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hey fr sure yrr wats dere in it
i always rate whoever gives an answer
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a fixed sphere of radius R and uniform mass density .. sigma has a cavity of radius R/3 d centre of d solid sphere is at O . a particle is released frm d point P assume dat d coefficient of restitution fr d collision is e and dere exists no gravitational field except due to particle n sphere a ) find vel. of particle just after n collisions wid d solid sphere b) for what value of 'e' will d particle just reach d centre of cavity after nth collisions.
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a double star with two star masses m1 and m2 rotates wid constant angular speed. if d maximum distance of seperation is R find d angular speed of each star in terms of m1, m2 and R
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do post ur comments plzz .. gud or bad
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Stars going out in style New images from NASA's Hubble Space Telescope show the evolution of gas ejected from dying stars. Provided by STScI Hubble captured this four planetary nebulae: He 2-47 (top left), NGC 5315 (top right), IC 4593 (bottom left), and NGC 5307 (bottom right). NASA, ESA, and The Hubble Heritage Team (STScI/AURA) [larger image] | | | | September 13, 2007
The colorful, intricate shapes in these NASA Hubble Space Telescope images reveal how the glowing gas ejected by dying Sun-like stars evolves dramatically over time.
These gaseous clouds, called planetary nebulae, are created when stars in the last stages of life cast off their outer layers of material into space. Ultraviolet light from the remnant star makes the material glow. Planetary nebulae last for only 10,000 years, a fleeting episode in the 10-billion-year lifespan of Sun-like stars.
The name planetary nebula has nothing to do with planets. They got their name because their round shapes resembled planets when seen through the small telescopes of the eighteenth century.
The Hubble images show the evolution of planetary nebulae, revealing how they expand in size and change temperature over time. A young planetary nebula, such as He 2-47, at top, left, for example, is small and is dominated by relatively cool, glowing nitrogen gas. In the Hubble images, the red, green, and blue colors represent light emitted by nitrogen, hydrogen, and oxygen, respectively.
Over thousands of years, the clouds of gas expand away and the nebulae become larger. Energetic ultraviolet light from the star penetrates more deeply into the gas, causing the hydrogen and oxygen to glow more prominently, as seen near the center of NGC 5315. In the older nebulae, such as IC 4593, at bottom, left, and NGC 5307, at bottom, right, hydrogen and oxygen appear more extended in these regions, and red knots of nitrogen are still visible.
These four nebulae all lie in our Milky Way Galaxy. Their distances from Earth are all roughly the same, about 7,000 light-years. The snapshots were taken with Hubble's Wide Field Planetary Camera 2 in February 2007. Like snowflakes, planetary nebulae show a wide variety of shapes, indicative of the complex processes that occur at the end of stellar life.
He 2-47, at top left, is dubbed the "starfish" because of its shape. The six lobes of gas and dust, which resemble the legs of a starfish, suggest that He 2-47 puffed off material at least three times in three different directions. Each time, the star fired off a narrow pair of opposite jets of gas. He 2-47 is in the southern constellation Carina.
NGC 5315, the chaotic-looking nebula at top right, reveals an x-shaped structure. This shape suggests that the star ejected material in two different outbursts in two distinct directions. Each outburst unleashed a pair of diametrically opposed outflows. NGC 5315 lies in the southern constellation Circinus.
IC 4593, at bottomleft, is in the northern constellation Hercules.
NGC 5307, at bottom right, displays a spiral pattern, which may have been caused by the dying star wobbling as it expelled jets of gas in different directions. NGC 5307 resides in the southern constellation Centaurus |
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awesome yr
really gud workk
keep it up
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Water vapor rains on star system New observations by the Spitzer Space Telescope show water vapor prevalent across young star system. Provided by JPL NASA's Spitzer Space Telescope observed a fledgling solar system like the one depicted in this artist's concept, and discovered deep within it enough water vapor to fill the oceans on Earth five times. This water vapor starts out in the form of ice in a cloudy cocoon (not pictured) that surrounds the embryonic star, called NGC 1333-IRAS 4B (buried in center of image). Material from the cocoon, including ice, falls toward the center of the cloud. The ice then smacks down onto a dusty pre-planetary disk circling the stellar embryo (doughnut-shaped cloud) and vaporizes. Eventually, this water might make its way into developing planets. NASA/JPL-Caltech/R. Hurt (SSC) [larger image] | | | | August 31, 2007
NASA's Spitzer Space Telescope has detected enough water vapor to fill the oceans on Earth five times inside the collapsing nest of a forming star system. Astronomers say the water vapor is pouring down from the system's natal cloud and smacking into a dusty disk where planets are thought to form.
The observations provide the first direct look at how water, an essential ingredient for life as we know it, begins to make its way into planets, possibly even rocky ones like our own.
"For the first time, we are seeing water being delivered to the region where planets will most likely form," said Dan Watson of the
University of Rochester. Watson is the lead author of a paper about this "steamy" young star system, appearing in the August 30 issue of Nature.
The star system, called NGC 1333-IRAS 4B, is still growing inside a cool cocoon of gas and dust. Within this cocoon, circling around the embryonic star, is a burgeoning, warm disk of planet-forming materials. The new Spitzer data indicate that ice from the stellar embryo's outer cocoon is falling toward the forming star and vaporizing as it hits the disk.
"On Earth, water arrived in the form of icy asteroids and comets.
Water also exists mostly as ice in the dense clouds that form stars," said Watson. "Now we've seen that water, falling as ice from a young star system's envelope to its disk, actually vaporizes on arrival.
This water vapor will later freeze again into asteroids and comets."
Water is abundant throughout our universe. It has been detected in the form of ice or gas around various types of stars, in the space between stars, and recently Spitzer picked up the first clear signature of water vapor on a hot, gas planet outside our solar system, named HD 189733b.
In the new Spitzer study, water also serves as an important tool for studying long-sought details of the planet formation process. By analyzing what's happening to the water in NGC 1333-IRAS 4B, the astronomers are learning about its disk. For example, they calculated the disk's density (at least 10 billion hydrogen molecules per cubic centimeter or 160 billion hydrogen molecules per cubic inch); its dimensions (a radius bigger than the average distance between Earth and Pluto); and its temperature (170 Kelvin, or minus 154 degrees Fahrenheit).
"Water is easier to detect than other molecules, so we can use it as a probe to look at more brand-new disks and study their physics and chemistry," said Watson. "This will teach us a lot about how planets form."
Watson and his colleagues studied 30 of the youngest known stellar embryos using Spitzer's infrared spectrograph, an instrument that splits infrared light open into a rainbow of wavelengths, revealing "fingerprints" of molecules. Of the 30 stellar embryos, they found only one, NGC 1333-IRAS 4B, with a whopping signature of water vapor. This vapor is readily detectable by Spitzer, because as ice hits the stellar embryo's planet-forming disk, it heats up very rapidly and glows with infrared light.
Why did only one stellar embryo of 30 show signs of water? The astronomers say this is most likely because NGC 1333-IRAS 4B is in just the right orientation for Spitzer to view its dense core. Also, this particular watery phase of a star's life is short-lived and hard to catch.
"We have captured a unique phase of a young star's evolution, when the stuff of life is moving dynamically into an environment where planets could form," said Michael Werner, project scientist for the Spitzer mission at NASA's Jet Propulsion Laboratory, Pasadena, California.
NGC 1333-IRAS 4B is located in a pretty star-forming region approximately 1,000 light-years away in the constellation Perseus. Its central stellar embryo is still "feeding" off the material collapsing around it and growing in size. At this early stage, astronomers cannot tell how large the star will ultimately become.
Other authors of the Nature paper include: Chris Bohac, Chat Hull, Bill Forrest, Ben Sargent, Joel Green and Kyoung Hee Kim of the University of Rochester; Elise Furlan of the University of California at Los Angeles; Joan Najita of the National Optical Astronomy Observatory; Nuria Calvet and Lee Hartmann of the University of Michigan, Ann Arbor; Paola d'Alessio of the National Autonomous University of Mexico; and Jim Houck of Cornell University.
JPL 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 in Pasadena. Caltech manages JPL for NASA. Spitzer's infrared spectrograph was built by Cornell University. Its development was led by co-author Houck. Watson and Forrest are also members of the team that built the spectrograph. |
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hehhehe wat a beginnin a n end.. mind blowin a salute 2 uuu
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u ve wriiten d truth in a shrt articlee.....guud job
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awesomeeee fantasticcc
a salute
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dangerous virus. Pass this to everyone...
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