Expert: Tom Whiting - 8/11/2009

Question
What are neutron stars? Is sun a neutron star? How many types of stars are there in our universe?

Answer
Hi Shameem,
The sun is not a neutron star...it is a common garden variety, normal, average Main Sequence star about 865,000 miles in diameter, composed mainly of hydrogen, helium, and other minor elements.  It produces energy by fusing hydrogen nuclei to helium nuclei in it's hot core.

A neutron star is about 10 miles in diameter, and is the result of core compression of a massive star going supernova. The pressure combines electrons and protons to form a big neutron ball about 10 miles across and very hot.  It does not generate any internal energy but enters a cooling state which takes millions of years to cool down to a small but massive black star.
It is the last stopping stage of core collapse during a supernova before the core becomes a black hole, which would be the last, and final step, in core compression.  If it happens to be a fast rotating body, giving off beams of energy, then we call the neutron star a pulsar, but it's still a neutron star.

Types of stars?  Oh, let's see...we have normal main sequence stars like the sun, white dwarfs, red giants, red supergiants, blue giants, blue white supergiants, red dwarfs (the most common star), neutron stars, brown dwarfs (bodies that just didn't quite make it to a full-fledged star-not enough mass, also called infrared stars), black holes, and different combinations of same, like variable stars, (many different families of variable stars, in fact), double/multiple stars, red carbon stars, spectroscopic binary stars...there may be other types we're not yet aware of like magnetic stars.
Some astronomers have even theorized the existence of quark stars. So right now we just don't know everything yet.  But at least that's pretty much the listing that we have now, that I can think of from memory.
Hope this helps,
Clear Skies,
Tom Whiting
Erie PA

FOLLOW UP:
And don't forget that tonight is the magical night of August 11th, the Perseids reach their
maximum intensity of 60-200 meteors per hour after midnight local time, with 1/4 strength
tomorrow night.
Clear skies,
Tom