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Imagine pointing one of the most powerful radio telescopes on Earth directly at the heart of our galaxy, hoping to eaves drop on an alien civilization. For hours, you sift through the blinding radiation and chaotic static of the galactic core and disappointingly don't find a single alien. It was worth a try. But you do spot the glimmer of something else. a faint rhythmic pulse. For 50 years, scientists had been searching for a signal like this. Evidence of a pulsar residing at the heart of the Milky Way. Our models say there should be thousands there. Yet, up until now, we'd only ever found one.
Finding where these pulsars are or why they aren't there could unlock the ultimate test of Einstein's theory of general relativity and confirm our cosmic models. But as quickly as this bright spark in the dark appeared, it vanished. Now we're left with a burning question. Has the mystery of the missing pulsars finally been solved? I'm Alex Mccoan and you're watching Astramm. Join me today as we get to grips with the mystery of the missing pulsars and reveal how the alien hunting powers of the breakthrough listen project may finally bring resolution to this cosmic conundrum.
The galactic center is the most densely packed energetic part of the entire Milky Way. A swirling mass surrounding Sagittarius A star, the super massive black hole at the core of our galaxy. And circling among the crowd are some truly gigantic stars, boasting masses as much as 130 times that of our own sun. While these Bermoths are impressive, it's the stars anywhere from 8 to 20 solar masses that we're interested in today. and more specifically their death. After these somewhat mid-range stars burn through their fuel, they don't go gently into that good night. No, they collapse inwards, crushing their stellar cores so densely that protons and electrons are forced together and combine to form neutrons
and electron neutrinos. If gravity continues to win against internal pressure, the star collapses in on itself until a black hole is formed. On the other hand, if the subatomic forces can withstand that final crush of gravity during collapse, which happens when the core is between 1.2 to three times the mass of our sun, the stars outer layers explode outward in a spectacular supernova, showering the galactic neighborhood in gas and dust. What gets left behind after that supernova is a stellar remnant called a neutron star. An object so dense that a teaspoon of its material would weigh billions of tons, similar to trying to hold a mountain in a spoon. I'll leave
that one up to your imagination. From here, the eventual fate of these new powerful cosmic remnants varies. Some slow down as they age, whilst others remain active as pulsars. As the core of a dying star collapses, it starts to spin faster and faster. Much like a figure skater who speeds up as they pull their arms and legs closer to their body due to the conservation of angular momentum. The forces involved are so great that the surface of these objects can reach 25% the speed of light, rotating as many as 716 times every second. To put that in context, it takes Earth just under 24 hours to complete just one rotation. In that time, the fastest spinning pulsar we found would have completed more than 61 million full turns. The most
interesting thing about this extreme spinning isn't the speed, however. It's the shocking irregularity. Why? Well, pulsars also have enormous magnetic fields that can be trillions of times stronger than Earth's. And this combined with the spinning turns them into cosmic lighouses. Let me explain. Just as neutron stars retain and amplify the spin of their parent stars, the same is true for magnetic fields, these amplified magnetic fields in turn create powerful electric fields thanks to the rapid rotation and Faraday's law of electromagnetic induction, which states that a changing magnetic field can induce an electric current. These electric fields then rip charged particles off the surface of the star, namely electrons and protons, and funnel
them into great beams that emanate from the magnetic poles. Just like a lighthouse, the beam spins with the neutron star, making it appear to us as if it's pulsing in regular predictable intervals as the stellar remnants take their final boughs. And because we humans have a knack for recognizing repeating patterns, we've been pretty good at spotting them in some places. Anyway, the very first pulsar was discovered in 1967 by graduate student Joselyn Bell along with her adviser Anthony Huish at the Mullled Radio Astronomy Observatory at Cambridge in the United Kingdom. That pulsar, now named PSR B1919 + 21, pulsed at intervals of 1.3373011 seconds. But initially, astronomers thought the repeating radio signal could be a beacon from extraterrestrial
intelligent life and jokingly named the unknown celestial phenomenon LGM1 for little green men. And so the extraterrestrial connection with pulsars began. But besides that, what I want you to take away from this is that pulsars are both bright and powerful. Things that you would assume are easy to spot when you're not talking about the galactic core. That is since the neighborhood around the center of the galaxy is so full of stars, new and old, large and small, the area should be packed with pulsars. We should find hundreds, if not thousands of them. But for decades, astronomers have been looking and have only found one. As usual for astronomers, they've given it an easy to remember name, PSRJ1745-2900.
And it was discovered in 2013 within one parseek of Sagittarius A star. So the question is, where are the rest of the pulsars? It's a mystery that's plagued scientists for almost as long as we've been studying these objects. And if we can't find them, then quite frankly, it means something in our understanding is wrong. And I hate it when I don't understand something, especially when there's no one to give me some help. But Brilliant, the sponsor of today's video, just fix that for everyone. Brilliant is a digital tutor that is a fantastic way to learn maths, coding, and more. It's a mixture of hands-on exercises and real-time personalized guidance. Let's say I want to learn about functions. I
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extraterrestrial communication in the form of radio and optical signals, what scientists call techno signature. Simply put, we are scanning the sky for any sign that aliens want to talk to us as much as we would want to talk to them. The project represents the largest scientific search for signs of intelligent life beyond Earth ever undertaken and includes surveying the 1 million stars closest to Earth, scanning the center of our galaxy and the entire galactic plane, and listening for messages from our closest 100 neighboring galaxies. The ambitious scan covers 10 times more sky than any previous survey and looks at a wider radio spectrum, all while doing it 100 times faster than ever before. A truly remarkable feat to undertake something
of such scale. The project utilizes a range of telescopes and the Green Bank telescope in West Virginia is one of the key instruments. This 100 meter wide radio dish is able to observe faint radio signals with extreme sensitivity and time resolution. The radio surveys are so sensitive they could hear something as small as an aeroplane transmitting from any of the 1,000 nearest stars. And the optical search is capable of detecting a 100W laser about the energy of a household light bulb from 40 trillion km away. That level of sensitivity and precision is what makes the data from the Greenbank Telescope such a pivotal tool in the search for extraterrestrial life. And it turns out that the same qualities that make a telescope good at hunting
for alien radio signals also make it potentially very good at, you've guessed it, finding pulsars. Being able to hunt for pulsars is important for two reasons. First up, finding another pulsar, particularly a millisecond pulsar, close to our galaxy's central black hole, Sagittarius A star, would be direct evidence of what astronomers have theorized for decades, that the pulsar population really is there. After all, one could just be a fluke. Maybe we got something wrong, find another, and the stakes change. It gives us reason to believe there could be many others waiting to be found. More on why that's easier said than done in a second. But even more exciting is that finding a faraway millisecond pulsar
would be like finding the most precise natural clock in existence. And having a precise clock that is orbiting close to a super massive black hole would also mean that we could test Einstein's theory of general relativity to see how it holds up in the most extreme conditions we know of. If a millisecond pulsar were confirmed in close orbit around Sagittarius A star, its extraordinarily regular pulses could act like a cosmic clock. The gravitational pole of the black hole would alter the orbit of the pulsar, while the black holes warp spaceime could also bend and delay the signals. Measuring those effects could provide an unusually precise test of Einstein's theory of general relativity.
The stakes are high as being able to conduct this kind of test would call into question the fundamentals of what we think we know about physics and relativity. But I'm getting ahead of myself. Let's go back to why these pulsars are so hard to spot. Recent studies have presented a theory that the reason we can't see these pulsars may be as simple as fog. And by fog, I'm referring to a veil of turbulent ionized gas. Enormous clouds of charged gas particles drift between us and the galactic center, scattering incoming radio waves as they pass through and distorting the view in exactly the direction we need to look.
Signals get delayed or smeared, kind of like how the beams of light from a lighthouse appear blurry from far away on a foggy night. This may seem insignificant, but for a pulsar whose beam flashes towards Earth hundreds of times per second, that signal distortion can prove fatal to detection. With a clear view, each pulse should look like a crisp spike of radiation for a fraction of a millisecond. But with the galactic fog in the way, the spikes get stretched and distorted into something that may last for seconds, effectively erasing the signal altogether, or at least erasing our ability to spot it.
Astronomers have traditionally searched for pulsars at lower radio frequencies because pulsars can be intrinsically brightest there, often peaking around 100 to 200 MHz. But those lower frequency signals are also more vulnerable to interference, making them harder to detect over long distances. But there is a way around this problem. Higher observing frequencies dramatically reduce the smear. In fact, doubling your observing frequency can cut the effect of scattering by a factor of roughly 16, making those otherwise smeared out pulses much easier to detect. And that's exactly what a team led by Karen Perez, at the time a PhD student at Columbia University and now a post-doal fellow at the SETI Institute,
did. They took Breakthrough Listen's galactic center data and turned it towards the missing pulsar problem. Just to get aliens out the way first, they fortunately or unfortunately, depending on your point of view, did not turn up. But buried in the data was one allimportant clue for our missing pulsar mystery. Perez and her collaborators looked towards the galactic center in the 8 to 12 gigahertz range known as Xband and commonly used for military and government communications to get a glimpse beyond the fog. The best frequency for observing in the galactic center can be as high as 9 GHz for ordinary pulsars and 22 GHz for millisecond pulsars. So the 8 to 12 GHz range at least covered a useful swath of
radio frequencies for the task. Between 2021 and 2023, the team logged nearly 20 hours of observations of the galactic center with 11 of those hours devoted entirely to the innermost region, the small patch of sky just around our galaxy's black hole, Sagittarius A star. At the sensitivity they achieved, the survey should have been able to catch roughly a tenth of the brightest millisecond pulsars and as much as half of the slower, more ordinary pulsars. That is if the galactic cent's population looked anything like what we see in the rest of the galaxy. But when the results came back almost completely empty, it only deepened the mystery and intrigue. But the key word here is almost.
Sifting through their data, the team's pulsar search turned up 5,282 separate signal candidates. 5,282 blips that were worth a second look. Nearly all of them turned out to be noise or interference or nothing at all. But one of them seemed to hold up after that second look. In the team's own words from their article in the Astrophysics Journal published in February 2026 among 5,282 signal candidates, we identify an interesting 8.19 millisecond SMP candidate. SMP just stands for millisecond pulsar. like a needle in a haystack. Out of thousands of may, exactly one looked like it might be a real millisecond pulsar, ticking
with a period of 8.19 milliseconds, spinning well over 100 times every second. It since picked up the name BLPSR for breakthrough listen pulsar, and this looks real. During a 1-hour scan, the signal held together with consistent timing, consistent frequency, and behaved similar to how a genuine pulsar should. It also carried a very large dispersion measure, or DM, a measure of how much ionized gas a radio signal has passed through on its journey to Earth. The team measured a DM of about 2775 parex per cubic cm, indicating that the signal had traveled through an unusually large amount of ionized material. The value is consistent with what you would expect from a source toward the distant
galactic center rather than a nearby object. And statistically, the signal is difficult to dismiss as simple noise fluctuation. In fact, the team's test found the probability of this being a false alarm was roughly one in a thousand based on its statistical properties alone and at around one in a million when the signal's coherent power and persistence are also taken into account. But despite those encouraging results, the researchers are careful about calling this a discovery. For one thing, BLPSR is not confirmed and it has a low signal to noise ratio. But what's perhaps most concerning is that BLPSR was only ever seen once. Every follow-up observation since has come back with nothing. That's a problem. In their own paper, the researchers
plainly write that they remain highly skeptical of BLPSR and that a much stronger burden of proof is required before anyone can responsibly claim it's real. That kind of honesty, while less exciting, is exactly what you want to hear from good scientists. So, what could explain a signal that showed up once and then vanished? Well, there are a few possibilities. Right now, the evidence isn't strong enough to claim this is a real pulsar, but that doesn't mean it isn't one. If BLPSR is a pulsar in a binary system, gas surrounding or flowing off a companion could sometimes obscure its radial pulses, making the pulsar detectable only during certain parts of its orbit.
The researchers also considered the possibility that complex orbital dynamics near the galactic center could make the signal harder to detect. That could help explain why it appeared during one observation, but wasn't recovered in subsequent searches. In an effort to find an answer, the team did something very unusual and made a decision that turned this from a very private mystery into a public one. Faced with an ambiguous, tantalizing, unconfirmed signal, the team didn't sit on it. They published it along with all their caveats and skepticism and then released the full observational data set publicly so that other astronomers
anywhere in the world could dig through it themselves, run their own analyses and either strengthen the case for BLPSR or rule it out. In a field this competitive, that is a very deliberate choice. Instead of keeping their research a secret and waiting to hopefully make the final confirmation themselves, the researchers invited the entire astronomical community to help. How fitting, I think, to share this journey of discovery. A discovery like this could help to answer questions that are bigger than any one research group. So, I love that it has been shared for the whole astronomical community to participate in. Let me know in the comments if you've taken a look at the data yourself and have any thoughts of
your own. And of course, there's always more searching still to do. The next generation of radio telescopes with instruments like the square kilometer array and the next generation very large array are being built with exactly this kind of problem in mind. more sensitivity, better frequency coverage, and a real shot at confirming BLPSR or catching other pulsars hiding behind the fog that obscures the galactic center. Whatever BLPSR turns out to be, one thing is certain, the fog around our galaxy's black hole is starting to clear, and on the other side of it may await the most important test of general relativity we've ever had the opportunity to run.
Somewhere out there, hundreds of these silent clocks are still ticking away in the dark, waiting for us to build a telescope sharp enough to find them. And when we finally do, we'll be listening to the universe check its own mass one pulse at a time. Thank you so much for watching all the way to the end of the video. And as a reward, I have a surprise for you. Some of you may remember the stunning Astron book we released a few years ago. Well, guess what? We have another limited run back on sale now, but only for US audience, I'm afraid. Unfortunately, everywhere else, they're all gone already. It's a spectacular journey through the solar system filled with not only the very best images, but explanations that will bring our cosmic
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