WHITE DWARFS

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WHAT IS WHITE DWARFS? 

A white dwarf is what stars like the Sun are after they've depleted their nuclear fuel. Near the end of its nuclear process of burning, this type of star expels most of its outer material, forming a planetary nebula. Only the warm heart of the star is left. This center becomes a very hot white dwarf with a temperature of more than 100,000 Kelvin. Unless it is accreting matter from a nearby star (see Cataclysmic Variables), the white dwarf will cool down over the next billion years or so. Several close, young white dwarfs have been observed as sources of weak and low-energy x-rays. Recently, the composition and structure of these stars ' thin atmosphere has become a powerful tool in the study of soft X-ray and extreme ultraviolet observations.

A typical white dwarf is half as heavy as the Sun, but slightly larger than the Moon. A white dwarf of Earth size has a mass of 1x 109 kg / m3. The average density of Earth itself is only 5.4x 103 kg / m3. This means that a white dwarf is as large as 200,000 times. It makes white dwarfs one of the densest content sets, exceeded by neutron stars alone.

 
White dwarf star Sirius B compared to Earth. One of the first white dwarfs to be found, Sirius B is merely the size of the Earth, making it quite small for a star. And yet it manages to cram about the same mass as our Sun, making it much denser. Sirius B’s powerful gravitational field is 350,000 times greater than Earth’s, meaning that a 68 kg person would weigh 25 million kg on its surface!


Astronomers have detected a bright X-ray outburst from a star in the Small Magellanic Cloud, a nearby galaxy almost 200,000 light-years from Earth.


A diagram of a cataclysmic variable, showing the normal star, the accretion disk, and the white dwarf. The hot spot is where matter from the normal star meets the accretion disk.

A crash course video for extra experience!



SEE MORE! 

  • Star ~ A large ball of gas that creates and emits its own radiation. 
  • Planetary nebula ~ A shell of gas ejected from stars like our Sun at the end of their lifetime. This gas continues to expand out from the remaining white dwarf. 
  • Accretion ~ Accumulation of dust and gas onto larger bodies such as stars, planets and moons. 
  • Cataclysmic Variables ~ Binary star systems that have a white dwarf and a normal star companion.

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