LOCATED ABOUT 6,500 light-years from Earth in the direction of the constellation Taurus, the Crab Nebula is the remnant of a star that began its life with about 10 times the mass of our own sun. Such a massive star consumes its nuclear fuel so rapidly that it lives only 50 million years or so before exploding as a supernova.
The end of the Crab star was seen on Earth on July 4, 1054. The explosion was witnessed as a naked-eye ?Guest Star? by Chinese astronomers, and is also depicted in rock paintings in the southwestern United States.
The Crab Nebula image was obtained by Hubble?s Wide Field and Planetary Camera 2 in 1995. Images taken with five different color filters have been combined to construct this false-color picture. Resembling an abstract painting by Jackson Pollack, the image shows ragged shreds of gas that are expanding away from the explosion site at more than 3 million miles per hour.
The core of the star has survived the explosion as a ?pulsar,? visible in the Hubble image as the lower of the two moderately bright stars to the upper left of center. The pulsar has about 1.4 times the mass of the sun, jammed into an object only about 10 miles in diameter. This neutron star even more remarkable because it spins on its axis 30 times a second.
The spinning pulsar heats its surroundings, creating the ghostly diffuse bluish-green glowing gas cloud in its vicinity, including a blue arc just to the right of the neutron star.
The colorful network of filaments is the material from the outer layers of the star that was expelled during the explosion and is now expanding outward at high speed.
The various colors in the picture arise from different chemical elements in the expanding gas, including hydrogen (orange), nitrogen (red), sulfur (pink) and oxygen (green). The shades of color represent variations in the temperature and density of the gas, as well as changes in the elemental composition.
These chemical elements, some of them newly created during the evolution and explosion of the star and now blasted back into space, will eventually be incorporated into new stars and planets. Astronomers believe that the chemical elements in Earth and even in our own bodies, such as carbon, oxygen, and iron, were made in other exploding stars billions of years ago.
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SUN-EARTH CONNECTION EXPOSED
Space physicists have made the first direct observations of the process that causes auroras and magnetic disturbances ? or space weather ? around Earth.
Settling a 50-year-old debate, scientists have directly measured the transfer of energy from the solar wind into the magnetic space around Earth, or magnetosphere, and down to the atmosphere. Such events can affect radio communications, spacecraft operations, and the control of electric power systems on Earth.
Relying on observations collected by NASA?s Polar spacecraft and Japan?s Geotail spacecraft, scientists associated with the International Solar-Terrestrial Physics program have gathered the first direct evidence that a process known as magnetic reconnection occurs naturally in the sun-Earth system. Until now, reconnection had been observed only under contrived conditions in a few physics laboratories.
The results were reported during this week?s meeting of the American Geophysical Union in Washington.
During reconnection, magnetic fields that are heading in opposite directions ? having opposite north or south polarities ? break and connect to each other. In space, reconnection between the magnetic fields of Earth and the sun allows the solar wind to break through the planet?s magnetic shell and flow into the space around Earth.
Along the way, magnetic energy gets converted to bursts of particle energy that create auroras ? northern or southern lights ? and space weather storms.
Indirect evidence of reconnection has provoked debate for more than half a century, as space physicists could only detect signs of reconnection after it had happened. But recently, the Polar spacecraft flew through a region on the sunlit side of Earth where reconnection was in progress, gathering the first eyewitness account of the process.
Using data collected from Geotail?s dozens of passes through Earth?s magnetic tail, scientists also have pinpointed the area on the night side where reconnection occurs, and have shown for the first time a clear association between reconnection and auroras.
An ultraviolet image, captured by the Extreme Ultraviolet Imager aboard NASA's Image spacecraft, shows sunlight scattered from Earth's extended atmosphere of helium. This image shows that the ionized helium atmosphere extends to about two to three times the size of Earth itself. Irregularities at the fringe of the image, such as the upper left, indicate magnetic storm activity.
The observations are considered crucial for understanding space weather ? and have implications for other fields of physics. For example, magnetic reconnection on the sun likely plays a role in the development of solar flares and of coronal mass ejections. Similar magnetic activity outside our solar system may explain some of the galactic X-rays that astronomers have detected. And observations of reconnection in nature may aid the study of nuclear fusion and other plasma processes in the laboratory.
The magnetosphere is the only place where reconnection has been observed firsthand as it occurs naturally.
A popular misconception holds that auroras and space weather are caused when electrically charged particles from the sun plunge directly into Earth?s atmosphere near the magnetic poles. In fact, the sun provides the energy ? but not necessarily the particles themselves ? to drive space weather activity around Earth. And rather than a direct trip from the solar atmosphere to Earth?s poles, solar wind and storms from the sun must pass through these small and elusive reconnection regions before they can stir up space weather
The first pictures from NASA?s Image spacecraft are providing additional insights into the interaction between the solar wind and Earth?s magnetic field. The Image spacecraft ? launched in March from Vandenberg Air Force Base in California ? can give scientists a complete picture of solar storms, just as weather satellites can reveal entire atmospheric storm systems.
?It?s like the difference between predicting rain storms by sticking your finger out the car window, versus looking at a satellite photo,? said Patricia Reiff, an astrophysicist at Rice University. ?We get the big picture, and we can see it changing all at once. And because we can see it all at once, we?re seeing changes that we only thought we could understand before, we?re seeing them happen.?
An Air Force rocket built from parts of scrapped missiles made a successful launch on Sunday from Vandenberg Air Force Base in California.
The rocket, designed to be used in creating the nation?s national missile defense system, was a hybrid made up of three stages from different Minuteman 2 intercontinental ballistic missiles, including one built in 1966, said Tech. Sgt. Buzz Ritchie, a spokesman for the base?s 30th Space Wing.
The launch under the military?s Orbital Suborbital Program was a test to determine if the hybrid could be used as a cheaper target for interceptor missiles. The recycled rocket launch cost $11 million, compared with $21 million for the use of a regular Minuteman 2, said Staff Sgt. Rebecca Bonilla, another base representative.
The rocket?s stages successfully separated, carrying the target launch vehicle into space for only about 30 minutes.
It was not immediately clear whether the target vehicle burned up in the atmosphere or fell back to Earth.
The military will determine whether the mission was a success by examining data to see how closely the rocket kept to its specified course, Ritchie said.
Space Shorts includes information from the Space Telescope Science Institute, NASA and the Associated Press.
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