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2020년 9월 3일 목요일
10.08 - 평가문제(Module 10: Riding the Gravity Wave)
10.08 - 평가문제(Module 10: Riding the Gravity Wave)
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10.07 - Summary: The Final Countdown
10.07 - Summary: The Final Countdown [커세라 강의 페이지]
Black holes on the media are portrayed as matter-thirsty objects with infinite hunger. They tear astronauts apart, cause incalculable damage, and facilitate impossible feats of time travel. These often misunderstood objects have been discovered and studied only over the last half century.
I want to thank you for joining us on this learning expedition. While black holes appear to be mysterious, we have learned that the basic ideas and observations can be described using known scientific principles.
Black holes on the media are portrayed as matter-thirsty objects with infinite hunger. They tear astronauts apart, cause incalculable damage, and facilitate impossible feats of time travel. These often misunderstood objects have been discovered and studied only over the last half century.
지난 50여년간 수많은 미디어에 노출되며 악명을 쌓아온 블랙홀. 이로인해 몰이해에로 이어졌다.
Black holes reveal to us the depth and breadth of the known universe, and the tremendous success of general relativity, but they do hide their dark sides.
As the brightest objects in the universe quasars and blazars are powered by supermassive black holes accreting material onto accretion disks. Recent black hole mergers observed by LIGO reveal just how many black holes are out there. And observations from the Event Horizon Telescope give us our first glimpse at Sagittarius A*, our galaxy's very own supermassive black hole. But physicists are well aware that we have much more to learn about black holes, and to pass that knowledge on to artists and filmmakers who have a passion for science.
최근들어 블랙홀 관측이 이뤄지면서 블랙홀을 더 이해하게 되었고 더많은 예술가들과 영화 제작자들이 과학적 열정을 가지게 됐다.
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In this course, we learned that a black hole forms, if we can find a way to squash the mass of an object down into a small volume with a radius less than or equal to the Schwarzschild radius.
It's difficult to make a black hole since this matter is squeezed into smaller volumes, other forces will tend to oppose this motion and push outwards.
For instance, in a star, nuclear reactions in the core of the star heat up the star and provide an outward gas pressure that balances gravity. As a result, we have stars that can live long stable lives for billions of years, potentially providing heat to life on orbiting planets.
정역학 평형으로 오랜동안 항성으로 지내다가,
Black holes can form when very high mass stars can provide enough heat from nuclear reactions, to provide the gas pressure and keep up hydrostatic equilibrium. The laws of nuclear fuel leads to the implosion of the star that can in some cases create a black hole. Another way to create a black hole is to smash two neutron stars together. If the resulting mass of material has a high enough mass it can collapse into a black hole.
핵반응이 넘쳐 초신성으로 폴발한 후 블랙홀로 변하기도 한다. 작은 블랙홀이 충돌하여 더 큰 블랙홀이 되기도 한다.
I don't know about you, but I'm feeling overwhelmed by all the information I learned from the course. I really want to go back now to the scenes in Star Trek that we discussed at the beginning of the course, to compare what we saw then to what we know now. As you probably recall, in 2009 Star Trek movie reboot, red matter is employed as a quick method of creating a black hole.
While there is still no scientific basis for red matter or even the creation of a black hole through current human technologies, the destruction of the planet Vulcan due to a black hole is still a frightening thought.
We now know that even if it were possible to create a black hole say in a particle accelerator like the Large Hadron Collider, the black hole would be tiny. It will be so small that its temperature would be millions of times hotter than the sun. And quantum effects would quickly work on evaporating the black hole through Hawking radiation.
If the mass of the red matter black hole were similar to the mass of a proton, then the Hawking radiation would make black hole unstable, and it would disappear in a tiny fraction of a second after it was formed.
This might create a small burst of energy, but not nearly enough to destroy a planet. That's not where the scientific inaccuracy stop either.
Let's say that red matter did create a miniature black hole that caused the collapse of the planet surface, the planet wouldn't vanish as it did in the movie instead, the infalling matter would accrete around the black hole, heating up to thousands and millions of degrees. Instead of watching the collapse, you would see instead blinding x-ray radiation, literally blinding if you happen to be close.
Although scientists have never observed such low mass black hole, it's likely that all models applied to accretion disks, larger black holes would scale appropriately.
I don't bring up these issues because the scientific inaccuracies make Star Trek a poor movie, quite the opposite in fact. Without shortcuts around some of the difficult scientific principles, Star Trek would just be another documentary about black holes. But when scientific principles are applied correctly like they were in Interstellar, the whole story gains a renewed significance. Where Star Trek lives in the realm of science fiction, we can envision ourselves in a scientifically accurate future like Interstellar portrays.
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We can often find shortcuts taken by filmmakers and artists while portraying the astonishing environments around black holes, but the reality of black holes is much stranger than anything that has yet been captured on film.
Science fact, as it were, still beats science fiction for the strangeness of black holes. Einstein's insights into the structure of space-time, insights that required a powerful imagination along with an app for mathematics, were a giant leap from the Newtonian framework of gravitation.
As a result, we know that in our universe there's a trade-off between how quickly you can travel and how quickly the clocks in your reference frame tick. Even thinking about that is giving me a bit of a brain cramp.
Imagining space-time is nothing compared to speculating about the interior of black holes. In both Disney's The Black Hole and Christopher Nolan's Interstellar, characters are portrayed as crossing the event horizon.
As astounding as the effects may be, the events portrayed in these movies taking place within the event horizon of a black hole is pure speculation.
Physicists make use of Penrose diagrams to try and explain the interior of black holes. Modern theories predict that anything that enters into a black hole will have to collide with the singularity, which is likely fatal. We talked about the escape from a black hole as an impossibility, but we also know that the process of Hawking radiation allows the escape of particles from a black hole when pairs of particles and anti-particles are created near the event horizon.
So, which is it? Can particles escape from black holes, but not something big like me? As quantum physicists are keen on saying, information cannot be destroyed. So, what happens when I drop a memory device into the black hole? Can I read that information out of the Hawking radiation at a later time? Does the black hole somehow encode everything falling into it as the universe's most compact hard-drive?
In time, we can observe black holes in greater detail, we may not be able to learn the answers to these questions. These are the questions that I spend a lot of time pondering and I hope that I've gotten you thinking about them as well. It has been an honor teaching you.
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The idea of a black hole has been around for a long time and more recently a key component of many science fiction tales. Optical observations of black hole binaries have allowed us to look at the companions to black holes, watching them move in orbit around the binaries common center of mass.
Using this information, we have been able to find out more about the types of stars that hang out with black holes. We have been able to learn about how they can transfer material to the black hole, and how black holes can get their food.
X-ray and radio observations of black hole binaries have given us the opportunity to learn more about what's going on close to the black hole by giving us an insight into accretion processes. These views allow us to test theories about the physics of matter in the presence of extreme gravity.
While we are currently unable to visit the black hole ourselves, observations of them have taught us much more about the universe.
The closest known black hole to us is V616 Monocerotis. It lives about 3,500 light years away from us. V616 Mon is a black hole that lives in a binary system with an orange companion star. The black hole weighs in at about seven solar masses.
The furthest known black hole, ULAS J1342+0928 was discovered in 2017. This supermassive black hole has a mass of 800 million solar masses. Its light has taken 13.1 billion years to get to us and was emitted only 619 million years after the Big Bang.
The discovery of distant black holes allows us to learn more about the early universe, the formation of the first supermassive black holes, and the formation of galaxies.
The smallest known black hole, XTE J1650-500, with a mass that is approximately five times the mass of our sun. This means the event horizon radius is only 15 kilometers. The largest known black hole is S5 0014+81, an optically violent variable quasar. This black holes mass is 40 billion solar masses.
And it's also one of the most luminous black holes, emitting radiation equivalent to 10 to the power 14 suns. The faintest black hole is something harder to determine. One contender is that is Swift J1357.2-0933, a stellar mass black hole in a binary system, located only 4,900 light years away. And it emits light that is only 100 times brighter than the sun in the X-ray band.
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I want to thank you for joining us on this learning expedition. While black holes appear to be mysterious, we have learned that the basic ideas and observations can be described using known scientific principles.
Astrophysicists are well aware that a theory of quantum gravity is required to explain quantum phenomena associated with black holes on tiny scales. However there are plenty more unknown unknowns, that we can only just begin pondering about, like the nature of gravitational waves.
The observations of gravitational radiation from merging black holes and neutron stars has opened up a new way to learn about black holes. We can't know what will be discovered, but we can guess some possibilities. I'm hoping we will observe gravitational waves from merging supermassive black holes at the centers of galaxies.
Maybe we'll get to see the first evidence for a binary system composed of a neutron star and a black hole, giving off gravitational waves as they merge. It may also be possible to see gravitational waves when stars are tidally disrupted by black holes.
I hope that you have gained the tools to understand new discoveries about black holes, and to communicate those ideas clearly. Maybe one day I will read about your new discovery.
Thank you.
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[인터뷰] [커세라 페이지]
How does a neutron star's vibrations affect binary inspiral?
Interview with Dr. Jocelyn Read, Professor at California State Fullerton
When we talk about a binary of black holes or a binary of neutron stars orbiting each other, the main signature of the gravitational waves comes at twice the frequency of the orbit basically. Each time one of the objects passes, say, in front of you, that's stirs up another cycle of the gravitational wave signal which eventually reaches the observer.
But just like you have, say, a wineglass has a particular resonant frequency and you see, say, an opera singer sings the right note and the wineglass can shatter. So one of the research projects that I worked on, was understanding how the energy of the orbiting system, when the orbital frequency, the frequency of the orbits matches up with the natural frequency of an individual star that can transfer energy into the stars vibration.
So this can do some pretty dramatic things like similar to how a wineglass can shatter if you hit the right note, the solid crust of the neutron star might shatter if it sweeps through the right frequency in the orbit. So some collaborators and I worked through, that that might cause some high-energy flares that you could see in association with a gravitational wave signal or independently even.
So these oscillations taking away energy from the orbits, if they're strong enough and it has to be a huge amount of energy to affect the gravitational wave, but they can also drive the stars to merge earlier, so instead of spending the energy in orbiting, the energy goes into the vibration of the stars instead and that actually leads them to crash together. So they're losing energy to gravitational waves and then they lose extra energy to this vibration.
10.06 – 펄사 타이밍 어레이(Pulsar Timing Arrays)
10.06 – 펄사 타이밍 어레이(Pulsar Timing Arrays) [커세라 강의 페이지]
Since existing gravitational observatories can only detect the strongest waves created in collisions of massive black holes and neutron stars, future detectors are being made with ever increasing sensitivities to find more subtle changes in the fabric of spacetime.
Since existing gravitational observatories can only detect the strongest waves created in collisions of massive black holes and neutron stars, future detectors are being made with ever increasing sensitivities to find more subtle changes in the fabric of spacetime.
현존하는 중력관측소는 아직 블랙홀이나 중성자별 처럼 강력한 중력파만을 감지할 수 있지만 미래에 감도가 더욱 향상되면 미세한 시공간의 변화도 탐지해 낼 수 있게 될 것이다.
One concept being developed is called a Pulsar Timing Array, which would allow scientists to probe Einstein's general theory of relativity and the effects of gravitational waves over thousands of light years.
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수천광년 떨어진 곳에서 날아오는 아인슈타인의 상대론의 중력파를 감지할 수 있는 중력파 관측 기술로 펄사 타이밍 어레이(Pulsar Timing Array)가 개발중이다.
Since a pulsar is a rotating neutron star which emits a jet of radiation, if the beam of the jet points towards Earth, we detect a short radio burst. Those radio bursts arrive at regular intervals, sweeping across the earth for every rotation of the pulsar.
펄사는 강력한 전파원이다. 펄사는 중성자별이 자전하면서 주기적으로 전파를 방출하기 때문에 지구에서 보면 펄스(주기적으로 간헐적인 전파신호)로 관측된다.
The fastest spinning pulsar, PSR J1748-2446AD, which lives within the globular cluster of Terzan 5, 18,000 light years from earth, rotates 716 times per second, which would sound like an F5 tone if the radio pulses were converted to sound. A spinning pulsar is of great interest, because some pulsar's rotation rates are incredibly stable. So much so, that they can arrival the precision of atomic clocks. So, PSR J1748, the fastest spinning pulsar has been measured to rotate exactly once every 0.01395952482 seconds, with an error of less than 600 femtoseconds.
1만 8천광년 떨어져 있는 빠르게 자전하는 펄사 PSR J1748-2446AD는 초당 716회 돈다. 지구에서 관측하면 716 헤르츠 신호의 펄스로 가청 주파수로 변환하면 '파'에 해당하는 음이다[Musical Pitches]. 펄사의 자전은 매우 안정되어 있어서 펄스의 주기가 원자시계 만큼이나 정확하다. 실제로 PSR J1748 펄사의 자전 주기는 0.01395952482 초로 오차는 600 펨토초(1백조 분의 1초, 10^-15초) 밖에 않된다.
This incredibly precise timing, is one of the most accurately measured observables in all of astrophysics. By the way, this pulsar was discovered by Dr. Jason Hessels, who graduated with a Bachelor of Science in Honors Physics from the University of Alberta.
The precision of a pulsars rotation rate is very much like a clock ticking at regular intervals. Just like the effects of gravitational Doppler shift that redshift photons as they escape from a gravity well, gravitational waves alter the timing of pulses from pulsars.
정밀한 펄사의 자전주기는 시계의 똑딱임과 유사하다. 광자가 중력 장벽을 빠져 나올때 적색 편이를 일으키듯이 중력파가 펄사의 똑딱임을 변화 시킨다.
In order to actually do anything useful though, you need several pulsars in an array. Now, you know why they're called pulsar timing arrays.
[원문 설명에 애매함이 있음]
이를 실제로 활용하기 위해선 배열형으로 펄사를 탐지해야한다. 이를 가리켜 펄사 타이밍 어레이라 한다. [여러개의 탐지 시설/혹은 안테나를 묶어 하나의 커다란 고성능 안테나로 사용하는 방법. 위상배열(Phased-Array)이 있다.]
It may be easier to imagine pulsar timing arrays as similar to the technology that underpins the Global Positioning System, or GPS. The GPS sensors in smartphones and navigation devices work by listening carefully for radio signals from GPS satellites high in orbit above Earth. By comparing the arrival time of the pulses from each GPS satellite, your device can triangulate your position on the surface of the earth.
펄사 타이밍 어레이는 GPS 기술에 비유할 수 있다. 다수의 GPS 위성에서 전파 신호를 수신하여 도착된 시각차를 삼각 측량법으로 계산하면 지표면상의 위치를 정확히 알 수 있다. [다수의 위성 사이에 정확하게 동기를 맞춰 발사한 펄스 신호가 지상에 도달하면 거리에 따라 시간차를 갖는다. 이 시간차를 측정은 위상차에 의해 계산된다. 이는 위상배열 안테나와 같은 원리다.]
NASA's NICER/SEXTANT X-ray telescope, which is on the International Space Station, is observing a collection of X-ray pulsars to test out the feasibility of using pulsar arrays as future navigational aids. By listening to the regular pulses from several nearby pulsars, you could triangulate your position anywhere in interstellar space around those pulsars.
우주정거장에 설치된 NASA의 NICER/SEXTANT X선 방원경으로 펄스 신호를 수집하여 미래의 우주선 항행 시스템을 실험하고 있다. 몇개의 펄사로부터 펄스 신호를 수집하여 삼각측량법으로 우주선의 위치를 파악하려는 것이다. [ISS Utilization: NICER/SEXTANT]
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This map, created by the Jet Propulsion Laboratory, was affixed to the Pioneer 10 spacecraft, which after completing a survey of Jupiter became the first satellite with sufficient escape velocity to leave the solar system. The image shows the relative positions of pulsars near Earth with their particular timings encoded on the line that joins them. If this map were discovered, the position of Earth could be deduced.
펄사를 활용한 위치지정은 이미 1972년과 1973년에 각각 발사된 파이어니어 10호와 11호에 장착된 '파이어니어 금속판(Pioneer Plaque)'에 지구의 위치를 새겨 넣었다. 지도에 위도와 경도로 위치를 특정 하듯이 지구에서 가까운 14개의 펄사의 거리와 방향 그리고 주기를 새겨 놓았다
14개 펄사의 방향이 모인 곳이 지구의 위치다. 펄사에서 지구의 거리와 방향을 선을 그어 표시 했고 각 펄사의 식별부호로 주기를 2진수로 기록했다. 펄사의 주기는 1973년에 관측한 것이므로 보이저호가 발사된 연도를 표시하시도 한다. 우주에서 가장 흔한 중성 수소의 천이시 방출되는 전자기파 1420Mhz의 주기(0.000000007=7x10^10초)를 시간의 기본단위로 사용했다.
But our civilization hasn't reached the point of navigating with pulsar timing arrays. Instead, we're patiently listening to them for evidence of large scale gravitational waves passing in between Earth and the pulsars.
아직 우리의 문명이 펄사 타이밍 어레이를 활용해 항성간 여행의 단계에 이르진 못했다. 하지만 펄사와 지구사이를 지나는 대규모 중력파를 꾸준히 탐지하는 중이다.
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When a gravitational wave passes in between the Earth and a pulsar, it causes a distortion of spacetime that affects how signals propagate. Generally speaking, the signals from pulsars will either appear delayed or accelerated due to the influence of a passing gravitational wave.
지구를 스치는 중력파가 시공간을 왜곡한 결과 신호전파[빛의 전달 경로]에 영향을 준다.
Just like a black hole creates a gravitational potential well and the associated effects of gravitational redshift and time dilation, so too can a gravitational wave create immeasurable effect as it passes by.
Imagine for example that you usually drive to work or school on a flat road. The time it takes you to get from point A to point B along your route takes about the same amount of time. What would happen if all of a sudden along the route, a hill appeared? Or what if a depression appeared in the road instead? In both cases, the time it takes you to go from A to B will change ever so slightly depending on the size of the hill. A gravitational wave in spacetime is just like this hill.
예를들어 A지점에서 B지점까지 이동하는 시간을 재보자. 평지라면 매번 이동할 때마다 시간은 동일하다. 갑자기 경로상에 언던이 나타나거나 웅덩이가 나타나면 이동시간은 느려지거나 빨라질 수도 있다.
Only since it's a wave, it will be a moving hill. If the timing of a gravitational wave is just right, it compresses the space time that the pulsar signals are travelling through offsetting the arrival time by a small difference, which is called the timing residual.
중력파는 움직이는 언덕과도 같다. 시공간을 줄일 수도 있고 늘릴 수도 있다. 이동 구간신호에 약간의 시간차를 잃으킨다. 이 시간차를 잔류시간(timing residual)이라 한다.
The timing residual is a measurement of the difference between the expected arrival time of the signal and the observed arrival time. Since gravitational waves can both stretch and squeeze spacetime whether the signal is delayed or accelerated will depend on the geometry of the pulsar timing array and the incident gravitational waves.
잔류시간은 예상 시간과 실제 소요사간의 차이를 측정한다. 시공간을 늘이거나 줄일 수 있는 중력파로 인해 신호전파는 펄사 타이밍 어레이와 입사되는 중력파에 의해 지연되거나 가속되기도 한다.
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So far, this method of monitoring pulsar timing arrays has not resulted in any observations of gravitational waves. However, techniques like these are a complement to the interferometer based gravitational observatories, and will eventually contribute to the detection of more massive binary collisions.
아직 펄사 타이밍 어레이 방식으로 이렇다할 관측 결과를 내고 있지는 않고있다. 하지만 이 방법은 간섭계 기반의 중력파 관측을 보완하여 이중성 관측에 효과를 보게될 것이다.
아직 펄사 타이밍 어레이 방식으로 이렇다할 관측 결과를 내고 있지는 않고있다. 하지만 이 방법은 간섭계 기반의 중력파 관측을 보완하여 이중성 관측에 효과를 보게될 것이다.
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[인터뷰] [커세라 페이지]
What is a pulsar timing array?
Interview with Dr. Ingrid Stairs, Professor at the University of British Columbia
For the poolside timing array, they were looking at an array of pulsars over the sky, but basically all around the sky. So we really need an international collaboration to use telescopes all over the world to do this and the idea is to look for correlations.
So commonalities in the pulse arrival times of these pulses that are around the sky.
So since they're acting like lighthouses though, these are very very regular spinners, stable rotators.
So if they have pulses that come a little earlier, a little late there's some reason for it.
And with the pulsar timing of array, we're looking for pulses that are close together in the sky to be early together or late together.
Pulses that are sort of 90 degrees apart to be out of sync, one comes early, the other comes late. And then pulsars that are a 180 degrees apart on the sky, opposite sides of the sky to be more in sync again, not completely, but mostly.
And so if we can see that pattern in the timing from the pulses all over the sky, we will have some confidence that we've seen a gravitational wave passing near the Earth.
And probably we're going to see gravitational waves from a whole collection of these supermassive black hole binaries, which are slowly spiraling into each other.
We're catching them, we're aiming to catch them at orbital periods of a few years. So not right at the point where they're about to merge, but getting in there.
And we think these should be all over the sky, because galaxy mergers are happening all over the sky.
And if every galaxy has a supermassive black hole at its center which we think they do, then those two black holes should naturally sink in together toward the center of the new galaxy and and produce gravitational waves as they're doing it.
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10.05 – 중력파 망원경(Gravitational Telescopes)
10.05 – 중력파 망원경(Gravitational Telescopes) [커세라 강의 페이지]
Gravitational waves are extremely weak. These waves wouldn't be felt by a human, for example, or any other living creature for that matter. So in order to detect gravitational waves, scientists must use the most sensitive instruments ever invented. What devices are suitable for measuring incredibly small changes? Well, lasers of course, and that means we'll also need our good friend, the Michelson-Morley interferometer.
Gravitational waves are extremely weak. These waves wouldn't be felt by a human, for example, or any other living creature for that matter. So in order to detect gravitational waves, scientists must use the most sensitive instruments ever invented. What devices are suitable for measuring incredibly small changes? Well, lasers of course, and that means we'll also need our good friend, the Michelson-Morley interferometer.
Remember interferometers leverage the wave nature of light to measure the difference in lengths between different beam paths. When coherent light, light that has the same phase such as laser light, is split between two different paths and is later recombined, its brightness will depend on how different the two paths were.
For example, if a red laser with a wavelength of 650 nanometers is introduced into an interferometer, it will produce a bright spot at the end of the detector if there's no difference in the beam path. If one of the arms differ in length by half of the red wavelength or 325 nanometers, the interference between the two beams produces zero light.
So small changes in the length of one arm of the interferometer can be measured by the changing brightness of the resulting pattern of light at the detector.
The original Michelson-Morley interferometer was developed to determine if the flow of ether caused a delay in one of the device's two arms instead of the difference in the arms' lengths. Like a boat travelling against the current of a river, the theory of light back then predicted that moving ether would cause a delay in the upstream arm.
The opposite was discovered; that there was never any delay no matter what the orientation of the device with respect to the motion through the supposed ether. This proved that light waves don't require a medium like ether to travel in and as a consequence, the speed of light is a constant.
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In order to leverage the sensitivity of interferometers, astronomers built the Laser Interferometer Gravitational-wave Observatory, whose acronym is LIGO, pronounced "L-eye-go" or sometimes "L-ee-go".
These are two massively improved versions of the Michelson-Morely interferometer built on either side of the continental United States. One detector is in Hanford, Washington while the other is precisely 3,002 kilometers away in Livingston, Louisiana. They each have two arms but instead of short meter long arms, like the original Michelson-Morley interferometer, each of the arms of LIGO is four kilometers long.
In addition to the length, each arm bounces light from the laser source back and forth about 280 times making each arm of LIGO equivalent to the length of 1,120 kilometers.
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Why are LIGO's arms so long? Well, it's hunting for some of the weakest signals that the universe has ever thrown at us. In fact, in order for LIGO to detect the strongest gravitational waves, it needs to be able to distinguish a change over the four kilometer length of its detector arms, a difference in length 1,000 times smaller than the radius of a proton.
But one LIGO isn't enough to catch a gravitational wave, we need at least two. There are several major gravitational wave observatories in operation around the world. The two LIGO observatories were the first, followed by Virgo, and a host of others in operation and under construction around the world.
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If one LIGO detector is sensitive enough to measure a change in its arm length down to the level below the width of an atom, why make more? Well, the first and most important reason is noise. Yes, sounds, footsteps, earthquakes, and cosmic gravity quakes, all register in LIGO as a change in the length of LIGO's arms.
In order to filter out footsteps from a colliding black hole, you need a second detector. LIGO second detector, built in Livingston, Louisiana, has a different set of sounds, footsteps, and earthquakes. But presumably, the two LIGO detectors would both see the same gravitational wave coming from an intergalactic source.
To determine whether a wiggle in one LIGO detector is the result of a gravitational wave, scientists compare the data from the second. If there's a wiggle at nearly the same time, remember the detectors are separated by 3,002 kilometers, with nearly the same shape, scientists can be confident that they really saw a gravitational wave and not some researcher sneezing in the control room.
But there's another important reason to have more than one gravitational observatory; direction. With only two LIGO detectors, an incoming gravitational wave will not have a well-defined direction. Just like having two ears gives a stereo hearing, two LIGOs let us determine approximately where the sources.
Although with only two, there's still uncertainty about which direction it came from. In order to pin down the source of gravitational waves, a third gravitational observatory is necessary. In the case of the Kilonova explosion resulting from the merger of two neutron stars in 2017, the gravitational wave signal was also detected by a third gravitational wave observatory, Virgo, in Italy.
With all three gravity wave observatories up and running, most major astrophysical merges will be detected. Over the next few decades, these types of observatories will get more and more sophisticated, detecting dozens of compact object collisions in the universe. But things will get really interesting once we send these massive observatories into space.
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In order to really make the most sensitive gravitational wave observatories, scientists work hard to remove sources of error. Just like telescopes, which are better if they're on mountain tops but best if they're in space, a space-based gravitational observatory wouldn't have to worry about earthquakes or someone tripping on a banana peel near the detector.
Know the next generation of gravitational observatories will be built in space. The Laser Interferometer Space Observatory, whose acronym is L-I-S-A, universally pronounced as "L-ee-sa" but I would argue it should be pronounced "L-eye-sa" in this case.
LISA consists of three spacecraft which will trail behind earth in its orbit around the Sun, flying in a triangular formation. Each of LISA's arms extend between the three spacecrafts. Instead of a puny 1,120 kilometer effective arm length, LISA will have three 2.5 million-kilometer-long arms.
LISA will still be sensitive to small changes in the length between the arms but we'll have an incredible sensitivity of 20 picometers over the 2.5 million-kilometer-long arms. As a result, LISA will be able to detect much smaller and quieter collisions than LIGO but also begin probing into the processes by which compact objects are captured by but not collided with black holes.
10.04 - 쌍성계와 중력파(Binaries and Gravitational Waves)
10.04 - 쌍성계와 중력파(Binaries and Gravitational Waves) [커세라 강의 페이지]
When two stars are in orbit around one another in a binary system, their positions change periodically in time. Since the gravitation force between an astronomer and a star depends on the distance and the direction to the stars, an observer will feel time changing gravitational force, as the two stars orbit one another. As we watch the stars in orbit, we will see the brightness of the system change as they pass in front of one another as they continue their dance through the universe.
To preserve causality, there has to be a delay there has to be a change in the gravitational force that is synchronized with the brightness changes as the locations of the stars change. In other words, the two stars changing positions cause gravitational waves to be emitted by the binary system.
These gravitational waves will distort spacetime and cause objects far away to be squeezed and stretched periodically. The energy for these distortions is carried away from the binary system by a wave. This means that the gravitational waves carry energy away from the binary, and the binary loses orbital energy.
중력파는 시공간을 왜곡 시키고 천체를 멀리 밀어내기도 하고 끌어들이기도 한다. 이 왜곡으로 인한 파동에 실려 에너지가 빠져나가면 쌍성계는 궤도 유지 에너지를 잃게 된다.
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The stars in a binary system are moving in ellipses in accordance with Kepler's Laws.
One component of the total energy is their kinetic energy, which is kept in balance by their gravitational potential energy. By summing both the kinetic and gravitational potential, we will obtain the total energy for the system.
This total energy is large when stars are far away from one another,
The process of gravitational wave emission and the inward spiral is incredibly slow. Therefore, at any moment in time, we can rearrange Kepler's Third Law to relate the distance between the stars, A, to the time it takes the stars to make one full orbit, P.
As the stars slowly spiral inward, their masses do not change, only the distance between the stars change.
질량의 변화 없이 나선을 그리며 안으로 궤도 반경 a가 줄어든다.
In Kepler's Third Law, when A gets smaller, so does the orbital period. The star takes less time to orbit when they're close to one another. The result of the loss of energy through gravitational radiation causes binary star systems to slowly spiral inward. As this process continues, the stars' orbits speed up, and they can come closer together, appearing to spin more rapidly around one another. This slow death spiral will eventually cause the two stars to collide, merging into one big star.
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This sounds dangerous. How common would such a phenomenon be?
쌍성계의 파국은 얼마나 자주 일어날까?
This death spiral only affects binary stars that are both tiny and extremely close together. In order for two stars in a binary to spiral in and merge within the present age of the universe, so about 13 billion years, the distance between the stars has to be no bigger than the diameter of our sun. That's pretty close.
Typical main sequence stars that are found in binary pairs in our galaxy, are but much further away from each other than one astronomical unit. And if you recall, one astronomical unit is the distance between the sun and the Earth. So these typical stellar binaries are in no danger of undergoing inward death spirals.
항성처럼 핵연료 소실에 따른 전자기 복사 에너지 방출로 인한 질량 감소로 생기는 총 에너지 변화는 매우 느리다. 주계열 별의 수명이 백억년에 달한다는 점을 상기하자. 게다가 두별의 거리가 1천문단위(1AU) 정도 떨어질 때 급격한 충돌을 일으킨다. 따라서 항성으로 이뤄진 쌍성계가 충돌하는 장면을 볼일은 거의 없다.
This would be long after both stars burn through their nuclear fuel anyway. In fact, the in-spiral of the Sirius binary system takes such a long time that we can ignore the effect of gravitational radiation on this system and all other binaries of main sequence stars.
It contains a pulsar and a neutron star that orbit one another once every eight hours. Therefore, they are separated by a mere three light seconds, which is similar to the diameter of the sun.
Together, the two neutron stars slowly spiral in towards each other, allowing Hulse and Taylor to detect the change by measuring the orbital period of the pair over time. They found that the orbit of the two starts slows by approximately one-tenth of a millisecond every year. This tiny change in orbital period agrees with the predictions of gravitational radiation coming from Einstein's theory of general relativity.
매년 공전 주기가 약 1/10 밀리초 가량 줄어드는 것으로 관측되었는데 이는 두 중성자 별이 천천히 나선을 그리며 접근하기 때문이다. 이런 미세한 (공전주기의) 변화는 아인슈타인의 상대론에서 제기된 중력파의 방출에 의한 에너지 손실과 일치 했다.
So in the years since 1974 scientists around the world have been working on the development of sensitive gravitational observatories that allow us to measure the stretch and squeezing of space time by a gravity wave passing by.
시공간을 줄였다 늘였다 하면서 지금도 우리 주위를 지나가고 있는 중력파를 감지하기 위해 1974년 이래로 전세계 과학자들이 정밀한 중력파 관측장치의 개발에 노력해왔다.
Modern gravitational observatories use LASERs to detect gravitational waves. These machines can identify the spiraling of neutron stars at a much later stage. These neutron star binaries have got so close together that they are able to orbit one another more than 25 times per second. Once a pair of neutron star orbit this quickly, they radiate energetic gravitational waves.
최신 중력파 검출기는 레이져를 이용한다. 이 장비는 중성자 별 쌍성계가 충돌 직전의 나선 움직임을 관측할 수 있다. 이 단계의 중성자별 쌍설계의 공전주기는 초당 25회가량 된다. 이정도 주기면 상당히 강력한 중력파가 방출된다.
The energy of the emitted gravitational waves increases more and more until the two stars spiral close enough that they collide and finally merge. A merger like this can happen in an order of minutes.
중력파를 따라 손실되는 에너지가 점점 많아 지면서 두 중성자 별의 나선 충돌은 가속된다. 마침내 충돌은 수분내에 끝난다. [언재 어디서 순식간에 일어나는 충돌을 관측해야 한다.]
In August of 2017, such an inspiral of a neutron star binary was detected. In this instance, astronomers also managed to observe the same part of the sky through gamma-ray, X-ray, visible light, and radio waves.
However, in August, 2017, the astronomers witnessed a short gamma-ray burst right after the merger. This confirmed the suspicion that astronomers had had that short gamma-ray bursts are the result of neutron stars smashing into one another.
The smashing together of neutron stars initiates nuclear reactions that allow the formation of elements more massive than those formed in stars. That is elements that are heavier than iron.
This includes elements such as gold, platinum, and heavy radioactive elements. So the next time you wonder where the gold for jewelry comes from, some large fraction of your ring or necklace is the debris of a collision of two neutron stars.
But what is made at the core of this merger? When two neutron stars merge, there are two possible outcomes for the object left behind. The remnant of the merger could either be a more massive neutron star, or it could become a newly formed black hole. The outcome of the merger depends on the mass that remains.
Neutron stars have a maximum allowed mass. This maximum mass is not exactly known, but it's somewhere between two and three times the mass of our sun. Astronomers commonly state that the maximum mass is three solar masses for ease of definition. But the largest mass is probably a bit smaller than this. If we knew this mass more accurately this would be helpful when we try to distinguish between neutron stars and black holes.
중성자 별이 될 수 있는 한계는 정확하지 않으나 태양의 3배정도 질량이다. 이 중성자 별의 한계질량을 정확히 안다면 블랙홀과 중성자별을 확실히 구분 할 수 있을 것이다.
When the two neutron stars merge, if the total merged mass is smaller than the maximum neutron star mass, then we will end up with a neutron star. But if the mass is too high, the neutron star will be unstable and will collapse to form a black hole.
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The collapse of a neutron star into a black hole should also create gravitational waves. These would be more difficult to detect. There was no evidence for waves like these in 2017 neutron star merger. Unfortunately, this means that we just don't know whether the collision resulted in a larger neutron star or a new black hole. This is an example when no detection does not answer the question.
At present, there has been no observable evidence for a binary system composed of a neutron star and a black hole. But there is no reason why such a binary shouldn't exist. Assuming that they do exist, there is also no reason why they should not also be able to in spiral and merge.
현재로선 블랙홀과 중성자별로 구성된 쌍성계가 있다는 관측된 증거도 없다. 그렇다고 그런 쌍성계가 없다고 할 수도 없다. 그런 쌍성계가 존재 한다 쳐도 나선형 충돌을 할지 안할지도 알 수 없다.
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Let's imagine what would happen if a black hole merges with a neutron star. Astronomers have tried to model this, and we think it would look very different to that of two neutron stars merging.
블랙홀과 중성자별의 충돌을 상상해보자.
While the neutron star and the black hole start to inspiral, it becomes clear that in the end, the neutron star will be ripped apart.
중성자별이 나선 궤도로 블랙홀에 접근하다 깨져 버리고 (조석력은 강력하다!),
If a merger of a neutron star and black hole is ever detected, it will be big news and we'll have to update this course.
중성자 별과 블랙홀의 충돌이라는 확실한 증거가 검출되기만 한다면 커다란 뉴스가 될 것이다. [중성자 별이 산산조각 날때 무슨일이?]
When a binary system consists of two black holes, they will also inspiral towards each other due to the emission of gravitational waves and ultimately merge together. The end state of two black holes merging will be a bigger black hole.
As the two black holes merge, for a brief period of time, the black hole is a highly distorted mess. But the no-hair theorem tells us that the normal state for a rotating black hole is a smooth event horizon.
During the final merger stage, the distorted black hole emits gravitational radiation in a process called Quasi-Normal Ringdown. Where all the bumps and wiggles gets moved out. The final resulting black hole is a Kerr Black Hole(=Rotating Black Hole), of the sort we looked at earlier in the course.
The data from black hole and neutron star mergers helps astrophysicists understand the distribution of black holes and neutron star sizes in our galaxy. But also, the wider universe. The merger of neutron stars can produce either a new neutron star, or a new black hole. When black holes merge, they form heavier.
This diagram summarizes the black hole food chain as we know it at the end of 2017.
Finally, at the top of the diagram, there are blue circles, which are joined by arrows that show the merger of lighter black holes, to form heavier black holes.
맨 윗층의 청색은 블랙홀 들로서 가벼운 블랙홀이 합쳐져 무거운 블랙홀이 된다.
Some of these black hole mergers start off with black holes that are about 30 solar masses, and create black holes that add up to about 60 to 70 solar masses. This is really exciting, as we can now witness the merger and growth of black holes. Perhaps, this process might lead to the formation of intermediate mass black holes.
Ground based gravitational wave observatories are responsible for the direct detection of merging black holes in a stellar mass range. But feature orbiting space-based gravitational wave detectors are needed before we can detect the merger of supermassive black holes.
We have discussed a lot about the detection of gravitational waves up to this point, but how do these detectors actually measure the effect of a passing gravitational wave? That is next on our agenda. So let's find out now.
When two stars are in orbit around one another in a binary system, their positions change periodically in time. Since the gravitation force between an astronomer and a star depends on the distance and the direction to the stars, an observer will feel time changing gravitational force, as the two stars orbit one another. As we watch the stars in orbit, we will see the brightness of the system change as they pass in front of one another as they continue their dance through the universe.
쌍성계는 두 천체의 질량중심으로 서로 공전한다.
To preserve causality, there has to be a delay there has to be a change in the gravitational force that is synchronized with the brightness changes as the locations of the stars change. In other words, the two stars changing positions cause gravitational waves to be emitted by the binary system.
쌍성계의 밝기변화가 두 별이 서로 공전하면서 위치가 바뀌는 것과 서로 인과관계가 있는지 알아보자. [무거운 밀집 천체(중성자별이든 블랙홀이든)가 쌍성을 이루며 돌 때 중력파가 발생하는지 볼 겸]
These gravitational waves will distort spacetime and cause objects far away to be squeezed and stretched periodically. The energy for these distortions is carried away from the binary system by a wave. This means that the gravitational waves carry energy away from the binary, and the binary loses orbital energy.
중력파는 시공간을 왜곡 시키고 천체를 멀리 밀어내기도 하고 끌어들이기도 한다. 이 왜곡으로 인한 파동에 실려 에너지가 빠져나가면 쌍성계는 궤도 유지 에너지를 잃게 된다.
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The stars in a binary system are moving in ellipses in accordance with Kepler's Laws.
One component of the total energy is their kinetic energy, which is kept in balance by their gravitational potential energy. By summing both the kinetic and gravitational potential, we will obtain the total energy for the system.
쌍성계가 가진 총 에너지는 운동에너지와 중력 포텐셜의 합이다.
This total energy is large when stars are far away from one another,
두별이 멀리 떨어져 있을 때 총 에너지는 크고
and smaller when stars are closer to each other.
가까이 있을 때 총에너지는 작다.
This effect is caused by the emission of gravitational radiation. Outgoing waves carry energy away from the binary, causing the stars to fall inwards, orbiting closer and closer to each other, shrinking the orbit of the system, and instead, forming an inward spiral.
두 별의 공전으로 시공간의 주기적 변화는 중력복사를 일으킨다. 중력파는 쌍성계 에너지를 밖으로 내보내게 되어 쌍성계의 총 에너지가 감소하고 별은 안으로 몰린다. 두별은 궤도 유지를 못하고 나선을 그리며 점점 가까워 진다. 마침내 충돌한다.
[이런 모형은 중력파에 의한 에너지 손실을 전제로 한다. 중성자별이나 블랙홀 처럼 아주 무거운 별이 쌍성계를 이룰 때 중력파가 발생한다. 블랙홀은 전자기 복사(핵융합 원료 소모) 따위는 없는 블랙홀 쌍성계에서 에너지를 잃게되는 요인은 중력파 뿐이다.]
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The process of gravitational wave emission and the inward spiral is incredibly slow. Therefore, at any moment in time, we can rearrange Kepler's Third Law to relate the distance between the stars, A, to the time it takes the stars to make one full orbit, P.
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Here, we see P, the orbital period, is equal to the square root of a cubed, divided by the sum of the masses of the two stars.
질량의 변화 없이 나선을 그리며 안으로 궤도 반경 a가 줄어든다.
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In Kepler's Third Law, when A gets smaller, so does the orbital period. The star takes less time to orbit when they're close to one another. The result of the loss of energy through gravitational radiation causes binary star systems to slowly spiral inward. As this process continues, the stars' orbits speed up, and they can come closer together, appearing to spin more rapidly around one another. This slow death spiral will eventually cause the two stars to collide, merging into one big star.
케플러 제3법칙에 따라 궤도 반경이 줄면 공전주기가 빨라진다. 중력복사로 총에너지 손실은 쌍성계가 천천히 나선을 그리게 한다. 두 별이 가까워 질수록 공전주기는 매우 짧아지고 중력 복사는 더욱 세게 나타난다. 마침내 커다란 하나의 별로 합쳐진다.
This sounds dangerous. How common would such a phenomenon be?
쌍성계의 파국은 얼마나 자주 일어날까?
This death spiral only affects binary stars that are both tiny and extremely close together. In order for two stars in a binary to spiral in and merge within the present age of the universe, so about 13 billion years, the distance between the stars has to be no bigger than the diameter of our sun. That's pretty close.
Typical main sequence stars that are found in binary pairs in our galaxy, are but much further away from each other than one astronomical unit. And if you recall, one astronomical unit is the distance between the sun and the Earth. So these typical stellar binaries are in no danger of undergoing inward death spirals.
항성처럼 핵연료 소실에 따른 전자기 복사 에너지 방출로 인한 질량 감소로 생기는 총 에너지 변화는 매우 느리다. 주계열 별의 수명이 백억년에 달한다는 점을 상기하자. 게다가 두별의 거리가 1천문단위(1AU) 정도 떨어질 때 급격한 충돌을 일으킨다. 따라서 항성으로 이뤄진 쌍성계가 충돌하는 장면을 볼일은 거의 없다.
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As an example, the brightest star that we can see in the Earth's night sky is called Sirius, the dog star. It is found in the constellation Canis Major, which is named after the mythical dog that guards Europa from abduction by Jupiter. Sirius is actually a binary system composed of two stars that orbit one another every 50 years. The distance between the two stars is similar to the distance between the sun and the planet Neptune.
큰개자리의 주성 시리우스가 쌍성인데 두별의 공전 주기는 50년이며 거리는 태양에서 해왕성 만큼 떨어져 있다.
큰개자리의 주성 시리우스가 쌍성인데 두별의 공전 주기는 50년이며 거리는 태양에서 해왕성 만큼 떨어져 있다.
Gravitational radiation emitted by the Sirius binary system is so weak that currently, it is impossible for earthlings to detect. The in spiral is so mind bogglingly slow, that it would take 10 zeta-years or 10 to the power of 22 years before the two stars merge.
이 시리우스 쌍성계에서 방출되는 중력복사는 너무나 미미해서 지구에서 감지될 수 없다. 나선궤도의 반경은 아주 찔끔 줄어드는데 [질량 변화가 없을 경우] 충돌 하려면 10^22 년 가량 걸린다.
이 시리우스 쌍성계에서 방출되는 중력복사는 너무나 미미해서 지구에서 감지될 수 없다. 나선궤도의 반경은 아주 찔끔 줄어드는데 [질량 변화가 없을 경우] 충돌 하려면 10^22 년 가량 걸린다.
This would be long after both stars burn through their nuclear fuel anyway. In fact, the in-spiral of the Sirius binary system takes such a long time that we can ignore the effect of gravitational radiation on this system and all other binaries of main sequence stars.
The only stars that are small enough to allow orbits to be close enough together to emit gravitational waves at observable rates are white dwarfs, neutron stars, and black holes.
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[Neutron Star-Neutron Star Binary]
The first detected binary star system demonstrating the emission of gravitational waves was a binary composed of two inspiraling neutron stars. The system was first observed by Russell Hulse and Joseph Taylor, using the Arecibo Radio Telescope in 1974.
최초로 중력파 방출의 발견은 중성자별 쌍성계였다. 러셀 헐스와 조셉 타일러가 1974년에 아레시보 전파 망원경을 사용해 이 쌍성계를 처음 관측 했다.
최초로 중력파 방출의 발견은 중성자별 쌍성계였다. 러셀 헐스와 조셉 타일러가 1974년에 아레시보 전파 망원경을 사용해 이 쌍성계를 처음 관측 했다.
It contains a pulsar and a neutron star that orbit one another once every eight hours. Therefore, they are separated by a mere three light seconds, which is similar to the diameter of the sun.
이 쌍성계는 펄사와 중성자별의 조합이었는데 공전주기는 8시간 이었다. 두 별의 거리는 3광초로 태양의 지름과 비슷했다.
매년 공전 주기가 약 1/10 밀리초 가량 줄어드는 것으로 관측되었는데 이는 두 중성자 별이 천천히 나선을 그리며 접근하기 때문이다. 이런 미세한 (공전주기의) 변화는 아인슈타인의 상대론에서 제기된 중력파의 방출에 의한 에너지 손실과 일치 했다.
Although indirect, this was the first evidence of gravitational radiation demonstrating that gravitational waves do carry energy away from binary systems. This led Hulse and Taylor to be awarded the Nobel Prize in Physics in 1993.
비록 중력복사에 대한 직접적인 관측은 아니었으나 중력파가 쌍성계에서 에너지를 외부로 빼낸다는 사실을 보여준다.[중력파의 존재에 대한 간접적 증거] 헐스와 타일러는 1993년에 이에대한 공헌으로 노벨상을 받았다.
The two neutron stars in the Hulse-Taylor Binary System are radiating gravitational waves so slowly that the stars won't collide for another several billion years. If we're wanting to catch neutron star collision, direct measurements of the source, or the radio telescope just don't cut it. ; the radio telescope just don't caught it
헐스와 타일러가 발견한 중성자별 쌍성계에서 방출된 중력파는 너무 미미해서 두별이 충돌하는데 수십억년이 걸릴 것이다. 만일 중성자 별의 충돌을 관측하려면 전파 망원경이 잡아내지 못한 (매우 정밀한) 직접 관측장비가 필요하다.
헐스와 타일러가 발견한 중성자별 쌍성계에서 방출된 중력파는 너무 미미해서 두별이 충돌하는데 수십억년이 걸릴 것이다. 만일 중성자 별의 충돌을 관측하려면 전파 망원경이 잡아내지 못한 (매우 정밀한) 직접 관측장비가 필요하다.
So in the years since 1974 scientists around the world have been working on the development of sensitive gravitational observatories that allow us to measure the stretch and squeezing of space time by a gravity wave passing by.
시공간을 줄였다 늘였다 하면서 지금도 우리 주위를 지나가고 있는 중력파를 감지하기 위해 1974년 이래로 전세계 과학자들이 정밀한 중력파 관측장치의 개발에 노력해왔다.
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Modern gravitational observatories use LASERs to detect gravitational waves. These machines can identify the spiraling of neutron stars at a much later stage. These neutron star binaries have got so close together that they are able to orbit one another more than 25 times per second. Once a pair of neutron star orbit this quickly, they radiate energetic gravitational waves.
최신 중력파 검출기는 레이져를 이용한다. 이 장비는 중성자 별 쌍성계가 충돌 직전의 나선 움직임을 관측할 수 있다. 이 단계의 중성자별 쌍설계의 공전주기는 초당 25회가량 된다. 이정도 주기면 상당히 강력한 중력파가 방출된다.
The energy of the emitted gravitational waves increases more and more until the two stars spiral close enough that they collide and finally merge. A merger like this can happen in an order of minutes.
중력파를 따라 손실되는 에너지가 점점 많아 지면서 두 중성자 별의 나선 충돌은 가속된다. 마침내 충돌은 수분내에 끝난다. [언재 어디서 순식간에 일어나는 충돌을 관측해야 한다.]
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In August of 2017, such an inspiral of a neutron star binary was detected. In this instance, astronomers also managed to observe the same part of the sky through gamma-ray, X-ray, visible light, and radio waves.
Several seconds after the gravitational wave observatory detected the merger of the neutron star binary, astronomers saw a bright gamma-ray burst in the same direction.
Gamma-ray bursts come in two types. Short bursts that last for less than a second and long bursts that last for closer to a minute.
Long gamma-ray bursts may be associated with collapsars and hypernovae, which might form some black holes.
2017년 천문학자들이 중성자별 충돌 직후에 짧은 감마선 분출을 관측했다. 이는 중성자 별이 충돌한 직후 짧은 감마선 분출이 있을 거라는 예상을 확인해 주는 것이었다.
두 중성자별의 충돌로 철보다 무거운 원소들을 생성하는 핵융합이 시작된다.
This includes elements such as gold, platinum, and heavy radioactive elements. So the next time you wonder where the gold for jewelry comes from, some large fraction of your ring or necklace is the debris of a collision of two neutron stars.
이렇게 생성되는 원소들로는 금, 백금 그리고 더 무거운 핵물질 원소들이다. 우리가 가진 귀금속이 바로 두 중성자별의 충돌한 결과다.
These heavy elements can be blown off into space and recycled into the next generation of stars and planets.
이 무거운 원소들이 멀리 퍼져나가 새로운 별이나 행성의 재료가 될 것이다.
But what is made at the core of this merger? When two neutron stars merge, there are two possible outcomes for the object left behind. The remnant of the merger could either be a more massive neutron star, or it could become a newly formed black hole. The outcome of the merger depends on the mass that remains.
충돌의 잔해는 더 큰 중성자 별이 되거나 블랙홀이 될 수도 있다. 그 결과는 질량에 달렸다.
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중성자 별이 될 수 있는 한계는 정확하지 않으나 태양의 3배정도 질량이다. 이 중성자 별의 한계질량을 정확히 안다면 블랙홀과 중성자별을 확실히 구분 할 수 있을 것이다.
When the two neutron stars merge, if the total merged mass is smaller than the maximum neutron star mass, then we will end up with a neutron star. But if the mass is too high, the neutron star will be unstable and will collapse to form a black hole.
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[Neutron Star-Black Hole Binary]
중성자 별이 블랙홀과 충동해도 중력파가 생긴다. 이런 중력파를 검출하기는 더 어렵다. [중성자 별끼리 충돌할 대 감마선 분출을 동반한다.] [표시가 없는] 중력파를 가지고 무엇이 충돌했는지 알 수 없다. 2017년 중성자별 충돌도 중력파로는 알 수 없었다. 아쉽게도 충돌의 결과가 블랙홀의 탄생이라는 확실한 증거는 아니다.
The total mass of the merged objects is 2.7 solar masses, and is very likely that this is larger than the maximum allowed neutron star mass. However, we don't yet have any evidence that tells us that a black hole formed.
(예를들어) 충돌로 생긴 천체의 질량이 태양의 2.7배라면 중성자별 일 수도 블랙홀 일 수도 있다는 것이다.
현재로선 블랙홀과 중성자별로 구성된 쌍성계가 있다는 관측된 증거도 없다. 그렇다고 그런 쌍성계가 없다고 할 수도 없다. 그런 쌍성계가 존재 한다 쳐도 나선형 충돌을 할지 안할지도 알 수 없다.
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Let's imagine what would happen if a black hole merges with a neutron star. Astronomers have tried to model this, and we think it would look very different to that of two neutron stars merging.
블랙홀과 중성자별의 충돌을 상상해보자.
While the neutron star and the black hole start to inspiral, it becomes clear that in the end, the neutron star will be ripped apart.
중성자별이 나선 궤도로 블랙홀에 접근하다 깨져 버리고 (조석력은 강력하다!),
It will then fall in towards the black hole, and be swallowed by the black hole's event horizon, and the black hole will grow.
블랙홀의 사건 지평선으로 빨려 들어갈 것이다. 중성자 별을 먹은 블랙홀은 성장한다.
블랙홀의 사건 지평선으로 빨려 들어갈 것이다. 중성자 별을 먹은 블랙홀은 성장한다.
Although it is quite possible that such a merger would also produce a gamma-ray burst and initiate nuclear reactions that form heavy elements.
이 경우에도 감마선 분출이 있을 수 있고 무거운 원소를 생산하는 핵융합도 일어날 수도 있다. [하지만 관측된 증거는 없다.]
이 경우에도 감마선 분출이 있을 수 있고 무거운 원소를 생산하는 핵융합도 일어날 수도 있다. [하지만 관측된 증거는 없다.]
If a merger of a neutron star and black hole is ever detected, it will be big news and we'll have to update this course.
중성자 별과 블랙홀의 충돌이라는 확실한 증거가 검출되기만 한다면 커다란 뉴스가 될 것이다. [중성자 별이 산산조각 날때 무슨일이?]
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[Black Hole-Black Hole Binary]
As the two black holes merge, for a brief period of time, the black hole is a highly distorted mess. But the no-hair theorem tells us that the normal state for a rotating black hole is a smooth event horizon.
During the final merger stage, the distorted black hole emits gravitational radiation in a process called Quasi-Normal Ringdown. Where all the bumps and wiggles gets moved out. The final resulting black hole is a Kerr Black Hole(=Rotating Black Hole), of the sort we looked at earlier in the course.
The first black hole merger was detected in 2015, and by the end of 2017 when we are filming this module, five black hole mergers have been measured. So by the time you take this course, more of these types of mergers will probably have been detected. And they might eventually seem commonplace.
2015년 처음 블랙홀 충돌이 발견된 이래 2017년 현재 5개가 더 관측됬다. 앞으로 흔히 발견될 것이다.
2015년 처음 블랙홀 충돌이 발견된 이래 2017년 현재 5개가 더 관측됬다. 앞으로 흔히 발견될 것이다.
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The data from black hole and neutron star mergers helps astrophysicists understand the distribution of black holes and neutron star sizes in our galaxy. But also, the wider universe. The merger of neutron stars can produce either a new neutron star, or a new black hole. When black holes merge, they form heavier.
This diagram summarizes the black hole food chain as we know it at the end of 2017.
위 도표는 2017년 말까지 우리가 알고 있는 블랙홀 먹이사슬이다.
If you look towards the bottom of the diagram, between one and two solar masses, there are a collection of yellow circles that represent neutron stars with known masses. In the middle of all the neutron stars, the two orange balls joined with an arrow that represents the two neutron stars that merged in August 2017. Since there isn't enough evidence to determine whether the neutron star became a neutron star or a black hole, the new object is represented with a question mark.
맨 아래 노란색은 질량이 알려진 중성자별들. 중간의 오랜지색은 2017년에 중성자별 둘이 합쳐져 뭔가 생성했는데 중성자별인지 블랙홀인지 알 수 없다.
If we move higher up the mass scale, between around 5 and 20 solar masses, there are a collection of purple circles representing known stellar mass black holes in x-ray binaries.
보라색은 X선 쌍성계를 이루고 있는 태양질량의 5배에서 20배에 달하는 항성급 블랙홀들이다.
보라색은 X선 쌍성계를 이루고 있는 태양질량의 5배에서 20배에 달하는 항성급 블랙홀들이다.
Finally, at the top of the diagram, there are blue circles, which are joined by arrows that show the merger of lighter black holes, to form heavier black holes.
맨 윗층의 청색은 블랙홀 들로서 가벼운 블랙홀이 합쳐져 무거운 블랙홀이 된다.
Some of these black hole mergers start off with black holes that are about 30 solar masses, and create black holes that add up to about 60 to 70 solar masses. This is really exciting, as we can now witness the merger and growth of black holes. Perhaps, this process might lead to the formation of intermediate mass black holes.
아마도 중간급 블랙홀이 어떻게 생성되는지 보여줄 지도 모른다.
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If we now consider the other end of the black hole mass spectrum by this, I mean, let's switch up to the size of galaxies. Observations of galaxies suggest that almost all galaxies have a supermassive black hole at their center.
Astronomers have been observing galaxies for a long time. While we're used to seeing pretty pictures of spirals and swirls, astronomers have discovered that things can also get a bit messy. This is because galaxies can also collide.
Astronomers have been observing galaxies for a long time. While we're used to seeing pretty pictures of spirals and swirls, astronomers have discovered that things can also get a bit messy. This is because galaxies can also collide.
When galaxies collide, the black holes can form a binary system, which will emit gravitational waves, inspiral and merge. The merger of supermassive black holes hasn't yet been observed, but hopefully, they will one day soon.
중심에 거대 블랙홀을 가진 은하끼리 충돌도 나선궤도를 그리며 충돌할 테고 이과정에서 중력파가 나올 것이다. [거대한 중력파 일텐데] 아직 검출되지는 않았다. 조만간 검출 되리라 예상한다. [이미 광학과 X선 관측으로 은하 충돌 장면이 관측되고있다.]
중심에 거대 블랙홀을 가진 은하끼리 충돌도 나선궤도를 그리며 충돌할 테고 이과정에서 중력파가 나올 것이다. [거대한 중력파 일텐데] 아직 검출되지는 않았다. 조만간 검출 되리라 예상한다. [이미 광학과 X선 관측으로 은하 충돌 장면이 관측되고있다.]
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[인터뷰] [커세라 페이지]
Where does the gold in your ring come from?
Interview with Dr. Rodrigo Fernandez, Professor at the University of Alberta
This ring is made of gold. Why gold? We think that the gold among those other heavy elements comes from collisions of the neutron stars that astronomers called neutron star mergers. Very recently a few months ago it was announced that the first neutron star merge was observed in gravitational waves, and in photons by the like of collaboration and a number of other observers in the world, and the signature of the formation of gold and other heavy elements called the r-process was detected in the signal. Okay. So, we have evidence that a significant fraction of that the gold in the Universe came from these types of events. Now, whether this golden in my ring comes from one close by merger, or for many of them, and then they go and mix up somehow we don't know. But it could be just one that happen not so far in the past.
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