The Discoveries of Radio Observatories: From Early Insights to Modern Breakthroughs

Key Takeaways

• Radio telescopes detect invisible cosmic signals, revealing phenomena optical telescopes can’t see
• Pulsars, quasars, and the cosmic microwave background were discovered through radio astronomy
• Modern facilities like FAST and the Event Horizon Telescope are redefining observable science

The Accidental Beginning

In 1931, a Bell Telephone Laboratories engineer named Karl Jansky was assigned a practical problem: find the source of static noise interfering with transatlantic radio communications. Nobody expected the answer to come from outer space. After months of rotating his antenna apparatus on a turntable assembled from a Ford Model T chassis, Jansky traced the persistent hiss to the center of the Milky Way. He published his findings in 1933, and the field that would eventually be called radio astronomy was born, mostly by accident.

The scientific establishment paid little attention. Optical astronomers, accustomed to peering through glass lenses and photographic plates, weren’t especially interested in someone listening to the sky rather than looking at it. Bell Labs redirected Jansky to other projects. His discovery sat largely dormant.

What happened next says something remarkable about how science sometimes advances: an amateur stepped in. Grote Reber, a radio enthusiast and engineer in Wheaton, Illinois, built the world’s first purpose-built radio telescope in his backyard in 1937. The parabolic dish was roughly 9 meters in diameter, assembled from galvanized iron. Using it, Reber produced the first radio maps of the sky, confirming Jansky’s detection and adding new detail about the Milky Way’s structure. He worked mostly alone and published his maps in astrophysical journals that treated his work as curious but peripheral. That changed dramatically after World War II, when an entire generation of engineers trained in radar technology turned their skills toward the cosmos.

How a Radio Telescope Actually Works

Everything in the universe radiates energy across a broad spectrum, not just visible light. Radio waves are a lower-frequency, longer-wavelength form of electromagnetic radiation, and celestial objects, from ordinary hydrogen clouds to spinning neutron stars to supermassive black holes, emit them as a natural consequence of their physical processes. The Earth’s atmosphere is largely transparent to radio waves, which means ground-based instruments can detect them without sending hardware into space.

A radio telescope collects incoming radio waves using a large dish-shaped antenna. The dish reflects those waves toward a receiver at the focal point, where signals are amplified and recorded. Bigger dishes collect more signal and resolve finer detail. A single 25-meter dish is already capable of detecting emissions far too faint for any optical instrument to perceive.

The main technical challenge is noise. Radio signals from space are extraordinarily weak, and the equipment itself introduces interference. Engineers spend considerable effort minimizing this noise, cooling receivers to near absolute zero in some cases, to extract clean data from the cosmic background hiss. Multiple dishes can be linked electronically to simulate a single much larger telescope, a technique known as aperture synthesis that transformed the field during the 1960s. The resulting resolution can far exceed what any individual dish could achieve.

Mapping the Galaxy’s Hidden Structure

Radio astronomy expanded rapidly after 1945, partly because wartime radar had produced a generation of engineers comfortable with sensitive receivers and large antenna systems. The transition from military to scientific use of this expertise happened quickly across Britain, Australia, the Netherlands, and the United States.

One of the field’s early triumphs came in 1951. Astronomers at Harvard University, working from a prediction made four years earlier by Dutch astronomer Hendrik van de Hulst, detected the 21-centimeter radio emission line of neutral hydrogen. The physics is specific: neutral hydrogen atoms occasionally flip the spin of their electron, and this flip releases a photon at a wavelength of precisely 21 centimeters. Because hydrogen is the most abundant element in the universe and fills vast clouds between the stars, detecting this emission line gave astronomers a way to trace the structure of the Milky Way in three dimensions.

Optical telescopes can’t see through the dust and gas that obscures large portions of the galactic disk. Radio waves pass through that material unimpeded. Using the 21-cm line as a tracer, radio astronomers in the 1950s and 1960s mapped the spiral arms of the Milky Way for the first time. Before this work, the galaxy’s shape had been inferred largely by analogy with others astronomers could observe. Now there was direct evidence. The Milky Way turned out to have the kind of barred spiral structure that would later be confirmed with much greater precision by infrared and millimeter-wave instruments. This mapping work might seem mundane compared to what came later, but it established radio telescopes as tools without which large-scale cosmic structure simply couldn’t be studied.

Pulsars and the Signal That Almost Wasn’t Published

On August 6, 1967, Jocelyn Bell Burnell, a graduate student at the University of Cambridge working under supervisor Antony Hewish, noticed a peculiar repeating signal on paper chart output from the Mullard Radio Astronomy Observatory. The pulses were arriving with such regularity, once every 1.3373 seconds, that the team initially wondered whether they’d detected an artificial beacon. They nicknamed the source LGM-1, for Little Green Men, half-jokingly.

The signal turned out to be natural, but the reality was almost stranger than the joke. What Bell had found was a pulsar, a rapidly spinning neutron star that emits a beam of radio waves like a cosmic lighthouse. Neutron stars form when massive stars collapse at the end of their lives, compressing a mass greater than the Sun into a sphere roughly 20 kilometers across. The rotation rate of these objects is so stable that early pulsars were considered among the most accurate clocks known to science.

The 1974 Nobel Prize in Physics for the discovery went to Hewish and radio astronomy pioneer Martin Ryle. Bell Burnell did not share it. Whether that was an appropriate decision is still contested, and it’s widely regarded by physicists and historians as one of the more glaring omissions in Nobel Prize history. Bell Burnell has handled the question with considerable grace. The astrophysical implications of pulsars unfolded quickly: by 1968, a pulsar had been found inside the Crab Nebula, the remnant of a supernova recorded by Chinese astronomers in 1054, confirming the theoretical link between supernovae and neutron stars.

In 1974, Russell Hulse and Joseph Taylor discovered the first binary pulsar, a system in which two neutron stars orbit each other. Measuring the decay of their orbit provided the first indirect evidence for gravitational waves, a prediction of general relativity that had never been observationally confirmed. Hulse and Taylor received their own Nobel Prize for this work in 1993. A single instrument, the radio telescope, had contributed to two Nobel Prizes by revealing objects that optical astronomy couldn’t have detected at all.

Quasars and the Uncomfortable Implications

In the early 1960s, radio astronomers were cataloging mysterious point-like sources of intense radio emission. When optical astronomers pointed their telescopes at these positions, they found objects that looked like faint blue stars. They were called quasi-stellar radio sources, eventually shortened to quasars.

The puzzle was their spectra. The spectral lines in their light were shifted so far toward the red end of the spectrum that it implied they were receding from Earth at a substantial fraction of the speed of light. If this was true, they had to be enormously distant, and since they were still detectable at that distance, they had to be astonishingly luminous, far more so than any ordinary galaxy.

Astronomer Maarten Schmidt made the key breakthrough in 1963 while studying the quasar 3C 273 at the Palomar Observatory in California. He recognized that the spectral lines, though displaced, matched familiar hydrogen emission lines shifted by about 16 percent in wavelength, corresponding to a recession velocity of roughly 47,000 kilometers per second. 3C 273 was about 2.4 billion light-years away and yet visible in a small telescope. A single quasar was outshining an entire galaxy by factors of hundreds to thousands.

The only mechanism that could plausibly account for that energy output was accretion onto a supermassive black hole. Gas falling into such a black hole converts a fraction of its mass directly into energy, far more efficiently than nuclear fusion. This helped establish the theory that supermassive black holes reside at the centers of most large galaxies and that quasars are what those black holes look like when actively consuming large amounts of material. The implication that nobody quite wanted to address initially was this: quasars exist only at great distances, meaning they existed only in the early universe. The universe was a fundamentally different place billions of years ago. That was uncomfortable for proponents of the Steady State model of cosmology, and quasar observations contributed directly to its eventual abandonment in favor of the Big Bang.

The Echo of Creation

The most widely known radio astronomy discovery of the 20th century happened in 1965, and it was, like Jansky’s original work, accidental. Arno Penzias and Robert Wilson were engineers at Bell Labs working with a highly sensitive horn antenna in Holmdel, New Jersey. They were trying to calibrate it for communication satellite work and couldn’t eliminate a persistent, uniform background noise. It was present regardless of where they pointed the antenna. They cleaned the equipment, removed pigeon nests from the horn, and methodically eliminated every possible source of interference.

The noise didn’t go away because it wasn’t interference. It was the cosmic microwave background radiation, the thermal afterglow of the Big Bang itself. Theoretical physicist Robert Dicke at Princeton had just predicted that such radiation should exist, a relic of the hot, dense early universe that had cooled as space expanded over roughly 13.8 billion years to become a faint glow of microwave radiation at about 2.7 Kelvin. Penzias and Wilson had detected it without trying to. They received the Nobel Prize in Physics in 1978.

Later measurements refined the picture dramatically. The COBE satellite, launched in 1989, found that the CMB wasn’t perfectly uniform but contained tiny temperature fluctuations at the level of one part in 100,000. These fluctuations were the seeds of all large-scale structure in the universe, the quantum wrinkles that eventually grew under gravity to become galaxy clusters and the vast cosmic voids between them. The Wilkinson Microwave Anisotropy Probe and the Planck spacecraft refined those measurements still further, giving cosmologists a remarkably precise portrait of the universe’s earliest moments.

The Search for Other Civilizations

No topic in radio astronomy has captured public imagination more persistently than the search for extraterrestrial intelligence. The reasoning is accessible: if other technological civilizations exist, they might communicate using radio waves, and radio telescopes are the instruments best suited to detect such signals.

The first serious scientific effort was Project Ozma, run by astronomer Frank Drake at the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, in 1960. Drake pointed a 26-meter telescope at two nearby Sun-like stars, Tau Ceti and Epsilon Eridani, and listened for structured signals for about 200 hours. Nothing was found.

Drake went on to formulate the Drake Equation in 1961, a framework for estimating the number of communicating civilizations in the galaxy. It was never intended as a precise calculation but as a way of organizing thinking about the problem. Several of its factors are now known with reasonable confidence: the rate of star formation, the fraction of stars with planets, the fraction of those planets in habitable zones. Others, particularly the fraction of civilizations that develop radio technology and how long they survive, remain entirely unknown.

In 1974, the Arecibo Observatory transmitted a brief message toward the globular cluster M13, roughly 25,000 light-years away. The Arecibo message was a 1,679-bit binary sequence encoding basic information about Earth, humanity, and the structure of DNA. Any reply would take at least 50,000 years to arrive, so it was as much a demonstration of human technical capability as a genuine attempt at dialogue.

No confirmed detection of extraterrestrial intelligence has been made. The Wow! signal, detected by astronomer Jerry Ehman at Ohio State University’s Big Ear telescope in August 1977, was a 72-second narrowband signal that matched the predicted characteristics of an interstellar transmission with uncomfortable precision. It was never detected again despite extensive follow-up observations over the following decades. Whether it was of natural or artificial origin remains genuinely unknown.

The SETI Institute, founded in 1984, has continued the search with increasing technological sophistication. The Breakthrough Listen project, launched in 2015 with funding from entrepreneur Yuri Milner, brought substantially more computing power and telescope time to the effort, surveying millions of stars across a broad range of frequencies. For readers who want to explore the scientific and cultural dimensions of this search further, Paul Davies’s The Eerie Silenceprovides a rigorous examination of why silence itself carries meaning.

The Great Observatories

By the 1960s, radio astronomy had outgrown backyard dishes and university department budgets. Several major national observatories were built during this period that would drive discoveries for the remainder of the century.

Jodrell Bank Observatory in Cheshire, England, opened its 76-meter Lovell Telescope in 1957, just in time to track the Soviet Sputnik satellite as it passed overhead. For years it was the largest steerable radio telescope in the world. Jodrell Bank’s contributions span from early pulsar research to pioneering work in very long baseline interferometry (VLBI), which allowed radio observatories on different continents to function as a single instrument.

The Parkes Observatory in New South Wales, Australia, opened its 64-meter dish in 1961. It played a significant role in receiving telemetry from the Apollo 11 mission in July 1969, a story that became the basis of the 2000 Australian film The Dish. More recently, Parkes was the facility from whose archived data the first confirmed fast radio burst was identified in 2007.

The Very Large Array (VLA) in New Mexico, operated by the NRAO, opened in 1980. It consists of 27 individual dish antennas, each 25 meters in diameter, arranged in a Y-shape across high desert terrain. By linking the dishes together electronically, the VLA achieves the resolution of a telescope 36 kilometers across. Its contributions range from detailed mapping of black hole jets to high-resolution images of distant radio galaxies and supernova remnants.

Arecibo, the 305-meter spherical reflector built into a natural limestone sinkhole in Puerto Rico, operated from 1963 until its collapse in December 2020. For 57 years it was the world’s most sensitive single-dish radio telescope. Among its discoveries: a measurement of Mercury’s rotation rate in 1965, the first exoplanets detected anywhere (identified in 1992 orbiting a pulsar by Aleksander Wolszczan and Dale Frail), and contributions to pulsar timing experiments that have since informed gravitational wave detection.

Fast Radio Bursts

Fast radio bursts (FRBs) are among the most perplexing phenomena in contemporary radio astronomy. They’re millisecond-duration flashes of radio waves so intense they briefly outshine entire galaxies before disappearing without apparent warning. The first confirmed one, now called the Lorimer burst after astronomer Duncan Lorimer, was identified in 2007 when Lorimer and his student Matthew Bailes were examining archival data from Parkes. The burst had actually occurred in 2001 but lay unrecognized in recorded data for six years before anyone understood what they were looking at.

For a time, astronomers weren’t certain whether FRBs were real astrophysical events. A subset of brief radio transients detected at Parkes turned out to originate from microwave ovens in the observatory’s break room, events researchers eventually named “perytons.” This discovery did not help FRBs’ credibility in some quarters. Years of accumulating events at multiple telescopes around the world were needed before the community was confident these signals were arriving from extragalactic distances.

The key turning point came in 2016 when the first repeating FRB, designated FRB 121102, was identified. Most bursts appear as one-time events, but this one was observed to fire repeatedly, making targeted follow-up possible. By 2017, its origin had been pinned to a dwarf galaxy about 3 billion light-years away. The leading explanation for most FRBs is magnetars, a type of neutron star with extraordinarily powerful magnetic fields. In April 2020, a magnetar in the Milky Way called SGR 1935+2154 produced a burst that, had it occurred in another galaxy, would have looked exactly like a fast radio burst from Earth’s perspective. That was a strong empirical case for the magnetar hypothesis, though some repeating FRBs show behavior complex enough that magnetars alone may not explain all variants.

The Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope in British Columbia consisting of four cylinder-shaped reflectors rather than a conventional dish, has detected hundreds of FRBs since beginning operations in 2018. Its design allows it to monitor a large swath of sky simultaneously, making it particularly well-suited to catching these fleeting events. FRBs are now being used as astrophysical probes in their own right: because radio waves disperse as they travel through intergalactic gas, measuring how much dispersion an FRB has experienced reveals information about the density of matter along its path. In 2020, this technique contributed to a measurement that confirmed the existence of the so-called “missing baryons,” ordinary matter that models predicted should be spread through intergalactic space but that had never been directly detected.

Imaging a Black Hole

No radio astronomy announcement in the 21st century matched the impact of April 10, 2019, when the Event Horizon Telescope (EHT) collaboration released the first image of a black hole’s shadow. The image showed the supermassive black hole at the center of the galaxy M87, about 55 million light-years away, surrounded by a bright ring of glowing gas with a dark center.

The EHT isn’t a single instrument. It’s a global network of eight radio observatories coordinated to function as a single Earth-sized dish through very long baseline interferometry. The facilities involved included sites in Chile, Spain, Mexico, Hawaii, the South Pole, and Arizona. By observing simultaneously at a wavelength of 1.3 millimeters and combining their data, the collaboration achieved angular resolution comparable to resolving an orange sitting on the Moon’s surface. The M87 black hole has a mass of about 6.5 billion times that of the Sun, and the image confirmed predictions of general relativity about how light bends near a black hole, with the shadow’s size and shape matching theoretical expectations within the measurement uncertainties.

In 2022, the EHT released a second image, this time of Sagittarius A*, the supermassive black hole at the center of the Milky Way. At roughly 4 million solar masses it’s far less massive than M87’s, but at approximately 27,000 light-years from Earth it’s far closer. Imaging it was technically harder because material orbiting it moves on timescales of minutes, while the observations took hours. The team developed new computational algorithms specifically to account for this blurring. The EHT project involved more than 300 researchers across 80 institutions in 20 countries, with data from all participating telescopes shipped physically on hard drives to processing facilities at MIT Haystack Observatory and the Max Planck Institute for Radio Astronomy in Bonn, because the total data volume, approximately five petabytes, was too large to transfer over any network.

Pulsars as a Gravitational Wave Observatory

The discovery of binary pulsars in 1974 hinted at an application for radio astronomy that’s only become clearer in recent decades. Millisecond pulsars, the fastest-spinning members of the pulsar family, keep time as accurately as atomic clocks. By monitoring the arrival times of pulses from dozens of millisecond pulsars distributed across the sky, astronomers can construct a gravitational wave detector on a galactic scale.

This technique, called a pulsar timing array, works because passing gravitational waves subtly stretch and compress the fabric of space-time, changing when pulses arrive at Earth by tiny but measurable amounts. The frequencies of gravitational waves detectable this way are far lower than anything LIGO or the Virgo detector are sensitive to, which means the two approaches are looking at entirely different populations of sources.

In June 2023, multiple pulsar timing array collaborations announced compelling evidence for a low-frequency gravitational wave background permeating the entire universe. The collaborations involved included the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), the European Pulsar Timing Array, and the Parkes Pulsar Timing Array. The most likely source of this background is the population of supermassive black hole binary systems across the cosmos, pairs of black holes each containing billions of solar masses, slowly spiraling toward merger as their host galaxies collide over billions of years. The result doesn’t announce itself dramatically, but once the implications settle in, it describes an extraordinary level of violent activity distributed throughout the universe at all times and at scales that human intuition isn’t really equipped to process.

FAST and What Comes Next

The Five-hundred-meter Aperture Spherical Telescope (FAST), built in a natural karst depression in Guizhou province, China, and completed in 2016, is the largest single-dish radio telescope in the world. Its collecting area is roughly twice that of Arecibo. The dish doesn’t physically move; instead, a receiver system suspended above it repositions to observe different parts of the sky. FAST began official scientific operations in January 2020 and has already produced a substantial body of work, discovering more than 600 new pulsars by 2022, more than any other facility had found in a comparable period. It’s also contributed to fast radio burst research and is conducting a systematic survey of hydrogen distribution across the Milky Way.

Something that deserves direct acknowledgment in discussions of FAST is that its construction required relocating approximately 9,110 residents from the surrounding area to reduce radio frequency interference from human habitation. The scientific return from the instrument is real and ongoing, but it came with a social cost that rarely appears in articles focused on its capabilities. Science rarely happens in a frictionless environment, and FAST is a sharp illustration of the trade-offs that accompany large infrastructure projects.

Whether FAST’s extraordinary sensitivity will detect something entirely unexpected, or whether its most lasting contributions will come from cataloging known phenomena in unprecedented detail, is a question that genuinely can’t be answered yet. The history of radio astronomy suggests the former is at least as likely as the latter.

The Square Kilometre Array

The next major leap in radio astronomy arrives with the Square Kilometre Array (SKA), an international project building the world’s largest radio telescope network, with facilities divided between South Africa and Western Australia. Construction was underway at both sites as of 2024, with initial science operations expected before the end of the decade.

The SKA-Low array in Western Australia will consist of thousands of simple dipole antennas sensitive to lower radio frequencies. It’s designed to probe the epoch of reionization, the era roughly a billion years after the Big Bang when the first stars and galaxies switched on and their radiation changed the state of intergalactic hydrogen. The SKA-Mid array in the Karoo desert of South Africa will use hundreds of dish antennas for higher-frequency observations, covering pulsar science, searches for prebiotic molecules, and detailed mapping of galaxies across a wide range of cosmic distances.

The SKA project involves 16 member countries and has been in development since the late 1990s. Among its science goals is measuring the distribution of hydrogen across billions of light-years of cosmic history, which would trace how large-scale structure formed and constrain the nature of dark energy with greater precision than any currently operational instrument allows. When complete, the SKA will be sensitive enough, at least in principle, to detect an airport radar operating on a planet 50 light-years from Earth.

The Chemistry of the Interstellar Medium

Radio telescopes have proven essential for a branch of research that doesn’t always receive the same attention as black holes and pulsars: mapping the molecular chemistry of space. Molecules in interstellar clouds emit and absorb radiation at specific radio wavelengths corresponding to their rotational and vibrational energy levels. By identifying these spectral signatures, astronomers can determine which molecules are present in the gas and dust between the stars.

The number of interstellar molecules detected this way has grown from a handful in the late 1960s to more than 200 as of the early 2020s. These include simple compounds like water and ammonia alongside surprisingly complex organic molecules. Glycolaldehyde, a simple sugar, has been detected in a star-forming region near the galactic center using radio telescopes. In 2022, propargylamine was found in a molecular cloud near the center of the Milky Way, adding to a growing inventory of organic chemistry occurring spontaneously in space.

This line of research connects radio astronomy to astrobiology in a way that goes beyond the search for signals from other civilizations. If complex organic molecules form naturally throughout the galaxy as a byproduct of stellar evolution and molecular cloud chemistry, the question of life elsewhere shifts. It becomes less about whether the raw ingredients exist and more about whether they’ve had the time and circumstances to assemble into something that replicates and evolves. Radio telescopes are providing an increasingly detailed answer to the first part of that question.

Summary

Radio astronomy has traced an arc that’s difficult to parallel in the history of science. The field began with an accidental detection in 1931, was sustained by an amateur working alone in suburban Illinois, and was then reshaped by wartime radar technology into a global enterprise that has since influenced every major branch of astrophysics.

The discoveries made by radio observatories don’t stay neatly within disciplinary lines. Pulsars became tools for testing general relativity. Fast radio bursts became probes of intergalactic gas density. The cosmic microwave background became the foundational evidence for Big Bang cosmology. Quasars demonstrated that the universe has a developmental history, that it was a different place in its youth than it is today. Interstellar molecular surveys are reframing questions about the origins of life. Each breakthrough opened questions that previous knowledge hadn’t even made possible to ask.

What often goes unremarked is how many of radio astronomy’s greatest discoveries were unplanned. Jansky was chasing noise. Penzias and Wilson were calibrating a communications antenna. Bell Burnell noticed an anomaly on paper chart output. The Lorimer burst sat in archived data for six years before being recognized. Even the Wow! signal was noticed by a human being reviewing printed readouts rather than automated analysis. The structured, hypothesis-driven international collaboration that produced the Event Horizon Telescope image represents an exception to the field’s dominant mode of discovery, not the rule.

There’s a new point that emerges from surveying this history, one that doesn’t follow directly from any single discovery: the universe is fundamentally stranger than any of the people who built the first radio telescopes could have anticipated. Not strange in ways that defeat understanding, but strange in ways that keep requiring new instruments and new ideas to even describe accurately. The SKA’s construction, FAST’s ongoing surveys, and the expansion of pulsar timing arrays all suggest the next unexpected discovery is more likely a matter of when than whether.

Appendix: Top 10 Questions Answered in This Article

Who made the first detection of radio waves from outer space?

Karl Jansky, an engineer at Bell Telephone Laboratories, detected radio waves originating from the center of the Milky Way in 1931 while investigating static interfering with transatlantic communications. He published his findings in 1933, effectively founding the field of radio astronomy, though the scientific community paid little attention for several years.

What is a pulsar and how was the first one discovered?

A pulsar is a rapidly rotating neutron star that emits beams of radio waves like a lighthouse, detectable as regular pulses from Earth. Jocelyn Bell Burnell discovered the first pulsar in August 1967 while analyzing paper chart data from the Mullard Radio Astronomy Observatory at Cambridge, and the discovery was initially so unexpected that the team nicknamed it LGM-1, for Little Green Men.

What is the cosmic microwave background and why does it matter?

The cosmic microwave background is the thermal afterglow of the Big Bang, a faint, uniform glow of microwave radiation at roughly 2.7 Kelvin that fills the entire observable universe. Arno Penzias and Robert Wilson detected it accidentally in 1965 while calibrating a Bell Labs antenna, and it remains the most direct observational evidence for the Big Bang model of cosmology.

What are quasars and how did radio observatories contribute to their discovery?

Quasars are extraordinarily luminous objects in the distant universe powered by supermassive black holes actively consuming surrounding matter, and they were first identified as unusual point-like radio sources before optical follow-up revealed their true nature. Astronomer Maarten Schmidt analyzed the spectrum of quasar 3C 273 in 1963 and recognized it was 2.4 billion light-years away, establishing that these objects existed only in the early universe.

How did the Event Horizon Telescope produce its black hole images?

The Event Horizon Telescope linked eight radio observatories across the globe to function as a single Earth-sized instrument through very long baseline interferometry, observing simultaneously at a wavelength of 1.3 millimeters. The 2019 image of the black hole at the center of galaxy M87 was produced by combining roughly five petabytes of data shipped physically on hard drives to processing centers at MIT and in Bonn, Germany.

What is a fast radio burst and what causes them?

A fast radio burst is a millisecond-duration flash of intense radio emission originating from extragalactic distances, briefly outshining entire galaxies before disappearing. The leading explanation for most FRBs is magnetars, a type of neutron star with extremely powerful magnetic fields, a hypothesis supported by a 2020 detection of a magnetar in the Milky Way that produced a burst matching the FRB profile.

What did pulsar timing arrays discover about gravitational waves in 2023?

In June 2023, multiple pulsar timing array collaborations including NANOGrav, the European Pulsar Timing Array, and the Parkes Pulsar Timing Array announced compelling evidence for a low-frequency gravitational wave background permeating the universe. The most likely source is the vast population of supermassive black hole binary systems across the cosmos, slowly spiraling together as their host galaxies merged over billions of years.

What is the FAST telescope and what has it achieved?

FAST, the Five-hundred-meter Aperture Spherical Telescope built in Guizhou province, China, and completed in 2016, is the world’s largest single-dish radio telescope with a collecting area roughly twice that of the former Arecibo Observatory. By 2022, it had discovered more than 600 new pulsars and has contributed to fast radio burst research, hydrogen mapping surveys, and the search for extraterrestrial signals.

What is the Square Kilometre Array and when will it be operational?

The Square Kilometre Array is an international radio telescope project under construction in South Africa and Western Australia, involving 16 member countries, with a total collecting area exceeding one million square meters. Construction was actively underway as of 2024, with initial science operations expected before the end of the decade, targeting goals including the epoch of reionization, pulsar science, and dark energy characterization.

What was the Wow! signal and has its origin been determined?

The Wow! signal was a 72-second narrowband radio signal detected by astronomer Jerry Ehman at Ohio State University’s Big Ear telescope in August 1977, matching predicted characteristics of an interstellar transmission well enough that Ehman circled it on the printout and wrote “Wow!” in the margin. It was never detected again despite decades of follow-up observations, and its origin, whether natural or artificial, has never been established.