Towards the beginning
Ken Tapping, 15th March, 2016
When we look at something 1 km away, we see it as it was a little over 3 millionths of a second ago. That is how long the light we are seeing took to get from the object to our eyes. For our everyday lives, such small delays are unimportant; we need precision devices even to detect them. When we get out into space, that transit delay becomes more obvious. Light takes about one and a quarter seconds to cover the distance between here and the Moon. Apollo astronauts left laser reflectors on the lunar surface, making it easy to measure the Earth-Moon distance with great precision. We see the Sun as it was 8.3 minutes ago. When we look at the bright star Sirius, flashing in the southern sky in the evening at the moment, we see it as it was 8.6 years ago. We are essentially looking back in time. Kilometres are inconvenient units for looking at such distant objects. One of the units we use is the Light Year. This is the distance light travels in a year: 9,460,700,000,000 km. When we look at a galaxy a billion light years away we are looking back in time a billion years.
We are pretty sure the universe started as something hot, dense and very small 13.8 billion years ago, so we are studying more and more distant objects as a means of looking back into the youth of the universe. At the moment the most ancient and distant thing we can see is the Cosmic Microwave Background, which was generated about 380,000 years after the beginning. In that radiation we can see the irregularities that we believe to be the first stirrings in the formation of the first stars and galaxies.
We want to bridge the gap between the galaxies we see around us today and those first stirrings, so the quest has been to use our steadily improving radio and optical telescopes to detect more and more distant objects. The latest has just been spotted by the Hubble Space Telescope. It is very faint, and lies 13.4 billion light years away, so we see it as it was 13.4 billion years ago. That is only 400 million years after the beginning. Unfortunately seeing this galaxy involved pushing the Hubble to its sensitivity limit. Luckily the Hubble's successor, the James Webb Telescope is coming along, and is scheduled for launch in 2018. When it goes into action, we hope to see more of what is going on. The point in the universe's history when the cosmic microwave background was formed marks the point where things had cooled enough for hydrogen atoms to form. Then, some currently unknown time later, the first galaxies and stars were born. We believe those first generations of stars were big, blue and very bright. They would have enjoyed short, eventful lives, ending by blowing themselves up. In their process of energy production, they used hydrogen as fuel, and produced all the other elements as waste products. After a few generations of these stars, the material filling the universe was enriched with everything needed to make planets – and people.
There are stars like this forming in our and other galaxies today, living their short lives and blowing up. However, most of the stars around us are smaller, less bright and last a lot longer; the Sun is a good example. What proportion of blue supergiants (or even super-supergiants) occurs in the galaxies back closer to the beginning? When we do get a better look at that ancient galaxy, known as GN-z11, what sort of stars will we see? When did the first galaxies form? We now know that at least one galaxy existed a mere 400 million years after the beginning. Are there other, even older ones out there for us to find?
At 9:30 pm PDT on 19 March, or 12:30am EDT on 20 March, the Sun will cross the equator heading north, marking the spring equinox. From then on, until the autumn equinox, we will have more than 12 hours between sunrise and sunset.
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