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If the thought of receiving radio signals from space conjures an image of Jodie Foster in the movie Contact,Watch Jeunes veuves lubriques (1995) hunched over a computer console and listening for spaceship schematics beamed to Earth by intelligent beings from Vega, that’s, um, adecent first steptoward understanding what scientists have in mind when they tune in to space’s radio signals. The reality is less cinematic, but that doesn’t make it boring. 

Radio telescopes — most famously the ill-fated Arecibo Observatory in Puerto Rico, but also peppered across deserts worldwide — are not really for detecting deliberate communications signals from aliens. That would be like saying the eyes on your head are for detecting rabid grizzly bears. That wouldn’t be a misuse, but it’s hardly a description of why they’re there.

In fact, radio telescopes really are a bit like the eyes on your head, in that they’re less listening, as the term "radio" suggests, and more seeing what’s sometimes called the "radio sky," meaning everything detectable in the broad spectrum of emissions given off by the cosmos itself from Earth’s vantage point — things like pulsar beacons, solar flares and their effects, and the universe's microwave background radiation. But the radio sky also includes signals from closer to home like space probes, and even the satellites orbiting around us. 

In 2024, the radio receivers on and around the human homeworld captured a variety of fascinating emissions, some of which are mysterious, none of which are probably from space invaders, and all of which are more interesting than fiction. Here are five of the most intriguing signals of 2024:

A mysteriously slow pulse

Picked up by the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope, this signal known as ASKAP J193505.1+214841.0 was spotted before this year, but the team that found it published its findings in June 2024. This is a deeply puzzling radio signal in that it repeats almost hourly — every 53.8 minutes to be more precise. That’s way too slow to be anything astronomers currently understand. 

The gap between ASKAP J193505.1+214841.0 emissions is too slow to be a pulsar, since pulsars emanate from neutron stars that are rotating fast — literally achieving drill bit-like RPMs. The length of this newly discovered gap has left scientists baffled so far, but every new discovery about nature starts off as the discovery of something that should be "impossible."

A powerful, faraway burst

Imagine "staring" up at the radio sky (we’re speaking figuratively here). To a radio stargazer, the radio wave bursts known as fast radio bursts (FRBs) might appear like quick blinding flashes that momentarily drown out all other signals before quickly disappearing. FRB 20220610A is one such powerful radio wave burst — one that happens to have traveled through space for 8 billion years before being detected. That’s old; the Big Bang was 13.8 billion years ago.  

Not only is FRB 20220610A — also detected by ASKAP, this time with the help of the Hubble Space Telescope — one of the most distant FRBs ever detected, but it’s also one of the "brightest" (actuallymost energetic) radio signal bursts ever picked up by humanity’s receivers. The source may have been a place in space with "as many as seven galaxies on a possible path to merging," according to a NASA blog post about the discovery.

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Radio pollution from Elon Musk

Researchers in the recent past have already complained about problematic signals given off by the over 6,000 SpaceX-operated Starlink satellites orbiting the Earth, beaming data down to internet users here on Earth’s surface. The signal given off by the satellites represents unwanted noise to certain instruments attempting to observe the radio sky. However, researchers at the Netherlands' LOFAR observatory discovered in 2024 that the brand new V2-mini line of satellites emit up to 32 times more unwanted noise than earlier Starlink models. 

Starlink noise is obscuring astronomers' observations of certain low frequency signals needed for the study of exoplanets, black holes, and ancient cosmic phenomena. It’s not unheard of for the law to step in and protect radio telescopes from such noise. Radio quiet zones exist for their benefit, but these zones are policed for things like interference from nearby mobile phones, and have nothing to say about objects launched into space. Satellite-based radio emissions are an unregulated frontier, and Starlink has tossed about 6,000 satellites into that regulatory void. Thanks as usual, Elon!

Another FRB with important clues for scientists 

Another FRB is shedding light on the mysterious origins of massive radio signal bursts in 2024. This is a fresh finding from the study of phenomena called magnetars — in this case magnetar SGR 1935+2154, which actually shot out its intriguing signal back in 2020. After pinpointing the source of magnetar SGR 1935+2154, the team at Caltech’s Deep Synoptic Array-110 (DSA-110) now says such signals come from neutron stars in massive, star-forming galaxies that are rich in metals. This finding significantly narrows the possibilities for finding neutron stars with FRB-creating attributes, meaning our understanding of where these extreme events occur is becoming more precise.