The Journey of Flight.pdf - Valkyrie Cadet

Chapter Chapter 25 25 - - Our Our Solar Solar System System
System
Hundreds of pulsars, found in supernovae nebulae, are now known. After a supernova explosion,
stars more than 1.4 times the size of our Sun leave behind a large core of solid iron. The absence of
fusion reactions allows the core of the star to collapse and presses the remaining star matter into a
smaller space where it continues to degenerate until only neutrons remain. The result is a dense
neutron star, about twenty miles across, in which matter is extremely dense (one centimeter of matter
would weigh one billion tons).
Spinning neutron stars have an axis of rotation that does not coincide with the axis of the magnetic
field of the star. This causes its radio beams to sweep across the sky and deliver short pulses of radio
waves to any receiver in its path.
Nebulae
Nebula is the Latin word for cloud and there are many dark and bright nebulae within our own
galaxy, the Milky Way. The dark nebulae simply are vast clouds of matter which have not yet formed
into stars. The bright nebulae may be studded with stars, and thus, send forth brilliant arrays of color.
Some bright nebulae are the remnants of supernova; one such example is the Crab Nebula seen below
left. Perhaps the best example of a dark nebula is also shown below right.
Several types of nebulae exist within the universe. In dark nebulae, both visible and ultraviolet
light are almost totally absorbed by dust within the nebula itself, making the nebula appear as a dark
smudge against the background. The dust within reflection nebulae reflects and scatters sufficient
starlight to make the nebula visible and causes it to glow faintly. The most visible nebulae, emission or
glowing nebulae, are three-fourths hydrogen (and nearly all the rest helium) heated by ultraviolet
radiation from nearby hot stars; energy is re-emitted in the form of visible light.
After a star has evolved into a red giant, it enters a brief phase in which the outer layers are blown
off. Eventually these layers become visible as a thin shell of gas around the star. Early astronomers
The Crab Nubula
The Horsehead Nebula in Orion
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