The energetic ultraviolet light from these first stars was capable of splitting hydrogen atoms back into electrons and protons (or ionizing them). Theory predicts that the first stars were 30 to 300 times as massive as our Sun and millions of times as bright, burning for only a few million years before exploding as supernovae. Illustration of the Timeline of the Universe.Īnother change occurred after the first stars started to form. When the first stars formed, it ended the dark ages, and started the next epoch in our universe.
Following this are the cosmic dark ages - a period of time after the Universe became transparent but before the first stars formed. This is what we see as the Cosmic Microwave Background today with satellites like the Cosmic Microwave Background Explorer (COBE) and the Wilkinson Microwave Anisotropy Probe (WMAP).
"The era of recombination" is the earliest point in our cosmic history to which we can look back with any form of light.
#FIRST LITE FREE#
Now that the free electrons were bound to protons, light was no longer being impeded. Light had formerly been stopped from traveling freely because it would frequently scatter off the free electrons. The Universe went from being opaque to transparent at this point. This process of particles pairing up is called "Recombination" and it occurred approximately 240,000 to 300,000 years after the Big Bang. Ultimately the composition of the universe at this point was 3 times more hydrogen than helium with just trace amounts of other light elements. These ionized atoms of hydrogen and helium attracted electrons turning them into neutral atoms. When the universe started cooling, the protons and neutrons began combining into ionized atoms of hydrogen and deuterium. There were no stars, and there were no galaxies.Īfter the Big Bang, the universe was like a hot soup of particles (i.e. Until around a few hundred million years or so after the Big Bang, the universe was a very dark place. To study reionization, high resolution near-infrared spectroscopy will be needed. To find the first galaxies, Webb will make ultra-deep near-infrared surveys of the Universe, and follow up with low-resolution spectroscopy and mid-infrared photometry (the measurement of the intensity of an astronomical object's electromagnetic radiation).
stars that fused the existing hydrogen atoms into more helium) looked like, and exactly when these first stars formed is not known. Exactly what the universe's first light (ie. The universe was no longer opaque! However, it would still be some time (perhaps up to a few hundred million years post-Big Bang!) before the first sources of light would start to form, ending the cosmic dark ages. These ionized atoms of hydrogen and helium attracted electrons, turning them into neutral atoms - which allowed light to travel freely for the first time, since this light was no longer scattering off free electrons. When the universe started cooling, the protons and neutrons began combining into ionized atoms of hydrogen (and eventually some helium). The Early UniverseĪfter the Big Bang, the universe was like a hot soup of particles (i.e. In fact the universe was a pretty dark place. But at that point there were no stars and galaxies. we haven't yet! The microwave COBE and WMAP satellites saw the heat signature left by the Big Bang about 380,000 years after it occurred. Why is a powerful infrared observatory key to seeing the first stars and galaxies that formed in the universe? Why do we even want to see the first stars and galaxies that formed? One reason is. Webb will be able to see back to when the first bright objects (stars and galaxies) were forming in the early universe.