But it could have been quite different in the very early universe. In fact, a recent study says that the earliest stars could have been gigantic but invisible.

The study was led by Paolo Gondolo of the University of Utah. It found that the first stars in the universe might have been kept dark by dark matter -- matter that produces no energy, but that exerts a gravitational pull on the normal matter around it.

Stars are born when giant clouds of gas collapse. When the gas gets packed tightly enough, it ignites the fires of nuclear fusion, and the star shines brightly.

But conditions in the first few hundred million years after the Big Bang were quite different. The universe was much smaller, so everything was packed tighter. As stars began to form, they contained high concentrations of dark matter.