Happy Sunday, everyone! Considerably later than promised (Science Gremlin hangs his head in shame), here is the first Astrophysics post of this blog. Enjoy!
To quote Douglas Adams’ ‘The Hitchhiker’s Guide To The Galaxy’, “Space…is big. Really big. You just won’t believe how vastly, hugely, mindbogglingly big it is”. This is absolutely true yet, this week, an international group of scientists reported their use of the latest imaging technology to calculate the age of a selection of incredibly distant galaxies. Their report fascinated me so I decided to learn about the science behind it and share it with you.
We can see planets, stars and galaxies because of the light energy they emit or reflect. Yet light from our own Sun takes roughly 8 minutes to reach Earth, which means that, by the time we see the Sun, it’s already 8 minutes older than it looks. So, imagine the effect this delay has upon our observations of objects halfway across the known universe. By the time we’ve seen another galaxy’s sun it could have died; by the time we know what materials a galaxy consists of its composition could have drastically changed. In other words, astronomers looking at distant galaxies are effectively looking into the past.
Astrophysicists can work out roughly how old the bodies that they see are by measuring how far away they are from us. In the world of astrophysics this is a relatively simple calculation. However, in some cases, it is complicated considerably by the fact that, ever since the Big Bang, our universe has been expanding, rather like a pond into which a bucket of sand is dropped. After the initial eruption as the bucket hits the pond, ripples carry the water and the sand now suspended in it farther and farther away from the bucket. In much the same way, the matter and energy that makes up the universe is spreading out as the space in which it is contained moves outwards like the pond’s water.
Now, remember that because here comes the tricky part…
Light travels in waves, very much like sound. The number of these waves that reach the observer in a given time is dubbed the ‘frequency’. As with sound waves, the frequency of light waves changes when the object being observed is moving to or from the observer. In the case of sound waves, this is called the ‘Doppler Effect’. We’ve all experienced this at some point when a police car or ambulance drives past us with its siren blaring. The pitch of the siren changes as the vehicle passes. This is because the wave frequency increases the closer the vehicle gets to us, raising the pitch. As the vehicle drives away, the pitch lowers, as the frequency decreases.
In the case of light waves, objects that can be seen with the naked eye that are moving farther away from the observer appear to move closer to the red end of the light spectrum as the wave frequency decreases. However, not all frequencies of light energy are visible. As we look at frequencies even lower than the visible spectrum, we move into infrared light energy, which is not visible to the human eye. To see such light, special equipment is required, such as that used by the research group I mentioned earlier.
So, remember we said that the universe is expanding? Well, galactic bodies in the regions of space that are still expanding are, as a result, moving away from Earth. This means that the frequency of the light waves coming from these bodies is reducing towards the red end of the light spectrum. Galaxies that fall into this category are referred to as being at ‘Redshift’; that is, they are shifting towards the low end of the light spectrum, thus appearing to be red or invisible to the naked eye. Scientists can use the level of redshift exhibited by a distant galaxy to compensate for the fact that it is moving away from us and work out how old it is.
Over the past 10 years, this knowledge has enabled us to learn fascinating things about the formative millennia of our universe. For example, stars and planetary bodies are formed from the myriad of gases and molecules making up young galaxies. Sometimes, galaxies output stars at a phenomenal rate, temporarily using up far more of their matter and energy than a galaxy would usually. It had been assumed that these ‘Starburst’ galaxies did not exist for a very long time after the Big Bang, requiring time to build up the materials and density necessary to enable such a high output. However, using the theories described in this post, scientists have been able to estimate that more of them existed than we knew about. Fascinatingly, the most recent findings suggest that many of them existed only 1 billion years after the Big Bang. Given that the universe is 13.77 billion years old now and still growing and producing new stars and planets, one can see why the scientific community is so excited to learn that this was happening when the universe was so relatively young.
Seeing how much we’ve learned in so little time, one can only imagine what amazing discoveries we’ll make about our universe in the future. Especially exciting is the prospect of developing increasingly powerful telescopes that can see even farther into the vastness of space and so, even further into the past. We can already see what some regions of space looked like when the universe was only 1 billion years old…what comes next?
- Antarctica Telescope Reveals Starburst Galaxies of the Early Universe (dailygalaxy.com)
- Galaxies produced stars shortly after Big Bang (slashgear.com)
- Galaxies ‘Birthed’ Stars Shortly After Big Bang: New Telescope Reveals Unprecedented Detail (scienceworldreport.com)