The heavy elements made in the core of these stars are recycled, and spit out throughout the galaxy. Some are even big enough to cause hypernovae and gamma-ray bursts, the most powerful events in the known Universe. Very quickly, many of these stars run out of fuel, and die in tremendous explosions known as supernovae. In the densest areas, after tens of millions of years, the hydrogen and helium gas become dense enough that - for the first time - nuclear fusion occurs. That tiny fraction of the Universe, billions of years later, would become our local group, with our Milky Way, Andromeda, and (initially) with hundreds of satellite galaxies and many thousands of globular clusters. Most of the neutral atoms in the Universe now start gravitationally collapsing, including in one tiny corner of the Universe less than one-trillionth of its size in volume. It isn't until much more expanding and cooling - to the tune of 380,000 years - that the nuclei and electrons can come together to make neutral atoms, which they all do. This makes hydrogen and helium nuclei, bathed in a sea of free electrons and billions and billions of ultra-hot photons. But the Universe was also expanding and cooling, and by time the Universe is 3 or 4 minutes old, the protons and neutrons can fuse into heavier elements without getting blasted apart by the photons.
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When the Universe was about one second old, it was very, very hot (many billions of degrees), and full of free protons, neutrons, and electrons, in addition to more than a billion photons for each proton. Not only can you check out the photo gallery from last year's Perseids, here's a long-exposure photo with a fisheye lens of a meteor shower over the course of a couple of hours.īut where do meteor showers come from in the first place? I've been asked to start at the beginning, so let's go all the way back to the early stages of the Big Bang.
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