How scientists look for anti-matter?

Question

If matter and anti-matter look exactly the same, then how can scientists look for anti matter from a distance (other galaxies)?

Answer 1

Generally what's looked for is the radiation from matter-antimatter annihilation.

When matter and antimatter get close enough to interact, they can produce gamma rays of specific energies. If you have a region that's full of antimatter and another region that's full of ordinary matter, then you'll see a bunch of gamma rays being produced at the boundary between those two regions. Space-based gamma-ray telescopes are sensitive to this kind of radiation, and we generally don't see such a boundary anywhere.