STARS
The life and death of star
A star is like our sun is a ball of
hydrogen gas. Pulled together by gravitational
forces so powerful that , at its core ,atoms of
Hydrogen fuse together . This fusion creates helium gas and causes energy to be released .The hydrogen is used up over billion of years , until the star becomes unstable ,swells into a red giant then dwindles into a tiny burnt out star – a white dwarf . Larger stars than the sun can destroy themselves in vast explosion ,called supernovae.
Nurseries of the stars
A star is born when pressure wave passes through a huge interstellar gas
cloud . The galaxy generates these waves as it rotates , or they can result from distant supernova explosions of huge stars. The waves compresses gas in the cloud , so that molecules begin to come together under gravity , pulling in more matter from around themselves to form spinning balls of gas. At the core of these balls , atoms are packed so closely together that their tiny nuclei , triggering a chain of nuclear reactions The energy released by these becomes the first light emitted by the new star.
Deathly glow
When a star of a similar size to the sun has almost run out of fuel for its internal nuclear reactions ,it undergoes a series of violent convulsions. These throw off the star outer gas layers ,which become a glowing nebula such as MyCn18 Often the nebula is seen as circles of bright gas around the dull dot of the dying star. The hourglass shape of MyCn 18 may be caused by a ring of matter which circles the star equator, absorbing some of the ejected material and forcing the gas to expand in two huge lobes above and below the star. Cooler ,outer gas layers are dark red while younger layers closer to the central star, glow white hot.
Trifid Nebula
The Trifid Nebula is cloud of dust and gas. It has no light of its own . and shines only by reflection . The region glowing red is made up of hydrogen gas .lit by the young stars forming within it. Above is an area of dust reflecting blue light from an older star within the Nebula.
Black holes
The centres of many galaxies may contain black holes :collapsed stars with gravity so powerful that even light is sucked in. In active galaxies gas is trapped in a black hole s magnetic field , and ejected at the poles, forming gas jets.
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