⏱️ 10 min read

In 1977, a radio telescope in Ohio detected a signal so powerful and unusual that the astronomer monitoring it scribbled “Wow!” on the printout—and to this day, no one can definitively explain what caused it. Our universe constantly broadcasts radio waves, gamma rays, and other electromagnetic signals across billions of light-years, and while most have natural explanations, some continue to baffle scientists. These mysterious transmissions from deep space challenge our understanding of physics and fuel speculation about everything from exotic stellar phenomena to technological civilizations beyond Earth.

Quick Facts

• The Wow! Signal lasted 72 seconds and was 30 times stronger than background radiation noise
• Fast Radio Bursts release as much energy in milliseconds as the Sun emits in three days
• Over 1,000 Fast Radio Bursts have been detected since the first confirmed discovery in 2007
• The BLC1 signal appeared to come from Proxima Centauri, our nearest stellar neighbor just 4.2 light-years away
• Some repeating signals from space occur with mathematical precision every 16.35 days

1. The Wow! Signal (1977)

On August 15, 1977, the Big Ear radio telescope at Ohio State University picked up a narrowband radio signal at 1420 MHz that stood out so dramatically from background noise that volunteer astronomer Jerry Ehman circled it on the computer printout and wrote “Wow!” in red ink. The signal originated from the direction of Sagittarius, near the Chi Sagittarii star group, and matched the expected signature of an interstellar transmission. Despite dozens of subsequent searches of the same region using more powerful telescopes, the signal has never repeated. In 2017, astronomer Antonio Paris proposed that a passing comet might have been responsible, but this explanation remains hotly contested because comets don’t typically emit at such specific frequencies.

2. Fast Radio Bursts (FRBs)

First discovered in 2007 by astronomer Duncan Lorimer while examining archival data from the Parkes Observatory in Australia, Fast Radio Bursts are millisecond-duration flashes of radio waves that can release more energy than 500 million suns. The vast majority appear to originate from distant galaxies billions of light-years away, making their incredible brightness even more puzzling. While most FRBs occur only once, some—like FRB 121102 discovered in 2012—repeat irregularly, and astronomers have traced this particular repeater to a dwarf galaxy three billion light-years away. Theories for their origin range from magnetar starquakes to colliding neutron stars, but the repeating nature of some FRBs has forced scientists to reconsider explanations that would destroy the source object.

3. The Lorimer Burst

The very first Fast Radio Burst ever identified, the Lorimer Burst (FRB 010724) was detected on July 24, 2001, but wasn’t recognized as significant until graduate student David Narkevic brought it to Duncan Lorimer’s attention in 2007. This signal originated approximately 3 billion light-years away and lasted just 5 milliseconds, yet swept across radio frequencies in a pattern that indicated it had traveled through intergalactic space. The dispersion measure—the way different frequencies arrived at slightly different times—told astronomers it had passed through enormous quantities of ionized gas. For six years, this remained the only known FRB, leading some skeptics to question whether it might be terrestrial interference or an instrumental artifact, but the subsequent discovery of hundreds more has validated its cosmic origin.

4. Breakthrough Listen Candidate 1 (BLC1)

In April 2019, the Parkes radio telescope in Australia detected a narrowband signal at 982.002 MHz that appeared to originate from the direction of Proxima Centauri, the closest star to our solar system at just 4.2 light-years away. The signal showed a slight frequency drift consistent with motion relative to Earth, and it appeared only when the telescope pointed at Proxima Centauri, disappearing when pointed elsewhere. Proxima Centauri hosts at least two confirmed planets, including Proxima Centauri b in the habitable zone, making this detection particularly intriguing. After exhaustive analysis published in 2021, researchers concluded that BLC1 was most likely radio interference from human technology, possibly from a malfunctioning electronic device, but the team acknowledged they couldn’t entirely rule out other explanations given the signal’s unusual characteristics.

5. Peryton Signals

For years, the Parkes Observatory in Australia detected mysterious millisecond-duration radio pulses that appeared to have astronomical origins, with scientists documenting them since 1998. These “perytons” showed dispersion patterns similar to cosmic sources and occurred irregularly, leading researchers to publish multiple papers speculating about their extraterrestrial nature. The mundane truth, discovered in 2015, proved both embarrassing and illuminating: staff members opening the facility’s microwave oven door before the timer finished created electromagnetic interference that mimicked cosmic signals. This revelation highlighted how even experienced research teams can be fooled by terrestrial sources, making astronomers more cautious about other unexplained signals and leading to improved protocols for distinguishing genuine cosmic phenomena from human-generated noise.

6. The SHGb02+14a Signal

In 2003, SETI@home—the distributed computing project that uses volunteers’ personal computers to analyze radio telescope data—flagged an unusual signal designated SHGb02+14a that has been detected multiple times near the 1420 MHz hydrogen line frequency. The signal originates from a point between the constellations Pisces and Aries, with no obvious star at that location, and it displays characteristics that don’t quite match either terrestrial interference or natural cosmic sources. What makes SHGb02+14a particularly puzzling is that it’s been observed on three separate occasions, yet not with enough consistency to definitively rule out terrestrial origins. Lead SETI scientist Dan Werthimer has emphasized that the signal is “probably nothing,” but its recurrence has kept it on the list of anomalies worth monitoring during future observations.

7. The Sagittarius A* G2 Cloud Signal

In 2014, astronomers monitoring the supermassive black hole at our galaxy’s center detected unexpected radio emissions as a mysterious cloud designated G2 made its closest approach. Predictions suggested G2 would be torn apart and consumed, producing dramatic fireworks, but instead it survived the encounter while emitting unusual signals that defied theoretical models. The object appeared to be either a gas cloud or possibly a star shrouded in gas, but its radio emissions showed characteristics inconsistent with both scenarios. Subsequent observations revealed G2 might actually be a binary star system, but the specific mechanisms producing the detected signals during its closest approach in 2014 remain incompletely understood, representing a gap in our knowledge of extreme gravitational environments.

8. Rotating Radio Transients (RRATs)

Discovered in 2006 by Maura McLaughlin and colleagues analyzing Parkes Observatory data, Rotating Radio Transients emit sporadic radio pulses separated by intervals ranging from minutes to hours. Unlike conventional pulsars that sweep radio beams across space with metronomic regularity, RRATs produce bursts seemingly at random, though statistical analysis suggests the underlying rotation is regular while the emission mechanism is intermittent. RRAT J1819-1458, one of the first discovered, emits a pulse lasting just 3 milliseconds roughly every 3 minutes, rotating once every 4.26 seconds. Scientists now believe RRATs might be a transitional phase in pulsar evolution or represent pulsars with extremely narrow emission beams, but the exact physics governing when and why they emit remains an active research question with implications for understanding neutron star magnetospheres.

9. The 2019 Canadian Hydrogen Intensity Mapping Experiment Signals

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope in British Columbia detected eight new repeating Fast Radio Bursts in 2019, including FRB 180916.J0158+65, which displays the first known periodicity in FRB activity. This source produces bursts during a 4-day window, then falls silent for 12 days, repeating this 16.35-day cycle with remarkable consistency. Located in a spiral galaxy roughly 500 million light-years away, the signal’s predictable pattern suggests a binary system might be involved—perhaps a neutron star orbiting a companion object. The mathematical precision of the periodicity rules out random astrophysical processes and points toward a regular physical mechanism, yet no existing model fully explains how such a system could produce the observed FRB characteristics, making this one of the most significant recent discoveries in the field.

10. The Stellar Radio Silence from Tabby’s Star

While not a signal from deep space in the traditional sense, the unusual light patterns from KIC 8462852 (nicknamed Tabby’s Star after astronomer Tabetha Boyajian) represent an unexplained electromagnetic anomaly that has perplexed scientists since 2015. The star, located 1,470 light-years away, exhibits irregular dimming events that block up to 22% of its light—far more than any known planet could cause. Extensive radio surveys by the SETI Institute and others searched for technological signatures that might explain the dimming as alien megastructures, but detected nothing. The absence of radio signals alongside the optical anomalies is itself puzzling; recent evidence suggests a debris field or dust cloud might be responsible, but the specific configuration required to match all observations remains elusive, and some aspects of the dimming pattern continue to defy conventional explanations.

Frequently Asked Questions

Has SETI ever detected an alien signal?

No confirmed extraterrestrial technological signal has ever been detected despite decades of searching. The Wow! Signal and BLC1 were both investigated as potential candidates but remain unconfirmed, with the latter most likely being terrestrial interference. SETI continues monitoring billions of radio frequencies, but has established rigorous protocols requiring repeated detection and verification before any signal could be confirmed as genuinely artificial and extraterrestrial in origin.

What causes most Fast Radio Bursts?

The leading theory suggests magnetars—neutron stars with extremely powerful magnetic fields—produce most Fast Radio Bursts through starquakes or magnetic reconnection events on their surfaces. This explanation gained strong support in 2020 when a magnetar in our own galaxy, SGR 1935+2154, produced an FRB-like burst that astronomers detected across multiple wavelengths. However, the repeating nature of some FRBs and the mathematical periodicity observed in sources like FRB 180916 suggest multiple mechanisms may be at work.

Could any unexplained space signals be alien communications?

While scientists cannot absolutely rule out technological origins for some unexplained signals, natural astrophysical phenomena remain far more likely explanations. The universe contains neutron stars, black holes, magnetars, and other extreme objects that produce electromagnetic radiation through processes we’re still working to fully understand. SETI researchers maintain that confirming artificial origin would require a signal to repeat on demand, show clear information content, or display characteristics impossible to produce naturally—criteria no detected signal has yet met.

Why do some signals never repeat?

Non-repeating signals might come from cataclysmic one-time events that destroy the source object, such as neutron star collisions or black hole mergers. Alternatively, the emission mechanism might be directional like a lighthouse beam—if Earth happens to be in the path during one rotation but the source’s orientation changes, we might never see it again. Some scientists also propose that emission occurs only under specific conditions that rarely align, making repetition possible but extremely infrequent on human timescales.

Key Takeaways

• Fast Radio Bursts represent the most active area of current research, with over 1,000 detected since 2007 and new discoveries revealing unexpected patterns like the 16.35-day periodicity of FRB 180916
• Historical “mysterious” signals like perytons demonstrate the critical importance of ruling out terrestrial interference before concluding a cosmic origin, a lesson that shapes modern SETI protocols
• Repeating signals provide the best opportunity for understanding unexplained phenomena because they allow follow-up observations across multiple wavelengths and with different instruments
• The absence of confirmed technological signals despite decades of searching doesn’t prove we’re alone—it reflects the immense difficulty of detecting faint transmissions across interstellar distances and the possibility that alien civilizations might use communication methods we haven’t yet imagined