- The Wow! Signal was an unusual radio signal from space detected in 1977 by the Big Ear radio telescope at Ohio State University.
- Astronomers have re-analyzed the old data, including related observations not previously published.
- It was not likely caused by terrestrial radio interference. It might have been a naturally occurring maser triggering a brief brightening in the hydrogen line of an interstellar gas cloud.
The Wow! Signal
Do you remember the Wow! Signal? It was a strong radio signal from deep space that the early SETI (Search for Extraterrestrial Intelligence) project at Ohio State University detected back on August 15, 1977. The enigmatic signal seemed like it might have been artificial in nature. But unfortunately, it was only detected once. Now, researchers from the Arecibo Wow! project at the University of Puerto Rico at Arecibo have re-analyzed this fleeting blip from the cosmos.
Researchers released a study on August 15, 2025, based on the signal and decades of unpublished, but related observations.
First, the findings suggest it was not caused by terrestrial radio interference. Their leading hypothesis is that it was from a maser. Masers are naturally occurring sources of stimulated spectral line emissions in the microwave portion of the electromagnetic spectrum. The Wow! Signal might have been a maser in an interstellar cloud of gas.
Astrobiologist Abel Méndez at the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo led the study. The study used archival data from the Ohio State University SETI program. In addition, it also used modern signal analysis techniques not available at the time of the initial detection.
The researchers submitted their findings to The Astrophysical Journal for peer-review. In the meantime, you can read the preprint version of the new paper on arXiv.
A mysterious radio signal from space
On August 15, 1977, astronomers at Ohio State University participating in the university’s SETI project detected the mysterious signal using the Big Ear radio telescope. It appeared to come from the direction of the constellation Sagittarius. Also, it seemed to have the characteristics that an artificial radio signal was expected to have, including being narrowband. Astronomer Jerry R. Ehman discovered the anomaly a few days later while reviewing the recorded data. On the computer printout, he circled the signal’s intensity, “6EQUJ5”, and wrote the comment “Wow!” beside it. The signal lasted for the entire 72 seconds of the observation window.
However, the signal was never detected again. So what was it?
New analysis of old data
The researchers from the Arecibo Wow! project re-analyzed the old data. That included the signal itself, as well as related observational records not published before. Also, the study also used modern signal analysis techniques. So, what did this new analysis show?
For one thing, they provide a more precise location of the signal in the sky. Specifically, using two adjacent sky fields, it was centered at right ascensions 19h 25m 02s ± 3s or 19h 27m 55s ± 3s, and declination –26° 57? ± 20? (J2000). Also, it suggested a stronger signal intensity of 250 Janskys (peak flux density of the signal). That is four times greater than previous estimates. Likewise, the analysis also revealed a frequency of 1420.726 MHz. That is within the hydrogen line, but with a greater radial velocity – the line-of-sight velocity of a target with respect to an observer – than previously believed.
New clues to the WOW mystery
To be sure, the findings still don’t reveal what the Wow! Signal was, but they do provide clues. Méndez said:
Our results don’t solve the mystery of the Wow! Signal, but they give us the clearest picture yet of what it was and where it came from. This new precision allows us to target future observations more effectively than ever before.
This study doesn’t close the case. It reopens it, but now with a much sharper map in hand.
New Study Narrows the Hunt for the Source of the Mysterious 1977 “Wow! Signal” phl.upr.edu/wow #AreciboWow #Astrophysics #SETI #WowSignal
— Prof. Abel Méndez (@profabelmendez.bsky.social) 2025-08-15T00:23:43.667Z
Today, August 15, 2025, marks the 48th anniversary of the Wow! Signal, and our Arecibo Wow! team has just revised its properties — they’re not exactly what we once thought. (1/n) phl.upr.edu/wow #AreciboWow #WowSignal #Astrophysics #SETI
— Prof. Abel Méndez (@profabelmendez.bsky.social) 2025-08-15T15:10:50.160Z
An astrophysical explanation?
Notably, the results of this new study suggest that the signal was not caused by terrestrial radio interference, as is often the case with unknown signals. On the other hand, it might not have been aliens. The researchers hypothesize that it might have been caused by a sudden brightening in the hydrogen line of an interstellar gas cloud. The hydrogen line – aka 21-centimeter radiation – is the electromagnetic radiation of radio wavelengths emitted by cold, neutral interstellar hydrogen atoms. In fact, astronomers believe it’s an ideal wavelength for alien civilizations to send radio messages.
As for the Wow! Signal, a powerful transient radiation source such as a magnetar flare or soft gamma repeater (SGR) could have triggered the brightening. But it’s still a hypothesis at this point.
In fact, a maser could have produced a narrowband signal with similar characteristics as the Wow! Signal. Masers are naturally occurring sources of stimulated spectral line emissions, typically in the microwave portion of the electromagnetic spectrum. See also this previous paper (2024) from Méndez et al.
Other possible sources for the Wow! Signal
In 2020, amateur astronomer Alberto Caballero had reported that the signal might have originated from a sunlike star – 2MASS 19281982-2640123 – 1,800 light-years away, in the direction of the center of our Milky Way galaxy.
And in 2016, astronomer Antonio Paris said that a passing comet might have been the source. However, that explanation was met with significant skepticism from some other astronomers at the time.
Bottom line: The Wow! Signal was a mysterious radio signal from space detected in 1977. To date, its source is not known, but a new analysis is narrowing the possibilities.
Source: Arecibo Wow! II: Revised Properties of the Wow! Signal from Archival Ohio SETI Data
Source: Arecibo Wow! I: An Astrophysical Explanation for the Wow! Signal
Via Planetary Habitability Laboratory
Read more: The Wow! Signal: New search comes up empty
Read more: Did the Wow! signal come from this star?
#analysis #closes #mysterious #source