Wednesday, March 20, 2013

What are PULSARS?


  • Pulsars are highly magnetized rotating neutron stars that emit a beam of electromagnetic radiation in the form of radio waves. Their observed periods range from 1.4 ms to 8.5 s.
  • The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name. 
  • Because neutron stars are very dense objects, the rotation period and thus the interval between observed pulses are very regular. For some pulsars, the regularity of pulsation is as precise as an atomic clock.
  • Pulsars are known to have planets orbiting them, as in the case of PSR B1257+12.
  • The first pulsar was observed in July 1967 by Jocelyn Bell Burnell and Antony Hewish. 
The Vela Pulsar and its surrounding pulsar wind nebula.
  • In 1974, Joseph Hooton Taylor, Jr. and Russell Hulse discovered, for the first time, a pulsar in a binary system, PSR B1913+16. 
  • This pulsar orbits another neutron star with an orbital period of just eight hours. 
  • Einstein's theory of general relativity predicts that this system should emit strong gravitational radiation, causing the orbit to continually contract as it loses orbital energy. 
  • Observations of the pulsar soon confirmed this prediction, providing the first ever evidence of the existence of gravitational waves. As of 2004, observations of this pulsar continue to agree with general relativity.
  • In 1993, the Nobel prize in physics was awarded to Taylor and Hulse for the discovery of this pulsar.

  • In 1982, a pulsar with a rotation period of just 1.6 milliseconds was discovered, by Shri Kulkarni and Don Backer. 
  • Observations soon revealed that its magnetic field was much weaker than ordinary pulsars, while further discoveries cemented the idea that a new class of object, the "millisecond pulsars" (MSPs) had been found. 
  • MSPs are believed to be the end product of X-ray binaries. Owing to their extraordinarily rapid and stable rotation, 

What are QUASARS ?

  • Quasars are compact, quasi-stellar objects. They are very bright and luminous, trillion of times brighter than the sun. 
  • A quasar is a whole galaxy that shoots out a beam of energy from its north and south poles. 
  • A quasar is powered by a supermassive black hole. 
  • When matter falls into the black hole, the high speed spinning causes some of that matter to be ejected as beams of energy. 

What are FLUX ROPES ?

  • Astronomers have spotted enormous magnetic entities - called flux ropes - stretching for hundreds of kilometres in Venus's upper atmosphere, above the poles.
  • The European Space Agency's Venus Express spacecraft observed the strange structures in Venus' atmosphere which has redrawn scientists' perceptions of the planet's magnetic environment.
  • Flux ropes have been seen before around other planets, including Earth. They transport superheated plasma gas from one side of the "rope" to the other. 
  • On Earth, flux ropes form near the face of the planet opposite the Sun. The stream of charged particles known as the solar wind flows around the planet and creates a "magnetotail" of charged particles on the other side. 
  • Periodic solar outbursts known as coronal mass ejections arise from a type of flux rope. The delicate structures sit on top of the Sun and transport matter and superheated gas from one part of the Sun to another. 
  • Venus stands apart from most other planets in the solar system, however, because it has no magnetic field. When Venus' atmosphere has a higher pressure than the incoming solar wind field, the ionosphere is considered "unmagnetised," meaning that it's free of all but the smallest magnetic field structures. 
  • The ionosphere of Venus stays unmagnetised most of the time, until the solar wind reaches a higher pressure than the surrounding atmosphere and magnetises it. 
  • In these conditions, relatively small flux ropes can form due to the higher speed of the solar wind rolling over the slower ionosphere, researchers said. 
  • The ionosphere is filled with these very small kilometres across - flux ropes,
  • Scientists determined that the flux ropes on Venus form from solar particles on the side of the planet facing away from the Sun, in the magnetotail. 
  • It seems to be associated with a process known as reconnection, which is magnetic field lines joining up together and forming a new magnetic configuration,giant flux ropes were previously found in the atmosphere of Mars ? but only in the southern hemisphere. Mars, like Venus, does not have a planet-wide magnetic field. 
  • The observation and formation of the large flux rope at Mars might raise speculative questions related to the giant flux ropes at Venus.

What is a spiral galaxy?

  • Spiral galaxies get their name from the shape of their disks. In a spiral galaxy, the stars, gas and dust are gathered in spiral arms that spread outward from the galaxy's center. 
  • Spiral galaxys are divided into three main types depending on how tightly wound their spiral arms are: Sa, Sb and Sc. 
  • Sa galaxies have very tightly wound arms around a larger central nucleus. 
  • Sc galaxies have very loosely wound arms around a smaller nucleus. 
  • Sb's are between, having moderately wound arms around an average sized nucleus. 

  • Spiral galaxies have a lot of gas, dust and newly forming stars. 
  • Since they have a lot of hot, young stars, they are often among the brightest galaxies in the universe. 
  • About 20% of all galaxies are spirals. 
  • We live in a spiral galaxy called the Milky Way.


What is a nebula?
  • A nebula is a cloud of gas and dust in space. 
  • Some nebulas are regions where new stars are being formed, while others are the remains of dead or dying stars. 
  • Nebulas come in many different shapes and sizes. 
  • There are four main types of nebulas: Planetary nebulas, Reflection nebulas, Emission nebulas, and Absorption nebulas. 
  • The word nebula comes from the Latin word for cloud.
What is a comet?
  • Comets are basically dusty snowballs which orbit the sun. 
  • They are made of ices, such as water, carbon dioxide, ammonia and methane, mixed with dust. 
  • These materials came from the time when the solar system was formed. 
  • Comets have an icy center (nucleus) surrounded by a large cloud of gas and dust (called the coma). 
  • The coma is created as the ice in the nucleus is warmed by the sun and vaporizes. 
  • Comets can develop 2 tails as they travel closer to the sun, a straight gas tail and a curved dust tail. 
  • The gas tail is created by the solar wind, whose magnetic fields pull the gas away from the comet's coma. 
  • The dust in the coma is not affected by magnetic fields but is vaporized by the sun's heat, and forms a curved tail which follows the comet's orbit.

What are asteroids?

  • Asteroids are rocky-metallic objects which range in size from about the size of pebbles to around 600 miles (~1,000 km) across. 
  • Although they orbit the sun, they are too small to be considered planets. Asteroids are thought to be leftover material from the formation of our solar system. 
  • Most are found in the Asteroid Belt, a doughnut-shaped ring which lies between the orbits of Mars and Jupiter. 
  • Astronomers have also identified a group of asteroids whose orbits cross Earth's orbit. 
  • Several hundred thousand asteroids are known to exist in our solar system, and many are yet to be discovered. 
  • Most of the undiscovered asteroids are the smaller ones (less than 100 km across) which are more difficult to detect. 
  • It is estimated that there are over a million of these smaller asteroids.
The largest asteroid is called Ceres. It is about one-quarter the size of our moon.


What is the difference between an asteroid and a comet?
  • The main difference between asteroids and comets is what they are made of. 
  • Asteroids are made up of metals and rocky material, while comets are made up of ice, dust and rocky material. 
  • Both asteroids and comets were formed early in the history of the solar system about 4.5 billion years ago. 
  • Asteroids formed much closer to the sun, where it was too warm for ices to remain solid. 
  • Comets formed farther from the sun where ices would not melt. Comets which approach the sun loose material with each orbit because some of their ice melts and vaporizes to form a tail.

Can asteroids have moons?
  • Yes, asteroids can have moons! Some of the larger asteroids in our solar system actually do have moons. 
  • In 1993, an tiny moon called Dactyl was discovered orbiting the large asteroid Ida. Dactyl is only about 1 mile wide, while Ida is about 19 miles across. Since then, several other moons have been discovered orbiting asteroids. 
  • In 1999 an 8 mile wide moon called Petit-Prince was discovered orbiting the 135 mile wide asteroid Eugenia. In 2000, the 90 mile wide asteroid Pulcova was discovered to have its own moon, about nine miles wide. Over two dozen more have been discovered.
NASA considers plan to capture an asteroid and turn it into a space station

  • NASA scientists are planning to capture a 5,00,000 kg asteroid, relocate it and transform it into a space station for astronauts to refuel at on their way to Mars.
  • It would be the first time a celestial object has ever been moved by humans, a media report said.
  • The White House's Office of Science and technology will consider the $2.6 billion plan in the coming weeks as it prepares to set its space exploration agenda for the next decade.
  • The technology would also open up the possibility of mining other asteroids for their metals and minerals.
  • An 'asteroid capture capsule' would be attached to an old Atlas V rocket and directed the asteroid between the Earth and the Moon.
  • Once close, the asteroid capsule would release a 50 ft diameter bag that wrap around the spinning rock using drawstrings, the paper said.
  • The craft would then turn on its thrusters, using an estimated 300 kg of propellant, to stop the asteroid in its tracks and tow it into a gravitationally neutral spot.
  • Some asteroids are full of iron which could be used for in the making of new space stations, others are made up of water which could be broken down into hydrogen and oxygen to make fuel.


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