Re: What is the hottest star or asteroid in the universe?

Asteroids are small cold chunks of rock and iron that orbit the Sun much like tiny planets.  As they get their heat from the Sun , unless they are crashing into the Sun or the atmosphere of a planet, their temperatures will be quite cold, lower than about -200 deg C.

Stars on the other hand produce their own heat by nuclear fusion.  Inside stars the temperatures reach several millions of degrees.  Astronomers define the temperature of a star as the effective temperature of a black body radiating the same energy per unit area.  The hottest stars are the blue white O type stars with temperatures in excess of 20,000 deg K.  Which star is the hottest in the Universe is kind of hard to answer.  The stars in other galaxies are too far away to be identified individually so we need to stick to the stars in the Milky Way.  Many of those stars are too far away for you to see with out fairly sophisticated telescopes, so I'll just give you one you can find for yourself.  Bellatrix, the other shoulder in Orion, is one of the hottest stars we can see with the naked eye with an effective temperature of about 30,000 deg K.

Mike Francis