Tuesday, 1 January 2008

General Relativity




General relativity


Added & Edited By:

Arip Nurahman, Department of Physics. Faculty of Sciences and Mathematics
Indonesia University of Education

&

Follower Open Course Ware at MIT-Harvard University, U.S.A.

General Relativity and Cosmology at Cambridge University 

The interests and membership of this large group overlap with those of the High Energy Physics group. It hosts the COSMOS supercomputer, a national facility dedicated to studies of early Universe physics and the new Centre for Theoretical Cosmology (CTC). Despite its infancy the CTC has already hosted several conferences and workshops, including ‘The Very Early Universe; 25 years on’. The group is active in numerical relativity, supergravity, discrete gravity, M-theory/string theory and cosmology.

Relativity and Gravitation Group

Cosmic Microwave Background Radiation
The Relativity & Gravitation Group is part of the Department of Applied Mathematics and Theoretical Physics, which in turn is part of the Faculty of Mathematics of the University of Cambridge. The group was founded by Dennis Sciama in 1961, and is currently headed by Professor Stephen Hawking, CH, CBE, FRS.

It is internationally renowned for a number of important developments in Einstein's classical theory of gravitation, including the no hair and area theorems for black holes and the theorems indicating that singularities would occur both in gravitational collapse and at the beginning of the expansion of the Universe.
In recent years the group's main effort has been towards the inclusion of quantum effects, and the development of a theory of quantum gravity; in particular, the semi-classical quantization of black holes (leading, e.g, to the discovery of the thermal radiation produced by them) and the formulation of the Euclidean path integral approach to quantum gravity (leading to the no boundary condition for the Universe).
Furthermore, the group has expertise in the areas of supergravity, string and membrane theories of gravity, cosmology, cosmic strings and other topological defects in cosmology, numerical relativity and Regge calculus.
In addition, the group houses and operates COSMOS, the UK national cosmology supercomputer.
Please feel free to browse our public pages, which attempt to describe our work in non-technical terms.

Contact details:

Department of Applied Maths and Theoretical Physics
Centre for Mathematical Sciences
Wilberforce Road
Cambridge, CB3 0WA

Telephone and Fax

Telephone: +44 1223 764 267
Fax: +44 1223 764 984

Location

Since 2000, we have been housed in The Märit and Hans Rausing Pavilion (Pavilion B) of the Centre for Mathematical Sciences.

Publications by Year

Recent Publications

An axisymmetric evolution code for the Einstein equations on hyperboloidal slices
by Oliver Rinne (2009-10-01)
Moment transport equations for non-Gaussianity
by David J. Mulryne, David Seery, Daniel Wesley (2009-09-16)
On the Stability of Static Ghost Cosmologies
by J. D. Barrow, C. G. Tsagas, Classical and Quantum Gravity 26, 195003, 2009. (2009-09-10)
Maxwell-Sim
by G. W. Gibbons, J. Gomis, C. N. Pope (2009-09-01)
The Classical Stability of Sudden and Big Rip Singularities
by J. D. Barrow, S. Z. W. Lip, Physical Review D 80, 043518, 2009 (2009-08-20)
Static Near-Horizon Geometries in Five Dimensions
by Hari K Kunduri, James Lucietti (2009-07-02)
Status of NINJA: the Numerical INJection Analysis project
by Laura Cadonati et al. (Oliver Rinne), Class. Quantum Grav. 26, 114008, 2009 (2009-06-01)
Gravity Dual of a Tachyon Condensation
by G. W. Gibbons, K. Hashimoto, S. Hirano (2009-05-29)
Bernstein's Conjecture, Minimal Cones and Critical Dimensions
by G. W. Gibbons, K. Maeda, U Miyamoto (2009-05-27)
Does Bulk Viscosity Create a Viable Unified Dark Matter Model?
by B. Li, J. D. Barrow, Physical Review D 79, 103521 (2009-05-21)
Generalized Killing-Yano equations and D=5 gauged supergravity
by D. Kubiznak, H. K. Kunduri, Y. Yasui (2009-04-30)
Collider constraints on interactions of dark energy with the Standard Model.
by P. Brax, C. Burrage, A. C. Davis, D. Seery, A. Weltman (2009-04-22)
Einstein Metrics on Group Manifolds and Cosets
by G. W. Gibbons, H. Lu, C. N. Pope (2009-03-06)
On the supersymmetric limit of Kerr-NUT-AdS metrics
by D. Kubiznak (2009-02-11)
Deformed General Relativity and Torsion
by Gary W. Gibbons, Steffen Gielen, Class. Quantum Grav. 26 (2009) 135005 (2009-02-11)

References

Sumber: 

The University of Cambridge

Wikipedia

To Be Continued

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Tuesday, 25 December 2007

10,000 Earths' Worth of Fresh Dust Found Near Star Explosion



10,000 Earths' Worth of Fresh Dust Found Near Star Explosion



By:
Arip Nurahman Department of Physic
Faculty of sciences and Mathematics
Indonesia University of Education

blown-out remains of a stellar explosion The supernova remnant Cassiopeia A is shown here in an infrared composite from NASA's Spitzer Space Telescope. A supernova remnant is the blown-out remains of a stellar explosion. Image credit: NASA/JPL-Caltech
› Full image and caption Astronomers have at last found definitive evidence that the universe's first dust - the celestial stuff that seeded future generations of stars and planets - was forged in the explosions of massive stars.

The findings, made with NASA's Spitzer Space Telescope, are the most significant clue yet in the longstanding mystery of where the dust in our very young universe came from. Scientists had suspected that exploding stars, or supernovae, were the primary source, but nobody had been able to demonstrate that they can create copious amounts of dust - until now. Spitzer's sensitive infrared detectors have found 10,000 Earth masses worth of dust in the blown-out remains of the well-known supernova remnant Cassiopeia A.

"Now we can say unambiguously that dust - and lots of it - was formed in the ejecta of the Cassiopeia A explosion. This finding was possible because Cassiopeia A is in our own galaxy, where it is close enough to study in detail," said Jeonghee Rho of NASA's Spitzer Science Center at the California Institute of Technology in Pasadena. Rho is the lead author of a new report about the discovery appearing in the Jan. 20 issue of the Astrophysical Journal.

Space dust is everywhere in the cosmos, in our own neck of the universe and all the way back billions of light-years away in our infant universe. Developing stars need dust to cool down enough to collapse and ignite, while planets and living creatures consist of the powdery substance. In our nearby universe, dust is pumped out by dying stars like our sun. But back when the universe was young, sun-like stars hadn't been around long enough to die and leave dust.

That's where supernovae come in. These violent explosions occur when the most massive stars in the universe die. Because massive stars don't live very long, theorists reasoned that the very first exploding massive stars could be the suppliers of the unaccounted-for dust. These first stars, called Population III, are the only stars that formed without any dust.

Other objects in addition to supernovae might also contribute to the universe's first dust. Spitzer recently found evidence that highly energetic black holes, called quasars, could, together with supernovae, manufacture some dust in their winds (http://www.spitzer.caltech.edu/Media/releases/ssc2007-16/index.shtml) .

Rho and her colleagues analyzed the Cassopeia A supernova remnant, located about 11,000 light-years away. Though this remnant is not from the early universe, its proximity to us makes it easier to address the question of whether supernovae have the ability to synthesize significant amounts of dust. The astronomers analyzed the infrared light coming from Cassiopeia A using Spitzer's infrared spectrograph, which spreads light apart to reveal the signatures of different elements and molecules. "Because Spitzer is extremely sensitive to dust, we were able to make high-resolution maps of dust in the entire structure," said Rho.

The map reveals the quantity, location and composition of the supernova remnant's dust, which includes proto-silicates, silicon dioxide, iron oxide, pyroxene, carbon, aluminium oxide and other compounds. One of the first things the astronomers noticed was that the dust matches up perfectly with the gas, or ejecta, known to have been expelled in the explosion. This is the smoking gun indicating the dust was freshly made in the ejecta from the stellar blast. "Dust forms a few to several hundred days after these energetic explosions, when the temperature of gas in the ejecta cools down," said Takashi Kozasa, a co-author at the Hokkaido University in Japan.

The team was surprised to find freshly-made dust deeper inside the remnant as well. This cooler dust, mixed in with gas referred to as the unshocked ejecta, had never been seen before.

All the dust around the remnant, both warm and cold, adds up to about three percent of the mass of the sun, or 10,000 Earths. This is just enough to explain where a large fraction, but not all, of the universe's early dust came from. "Perhaps at least some of the unexplained portion is much colder dust, which could be observed with upcoming telescopes, such as Herschel," said Haley Gomez, a co-author at University of Wales, Cardiff. The Herschel Space Observatory, scheduled to launch in 2008, is a European Space Agency mission with significant NASA participation.

Rho also said that more studies of other supernovae from near to far are needed to put this issue to rest. She notes that the rate at which dust is destroyed - a factor in determining how much dust is needed to explain the dusty early universe - is still poorly understood.

The principal investigator of the research program, and a co-author of the paper, is Lawrence Rudnick of the University of Minnesota, Twin Cities. Other co-authors include W.T. Reach of the Spitzer Science Center; J. D. Smith of the Steward Observatory, Tucson, Ariz.; T. Delaney of the Massachusetts Institute of Technology, Cambridge; J.A. Ennis of the University of Minnesota; and A. Tappe of the Spitzer Science Center and the Harvard Smithsonian Center for Astrophysics, Cambridge, Mass.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology. Caltech manages JPL for NASA. Spitzer's infrared spectrograph was built by Cornell University, Ithaca, N.Y. Its development was led by Jim Houck of Cornell. For more information about Spitzer, visit http://www.nasa.gov/spitzer and http://www.spitzer.caltech.edu/spitzer .

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Thursday, 20 December 2007

Teknologi Penjelajahan Bulan




Edited and Added By:
Arip Nurahman Department of Physics, Faculty of sciences and Mathematics
Indonesia University of Education
&
Follower Open Course Ware at MIT-Harvard University, U.S.A.


NASA's blueprints for an outpost on the moon are shaping up. The agency's Lunar Architecture Team has been hard at work, looking at concepts for habitation, rovers, and space suits.







Image left: Concept of one potential design for a future lunar rover. Spacesuits would be attached to the exterior of the rover. Credit: NASA











NASA will return astronauts to the moon by 2020, using the Ares and Orion spacecraft already under development. Astronauts will set up a lunar outpost – possibly near a south pole site called Shackleton Crater – where they’ll conduct scientific research, as well as test technologies and techniques for possible exploration of Mars and other destinations.

Even though Shackleton Crater entices NASA scientists and engineers, they don’t want to limit their options. To provide for maximum flexibility, NASA is designing hardware that would work at any number of sites on the moon. Data from the Lunar Reconnaissance Orbiter mission, a moon-mapping mission set to launch in October 2008, might suggest that another lunar site would be best suited for the outpost.

First, astronauts on the moon will need someplace to live. NASA officials had been looking at having future moonwalkers bring smaller elements to the moon and assemble them on site. But the Lunar Architecture Team found that sending larger modules ahead of time on a cargo lander would help the outpost get up and running more quickly. The team is also discussing the possibility of a mobile habitat module that would allow one module of the outpost to relocate to other lunar destinations as mission needs dictate.

NASA is also considering small, pressurized rovers that could be key to productive operations on the moon’s surface. Engineers envision rovers that would travel in pairs – two astronauts in each rover – and could be driven nearly 125 miles away from the outpost to conduct science or other activities. If one rover had mechanical problems, the astronauts could ride home in the other.




Image left: Concept of one potential design for a future lunar rover. Spacesuits would be attached to the exterior of the rover. Credit: NASA














Astronauts inside the rovers wouldn't need special clothing because the pressurized rovers would have what's called a "shirt-sleeve environment." Spacesuits would be attached to the exterior of the rover (see images). NASA's lunar architects are calling them "step in" spacesuits because astronauts could crawl directly from the rovers into the suits to begin a moonwalk.




NASA is also looking to industry for proposals for a next-generation spacesuit. The agency hopes to have a contractor on board by mid-2008.


NASA will spend the next several months communicating the work of the Lunar Architecture Team to potential partners -- the aerospace community, industry, and international space agencies -- to get valuable feedback that will help NASA further refine plans for the moon outpost. The agency's goal is to have finalized plans by 2012 to get "boots on the moon" by 2020.

Semoga Bermanfaat!

Sumber:

http://www.nasa.gov/exploration/lunar_architecture.html

Arip Nurahman

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