Sunday, 9 October 2016

White Dwarfs- Facts And Info

A white dwarf is a remnant of a low mass dead star. White Dwarfs are one of the dimmest objects in the observable universe. The stars with mass lower than 10 solar masses when completely burn their fuel both hydrogen and helium, will not be able to burn carbon, buffed off their outer layers to form a planetary nebula. This planetary nebula will shine for almost 20,000 to 50,000 years. This planetary nebula will expand outwards and will fade slowly with time. White Dwarf mostly contains carbon and hydrogen equal to the mass of the sun and are smaller in size (similar to earth). The core of planetary nebula forms white dwarf.
White Dwarf have a temperature of about 100,000 Kelvin. White Dwarf cools down in some billion years. Many nearby white dwarfs are detected. Detected white dwarfs are young and emit low energy X-rays. The average density of a white dwarf is about 1,000,000 times denser than that of the Sun. A sugar cube sized quantity of white dwarf would weigh about 1 ton. The core of the white dwarf is made of carbon. A white dwarf can collapse down to a more compact object, like a neutron star or a black hole but for this the star would have mass more than 5 solar masses.

In a white dwarf, the density is much higher, and all the electrons are much closely bound together and it is stated to as a "degenerate" gas. It means that all the energy levels in atoms are filled with electrons. Once s star has degenerated than gravity cannot compress it any longer since quantum mechanics dictates that there is no more accessible space to be occupied. So the white dwarf survives by quantum mechanical rules that prevent its complete collapse. This degenerated matter has many other properties. For example, more massive the white dwarf is, the smaller it will be in size. There is a limit of mass of a white dwarf. Subrahmanyan Chandrasekhar, Indian astrophysicist, discovered this boundary to be 1.4 times the mass of the Sun. This appropriately is well-known as the "Chandrasekhar limit."

Scientists think that there is a coating 50 km thick below the atmosphere of several white dwarfs. At the bottom of this coating there is a crystalline lattice of carbon and oxygen atoms. Subsequently a diamond is just crystallized carbon, so it is possible that one might make the evaluation between a cool carbon/oxygen white dwarf and a diamond.

Several nearby white dwarf stars can be witnessed directly through telescopes, however they are very dim. M4 is the nearest globular cluster to the Earth. It contains hundreds of thousands of stars and is expected to have about 40,000 white dwarfs. This globular cluster formed initial in the history of our Milky Way Galaxy, and today is an absolute cosmological retirement community. It is about 14 billion years old and all of its stars that began with 80% or more of the Sun's mass and have already evolved off the Main Sequence to become red giants, and many have turned into white dwarfs. The brightest of the detected white dwarfs is no more luminous than a 100-watt light bulb seen at the Moon's distance (239,000 miles).

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