Are all the stars same?
No, Every star is unique. With the exception of the Sun, stars are all so far away from the Earth that they appear as pinpoints of twinkling light us. But even though they may look the same to the naked eye, they all have their own characteristics, differing in size, temperature, colour, and brightness, depending on how old they are.For example, hot blue-white stars can reach 54,000°F (30,000°C) at their surface, ten times hotter than the coolest stars. A supergiant star can be 600 million miles (1 billion km) across, but a neutron star is only the size of a city.
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| Arcturus Distance: 37 light years Brightness scale -0.05 |
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| Sirius Distance: 8.6 light years Brightness Scale -1.44 |
HOW DO STARS PRODUCE THEIR ENERGY?
Energy is produced in a star’s center, or core, where pressures are enormous and temperatures reach 27 million°F (15 million°C). This causes nuclear fusion—atoms of hydrogen are ripped apart and fuse (join) to form helium. These reactions release vast amounts of energy, which makes the star shine.
In the constellation Hercules is this cluster of hundreds of thousands of stars packed close together. Known as M13, it is a globular cluster. Globular clusters are found orbiting the center of our galaxy. Looser, open clusters of hundreds of stars are found in the galaxy’s spiral arms.
Since 1995, astronomers have found many planets circling other stars. These extrasolar planets are too far away to see, but we can detect them because their gravity pulls at the stars, making them wobble.
Astronomers measure star brightness in magnitudes. The lower the magnitude, the brighter the star. Most stars we can see with our eyes are magnitude 1–6, but the faintest stars visible with telescopes are magnitude 22. Exceptionally bright stars have negative magnitudes, such as –1.44 for Sirius.
HOW STARS LIVE AND DIE
A star is born when a dense region of a nebula collapses under its own gravity. It shrinks into a denser, hotter ball, called a protostar. When the protostar gets hot enough, nuclear fusion begins inside it, and it starts to shine as a new star. After billions of years, the star runs out of fuel and starts to die, expanding hugely and becoming cooler and redder. Small dying stars swell into red giants, and massive dying stars swell into supergiants. A red giant blows out its outer layers to become a planetary nebula and finally becomes a dense dwarf star. A supergiant explodes as a supernova. It may end up as a neutron star or a BLACK HOLE.
NEBULAS
A nebula is a huge cloud of gas and dust found in the space between the stars. Some nebulas glow. Others are dark—we can see them only when they are silhouetted against stars or bright clouds. New stars are born inside dark nebulas.
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| Orion Nebula
Apparent magnitude (V): +4.0
Right ascension: 05h 35m 17.3s
Radius: 12 ly
Declination: −05° 23′ 28″
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Nebulas contain all the ingredients needed to form stars and planets, including atoms of hydrogen, oxygen, and nitrogen, and graphite, a form of carbon. They also contain water and many other molecules.
Many nebulas shine. Some shine by reflecting the light from nearby stars. Others create their own light—their gas particles glow when they are energized (given energy) by radiation from nearby stars.
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| Ant-Nebula
Apparent magnitude (V): 13.8
Radius: 1.0 ly ly
Absolute magnitude (V): 1.8
Distance: ~8,000 ly (~2,500 pc) ly
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A black hole is a region of space with such strong gravity that it swallows up everything that comes near it, even light. A black hole may form when a very massive star blasts itself apart as a supernova. The core of the star collapses so violently that all its matter is crushed into almost no space at all, leaving behind a region of intense gravity—a black hole.
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| Black_hole_Cygnus |
Ordinary black holes are formed when massive stars die, and they typically have the mass of about 5–10 Suns. A supermassive black hole, however, has a mass millions of times greater, and is formed when huge gas clouds collapse. Supermassive black holes seem to be the power source of high-energy active galaxies, such as quasars. Astronomers believe that a supermassive black hole lurks at the center of our own galaxy.
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