It took a remarkably long time for the light emitted by a group of ancient galaxies to reach the James Webb space telescope last year. Astronomers have calculated that the photons were in transit for more than 13bn years – almost the entire history of the cosmos – before they reached the orbiting observatory.
The results are scientifically dramatic and have revealed that the universe was already deep into the process of star formation only a short time after its big bang birth – although the photographs themselves are scarcely stunning in appearance: a handful of smudges, a couple of glowing spheres and an image that has been described as a glowing dog bone.
The world of astronomy has been dazzled, nevertheless. Among the objects caught in the telescope’s giant mirror is one that turns out to be the oldest known galaxy in the universe. The prosaically named JADES-GS-z13-0 appears as it did a mere 320m years after the big bang, long before the creation of our own planet. It also turns out to be tiny compared with our own galaxy, yet it was clearly creating new stars at a rate comparable to the Milky Way.
Intriguingly, this stellar fecundity is shared by several other ancient galaxies photographed by the James Webb telescope (JWST). These snapshots of the infant universe show that the first stars and galaxies had already formed and were evolving much earlier than most scientists had expected.
“These galaxies are very, very young yet they have already become hotbeds for star formation. It’s remarkable,” said Prof Brant Robertson, an astrophysicist at the University of California, Santa Cruz.
This enthusiasm was shared by Kevin Hainline, an astronomer at the University of Arizona, Tucson. “We have observed the earliest galaxies in the universe and it has been thrilling,” he told the Observer. “It has opened an entirely new chapter in the history of astronomy. It is telling us the universe was dynamic from the beginning.”
The £6.8bn James Webb telescope – the most ambitious, costly robot probe ever built – was launched on Christmas Day 2021, and took six months to position itself in deep space while its 18 hexagons of gold-coated beryllium mirror were unfurled and slotted together like a blooming flower to create a huge 6.5-metre (21ft) mirror. Then, exactly a year ago, the James Webb began taking its first images of the cosmos.
The completion of its first year of operations was celebrated last week by Nasa who built the observatory with European and Canadian space agency collaboration. The US space agency released images which depicted stars in our own galaxy that were coalescing out of clouds of interstellar dust. Given that it had taken more than 30 years to design and build the James Webb telescope – which endured major delays and threats of cancellation throughout its history – the anniversary was always going to be marked as an occasion that mixed relief with spectacle.
And the photographs of the Rho Ophiuchi star field are certainly stunning. However, the far more muted images of JADES-GS-z13-0 and its ancient partner galaxies are causing real excitement among cosmologists and astrophysicists.
More than any other set of observations, they underline the true potential of the James Webb telescope, it is argued.
“What is so surprising is the detail of the early universe that it has revealed,” said Sandro Taccella, a Cambridge University astrophysicist. “Theory predicted that very complex cosmological processes would be occurring at this time, though I did not expect to be able to observe them. However, the telescope takes such magnificently sharp images, we can actually see this complexity in operation. It was surprising – and very gratifying.”
In the first moments after the big bang, the universe was extremely hot and dense. As it cooled, protons and neutrons combined to form atomic nuclei which – after a few hundred thousand years – trapped electrons to create the first atoms. These coalesced into clouds of gas from which the first stars emerged hundreds of millions of years later.
However, another type of matter also emerged from the big bang, one that accounts for a very large fraction of all the mass in the universe. This is called dark matter and is only known through its gravitational effects – which were considerable, it transpires. “Dark matter assembled first after the big bang and began creating halos of unseen material which then attracted hydrogen and helium atoms to create gas clouds from which stars and galaxies eventually formed,” said Taccella.
“If it hadn’t been for dark matter, stars and galaxies would not have appeared until much later in the universe’s history. Now we have the James Webb, we can study how that happened in detail and hopefully get a better understanding of the role of dark matter in shaping the cosmos.”
The fact that dark matter played a key role in greatly speeding up the formation of the first stars and galaxies is highlighted through the photographs taken of ancient galaxies that include JADES-GS-z13-0. “It is already a complex structure, and that is mindblowing,” said Hainline. “We can see that it is a growing galaxy and that is a really beautiful thing.”
Only a handful of ancient galaxies had been discovered before the launch of the James Webb telescope. Using the observatory, the project known as JADES – the JSWT Advanced Deep Extragalactic Survey – has identified a total of 717 such objects in less than a year.
“The really interesting question is what then happened to these galaxies,” added Robertson. “It is clear that they did not stay that way for the next 13bn years, but merged with other galaxies over time. That is how gravity works its wonders. It pulled them together so that they became bigger and bigger galaxies. And that is what you see in our own Milky Way today.
“We can actually see the remnants of other galaxies that were pulled in and accreted into our own galaxy. The images from the James Webb are showing us how that process began.”
How it all works
Designed as a replacement for the Hubble space telescope – launched in 1990 and still in operation – the James Webb is a far bigger, much more complex instrument with many more ambitious goals. These include studying the early universe, pinpointing possible life-supporting planets, and understanding how stars form.
However, to carry out these tasks, the observatory avoids using the visible part of the electromagnetic spectrum – unlike the Hubble and most ground-based telescopes – and instead gathers only infrared radiation. This is better for peering through dust and observing stars and planets as they coalesce out of clouds of gas and other material. In addition, the atmospheres of planets that contain chemicals such as methane – a gas associated with biological processes – are also best studied by using infrared radiation.
But most important of all is the role of infrared detectors in revealing the secrets of the early universe. Light gets fainter and redder the further back you look into the cosmos until its wavelength reaches the infrared part of the spectrum. You therefore need an infrared telescope if you want to study how the first stars, black holes and galaxies formed.
Operating infrared detectors is not easy, however. The James Webb telescope has to function at about 40C above absolute zero (about -233C) so that its instruments do not generate spurious heat signals that could swamp the faint infrared radiation it receives from the other side of the universe.
Far away from its warm home planet, the telescope is protected by a five-layer-thick shield that blocks out radiation from the sun and Earth while its instruments are chilled by a liquid helium refrigerator that is expected to keep it cool and operational for more than a decade.
