the hottest stars

[ispom]

todays APOD shows the bug nebula,
http://antwrp.gsfc.nasa.gov/apod/ap070429.html

a planetary whose central star is 250,000 degrees Celsius hot (surface temperature),

what is the hottest stellar surface temperature? May be 1 million degrees?

[[1ponders]]

If you are talking about main sequence stars on the Hertzsprung-Russell diagram then 50,000k is about the hottest surface. Degenerate stars like White Dwarfs come next (250,000 K + ) and then neutron stars upwards of 3.5 million K.

This isn't taking into account core temperatures.

[ispom]

well Paul,
so the star inside the planetary is a white dwarf of course...
I see: there is a gap in temperatures between main sequence stars and white dwarfs, no stars with surface temperatures of 100,000 degrees possible,
right?

[[1ponders]]

Yes and no. The white dwarfs will eventually cool off (passing the 100,000 mark on the way down) to form black dwarfs, but the Universe isn't old enough yet for black dwarf to have occurred.