The Hubble telescope has taken some distant pictures of star formation. My very basic explanation is below. Follow the link for Alan Boyle’s description of the science behind this new image.
Just as each of us is in the centre of our own personal observable universe, so our earth is in the centre of astronomy’s observable universe. Light travels 186,000 miles per second. The light from our home star, the sun, takes about 9.3 minutes to reach us. The light reflected from planets takes several hours. The light from Alpha Centauri, the next nearest star, takes 4.2 years. So, when we look at distant galaxies, we are effectively looking back in time, at younger and younger objects. Thus, powerful telescopes enable us to see developments of stars and galaxies at different times in the past. Galaxy M83 is 15 million light-years away, so we are seeing it as it was 15 million years ago; and we can’t see it any older.
If we look far enough, we can see first-generation stars. The big bang, a sudden expansion of space-time, produced almost entirely hydrogen and helium, the two lightest atoms. Stars burn by fusion, joining nuclei to release energy and creating heavier atoms. They can continue until they get to iron, which has the lowest-energy nucleus. Creating heavier atoms would use up energy. After it creates iron, a sun’s nuclear fires burn down. Without the energy of fusion to keep it hot, the star collapses inwards because of its own gravity. The energy from gravity smashes iron atoms together and creates heavier atoms.
That’s how we know our sun is a second-generation star: our solar system contains heavier atoms than iron. The atoms in our body have already been through one star’s furnace.