Re: How small can stars get?

Actually, stars do not get very small. Here is the standard definition of a star: a ball of gas held together by its own gravity which uses nuclear fusion reactions to shine. Fusion occurs only under the extremely high pressures and temperatures found at the centers of stars. But the star must be very massive to provide enough self-gravitational attraction leading to high temperature and pressure. The smallest star you could have like this is one-tenth the mass of our Sun -- this is still 100,000 times the mass of Earth!

One could extend the definition of stars to include white dwarfs, neutron stars and black holes as well, since these are the "dying embers" of the gaseous star that once was. White dwarfs are about the size of the Earth, but their mass is still enormously greater. You couldn't break off a piece and put it in a jar, because it would immediately explode because its gravity wouldn't hold it together. The same thing would occur with a neutron star. A black hole wouldn't do this, but it would fall right through your jar, making a hole on its way down to the center of the Earth.

If you really want a piece of a star, all you need is a jar of hydrogen and helium (like the Hindenburg, with helium). Same material, just much colder.

Of course, you could find another way to artifically increase the pressure and temperature -- maybe with a magnetic field. This is the idea behind fusion reactors -- make a "star" in a magnetic bottle. So in principle, you could have a star in a bottle, although it would take a lot more technology than we now have (and it wouldn't be a natural star).

-Aaron