Pulsars are some of the brightest objects we have found in the universe; they are dense spitting neutron stars that emit powerful beams of radiation at regular intervals, you can think of them as like the lighthouses of the universe. Over the years we've figured out how to harness some of that brilliance to help us find new planets, create entirely new fields of astronomy, and explore the ancient universe. We can create all the technology in the world, but sometimes nature has our solutions pre-made, like why build an exoplanet detector when we already have pulsars? Here's Reid to tell us why pulsars were the tools that helped us discover the first exoplanet.
if you're a fan of astronomy, you probably think you know the story of the first time we discovered a planet outside our solar system. It goes something like this Once Upon a Time long ago it was 1995. [Laughter] and by observing changes in a star's motion, Swiss astronomers found our very first exoplanets, orbiting the star 51 pegasi. It's an amazing story, but it has just one problem the planet that came to be known as 51 Pegasi b wasn't the first planet discovered around another star, or the second or even the third. It just happened to be the first planet we found around a star like our sun people often forget about the first true exoplanets because they orbit something very different, a pulsar. That's right, between 1992 and 94 astronomers discovered a whole star system around one of the weirdest objects in the universe. The Pulsar in question is psrb1257 plus 12 which thankfully some astronomers nickname Lich it's about 2300 light-years from Earth. Like all pulsars Lich is a special version of a neutron star an object with a kind of misleading name, they aren't stars in the normal sense because they don't convert High hydrogen into helium in their cores. Instead, these objects are actually the leftover cores of other stars they form when stars more massive than our sun and their lives and powerful supernova explosions, which are some of the most violent events in the universe. As the star explodes outward its core is compressed under unimaginable pressure, so much pressure in fact that the electrons and protons inside its atoms are literally crushed together into neutrons. What's left is basically a ball of solid neutrons about 20 kilometers across and because that ball is a lot smaller than what the course started as it also spins a lot faster just like how a dancer does when they pull in their arms Lich for example makes an entire rotation every 6.22 milliseconds most neutron stars have powerful magnetic fields which can blast out beams of radiation like radio waves depending on the star's orientation that beam can sweep across earth like a lighthouse as the star rotates sending a pulse of radio waves our way if it does we call it a pulsar timing this beam is how astronomers figure out a pulsar's rotation rate, and they're some of the most accurate clocks in existence I'm not kidding lich's period isn't exactly the 6.22 milliseconds I mentioned earlier it's actually well this and that incredible Precision is how the very first exoplanets were found in 1992 astronomers studying this recently discovered Pulsar noticed something unusual the timing of this supposedly super accurate clock seemed to be drifted it was a tiny change, but it was enough to alter the exact distance between Lich and Earth meaning its pulses sometimes arrived a little early or a little late and since we can normally rely on a pulsar's timing to be very steady these changes must have corresponded to stuff around it tugging on the star and affecting its orbit by looking for a pattern in the timing variations astronomers were able to figure out not only that there were planets three of them but also how massive they were they started out with some pretty technical names, but they've since been nicknamed Poltergeist phobiter and Drago and their masses were one of the real surprises not only do two of the planets have masses only a few times as much as Earth but one has a mass similar to our moon this makes them some of the smallest exoplanets ever detected, but you probably wouldn't want to visit there all three orbit their pulse are at least twice as close as the Earth orbits the sun which is probably a bad place to be with all those powerful magnetic fields actually if you think about it. It seems like these planets really shouldn't exist at all they shouldn't have been able to survive the Supernova that destroyed their original Star so how'd they do it easy they probably didn't it's much more likely that they formed after their host star blew up from another star that was also destroyed seriously if you see a star about to blow up just back away very, very quickly it gets nasty in there many neutron stars also have companion stars in orbit around them and Lich may have been no exception sometimes in systems like this material from that companion star gets pulled onto the neutron star it might even be an especially common process for pulsars eventually if enough material gets stolen the companion star basically descend integrates forming a disk of debris around the Pulsar now around regular young stars planets form from disks like this, so it's reasonable to say that that would happen around dying stars too. As far as we can tell that's likely how Poltergeist and its friends ended up in the universe, of course if that all sounds like a pretty unlikely scenario to you the data would agree while planets seem to be incredibly common around normal stars we found them orbiting less than one percent of known pulsars., and that's probably a good thing because Pulsar planets have to be among the universe's most tortured objects. I mean how many planets are born from a dying star while in orbit around another dying star it's not exactly a field of daisies the first exoplanets we ever found might often get overlooked but studying them can remind us that the universe is rarely what we think it's supposed to be like from the very beginning we knew exoplanets were going to be weird and since the 1990s we've been proven right over and over again having an object nearby tugging on the neutron star can throw its Pulsar signal off schedule and by following the timing of those signals very closely researchers have discovered the first exoplanet and provided the first evidence that gravitational waves exist here is how astronomers turn gravitational waves from thought experiments to real-life space experiments you might remember when scientists first detected gravitational waves back in 2015. It was a pretty huge deal they'd spent decades trying to prove this foundational piece of general relativity and the discovery gave us a whole new window into the universe but decades before all that excitement came to radio astronomers named Russell Hulse and Joe Taylor they made their own smaller discovery that paved the way for one of the biggest achievements in observational astronomy pulse was Taylor's Ph.D. student in the early 70s, and he was using the Arecibo telescope in Puerto Rico to look for pulsars dollars are neutron stars that spin really fast and emit Jets of energy from their poles so from Earth they look like blinking stars the astronomer Jocelyn Bell Bernell discovered the first one just a few years earlier in 1967. After finding some odd looking data while studying black holes and in the next few years scientists discovered dozens more, but pulsars were still kind of mysterious Hulse and Taylor wanted to learn more about these stars, and they had an idea if they could find a pair of pulsars in a binary system they could use information from their orbit to calculate some basic information like their masses so Hulse began an astronomical survey which means he basically just pointed the telescope at the sky and the hopes of finding something exciting after two years and 32 discoveries of Lone pulsars in 1974 he found well something weird it seemed to be a pulsar, but its flashing was uneven which was totally out of character see usually pulsar's flash like clockwork literally the timing of their pulses is more precise than an atomic clock Bell Bernal and her fellow researchers actually called the first Pulsar lgm1 because the timing was so reliable that it seemed like a signal from Little Green Men, but this pulsar's flashes varied by as much as 80 milliseconds so unless this was an entirely new astronomical object something seriously odd was going on here the weirdness of this object actually gave Hulse and Taylor some hope though if the variation happened regularly that would suggest that something was orbiting the Pulsar giving it a periodic tug and once they broke down the signal that's exactly what they found the Pulsar had a companion even though they couldn't actually see the second object they could tell a lot about it based on the pulsar's signal the companion was orbiting the Pulsar once every eight hours in a very eccentric or oval shape shaped orbit, and it exerted a serious gravitational pull on that Pulsar enough of a pole that it was probably a compact object either another neutron star or a small black hole so success they'd found what they were after but when Holston Taylor published their results in 1975 the astronomy World lost its Collective mind this system was like a ready-made laboratory for testing whether or not gravitational waves actually existed because back then gravitational waves were pure Theory general relativity predicted that they should exist and that they should Ripple through space-time itself and yeah general relativity seemed like a pretty solid Theory but this was a really wild consequence, and we had absolutely no evidence of it technically anything that has mass and moves like the Earth or even your hand emits gravitational waves but the vast majority of the time they're so incredibly weak that we have no way of detecting them, but two massive objects like neutron stars swinging around each other close to the speed of light that should make a gravitational splash in a system like this the gravitational waves should be big enough to carry away a significant amount of energy enough for astronomers to measure the effects unfortunately that's not the kind of setup scientists can just whip up in a lab, and it's not that easy to find in space either in fact before Holston Taylor came along we had never seen such a system like out in the wild, so people were excited to see what would happen with the Holst Taylor Pulsar if general relativity was right some of the gravitational energy that was keeping the pulsars in orbit should radiate out of the system in waves as the pulsars lost that gravitational energy they should drop into a closer orbit at the same time as the orbit tightened we should see the Pulsar speed up to conserve momentum in 1978 Taylor did some follow-up observations on the pulsar's timing, and he found just that in around four years the orbit sped up by a fraction of a second which was something scientists could actually measure and the amount of orbital energy being lost to the gravitational waves lined up exactly with what general relativity predicted it was the first observational evidence that gravitational waves actually existed and now that astronomers were as certain as they could be that these waves were a thing they could focus their efforts on detecting them directly soon after these results were published the first proposal for a large-scale gravitational wave detector was submitted to the National Science Foundation it took about 20 years to conceive and build the sucker but in 2002 the laser interferometer gravitational wave Observatory or ligo went online ligo is sensitive enough to detect the expansion and contraction of space as much as 10 000 times smaller than a proton but for the first eight years of operation it picked up nothing but violence in 2010 ligo shut down for some serious upgrades sudo souped up ligo reopened in the fall of 2015. Days later it made the first detection of gravitational waves which astronomers were able to trace back to a pair of merging black holes nearly 1.3 billion light years away all told we've directly detected gravitational waves from 23 collisions and two of them have been neutron star mergers systems similar to the Hulse Taylor binary until we found gravitational waves we relied on light to tell us just about everything we know about the universe but for the first time we have an entirely new medium to probe what's out there and while lots of things get in the way of light gravitational waves go through everything because they travel through space-time itself that means these gravitational waves give us a whole new window into the universe, and they have a ton to show us, but before we get ahead of ourselves we owe a lot the chance Discovery by a grad student nearly 50 years ago that led us here, so we have pulsars to thank for a new field of astronomy but aside from directing our attention to what's new pulsars can also take us very far back in time like to the first nanoseconds of the universe here's Caitlyn to explain how pulsars let us travel back in time telescopes you may have heard are time machines because light has a speed limit the deeper into space we look the older the signal we receive the oldest light we can see is called The Cosmic microwave background, and it comes from when the universe was less than 400 000 years old and while that's great and all it also means there are 400 000 years of History we just can't study using traditional methods that's why astronomers are so interested in finding techniques that don't rely on light and luckily for them and us there are some other waves out there that could reveal the universe when it was a teeny tiny fraction of a second old I'm talking about gravitational waves over a century ago Albert Einstein taught us that mass deforms the fabric of space-time kind of like how a bowling ball deforms a trampoline, but he also predicted that accelerating Mass would cause space itself to Ripple like the surface of a pond and back in 2015 we directly detected these gravitational waves for the first time that was thanks to a pair of black holes spiraling Inward and merging with one another but technically lots of things in space can cause gravitational waves and if we think of space-time like the surface of a lake all of these astronomical events are like raindrops whose gravitational waves interfere with one another and generate a kind of noise theoretically we could someday pick apart that noise to study specific events but what's maybe even more interesting is that beneath that noise space is actually filled with evidence of other older gravitational waves and those waves could teach us about the birth of the universe itself waves from way back then are called primordial gravitational waves and there are a few proposed sources for them according to many cosmologists some were generated by the formation and merger of still hypothetical primordial black holes these objects would act like regular black holes but would be less massive and may have sprung up from pockets of super dense matter in the very early Universe other primordial gravitational waves could have been generated by the formation of various particles as the universe cooled down the ultimate primordial waves though weren't caused by stuff in space they were made by space itself they come from a hypothetical period in the universe's history called inflation it's the time a tiny fraction of a second after the big bang around 10 to the negative 32nd to 10 to the negative 36 seconds when most cosmologists believe the universe expanded way faster than the speed of light for the record this wouldn't break the law that says nothing can travel faster than the speed of light because that not only applies to matter in space not to space itself regardless inflation still isn't set in stone there are definitely alternative interpretations for what could have happened back then gravitational waves are predicted in these alternative hypotheses too but detecting primordial waves will hopefully give cause cosmologist the data they need to pin down what actually happened for example they could use the amplitude of the waves to help define how fast everything expanded the energy involved in inflation and exactly when and for how long it happened and through other methods they could learn how consistent that inflation was across the whole universe of course before we can figure out any of that we have to actually detect these waves, and we do have a few options first there's the indirect method of detection which comes from looking at the cosmic microwave background according to the math gravitational waves older than the CMB would have influenced what it looks like specifically they would have caused a certain spiral pattern in the light that cosmologists call b-mode polarization we can already detect a different kind of polarization in the CMB called e mode and scientists are investigating the B mode kind but it's hard because it's a way weaker effect and these signals can also come from things like dust in the Milky Way the other option of course is just try to directly detect primordial gravitational waves using equipment similar to what we've used to detect the waves from black people merge right now to detect those events we mainly use interferometers like ligo which then laser pulses down two perpendicular arms if a gravitational wave passes through the system it'll compress or stretch things meaning one laser beam will have to travel farther than the other unfortunately none of our current interferometers is sensitive enough to detect primordial waves, but there are future projects in the works the main one is Lisa which will work roughly the same way as ligo except in space it'll consist of three spacecraft arranged in a triangle and separated by millions of kilometers and is scheduled to launch in 2034. The other direct detection method uses dense spinning objects called pulsars they shoot out beams of radiation as they rotate which can hit Earth at really regular intervals but if a gravitational wave pass through the space between the pulsar and Earth that interval would change and astronomers would be able to use details about the wave signal to figure out if they came from primordial or recent sources still figuring out what normal means is complicated because even if pulsars are known for being predictable there are still other factors that can affect how fast they rotate, and it's going to take time for scientists to pin down a model that's good enough to use pulsars effectively but once we find those elusive primordial waves it'll mean big things for astronomy we'll be able to figure out more about inflation and see back further than we ever have before and with more research we're getting closer and closer to understanding the moment our universe's story began even if the signals are only changing by a fraction of a second these pulsars have a lot to tell us when we bother to pay attention and while we have your attention here's a huge shout out to the incredible patrons of SciShow space's Patreon it is very, very good to have a community of people who love space and SciShow and learning new things about the final frontier we cannot thank those people enough for supporting these videos if you'd like to join that Community you can go to patreon.com space to sign up and when you join the most affordable tier whereas we sometimes say when you join The Space Cadets you can chat with your fellow Cadets in our Sideshow Patreon Discord server thank you for watching and as always thank you for your support.