A nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, the term was used to describe any diffused astronomical object, including galaxies beyond the Milky Way. The Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula (and spiral galaxies in general as "spiral nebulae") before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and others.
The Crab Nebula ( also known as Messier Object 1 or M1 ) is unarguably one of the most intensively studied objects in all of astronomy. A gaseous diffuse nebula located in the constellation Taurus, it is the supernova remnant of a star that was observed to explode by Chinese and Arab astronomers in 1054. Chinese astronomers in that year reported a " guest star " that appeared suddenly and remained visible for 23 days, even during day time. Despite a distance of about 6,000 light years from earth, the supernova was brighter than Venus for weeks before fading from view after nearly two years. Even today, the nebula is still expanding at more than 3 million miles per hour and emit radiation in all wavelengths, from gamma rays to X-rays, UV, optical and infrared radiation, and radio waves.
At the center of the Crab Nebula is the Crab Pulsar, also known as PSR BO531 + 21, a neutron star remnant of the supernova which is roughly 10 km in diameter. The Crab Pulsar rotates once every 33 millisecond, or 30 times each second, and the beams of radiation it emits interact with the nebular gases to produce complex pattern of wind and fluorescence. Neutron stars are formed in the seconds before a supernova explosion when gravity crushes the central core of the star to densities 50 trillion times that of lead and a diameter of only 12 miles. Another consequence of the dramatic collapse is that neutron stars are rapidly rotating and highly magnetized. Like a gigantic cosmic generator, the rotating magnet generates 10 quadrillion volts of electricity, 30 million times that of a typical lightening bolt.
Appearing like a winged fairy-tale creature poised on a pedestal, this object is actually a billowing tower of cold gas and dust rising from a stellar nursery called the Eagle Nebula. The soaring tower is 9.5 light-years or about 57 trillion miles high, about twice the distance form our Sun to the next nearest star.
Stars in the Eagle Nebula are born in clouds of cold hydrogen gas that reside in chaotic neighborhoods, where energy from young stars sculpts fantasy-like landscapes in the gas. The tower may be a giant incubator for those new born stars. A torrent of ultraviolet light from a band of massive, hot, young stars ( off the top of the image ) is eroding the pillar.
The starlight also is responsible for illuminating the tower's rough surface. Ghostly streamers of gas can be seen boiling off this surface, creating the haze around the structure and highlighting its three-dimensional shape. The column is silhouetted against the background glow of more distant gas.
Inside the gaseous tower, stars may be forming. Some of those stars may have been created by dense gas collapsing under gravity. Other stars may be forming due to pressure from gas that has been heated by the the neighboring hot stars.
The first wave of stars may have started forming before the massive star cluster began venting its scorching light. The star birth may have begun when denser regions of cold gas within the tower started collapsing under their own weight to make stars.
The dominant colors in the image were produced by gas energized by the star cluster's powerful ultraviolet light. The blue color at the top is from glowing oxygen. The red colour in the lower region is from the glowing hydrogen. The Eagle Nebula image was taken in November 2004 with the Advanced Camera for Surveys abroad NASA's Hubble Space Telescope.
Credit : NASA, ESA and The Hubble Heritage Team
The Spacestellar Creations