The Universe’s Darkest Hour

"These stars we're travelling past, were they all made in the Big Bang?"

Not at all, the stars you can see now were born well after that. Even though all the matter in the universe was made in the Big Bang, it's been rearranged a few times since them. New stars are being created all the time in space from clouds of gas and space dust. Some of this dust has been here since the Big Bang and the rest is the leftovers from stars that have long since exploded.

"How can a star form out of just gas and dust in the middle of space?"

It all comes back to gravity. After the Big Bang, all the matter started to spread out in all directions. If all the matter spread too evenly then the universe would have just got thinner and thinner and fizzled into nothing; no stars, no galaxies. On Earth they talk about the dark ages lasting from the end of the Roman empire to the time when Europe became civilised again. That was only about 500 years. After the Big Bang, the Universe was dark for 150 million years. Not a single star and no light. Total darkness.

“No stars for 150 million years? Are you serious?”

Absolutely. But remember those microwave ripples formed by the Big Bang? Well, luckily for us, they showed that the universe just after the Big Bang was lumpy. From these microwave ripples scientists at NASA have worked out the lumpiness of the universe 300,000 years after the Big Bang. Look here is a picture of the lumpiness of the universe in terms of temperature back then. The yellow and red bits are hot and the blue bits are cold.


"Why are lumps lucky for us?"

Because without the lumps, there wouldn't be any stars and without our star we wouldn't be here. For gravity to be able to collect matter together into stars there needs to be a few irregularities or lumps. The bigger you are the more gravitational pull you have. So it takes one lump of matter in the centre, or anywhere, to start slowly pulling in other smaller pieces of matter. The central lump then starts getting bigger and bigger and so its gravity gets stronger and stronger. The whole process speeds up with more and more atoms being pulled into a big ball.

“So why did it take 150 million years to make a star?”

Because the ripples were very small so the first lumps didn’t contain much and it took ages for gravity to pull in enough gas to make a star.

"And what exactly is in these balls?"

Three quarters of it would have been hydrogen, remember that's the simplest and smallest type of atom. Nearly all the rest was Helium which is the next smallest. Between them, hydrogen and helium make up most of the universe. As these balls of gas got pulled together by gravity, they got hotter and hotter like I explained before. Now hot things glow, but gravity alone will not make hydrogen glow as brightly as a star. When they get really hot, the hydrogen inside starts combining with itself by nuclear fusion reactions and ....carrummmph..... there you have it.

"Have what exactly?"

A fully fledged star using nuclear fusion energy to shine for millions or billions of years.

“How can we know how stars were made billions of years ago?”

Because we can see it happening today.

“Where”

The easiest place to see where stars are being born is in the constellation Orion, the hunter. That’s one of the easiest constellations to see. It has a belt of three stars, just below the belt is what looks like a hazy area. That is a massive cloud of dust and gas where stars are being made as we speak. It looks like tiny fuzzy blob when you look up at Orion at night but it is huge, 30 light years across. With the Hubble telescope, scientists have even seen new stars with discs of gas around them. Look this picture taken about ten years ago. Those fuzzy beige blobs are stars being born surrounded by swirling discs of dust that one day may become planets.


“Albert, how can you know about all this stuff that happened after you died, like the Hubble telescope?”

Well, when I was rebuilt in this computer system I found I could roam about cyberspace catching up on all the science I missed out on by dying. What do you think I do when I’m not talking to you?

“Be careful there is a lot of rubbish out there on the Internet too.”

Sparks of brilliance and generosity in a sea of dross and unpleasantness.

“Is that one of your famous quotes?”

No, I just made that one up. But it sums up the Internet pretty well don’t you think?