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D Type White Dwarf and Giant Stars

White Giant and Main Sequence Stars

White giant stars are rare, they tend to be classified as Blue Giant Star. Thuban, the brightest star in the constellation of Draco, the Dragon is sometimes seen as a White Giant star, other times its blue. Thuban was once the Pole Star before Polaris received the title.

Giant White Stars will have a Spectral type of A rather than D. White Giants tend to be at the hotter end of the star spectrum. The opposite end are red, brown and black stars.

White or Green Stars

The Sun although it is a G Type star, a yellow star is actually a white star when looked at from space. The atmosphere causes the star to appear yellow. the Sun has been referred to as a Yellow dwarf star because it is smaller than the larger supergiant yellow stars such as V766 Centauri. It is incorrect to refer to it as a White Dwarf Star therefore.

In the picture below, the coloured green is where white stars inhabit in the Hertzsprung Russel diagram. In theory, the stars in the middle should be green but because stars show in a range of colours, green is merged with colours on either side to appear white.

Hertzsprung Russel Diagram of Stars

What is a White Dwarf Star?

The first White Dwarf star was discovered by Sir William Herschel, the German born British Astronomer who discovered 40 Eridani B on 31st January 1783. Wiki

A White Dwarf star marks the penultimate end of a star's life such as our own star, the Sun. For billions of years, our star has been turning hydrogen into helium through chemical reaction in a phase known as the Main Sequence. When it has used up all its hydrogen, it will start to convert helium to carbon or oxygen.

A White Dwarf are compact stars, their radius is less than 1% of our own star, the Sun but their mass could be the same as our Sun. The mass would be compressed into a much smaller area. National Geographic

When the star moves past the main sequence, it will grow due to the outward pressures overcoming the inward pressures of gravity. The Sun will expand and consume Mercury and then Venus. As the Sun expands, our planet will not longer be able to support life.

The Sun will keep converting the materials up and until it gets to Iron when it will not then be able to convert anymore and then explode. The result of the explosion will depend on its and mass and size before it exploded.

White Dwarf Stars would have at one been surrounded by a Planetary nebula, an area of dust and cloud created as the star entered the death stage. Over time, the cloud would have dispersed leaving just the dwarf or neutron star.

A white dwarf star will be illuminated by the heat the remains gives off. Eventually, the heat will die and the cold remains will become known as Black Dwarf Star. As yet due to how long a white dwarf star takes too cool down, it is thought there are no black dwarfs out there. It is thought that the Black Dwarf star will dissipate or remain as was, no longer hot enough to be visible.

White Dwarf stars have been found in orbit to a much larger star such as in the case of Sirius B. Sirius is the brightest star in the night sky but it is a binary star, the smaller of the two which can't be seen with the naked eye is a white dwarf star.

A White Dwarf can leech hydrogen from its larger neighbour, appearing as though it has come back from the dead. This type of star is known as a vampire star or a zombie star. A Zombie Star is one that had died but has come back to life. So although apparently dead, a White Dwarf star can go supernova more than once. Its been known that a star can go supernova more than once as in the case of iPTF14hls

White Dwarf stars have been discovered in orbit round dwarf stars. A planet has been found orbiting PSR B162026 in the constellation of Scorpius. The star is actually two stars, a Pulsar and a White Dwarf. Before you ask, there's no chance of there being life on the planet as it would have been destroyed long ago when the pulsar went supernova.

Diferences between Neutron Star and White Dwarf Star

A white dwarf will exist for many more years as a white dwarf than as it did as a main sequence star. After an unimaginably long time, it will turn into a black dwarf having run out of energy to shine. Whilst no black dwarf exists yet, there are a number of white dwarf stars out there, the nearest being a mere 8.6 light years away as the companion star to Sirius.

Names of Example White Dwarf Stars


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