JWST unveils most complex map of cosmic dark matter yet
Astronomers smoothed out minor distortions in images of distant galaxies taken by JWST to chart the invisible.
Containing approximately 800,000 galaxies, this image from NASA’s James Webb Space Telescope (JWST) is overlaid with a dark matter map, shown in blue. Researchers used JWST data to find invisible matter through its gravitational influence on regular matter.
NASA/STSCI/J. DePasquale/A. Pagan
It’s an open secret in astronomy that, practically wherever the James Webb Space Telescope (JWST) looks in the sky, a vast, clump-filled haze fills its view. But fortunately for everyone who marvels at JWST’s clear snapshots of distant galaxies, this dense haze is completely invisible.
That lightless, transparent, blurry substance is black matter. Think of dark matter as a scaffold for all the bright, normal things out there – the former weigh five times more than the latter – like a gravitational glue that holds everything else together. But scientists don’t know what this “glue” is made of and it hasn’t been discovered directly yet; They have only guessed its presence through subtle but unmistakable clues. Despite being so integral to everything we see, it is surprisingly hidden from our cosmic view.
Now astronomers have detected a ghostly shape of dark matter in the foreground of one of JWST’s deep-sky images. They have transformed the Cosmic Evolution Survey (COSMOS) field survey – one of the best-studied patches of the sky – into the most finely detailed dark matter map in existence. With it, they hope to learn more about how galaxies depend on its appearance. A study reporting results appears in today nature astronomy.
On supporting science journalism
If you enjoyed this article, consider supporting our award-winning journalism Subscribing By purchasing a subscription, you are helping ensure a future of impactful stories about the discoveries and ideas shaping our world today.
“We can see the effect of gravity on galaxy formation,” says Diana Scognamiglio, a postdoctoral fellow at NASA’s Jet Propulsion Laboratory, who co-led the study. “It’s really a way to explore the backbone of the universe.”
Take a look at a JWST image of a distant galaxy. What you actually see is where each beam of light hits the JWST’s optics during the observation. The image essentially traces each ray to its source within the target galaxy.
But that beam’s journey from the galaxy to the JWST is not actually a straight line. On its journey through intergalactic space, that light passes countless clumps of dark matter. Each clump slightly distorts the spacetime around it, changing the path of a light beam like a glass lens.
That distortion distorts the image in the same way that wearing someone else’s glasses blurs your vision. For images from JWST, this effect is imperceptible to the eye, which is why it is called “weak gravitational lensing”. But the images encode all of the dark matter between the distant object and the telescope.
However, until the beginning of the third millennium no one knew how to understand this pathology. “People were saying there’s no way you can measure 1 percent distortion, given everything else that’s going on,” says Catherine Heymans, professor of astrophysics at the University of Edinburgh and Astronomer Royal for Scotland. Heymans and his colleagues proved them wrong, introducing the field of “weak lensing”, which has since shed much light on dark matter.
Heymans helped create the first dark matter map of the COSMOS region using the Hubble Space Telescope, the JWST’s predecessor. “It was really a pioneering work,” Scognamiglio says.
Two decades later Scognamiglio’s team of cosmic cartographers has updated that map using more galaxies present in JWST’s images. “The sheer number of galaxies and the resources they can use, so it’s extremely exciting,” says astronomer Zoltan Hamann of Columbia University. The new map shows an area in the sky only twice as large as the full Moon – a quarter of the original size – but it is far more detailed, pointing out blobs of dark matter that are too small for Hubble to discern.
And the JWST’s larger, more sensitive optics can collect light from farther out in the universe – and thus even further back in cosmic time. So it may see weak lensing caused by dark matter clumps from 10 billion or 11 billion years ago, when the universe was most prodigiously forming stars and galaxies. Studying these clusters – which likely host clusters of teenage galaxies – is a rare chance to learn more about the role of dark matter in the era known as “cosmic noon” and how the universe has evolved since then. The team then wants to estimate different distances to the structures the researchers observed and use them to make the map more dynamic and three-dimensional.
For now, the map clearly reveals one of the universe’s most elusive sculptors. “Before this we only had dark matter simulations, and I always wanted to be able to see it,” says Heymann. “What I love about weak lensing is this: It allows us to see the invisible.”
In the coming years, astronomers’ dark matter maps will be expanded to a larger scale – though with less fine detail. Weak lensing is part of the announced mission of new space telescopes such as the European Space Agency’s Euclid, which is already in orbit, and NASA’s Nancy Grace Roman Space Telescope, which is scheduled to launch this year. Ground-based projects like the Dark Energy Survey, which released a new trove of data last week, and the Vera C. Rubin Observatory also use weak lensing to study the expansion of the universe.
A generation after the pioneering Hubble Dark Matter Map, Scognamiglio is proud to help extend its legacy. “I like this continuity,” she says. “I hope that, 20 years from now, my student will be able to make an even better map.”
It’s time to stand up for science
If you enjoyed this article, I would like to ask for your support. scientific American He has served as an advocate for science and industry for 180 years, and right now may be the most important moment in that two-century history.
i have been one scientific American I’ve been a member since I was 12, and it’s helped shape the way I see the world. Science Always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does the same for you.
if you agree scientific AmericanYou help ensure that our coverage focuses on meaningful research and discovery; We have the resources to report on decisions that put laboratories across America at risk; And that we support both emerging and working scientists at a time when the value of science is too often recognised.
In return, you get the news you need, Captivating podcasts, great infographics, Don’t miss the newsletter, be sure to watch the video, Challenging games, and the best writing and reporting from the world of science. you can even Gift a membership to someone.
There has never been a more important time for us to stand up and show why science matters. I hope you will support us in that mission.
