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Sirius A with Sirius B, a white dwarf, indicated by the arrow
Sirius A with Sirius B, a white dwarf, indicated by the arrow

A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter, supported against its own gravity only by electron degeneracy pressure. A white dwarf is very dense: in an Earth sized volume, it contains a mass comparable to the Sun. What light it radiates is from its residual heat. White dwarfs are thought to be the final evolutionary state of stars whose mass is insufficient for them to become a neutron star or black hole. This includes more than 97% of the stars in the Milky Way. After the hydrogen-fusing period of such a main-sequence star ends, it will expand to a red giant and shed its outer layers, leaving behind a core which is the white dwarf. This, very hot when it forms, cools as it radiates its energy until its material begins to crystallize into a cold black dwarf. The oldest known white dwarfs still radiate at temperatures of a few thousand kelvins, which establishes an observational limit on the maximum possible age of the universe. (Full article...)

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Springbok

The springbok (Antidorcas marsupialis) is a medium-sized antelope found mainly in the dry areas of southern and southwestern Africa. A slender, long-legged bovid, it reaches 71 to 86 cm (28 to 34 in) at the shoulder and weighs between 27 and 42 kg (60 and 93 lb). Both sexes have a pair of long black horns that curve backwards, a white face, a dark stripe running from the eyes to the mouth, a light-brown coat with a reddish-brown stripe, and a white rump flap. Primarily browsing at dawn and dusk, it can live without drinking water for years, subsisting on succulent vegetation. Breeding peaks in the rainy season, when food is more abundant. A single calf is weaned at nearly six months of age and leaves its mother a few months later. Springbok herds in the Kalahari Desert and the semi-arid Karoo used to migrate in large numbers across the countryside. The springbok is the national animal of South Africa. This male springbok was photographed in Etosha National Park, Namibia.

Photograph credit: Yathin S Krishnappa

 
 
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