• Question: How do you know if a star is dead? Do they stay in space?

    Asked by to Sarah on 16 Jun 2014. This question was also asked by .
    • Photo: Sarah Casewell

      Sarah Casewell answered on 16 Jun 2014:

      Dead stars – white dwarfs are really dense and small, but very hot. We detect them using ultraviolet light, and by looking at their spectrum. This shows us broad hydrogen lines, the hallmark of a white dwarf.

      They do stay in space – they just cool with time where they were formed. Some of the white dwarfs in the Praesepe cluster have been cooling for 300 million years and have cooled from 100 000 degrees to 15 000 degrees!

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