Read | Telescope or time machine?
by Adam Richardson
Header image credit: ESA
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Families and adults
The James Webb Space Telescope can see back to some of the earliest galaxies to ever form. But how can that be? Surely telescopes are for studying the night sky, not the history of the Universe?
To understand how we use telescopes today to piece together distant yesterdays, let's start a little closer to home.
Seeing the past
Have you ever counted the gap between a flash of lightning and crack of thunder during a storm? It’s a great trick for guessing how far away lightning has struck. It works like this - both the flash and the thunder are created at the same time as the lightning strikes the earth but the light travels much faster than the sound. This means that the further away you are from the lightning, the longer the gap between the two (count the number of seconds and divide by 3 gives you a rough idea of the distance in km). By the time the sound reaches you, the flash of lightning that created it is in the past!
Credit: Mathias Krumbholz, CC BY-SA 3.0, via Wikimedia Commons
The speed of light is very fast and the distances on Earth are relatively small so when we see the flash of lightning it appears to be instant. Move away from our home planet a little and the picture quickly changes.
“When we look further away the light takes longer to reach us as it has further to travel” explains Hattie Stewart, an astrophysicist studying the early universe at University of Bristol. “For example, it takes around 8 minutes for light to travel from the Sun to us. This means that when we look at the Sun, we are observing it as it was 8 minutes in the past.”
So, when astronomers look into space, they’re not just observing space, they’re observing it as it was minutes, years or even billions of years in past. Powerful telescopes, both in space and on Earth, can provide a window to the early universe. What secrets might they reveal?
What does the outside of our solar system look like?
Credit: NASA, ESA, and G. Bacon (STScI)
The most distant human-made objects are the Voyager 1 & 2 probes that left our solar system in 2012 and 2018 respectively. Voyager 1 is currently around 22.6 Light-hours away from Earth. In other words, it takes light 22.6 hours to travel that distance.
If you look up in the night sky on a winter evening you might see Sirius - the brightest star in the night sky. Despite being one of our closest stellar neighbours, it takes 8 years for the light to reach us! My daughter is 7 years old, when she looks at Sirius, she’s seeing it as it was before she was born!
Using telescopes, we can see much further into space and the further into space we look, the further into the past we look. The Hubble Space Telescope launched in 1990 and sits in orbit around the Earth. From up there, above the atmosphere of the Earth, it’s able to see not just outside our solar system but beyond our galaxy into deep space.
“The Hubble Space Telescope can allow us to see back to around 1 billion years after the Big Bang" Hattie explains, “it can observe galaxy evolution of infant galaxies.”
In 1995 a group of astronomers used Hubble to gaze at a small piece of sky about the size of a tennis ball over the course of 10 days. Hattie chose the resulting image as one of her favourites. “By taking a long exposure, we are able to see much more than can be seen by the naked eye… It’s an amazing image that shows how rich and varied the Universe is.”
Hubble is not the only space telescope to tell us things about the early universe. 2009 saw the launch of Planck Telescope. It told us about the moments shortly after the Big Bang and gave us our most accurate estimate of the age of the Universe so far, 13.8 billion years! That’s a lot of birthday parties…
Credit: NASA GSFC/CIL/Adriana Manrique Gutierrez
25th December 2021 saw the launch of the James Webb Space Telescope. This telescope is incredibly exciting as it’s able to see even further back than Hubble due to its ability to explore the universe in infrared – the colour of heat!
“Looking at the Universe with an optical telescope is like looking through a filter” explained Hattie. “Although [Hubble] has an infrared camera … the James Webb Space Telescope [is] able to observe a broader range of wavelengths." Also, the mirror on Webb is 100 times more sensitive than Hubble.
To get the best infrared signal possible, Webb has been sent much further away from the earth than Hubble, around 1.5 million kilometres. It also has a huge sunshield to block the heat from the sun. The side of the telescope facing the sun reaches temperatures of around 110c but the side facing away operates at around -234c – that’s only 39c above absolute zero! This is a perfect place to look for infrared light without noise and interference.
But why go to all this trouble to see infrared light? Hattie explains, “light that was emitted in the optical or ultra-violet band might be observed in infrared when it reaches us” - this is due to the way that light is stretched as it travels through our expanding universe. “This means that Webb [is] able to look even further back in time than Hubble and tell us about the very first galaxies in the Universe.”
On July 11th 2022 the first image to be created by Webb was revealed. Webb's First Deep Field is a picture of a galaxy cluster called SMACS 0723. The image is roughly the size of a grain of sand held at arm’s length and yet thousands of galaxies are visible. It's the highest resolution image of the early Universe ever taken. Some of these galaxies are as old as 13 billion years.
Credit: NASA, ESA, CSA, and STScl
Just one piece of the puzzle
So, is Webb the only way to build up a picture of the past? Hattie’s own area of work focuses on a telescope which is still under construction here on Earth - the Square Kilometre Array or SKA for short. Despite being on earth, this is still a huge engineering challenge. The SKA is planned for two sites, one in Australia and one in South Africa - it’s made up not of one huge telescope like Webb but of many antennae working together. The Australia site alone will have 130,000 individual antennae spread across 512 stations which is why Hattie’s work is focused on how to deal with the expected 1TB of data per second that will be collected by the SKA.
Credit: SPDO/TDP/DRAO/Swinburne Astronomy Productions, CC BY 3.0, via Wikimedia Commons
“A key science goal of the SKA is to observe Neutral Hydrogen in the early Universe.” To do this the SKA uses yet another frequency of light – radio waves. Looking at this Neutral Hydrogen is a way of mapping out the impact of the very first light sources in the universe. “In combination with the data from [Webb] and … the Planck telescope we can hope to observe the evolution of the early Universe at multiple wavelengths.” Slowly, piece by piece we can build a cosmic jigsaw which will bring us closer to understanding the origins of the universe.
Sadly, we’ll have to wait until at least 2023 before the first phase of the SKA is ready for use with the completion of both sites not expected before 2030. In the meantime, researchers continue to use Webb to gaze back through time. Who knows what secrets will soon be revealed?
Thanks to Hattie Stewart for her contributions to this article. Hattie is a PhD student in Artificial Intelligence, Machine Learning and Advanced Computing in the field of High Energy Astrophysics and Radio Astronomy at the University of Bristol. A massive thanks to the Year 6 pupils at Hareclive E-Act Academy whose ideas, questions and prototypes have inspired this article as part of our Hareclive in Space project.
This article was inspired by the question, 'What is on the outside of our solar system?' and by the amazing cardboard prototypes of telescopes and time machines created by the Hareclive pupils.