One of the main purposes of the James Webb Space Telescope (JWST) is to probe the most distant reaches of the universe to see how the first galaxies formed, and when.
The observational results are now rolling in, and they are not exactly as expected. We see new research directions opening up. Our ability to do a project like this depends on one big thing. We need to know how far away the earliest galaxies are, because looking across those huge cosmic distances means seeing far back in time, into the youth of the universe.
When we look at something 300 metres away, we see it as it was a millionth of a second ago. That is how long light takes to cover that distance. This is nothing much, but as we look out into space beyond the Earth, the time needed for the light from an object to reach us becomes significant.
We see the Moon as it was about one and a quarter seconds ago, and the Sun as it was 8.6 minutes ago. Then the numbers start getting large. Proxima Centauri, the nearest star after the Sun, lies 4.3 light years away, which means we see it as it was 4.3 light years ago. Light from the Andromeda Galaxy takes some 2.5 million years to get here. Our quest for the first galaxies takes us billions of light years away. This means we are looking billions of years back in time.
The universe is expanding, at a rate that increases with distance. Galaxies a million light years away are receding from us at around 230 kilometres per second. Those a billion light years away are flying away from us at around 230,000 kilometres per second. Thirteen billion light years away, close to the beginning of the universe, and that recession velocity reaches almost three million kilometres per second.
Therefore, by measuring how fast galaxies are flying away from us, we can estimate their distances. There is another way. There is a class of variable star called cepheids, which cycle in brightness at a rate connected to their brightness. If we can spot a cepheid, we can measure how long it takes to cycle in brightness, estimate how luminous it is, measure how bright it looks from here on Earth, and calculate how far away it is.
So, if possible, we search distant galaxies for cepheids.
Until the JWST our idea was that the universe began some 13.7 billion years ago, in an event that has become known as the Big Bang. It cooled to the point it became transparent around 380,000 years later. When we look at the radiation from that time, known as the cosmic microwave background radiation, we can see the first clumpings of material that would eventually become galaxies.
On the basis of our ideas about galaxy formation, we thought we would be able to observe young galaxies forming some billion years or so after the Big Bang. That seems to be wrong. The JWST has found young galaxies were present around only 200 million years after the Big Bang.
These galaxies are clumpy, still in the process of pulling themselves into shape and assimilating other galaxies, which is how galaxies grow. They are producing stars at a horrendous rate. These bright, short-lived stars are the sources of the elements needed to make planets, and us. Before these stars formed there was only hydrogen and helium, which is great for making stars but not much else. We see this enrichment process taking place a lot earlier than we expected.
Explaining the presence of galaxies that soon after the Big Bang will require some changes to our ideas as to how galaxies form. Also, if the production of the elements necessary for planets and life got going earlier, life could have appeared in the universe sooner than expected. Our Solar System has only been around for a mere 4.5 billion years. There could be beings out there who are a lot older and wiser than we are. Here's hoping.
• Saturn rises soon after sunset, with Jupiter following three hours later.
• The Moon will reach its last quarter on Aug. 8 and will be new on Aug. 16.
Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory near Penticton.
This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.