kilonova: When Neutron Stars Collide

we all know that neutron stars are pretty extreme Stellar phenomena but what would happen if two of them ever collided Welcome to The Strange World of the killer Nova let's find out more kill anovas get their name from the fact that they are about a thousand times brighter than an over this does mean that they're about a tenth to a hundredth the brightness of a supernova and because of how they form they're incredibly interesting indeed I've made several videos discussing the formation of neutron stars in detail so I'll skip that bit and put a link in the doobly-doo below if you want to go and watch one of those very simply when a star with a mass between 10 and 25 times the mass of our sun comes to the end of its life it will explode in a supernova explosion This Will Blow Away much of the outer layers of the star and what you're left with is a neutron star this has the mass of a star but a diameter of only about 10 to 15 kilometers because of this these stars are some of the most extreme objects in the known universe if the star had been much bigger it would have formed a black hole instead so neutron stars have pretty extreme gravity and do weird things to the space around them so that's neutron stars in a very brief nutshell but why would two of them ever come close enough to collide well to answer that we need to explore the nature of star systems and gravity when we think of stars we tend to think of solitary Stellar objects maybe with some planets orbiting it the reality is quite different it would appear that the majority of stars maybe even up to 85 percent of stars exist in binary pairs or configurations involving an even higher number of stars this means that there are a large number of stars out there that exist in binary pairs were two stars orbit around a Common Center of mass even some of our nearest neighbors exist as pers or even larger relationships between Stars if two stars in a binary pair are both massive stars then at the end of their lives each of them will undergo a supernova explosion to produce two neutron stars now orbiting the Common Center of mass as they orbit each other they will gradually spiral inwards as they emit gravitational radiation in the form of gravitational waves and I'll talk about gravitational waves in a little bit as they spiral inwards they will gradually orbit faster and faster and the gravitational waves they emit will be stronger and stronger eventually the two neutron stars will be orbiting so quickly that they'll be completing about a thousand orbits per second these two stars will finally merge in just a few milliseconds they are spinning so fast that by this point that the material will be ejected in the shape of a donut this merger will cause another burst of gravitational waves and an intense burst of radiation in the form of gamma rays it also forms a number of heavy elements that are rejected as the two stars collide these elements are formed by a process called rapid Neutron capture process or the r process normally when Atomic nuclei gain neutrons the neutrons will Decay by Beta Decay so the neutron becomes a proton and an electron is emitted the nucleus then becomes stable again however in the r process the atomic nuclei gain the neutrons so quickly that they gain them faster than those neutrons can decay this means that the neutron number goes up and up in the nucleus this makes the nuclei more and more unstable until it comes to a point where no more neutrons can be added the atomic nucleus will then undergo beta Decay forming very heavy elements it's been calculated that a single neutron star merger could produce between 1 and 5 Earth masses of the element europium this is a soft metallic element that's rare on Earth they could also have produced between 3 and 13 Earth masses of gold what results from this merger very much depends on their combined mass below a certain Mass which is called the Tolman Oppenheimer volkov limit the merger will form a more massive neutron star above the Tov limit and the merged Stars will have too much mass to keep the star as a neutron star and gravity will crush it smaller and smaller until a black hole forms so what about gravity waves well gravity is one of the four fundamental forces of the universe but gravity is different it isn't a force in the same way that the strong nuclear force is a force but these four fundamental forces do govern the way that the Universe Works gravity exists as a result of mass all objects that have mass Bend space time and more massive objects Bend space-time more a good way to imagine this is to imagine the universe as a sheet of rubber in reality this will be a three-dimensional sheet of rubber but I've tried modeling this in three dimensions and it just looks a mess so if I put a massive object onto the rubber sheet it will bend the sheet this is gravity if I take a small ball and roll it along the sheet in a straight line the path of its movement will be bent by the warping of the sheet by the heavy object objects in the universe tend to want to move in a straight line but if they come too close to a very massive object like a star that movement will be warped into a circular orbit around the star so gravity warps space-time gravitational waves are massive pulses of gravitational energy that warp space-time around it these waves are created by the intense energies involved in the orbiting of the huge masses of the neutron stars these waves move outward at the speed of light warping space time as they move we can detect these gravitational waves to do this we use a magnificent piece of equipment called ligo or laser interferometry gravitational wave Observatory this consists of two detectors located three thousand kilometers apart in the USA each detector has two 1.2 meter diameter steel vacuum tubes four kilometers long the tubes are pointed at right angles to each other this detector actually works in the same way as the interferometers do that I talked about in my speed of light video a gravitational wave will change the length of one of these tubes and this can be detected in fact the first detection of gravitational waves was in 2015. these waves were caused by a merger of two black holes about 29 and 36 solar mass is Big even though the waves were huge by the time they traveled the billion light years to us the wave changed the length of one of the four kilometer tubes by a thousandth of the width of a proton or in other words it changed the distance from us here on Earth to the nearest star at Proxima Centauri by the width of a single hair so have we found any neutron star mergers and thus kill anovas well it appears the answer is yes the first candidate was grb 080503 the grb standing for gamma-ray burst and this was discovered by the Swift Space Telescope in 2008 this detection however proved to be inconclusive the next candidate was discovered in June 2013 as a short gamma-ray burst grb130 603b and this was then observed by the Hubble Space Telescope some days later however in 2017 we detected gravity waves and a gamma-ray burst nearly simultaneously coming from the same Source in the Galaxy NGC 4993 that's about 140 million light years away this also gave us some interesting information about the speed of gravity but that's for another video I've come to observe a killer Nova up close the gravity waves and gamma rays pass by some time ago and I'm watching the beautiful light show if you enjoy my Journeys around the universe then please consider subscribing and if you hit the Bell icon you'll be notified when a new video is released but for now and until next time thank you for watching [Music]

Channel: Learning Curve

Views: 155,913

Keywords: neutron star, ngc 4993, gamma-ray burst, gravitational wave, kilonova explosion, european southern observatory, gravitational waves, neutron star collision

Id: 7wKFxSwI_84

Length: 10min 2sec (602 seconds)

Published: Sun Mar 26 2023