Why we connot observe H2 which existe in the galaxies?

Answer 1

The other answers are all incorrect. Eri's answer about a 21 cm line is for ATOMIC hydrogen, not H2.

The actual reason the H2 is difficult to observe is that it does not have good microwave emission lines. It has collisionally excited infrared lines but these are so-called 'forbidden" transitions that occur only in a very low density range. (They can be seen in planetary and star formation nebulae.)

H2 is almost always found in molecular clouds and planetary nebulae that also have an abundance of CO. CO has a bunch of good microwave and millimeter emission lines, so you can use it as a tracer of H2.

Answer 2

H2 is basically neutral, so theoretically it would be hard to observe since it has a 1/2 chance of making a transition every million years. However, there is so much of it out there that it's actually not hard to detect using radio telescopes and observing in the 21 cm band. It's a spin-flip transition that we're observing, known as a 'forbidden' transition because it happens so rarely. But it happens quite often if you have trillions of atoms.

Answer 3

If a mass under goes a nuclear reaction it is possible to observes the light spectrum of the radiation emmited.. Hence if we know the spectrum paterns of materials ,it can be determined what kind of materials mass structures exist in the galaxy.

Answer 4

F2 94G which existe in galaxies too! Then it was said they connot! (But I think, we observe it con)!

Answer 5

I think you may be confused.

We can...

http://en.wikipedia.org/wiki/Hydrogen_line