Page 33 - Curriculum Visions Dynamic Book

 This picture shows the Crab Nebula (catalogue numbers NGC 1952 and M1). It is one of the most-studied objects in the sky. It is about 5,000 light-years from the Earth and about 10 light-years across. It
is the remnant of a violently exploding star, or supernova. It was the first object listed (hence M1) in Charles Messier’s catalogue of nebulous objects (see page 12).
In the year a.d. 1054 Chinese astronomers saw a new star appear. This star was so bright that it was visible in broad daylight for several weeks. Today the Crab Nebula is visible at the site of that bright star.
The Crab Nebula is still expanding after its explosion at the rate of 1,100 km per second. It contains an object called a pulsar (see page 34), which might be one feature of the collapsed supernova.
Because the gases in the expanding shell are extremely
hot, they release light, and that is why they can be seen. It is from this cloud of elemental particles thrown into space that material is produced ready to form a new star such as our Sun.
Meanwhile, the neUtron star that forms in the center may be just 20 km across but may have a weight equal to several Suns. In this case it may be associated with a pUlsar (page 34) and a qUasar (see page 35).
In some cases it may grow even bigger and denser. When this happens, it is so dense that its gravitational force is once more enormously high, and that turns the neutron star into a black hole (see pages 35–39). The black hole will then start sucking in everything that comes within its reach.
A supernova event happens frighteningly fast. After millions of years of stability the supernova event happens in days, the brightness lasting for only a matter of weeks.
During this event the explosion makes the star shine more brightly than all of the rest of the stars in its galaxy put together.
The most famous supernova that has been recorded was observed in A.d. 1054. Its remains are now called the Crab Nebula. The Crab Nebula is different from a planetary nebUla because in its center there is a rapidly spinning, pulsating neutron star called a pulsar.
Because most of the stars in the Universe are small, most of those that can be seen in their last stages are decaying to white dwarfs without any spectacular explosion to mark their dying days.
black hole An object that has a gravitational pull so strong that nothing can escape from it.
neUtron star A very dense star that consists only of tightly packed neutrons. It is the result of the collapse of a massive star.
planetary nebUla A compact ring or oval nebula that is made of material thrown out of a hot star.
pUlsar A neutron star that is spinning around, releasing electromagnetic radiation, including radio waves.
qUasar A rare starlike object of enormous brightness that gives out radio waves, which are thought to be released as material is sucked toward a black hole.
sUpernova A violently exploding star that becomes millions or even billions of times brighter than when it was younger and stable.
 A neutron star (arrowed).
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