Tuning in to the Cosmos
When you look up at the night sky you might see a scattering of stars, twinkling pinpricks of light against the darkness. But if your eyes were capable of seeing radio emissions, the stars would mostly disappear and the night sky would reveal entirely different phenomena, including clouds of star-forming gas and the large black holes lurking at the centers of massive galaxies.
“Radio astronomy is simply looking at the universe in its radio emission,” says Allison Matthews, a postdoc at the Carnegie Science Observatories, who studies the cosmos in wavelengths far longer than can be perceived by human eyes.
The field itself owes its existence to accident and curiosity. In the early 20th-century experts at Bell Laboratories were trying to improve telecommunications capabilities and noticed a persistent source of static. An engineer named Karl Jansky was sent to some potato fields in New Jersey to track down the origin of this mysterious source. It took him more than a year of painstaking effort to conclude that he was detecting radio emission from the Milky Way galaxy itself, a serendipitous discovery that transformed our ability to probe the universe.
A radically different sky
Thanks to Jansky's unlooked-for discovery, astronomers were able to see aspects of the universe that had previously been undetectable to them such as quasars, supermassive black holes that sometimes emit jets of plasma, and pulsars, highly magnetized rotating neutron stars. Radio astronomy also first revealed the cosmic microwave background, which represents the relics of the Big Bang. The radio astronomy-powered discoveries of quasars and the CMBR both received Nobel Prizes in Physics.
“Radio astronomy unveiled some of the most energetic physics occurring in the cosmos,” Matthews explains. “We can see the dynamic processes occurring within and around the objects in the universe in a totally different way than optical astronomers do.”
Karl Guthe Jansky is known as the father of radio astronomy, because in 1933 he discovered that the center of our Milky Way Galaxy emits radio waves.
Karl Guthe Jansky joined the staff of the Bell Telephone Laboratories in Holmdel, New Jersey in 1928.
Computing: the invisible telescope
Modern radio astronomy has become as much a triumph of computation as of antennas, according to Matthews.
Many radio telescopes are actually arrays of smaller dishes whose signals are combined by powerful computers to synthesize a much larger telescope, relying on a phenomenon called interferometry to maximize their power.
“Interfermoetry is basically taking a huge dish of a telescope like the former Arecibo in Puerto Rico and breaking it up into little parts and then using math and computers to connect those after the fact,” Matthews elucidates.
The size of radio arrays used to top out due to the limits of computing power, but now faster processing speeds are pushing the field into new frontiers. Advances in high-performance computing have enabled astronomers to scale up arrays and process vast data streams in ways that were impossible a decade ago.
Seeing to the heart of star formation
Matthews uses radio astronomy to study star formation and galaxy evolution.
Stars are born in big clouds of dust and gas and there are a lot of outstanding questions about the factors that govern how quickly this occurs and what makes it slow down or even stop. Expanding our knowledge of these processes will enhance what we know about how galaxies grow and change over time.
However, the reservoirs of dust and gas that are so essential for star formation block a lot of the visible and ultraviolet light from being detected by optical telescopes like those at Carnegie’s Las Campanas Observatory in Chile.
Luckily, radio arrays have no such issue.
“Because the wavelength of radio emission is so long, it can travel straight through all of that material and enable us to get a clean view of how quickly star formation is occurring,” Matthews shares. “That’s one very cool advantage of radio astronomy that I personally take advantage of for my own research.”
Her work has been conducted by radio facilities around the world, including the Karl G. Jansky Very Large Array (JVLA) in New Mexico, the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, and the MeerKAT—formerly Karoo Array Telescope—in South Africa.
Each of the VLA’s 28 antennas (including the one that is a spare) is an 82-foot dish with 8 receivers tucked inside. The dish moves on an altitude-azimuth mount, which looks like a classic tripod mount: it tilts up and down and spins around.
The iconic “Y” shape of the VLA is not for looks, it’s for function. The wider an array is, the bigger its eye is, and the more detail it can see out in space. The VLA’s unique shape gives the observatory three nice long arms of nine telescopes each. It also features the flexibility of stretching the arms when we need to zoom in for more detail. Credit: Allison Matthews.
The telescope was originally known as the Karoo Array Telescope (KAT) that would consist of 20 receptors. When the South African government increased the budget to allow the building of 64 receptors, the team re-named it “MeerKAT” – ie “more of KAT”. The MeerKAT (scientific name Suricata suricatta) is also a much beloved small mammal that lives in the Karoo region. Credit: South African Radio Astronomy Observatory (SARAO)
ALMA's large antennas have a diameter of 12 metres, while 12 smaller antennas with a diameter of 7 metres make up the ALMA Compact Array (ACA). On the horizon, the main peaks from right to left are Cerro Chajnantor, Cerro Toco, and Juriques. This photo was taken in December 2012, four months prior to the ALMA inauguration. Credit: Clem & Adri Bacri-Normier (wingsforscience.com)/ESO
A photo from the Very Large Array in New Mexico taken by Allison Matthews.
The MeerKAT telescope is an array of 64 interlinked receptors (a receptor is the complete antenna structure, with the main reflector, sub-reflector and all receivers, digitisers and other electronics installed).
This image shows an aerial view of the Chajnantor Plateau, located at an altitude of 5000 meters in the Chilean Andes, where the array of ALMA antennas is located.
Making magic at MeerKAT
MeerKAT array received its adorable savannah-themed rebrand shortly after the facility expanded from having 20 receivers to 64. Matthews, a graduate student at the time, was part of the team tasked with evaluating its new capabilities.
“So, one of the tests that the research team I was part of was tasked with performing was to figure out how sensitive an image this array could possibly take,” says Matthews. “I got to pick the quietest area of the radio sky, and we pointed MeerKAT at it for 150 or so hours.”
The result exceeded everyone’s expectations, producing the most-sensitive radio image at that frequency ever taken.
“It was absolutely amazing to be a graduate student and get to help take and make the radio astronomy equivalent of the Hubble Ultra Deep Field,” Matthews enthuses.
This single deep radio image let the team measure dust-unbiased star formation rates across vast stretches of cosmic time and helped reshape ideas about how galaxies grew. MeerKAT enabled them to trace star formation in galaxies from 10 billion years ago, revealing that the universe made more stars across cosmic history than earlier optical surveys suggested.
Radio’s Achilles’ heel
Despite this, there are still new horizons to explore. Part of this is due to the field’s one big drawback.
Radio astronomers fight a constant battle against Earthly interference. Cell phones, television broadcasts, and satellite transmissions swamp faint cosmic signals, which is why radio arrays are built in remote deserts far from human activity.
“If you take out your cell phone at a radio array site, one text might be brighter in radio emission than anything coming from the sky,” Matthews laughs.
Additionally, Earth’s ionosphere blocks the very longest radio wavelengths, leaving a slice of the electromagnetic spectrum effectively off-limits.
That’s where the Moon—and missions like Artemis II—come in. The far side of the Moon, shielded from Earth’s radio noise and our ionosphere’s interference, could host telescopes that open this unexplored window for the first time.
The brightest spots are luminous radio galaxies powered by supermassive black holes. The myriad faint dots are distant galaxies like our own Milky Way, too faint to have been detected before now, which reveal the star-formation history of the universe. Most galaxies are visible in the central part of the image, where the telescope is most sensitive. Allison Matthews, who was a Ph.D. student at the time this was made, said: "“Previous images could only detect the tip of the iceberg, the rare and luminous galaxies that produced only a small fraction of the stars in the universe. What we see now is the complete picture: these faint dots are the galaxies that formed most of the stars in the universe.” Credit: SARAO; NRAO/AUI/NSF
Many new and previously known radio features are evident, including supernova remnants, compact star-forming regions, and the large population of mysterious radio filaments. The broad feature running vertically through the image is the inner part of the radio bubbles, spanning 1,400 light-years across the center of the Galaxy. Colors indicate bright radio emission, while fainter emission is shown in grayscale. | I. Heywood, SARAO.
The Los Angeles County Museum of Art’s Mapping the Infinite: Cosmologies Across Cultures exhibition spaned centuries and probed the various relationships that roughly 15 different civilizations—from the Neolithic to the modern—developed with the universe. Part of the Getty Foundation’s PST ART: Art & Science Collide initiative, Mapping the Infinite was curated in partnership with more than 40 different institutions, including Carnegie Science. The MeerKAT image of the heart of the Milky Way was one of three Carnegie-provided images that were part of the exhibition.
MeerKAT image of radio galaxies: Thousands of galaxies are visible in this radio image covering a square degree of sky near the south celestial pole, made by the MeerKAT radio telescope array in South Africa.
The MeerKAT image of the Galactic center region is shown with the galactic plane running horizontally across the image.
Allison Matthews poses with an image of the Milky Way’s central region captured from the MeerKAT radio telescope and on display in the Los Angeles County Museum of Art’s exhibit Mapping the Infinite: Cosmologies Across Cultures.
Moments that matter
For Matthews, radio astronomy’s appeal has always been tactile. A formative moment occurred at Arecibo when she was an undergraduate. She was awestruck by standing before a wall of oscilloscopes and watching electromagnetic waves from space ripple across screens.
“You’re seeing the waves that are coming from the universe, rather than an optical picture,” she concludes. “That directness—the feeling of listening to signals rather than looking at photons—hooked me.”
Radio telescopes change how we think about the cosmos. They reveal structures and dynamics that visible light hides, let us peer into dusty stellar nurseries, and offer new paths toward detecting the universe’s most titanic mergers.
From accidental discovery in a New Jersey potato patch to MeerKAT’s record-breaking deep fields and plans to listen from the Moon’s far side, the story of radio astronomy is a reminder that sometimes the most revolutionary discoveries come when we learn to listen in a new way.
Allison Matthews had a very rare and special experience on a visit to the VLA. She and some colleagues were able to climb one of the anteanne that comprises the array! Credit: Allison Matthews
The VLA is located in the Plains of San Agustin in New Mexico, northwest of Socorro, on a flat stretch of desert far from major cities. The plains are ringed by mountains, which act like a natural fortress of rock that keeps out much of the radio interference from cities even hundreds of miles away. Credit: Allison Matthews
Allison Matthews slides down the side of one of the antennae in the Very Large Array.
Peering down into at the heart of one of the antennae that comprise the Very Large Array.
