars.
Helsinki neutrino pages
Argonne National Laboratory site with links
Super-Kamiokande Site
See also the article "Neutrino oscillations" by Kenji Kaneyuki and
Kate Scholberg in American Scientist, 87, May-June 1999, pp. 222-231.
PPARK Press Release, April 4, 2002 (PPARK is the UK equivalent of NSF)
It is not only teenagers who like to congregate in intimate groups and disturb their neighbours and surroundings.
As Matthew Bate (University of Exeter), will be explaining to the UK National Astronomy Meeting in Bristol on Friday 12 April, young stars also like to hang around in crowds and undergo chaotic close encounters with each other during their formative years.
After performing one of the largest and most complex simulations of star formation to date, Matthew Bate, Ian Bonnell (University of St Andrews) and Volker Bromm (Harvard-Smithsonian Center for Astrophysics) have found that these cosmic furnaces form in a much more chaotic manner than is generally believed.
To perform the calculation, the astronomers used the supercomputer at the United Kingdom Astrophysical Fluid Facility (UKAFF), a national computing facility for astronomy sited at the University of Leicester. The calculation was so enormous that it required 100,000 hours, roughly 10% of the time available on the supercomputer during 2001.
The simulation followed the collapse of an interstellar gas cloud which was over one light year across and 50 times the mass of the Sun, eventually resulting in the formation of a cluster of 50 stars and brown dwarfs.
One of the big surprises found by the astronomers was how chaotic and dynamic the process of star formation is. The results showed that stars form so close together that they often interact with each other well before they have grown to full size.
In the small, new-born stellar groups, the stars compete with each other for the remaining gas. This process is inherently unfair, with the more massive stars tending to gather more gas than the lower mass stars, while the lowest mass stars are kicked out of the group.
About half of the objects are ejected so quickly that they don't manage to gather enough gas to become stars at all. Rather, they become brown dwarfs, objects with less than 1/13 the mass of the Sun. Unable to generate energy by fusing hydrogen into helium, they cannot continue to shine like the Sun and quickly fade away.
The new calculation supports recent astronomical surveys suggesting that there may be as many brown dwarfs as stars in our Galaxy, and indicates that the high frequency of brown dwarfs is a natural consequence of the competition between stars during their formation.
Another surprise is that many of the encounters between the stars and brown dwarfs in such clusters are close enough to strip off the outer parts of the dusty discs surrounding the young stars. Although many of the discs are initially very large, by the end of the calculation the majority of them have been truncated to less than the size of our Solar System.
Since most stars are believed to form in large star clusters, this suggests that planetary systems like our own may be the exception rather than the rule.
A paper discussing the first analysis of the simulation has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.
ANIMATIONS AND STILL IMAGES (BOTH HIGH AND LOW RESOLUTION) ARE AVAILABLE ON
THE WEB AT:
http://www.astro.ex.ac.uk/people/mbate/Research/pr.html
Time-lapse movies made from a series of pictures taken by NASA's Hubble Space Telescope are showing astronomers that young stars and their surroundings can change dramatically in just weeks or months. As with most children, a picture of these youngsters taken today won't look the same as one snapped a few months from now. The movies show jets of gas plowing into space at hundreds of thousands of miles per hour and moving shadows billions of miles in size. The young star systems featured in the movies, XZ Tauri and HH 30, reside about 450 light-years from Earth in the Taurus-Auriga molecular cloud, one of the nearest stellar nurseries to our planet. Both systems are probably less than a million years old, making them relative newborns, given that stars typically live for billions of years.
To view the movies and read more, click on:
http://oposite.stsci.edu/pubinfo/pr/2000/32
Sudbury Neutrino Observatory SNO http://www.sno.phy.queensu.ca
Gallium Neutrino Observatory (formerly Gallex)
URLs for solar neutrino experiments http://www.sns.ias.edu/~jnb/SNexperiments/experiments.html
John Bahcall's Neutrino References http://www.sns.ias.edu/~jnb/
Additional details and graphics available at www.phys.hawaii.edu/~jgl/neutrino_news.html
A team of Japanese and American physicists have produced evidence of mass and oscillations in neutrinos, elementary particles that individually have the smallest mass yet collectively may account for much of the mass of the universe. In a paper to be presented at the Neutrino '98 Conference in Japan on June 5 and submitted to the leading physics journal, the scientists present evidence that the ghostly elementary particles called neutrinos do possess mass and that they alternately change their identities in time as they travel.
The results come from the first two years of data from Super-Kamiokande, a $100 million experiment in a 12.5-million-gallon, stainless steel-lined cavity carved out beneath the Japanese alps, filled with ultra pure water and observed by 13,000 large area light detectors.
One of the three kinds of neutrinos, the muon flavor, has been found to disappear and reappear as it travels hundreds of kilometers through the Earth. The energy and flight distance, from neutrino production in the atmosphere by cosmic radiation to the underground instrument, provide a measure of the difference between neutrino masses. This mass, while the smallest yet observed for elementary particles, is still sufficient that the relic neutrinos made in staggering numbers at the time of the Big Bang, account for much of the mass of the universe.
"These new results could prove to be the key to finding the holy grail of physics, the unified theory," observes University of Hawaii Professor of Physics and Astronomy John Learned, one of the authors. "Neutrinos cannot now be neglected in the bookkeeping of the mass of the universe. One only gets such great data once or twice in a professional lifetime, maybe never."
The collaboration is led by University of Tokyo's Institute for Cosmic Ray Research and includes six U.S. groups (Boston University; University of California, Irvine; University of Hawai'i; Louisiana State University; State University of New York at Stony Brook; and the University of Washington) and eight from Japan (Gifu University, High Energy Research Organization (KEK), Kobe University, Niigata University, Osaka University, Tohoku University, Tokai University and Tokyo Institute of Technology) as well as other collaborators from both countries.
NEUTRINO DISCOVERY -- A FACT SHEET
THE DETECTOR
The Super-Kamiokande detector is a 50,000-ton double-layered tank of ultra pure water observed by 11,146 photomultiplier tubes, each 20 inches in diameter. The equivalent of an acre of photocathode, it is the largest light detection area ever assembled by more than a factor of ten. Located in a specially carved out cavity in an old zinc mine 2,000 feet under Mount Ikena near Kamioka in the Japanese alps, the detector is reached by driving through a 2 km-long tunnel. The underground site also includes a huge reverse osmosis water filtration system, calibration electron accelerator, five trailers of electronics, the main control room, preparation areas, etc.
DATA COLLECTION
The Super-Kamiokande project has been collecting data since April 1, 1996. This discovery is based on data collected through January 15, 1998. Energetic charged elementary particles traveling at close to the vacuum speed of light (300,000 km per second) exceed the speed of light in water. This results in the optical equivalent of a sonic boom, Cherenkov radiation, in which a flash is emitted in a 42-degree half-angle cone trailing the particle. This nanosecond directional burst of blue light is detected with photomulitpliers. Its pattern, timing and intensity allow physicists to determine the particle's direction, energy and identity. Data are acquired at a high rate (about 100 triggers per second), partially processed and sent via fiber optics to the laboratory outside the mine, where they are archived and filtered into different analysis streams. Most of the results discussed in the current paper are deduced from the cases (two-thirds of the time) when a neutrino produces either a single electron or a single muon. These interactions are recorded in the inner 22.5 kilotons of water about 5.5 times per day.
THE CLAIM
Super-Kamiokande Collaboration claims the discovery of neutrino mass and oscillations. The claim is based upon atmospheric neutrino data, which resolves an anomaly uncovered in 1985 and confirmed and elaborated by subsequent experiments. In its analysis of the present data base, the team observed a deficit of muon neutrinos coming from great distances and at lower energies; the functional behavior of this deficit indicates that muon neutrinos oscillate, thus they have mass.
IMPLICATIONS OF THESE FINDINGS
Oscillations require neutrinos to have mass. Finding non-zero neutrino mass is big news for elementary particle physics, requiring revision of the Standard Model, which has fit all elementary particle data to date, but sets neutrino masses at zero.
The Super-Kamiokande team hopes the insight gained from the peculiar mixing observed between neutrinos spurs progress toward a unified theory that explains the generations or flavors and predicts particle masses. The team also infers that the total mass of neutrinos in the universe must be significant--at a minimum amounting to a significant fraction (10 - 100 percent) of the baryonic mass of the universe and perhaps representing the dominant mass in the universe.
In any event, neutrinos cannot now be neglected in the bookkeeping of the mass of the universe. Indeed, some theoretical calculations indicate that neutrinos may have played a crucial role in the production of an excess of matter over anti-matter, and are thus intimately linked to our very existence.
Clearly this is the single most important finding about neutrinos since their discovery. Some experts call this result the single most important result of the decade in elementary particle physics.
THE PHYSICS TEAM
The collaboration team includes about 100 physicists. from Japan and the United States.
The lead Japan group is from the University of Tokyo's Institute for Cosmic Ray Research, whose director, Professor Yoji Totsuka, is spokesman for the collaboration.
Other Japanese institutions are Gifu University, the High Energy Research Organization (KEK), Kobe University, Niigata University, Osaka University, Tohoku University, Tokai University and Tokyo Institute of Technology.
Major U.S. collaborators are from Boston University; University of California, Irvine; University of Hawaii; Louisiana State University; State University of New York at Stony Brook; and University of Washington. Other collaborators are from Brookhaven National Laboratory; California State University, Dominguez Hills; Los Alamos National Laboratory; University of Maryland and George Mason University.
U.S. team coordinators are Professors Hank Sobel, UC Irvine (head of the old Reines neutrino group), and Jim Stone of Boston University. U.S. collaborators include many veterans from the IMB experiment.