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The image of Sirius A and B is courtesy of Lick Observatory.White Dwarf is Games Workshop's premium Warhammer Magazine, packed with amazing content each month such as new rules and background, short stories, regular columns, special guests and more. Naval Observatory, Yervant Terzian, Cornell University, Mario Perinotto and Patrizio Patriarchi, Observatorio Arcetri (IT) The two planetary nebulae images are courtesy of Bruce Balick and Jay Alexander, University of Washington, Arsen Hajian, U.S. The above images of Betelgeuse and M4 were created with support to Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., from NASA contract NAS5-26555, grant number STScI-PRC96-04, and are reproduced with permission from AURA/STScI. A white dwarf's outer layers contain just helium and hydrogen and so are essentially transparent to the X-rays that are emitted by the much hotter inner layers. This region is very dense and can be as hot as 100,000 degrees in a very young white dwarf. X-rays come from inside the visible surface of the white dwarf. The white dwarf HZ 43 was observed by the X-ray satellite ROSAT. Optical telescopes are not the only way to view white dwarfs. It is also approximately 14 billion years old, which is why so many of its stars are near the end of their lives. M4 is located 7,000 light years away but is the nearest globular cluster to Earth. These white dwarfs were so faint that the brightest of them was no more luminous than a 100 watt light bulb seen at the moon's distance. In August of 1995, this camera observed more than 75 white dwarfs in the globular cluster M4 in the constellation Scorpius. The Hubble Space Telescope, with its 2.4 meter mirror and advanced optics, has been successfully viewing white dwarfs with its Wide Field and Planetary Camera. Upon close inspection we may find that it has a white dwarf companion. As with the Sirius system, if a star seems to have some sort of unexplained motion, we may find that the single star is really a multiple system. Since white dwarfs are very small and thus very hard to detect, binary systems are a helpful way to locate them. The orbital period of this system is about 50 years. This pair are now referred to as Sirius A and B, with B being the white dwarf. This companion star was later determined to be a white dwarf. In 1863, the optician and telescope maker Alvan Clark spotted this mysterious object.
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In 1844, astronomer Friedrich Bessel noticed that Sirius had a slight back and forth motion, as if it was orbiting an unseen object. The first white dwarf to be discovered was found because it is a companion star to Sirius, a bright star in the constellation Canis Major. There are several ways to observe white dwarf stars. The arrow is pointing to white dwarf, Sirius B, next to the large Sirius A. In about half of them, the central white dwarf can be seen using a moderate sized telescope. There are some planetary nebulae that can be viewed through a backyard telescope. They are called this because early observers thought they looked like the planets Uranus and Neptune. The white dwarf will be surrounded by an expanding shell of gas in an object known as a planetary nebula.
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The core of the star, however, remains intact, and becomes a white dwarf. This continues until the star finally blows its outer layers off. The Sun will not be very stable at this point and will lose mass. Now the star has become an even bigger giant than before! Our Sun's radius will become larger than Earth's orbit! When the core of the star contracts, it will cause a release of energy that makes the envelope of the star expand. Since our Sun won't be hot enough to ignite the carbon it its core, it will succumb to gravity again. But when it's finished its helium, it isn't quite hot enough to be able to burn the carbon it created. But what happens after that? Our red giant Sun will still be eating up helium and cranking out carbon. We already know that medium mass stars, like our Sun, become red giants. The Sun will only spend one billion years as a red giant, as opposed to the nearly 10 billion it spent busily burning hydrogen. Eventually, it will transform the helium into carbon and other heavier elements. But the core temperature of our red giant Sun increases until it's finally hot enough to fuse the helium created from hydrogen fusion. When a star gets bigger, its heat spreads out, making its overall temperature cooler. When this happens, our Sun will become a red giant it will be so big that Mercury will be completely swallowed! This burning shell of hydrogen expands the outer layers of the star. January 15, 1996, Hubble Space Telescope Captures First Direct Image of a Star, A.