Orbiting the Sun a million miles from Earth, the James Webb Space Telescope has begun flipping through the back pages of cosmic history. Before long, it could reach the very start. The beginning of everything.
The $10 billion instrument – which only became operational a few months ago – is already helping astronomers worldwide explore the Universe in unprecedented depth and detail.
Among the hundreds of scientists already harnessing Webb’s revolutionary power are researchers from the University’s School of Physics and Astronomy.
Galaxies far, far away
In many respects, powerful telescopes like Webb are visual time machines. To our eyes, light travels in an instant, but even it can only go so fast – about 186,000 miles per second, to be precise. That means when we point a telescope at a far-off object in space, the light we see took time – often an astronomically long time – to get here. What we’re seeing are images from the past.
We have always been able to do some time travel with our own eyes. At 93 million miles, the Sun is only a galactic stone’s throw from Earth. When we look at it (but not directly, of course), it offers us a glimpse of the very recent past – what we see is how it looked around eight minutes ago.
One of the things that’s so revolutionary about Webb is that it’s capable of seeing back more than 13.5 billion years, to the very dawn of the Universe, when the first stars and galaxies formed after the Big Bang.
“The Holy Grail is finding the first galaxies and discovering what they’re made of,” says Professor Jim Dunlop, Head of the School of Physics and Astronomy. He leads one of the largest of Webb’s research programmes, which it is predicted could reveal around 120,000 galaxies, most of which have never been seen before.
“There are various phases in the history of the Universe,” Dunlop explains. “There’s the very beginning of it and there’s the beginning of life, and somewhere in between is the period when the elements of life were made inside the first stars. That phase must be there, but we’ve not yet been able to find it. If we can’t do it with Webb, I don’t know if we ever will.”
After launching in December 2021, Webb spent several months travelling to an observational sweet spot – known as Lagrange Point 2 – about four times farther away from Earth than the Moon. There, with a sunshield the size of a tennis court, and the gravity of the Sun and the Earth keeping its orbit in lockstep with our planet, Webb is perfectly positioned to scour far corners of the Universe.
Dr Adam Carnall’s work is focused on studying the early formation and evolution of the most massive galaxies in the Universe – which also happen to be the oldest.
“The largest galaxies in the Universe are true giants, containing tens to hundreds of times as many stars as our own Milky Way galaxy. To understand these ancient galaxies, which formed most of their stars more than ten billion years ago, we must look for light from the most distant parts of the Universe, which has been travelling to us for most of cosmic history. Webb will allow us to see far further back than ever before.”
Trick of the infrared light
Part of the difficulty with spotting light from the farthest reaches of the Universe is that having travelled across such vast distances, it is extremely faint. But Webb is able to see farther back through cosmic history than ever before because it has been built specifically to detect infrared light.
As the universe has expanded over time, ultraviolet and visible light emitted by the first galaxies and stars has been stretched – known as redshifted – turning it into infrared light by the time it reaches us today.
Infrared light is essentially radiated heat, so Webb has to be extremely cold if it is to detect the vanishingly faint traces emitted by distant galaxies. Webb’s design enables it to passively cool most of its scientific instruments to 37 Kelvin, which is -236°C. One of its instruments – the Mid-infrared Instrument, or MIRI – has sensors so sensitive it needs a special cryogenic cooler to keep it below 7 Kelvin, or -266°C. In the coldest place on Earth, Antarctica, temperatures are a comparatively balmy -94°C. But in the icy depths of space, this Goldilocks instrument is in its element.
Professor Philip Best is trying to precisely measure how, when and where galaxies that existed less than a billion years after the Big Bang formed their stars. This was virtually impossible before Webb, he says. “A huge advantage we have now is that, compared to techniques normally used to study galaxies in the very early Universe, Webb’s instruments are relatively insensitive to the effects of interstellar dust, which is found in huge quantities in star-forming regions.”
He continues: “The telescope has sufficient image sharpness that we can not only detect which early galaxies are forming stars, but we can map the distribution of star formation within the galaxies.”
When and how did the first galaxies form? How quickly did they build up their populations of stars? What impact did this have on the rest on the Universe around them? “Webb’s ability to see so deeply into cosmic history, to detect and study the stellar populations in the very early Universe, could be the key to answering some of these big unanswered questions,” says Best.
Since it returned its first data in June 2022, researchers using Webb have already helped make remarkable discoveries, including locating the most distant galaxy – and therefore the oldest – ever found. The galaxy, the snappily named CEERS-93316, was spotted 35 billion light-years from Earth. If you crunch the numbers, that means the galaxy existed just 235 million years after the Big Bang.
Dunlop and Carnall, together with PhD student Callum Donnan and Edinburgh researchers Ross McLure, Derek McLeod and Fergus Cullen, were key members of the team that found CEERS-93316. Undergraduate students Sophie Jewell and Clara Pollock created a colour image of the galaxy during summer projects in the University’s Institute for Astronomy.
As well as enabling astronomers to observe never-before-seen parts of space, Webb also makes it possible to study the atmospheres of some of our nearest neighbours in unprecedented detail.
“Some of the work people are doing with Webb is about studying very ancient, distant objects,” says Professor Beth Biller, who co-leads another of Webb’s research programmes. “The things I’m interested in are comparatively close by and happening right now.”
Biller’s work focuses on identifying and better understanding exoplanets – planets outside our solar system – and she was part of an international team that captured the first image of one using Webb. Again, that was all down to Webb’s ability to detect infrared light with unprecedented sensitivity.
“Imagine it’s a foggy day,” says Biller. “We can’t see through the gloom with our eyes because the visible light is blocked out. But if, like Webb, you’re looking at it in infrared, you can see what’s inside.”
This ability to observe the atmospheres of exoplanets in unprecedented detail could even one day help reveal if life exists in other parts of the Universe.
Much like the light it detects from ancient galaxies, the Webb telescope – which was constructed through a collaboration between NASA, the European Space Agency and the Canadian Space Agency – was a long time coming.
And researchers from Edinburgh and the UK Astronomy Technology Centre (UK ATC), which is based at the Royal Observatory in Edinburgh and has close ties with the University, have been involved since those early days of its development more than 25 years ago.
Tim Hawarden, who passed away in 2009, worked at the Royal Observatory Edinburgh and pioneered the concept of passive cooling – the main way that Webb’s temperature is kept so low. The year after he died, Hawarden was posthumously awarded the NASA Exceptional Technology Achievement Medal for this fundamental work. The telescope’s MIRI instrument – the one that’s cooled to -266°C – was in part built in Edinburgh by a team led by the director of the UK ATC, Professor Gillian Wright.
“Edinburgh has a rich heritage of expertise in infrared, low-temperature astronomy,” says Jim Dunlop. “Webb is an instrument that, both technically and scientifically, Edinburgh has been involved in for a long time. Our links with it are deep and genuine.”
Picture credits: cosmic cliffs – NASA, ESA, CSA & STScI; rocket – NASA Bill Ingalls; deep space – NASA, ESA, CSA & STScI; CEERS-93316 – Sophie Jewell and Clara Pollock; artist’s impression – NASA, GSF, CCIL & Adriana Manrique Gutierrez