Incromphensibly large. The first Gen star is the blue one on the bottom.
The first stars are called Population III stars, and they were made of only hydrogen, helium and a bit of lithium.
That's because those were the only elements around right after the Big Bang.
All the other stuff we have now, like carbon, oxygen, iron and so on, they were cooked up inside the stars and then blown out into space when they exploded.
Now, because the first stars had no metals (that's what astronomers call anything heavier than helium), they had a harder time cooling down.
Cooling is important for star formation, because it allows the gas to clump together and collapse under gravity.
Without metals, the gas stayed hot and puffy, so only the most massive clumps could form stars. And I mean massive. Like, hundreds or even thousands of times the mass of our sun.
These stars were so big that they burned very brightly and very fast. They only lived for a few million years, which is nothing compared to the billions of years that stars like our sun can last.
And when they died, they went out with a bang. A huge bang. A supernova that was so powerful that it could rip apart the star completely and leave no remnant behind.
These explosions were the first sources of light in the universe, and they also seeded the cosmos with the first metals.
So how do we know all this?
Well, we haven't actually seen any of these stars yet, because they are too faint and too far away.
But we have some clues from looking at distant galaxies that formed soon after the first stars.
The Very Large Telescope
We can use telescopes like Hubble, Spitzer, and the Very Large Telescope to study these galaxies and see what kind of stars they have.
And guess what? We don't see any signs of Population III stars in these galaxies, which means they must have formed earlier than we thought.
Some scientists think that the first stars formed in dark matter halos, which are clumps of invisible matter that make up most of the mass in the universe.
Dark matter could have helped the gas to collapse and form stars faster than normal. And some scientists think that there might have been a special kind of star that was powered by dark matter instead of nuclear fusion.
These are called dark stars, and they could have been even bigger and longer-lived than normal Population III stars.
So there you have it. The first stars in the universe were ginormous beasts that lit up the dark ages and changed the course of cosmic history.
