Melbourne, June 27 (The Conversation) – Around midday on June 13 of the previous year, my colleagues and I, using a large radio telescope, detected what appeared to be an intriguing new celestial object. We observed a rapid flash of radio waves emanating from a location within our galaxy.
After a year of thorough research and analysis, we traced the source of the signal, which turned out to be much closer than anticipated.
A Discovery in the Desert
Our equipment was set up at Inyarrimanha Ilgari Bundara, also known as the Murchison Radio-astronomy Observatory, situated in the remote expanses of Western Australia, where the skies above the red desert plains are vast and awe-inspiring.
We employed a new detector on the radio telescope known as the Australian Square Kilometre Array Pathfinder (ASKAP) to hunt for rare flickering signals from distant galaxies, referred to as fast radio bursts.
During the investigation, we detected a burst. Notably, this burst lacked evidence of a time delay between high and low frequencies, commonly referred to as "dispersion".
This absence implied that the origin was within a few hundred light years from Earth, suggesting it was inside our galaxy, unlike other fast radio bursts that originate billions of light years away.
A Conundrum Arises
Fast radio bursts rank as the brightest radio flashes in the Universe, delivering 30 years’ worth of the Sun’s energy in under a millisecond. However, the mechanisms behind their creation remain largely speculative.
A few hypotheses suggest these bursts stem from "magnetars"—highly magnetized remnants of massive stars—or from cosmic collisions between these dead celestial bodies. Regardless, fast radio bursts serve as a crucial tool for mapping the so-called "missing matter" in the Universe.
Upon re-evaluating our data, we encountered a surprise: the signal seemed to vanish. After two months of trial and error, we identified the issue.
ASKAP comprises 36 antennas that, collectively, act like a large zoom lens spanning six kilometers. Much like a camera lens, attempting to capture something too close results in a blurry image. We resolved this by reducing the number of antennas, thereby minimizing the "zoom" effect, allowing us to image the burst.
Contrary to initial excitement, we felt disappointed, as no astronomical phenomenon exists close enough to cause such blurriness.
This led us to conclude it likely arose from radio-frequency “interference,” wherein human-made signals intrude on our data.
The typically discarded data was puzzlingly intriguing due to the burst's characteristics. It transpired swiftly—the fastest known burst lasted around 10 millionths of a second. This particular burst was a bright pulse, lasting mere billionths of a second, followed by two dimmer after-pulses, cumulatively spanning 30 nanoseconds.
The Mysterious Source: A Space "Zombie"?
We pinpointed its direction, estimating a distance of 4,500 km. The sole entity in that direction and distance at the time was a defunct 60-year-old satellite called Relay 2.
Relay 2 was among the pioneering telecommunication satellites, launched by the United States in 1964, operational until 1965, ceasing its functions in 1967.
But how did Relay 2 produce such a burst?
Some seemingly defunct satellites resume function and are termed "zombie satellites."
Yet, Relay 2 was not one of them. None of its systems could ever generate a nanosecond radio wave burst, even during its active phase.
The most plausible explanation appears to be an "electrostatic discharge." As satellites traverse electrically charged gases in space known as plasmas, they accumulate charge, akin to static electricity. This charge can discharge as a spark, causing a radio wave flash.
Electrostatic discharges are common and pose risks to spacecraft; however, known discharges last much longer than our signal and typically coincide with Earth’s magnetosphere activity. However, the magnetosphere was unusually quiet during our observation.
An alternative explanation involves a micrometeoroid—a tiny space debris piece—impact, similar to the James Webb Space Telescope incident in June 2022.
According to calculations, a 22 micro-gram micrometeoroid traveling at 20km per second striking Relay 2 could have resulted in a strong radio wave flash. However, the odds of such a phenomenon causing our detected burst hover around 1%.
The Pervasive Mysteries of Space
Ultimately, while the exact reason for the Relay 2 signal remains elusive, it unveiled a significant insight: monitoring electrostatic discharges from satellites using ground-based radio antennas is feasible. Given the burgeoning satellite population, alternative monitoring methodologies are increasingly critical.
And did our team eventually discover new celestial signals? Indeed, we did. The universe undoubtedly holds countless more waiting to be unearthed. (The Conversation) RD RD
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