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Why is Sirius B hotter than Sirius A?
Hi
Sirius B, a white dwarf, has a surface temperature of around 25,000 degrees C. Sirius A, a blue/white main sequence star has a surface temperature of around 12,000 degrees C. Usually the bluer a star is, the hotter it is. Just wondered why it's not the case here. |
#2
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"me" wrote in
. uk: Hi Sirius B, a white dwarf, has a surface temperature of around 25,000 degrees C. Sirius A, a blue/white main sequence star has a surface temperature of around 12,000 degrees C. Usually the bluer a star is, the hotter it is. Just wondered why it's not the case here. The term white dwarf is just a name to distinguish from red dwarf. The spectra of Sirius B versus A is just as expected by the surface temperature difference. Note that white dwarf's are slowly cooling down as they have no internal source of energy production. K. |
#3
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me wrote:
Hi Sirius B, a white dwarf, has a surface temperature of around 25,000 degrees C. Sirius A, a blue/white main sequence star has a surface temperature of around 12,000 degrees C. Usually the bluer a star is, the hotter it is. Just wondered why it's not the case here. Essentially, you have answered your own question, assuming you know what a white dwarf is supposed to be. A white dwarf is supposed to be the core of a now dead star, a low mass type like our Sun. As the core of a star, they simply retain the heat from those nuclear fusion processes that were proceeding prior to the end of the star's life. Now, heat stored within them, they simply radiate that heat, lowering their temperature eventually to absolute zero over 10s and possibly 100s of billions of years. And, since they are not generating their own energy but simply radiating stored energy, comparisons of their color to that of stars is comparing apples to oranges. |
#4
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"J. Scott Miller" wrote in message ... me wrote: Hi Sirius B, a white dwarf, has a surface temperature of around 25,000 degrees C. Sirius A, a blue/white main sequence star has a surface temperature of around 12,000 degrees C. Usually the bluer a star is, the hotter it is. Just wondered why it's not the case here. Essentially, you have answered your own question, assuming you know what a white dwarf is supposed to be. A white dwarf is supposed to be the core of a now dead star, a low mass type like our Sun. As the core of a star, they simply retain the heat from those nuclear fusion processes that were proceeding prior to the end of the star's life. Now, heat stored within them, they simply radiate that heat, lowering their temperature eventually to absolute zero over 10s and possibly 100s of billions of years. And, since they are not generating their own energy but simply radiating stored energy, comparisons of their color to that of stars is comparing apples to oranges. So what, they don't emit standard black-body radiation? |
#5
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me wrote:
Hi Sirius B, a white dwarf, has a surface temperature of around 25,000 degrees C. Sirius A, a blue/white main sequence star has a surface temperature of around 12,000 degrees C. Usually the bluer a star is, the hotter it is. Just wondered why it's not the case here. A and B type stars (in the Hertzprung-Russell diagram), and white dwarf stars, have a white to a blue-white color appearance. I think this is because the Planck radiation curve peak is broad at those temperatures and it causes a mixing of colors that we see as looking like white or blue-white ... this is my opinion ... I've looked for a definitive reference but have not found it yet ... Al |
#6
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"me" wrote in message . uk... Hi Sirius B, a white dwarf, has a surface temperature of around 25,000 degrees C. Sirius A, a blue/white main sequence star has a surface temperature of around 12,000 degrees C. Usually the bluer a star is, the hotter it is. Just wondered why it's not the case here. Why do you say Sirius B is less blue than Sirius A? |
#7
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me wrote:
Hi Sirius B, a white dwarf, has a surface temperature of around 25,000 degrees C. Sirius A, a blue/white main sequence star has a surface temperature of around 12,000 degrees C. Usually the bluer a star is, the hotter it is. Just wondered why it's not the case here. A very nice web site where you can study the color of stars is the Sloan Digital Sky Survey site: http://cas.sdss.org/dr3/en/proj/advanced/color/ |
#8
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Peter Webb wrote:
So what, they don't emit standard black-body radiation? More likely a better representation of a blackbody curve than that of a star, as a star's spectrum is littered with spectral lines. But to see it appear bluish white it must also release enough light from its surface to trigger the color receptors in our eyes, and they can't do that because of their small surface area. |
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