Astronomy

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When the Sun ends up as a white dwarf, billions of years from now, it will contain about 40 percent of its present-day mass and have the same radius as Earth. What will be its density? How many times more dense is that than the present-day Sun?

  • Astronomy -

    We are going to have to have to look up some numbers. You can use Google for that.
    Solar mass (now): 1.989*10^30 kg = M1
    Solar mass (future): 0.4*M1 = 7.956*10^29 kg = M2
    Solar radius (now): 6.96342*10^5 km = R1
    Earth radius (now): 6378.1 km
    Solar radius (future): 6378.1 km = R2

    Solar density increase factor:
    (M2/M1)*(R1/R2)^2 = 4769

    Future solar density as white dwarf:
    = M2/[(4/3)*pi*R3^3]= ____
    Your turn.

  • Astronomy (correction) -

    I used the wrong exponent for R

    Solar density increase factor:
    (M2/M1)*(R1/R2)^3 = 0.4*1.30*10^6
    = 5.2*10^5

    Currently, the sun's density is 1.4 times that of water: 1.4 g/cm3.
    It will become nearly 1 million times more dense as a white dwarf.

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