So, you want to find a black hole. Let's get started by evaluating some of the tools available to us. Obviously, when astrophysicists study objects in the sky, they typically use telescopes. Telescopes allow us to collect light and produce images of the features near a black hole.
블랙홀을 관측하기 위해 우리가 사용할 수 있는 도구들이 어떤 것들인지 살펴보자. 천문학자들이 밤하늘을 관측하기 위해 망원경을 사용한다는 점은 의심할 여지가 없다. 망원경은 빛을 모아 블랙홀 주면의 영상을 얻을 수 있게 해준다.
But there are many different types of telescopes, so it's important to choose the best one in order to be certain that what you are in fact looking at is a black hole.
다양한 종류의 망원경이 있으나 블랙홀을 관측하기 위해 어떤 종류의 망원경을 선택해야 최적인지 알아야 한다.
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You may have seen a telescope like this one that we have at the University of Alberta's observatory. This is a fairly standard type of telescope that gathers and focuses light using curved mirrors called a reflecting telescope. Historically, it was much easier to make lenses rather than mirrors. So, early telescopes like the ones used by Galileo used to discover the moons of Jupiter are called refracting telescopes.
광학 망원경은 아주 전형적인 망원경이다. 반사망원경과 굴절망원경이 있다. 예전에는 렌즈 제작이 거울을 깍기보다 쉬웠다. 갈릴레오가 목성의 4대 위성을 관측한 것도 굴절 망원경이었다.
In modern times, it is much easier to build large mirrors than it is to build large lenses. So, the enormous telescopes used in astrophysical research are reflecting telescopes.
현대에 들어 대형 거울을 만들기가 수월해졌다. 오늘날 천체물리학자들이 사용하는 망원경은 반사 망원경이다.
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When we talk about ground-based reflecting telescopes, the majority collect light in the optical spectrum. That is the light which humans can see with their eyes.
지구상에 설치된 망원경의 대부분은 반사 망원경으로 주로 가시광선 대역의 빛을 모아 관측한다. 인간이 눈으로 볼수 있는 빛이다.
For example, this Schmidt cassegrain telescope has two mirrors: a big primary mirror at the back and a secondary mirror at the front. It also has a corrective lens, but this is quite an expensive telescope.
The purpose of a telescope's primary mirror is to collect as much light as possible from faint objects. The larger the diameter of the mirror, the more light is collected.
망원경의 대물경(1차거울)은 많은 빛을 모을 수 있어서 어두운 천체를 관찰할 수 있게 해준다. 대물경의 지름이 클수록 더많은 빛을 모을 수 있어서 유리하다.
Think of it like a big bucket. It becomes easier to see faint celestial bodies, but a larger mirror also means a larger more expensive telescope, which is a trade off that we have to pay in order to get better resolution of distant objects.
For example, if something looks like a blurry smudge through a small telescope, a bigger telescope will produce a clear image without changing the magnification. Larger telescopes may also allow for more magnification, but magnification should be second to the mirror diameter.
작은 망원경으로 희미하게 보이는 천체도 큰 대물경의 망원경으로 보면 배율을 높이지 않고도 선명하게 볼 수 있다. 물론 큰 대물경 망원경으로 배율을 높일 수 있는데, 배율을 정하는 것은 2차렌즈(대안렌즈)다.
Dim and distant astrophysical objects like nebula and galaxies are easily resolved by small telescopes with low magnification, but they require lots of light in order to be visible.
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My family invested in a four-inch Newtonian reflector when I was young. It was a present from my dad. This telescope encouraged my interest in astronomy and it taught me an important lesson. If you're purchasing a telescope, do not purchase one that advertises its magnification. This is a sign of a poor-quality telescope. Instead, a good-quality telescope is described by the diameter of the primary mirror or for a refracting telescope the diameter of the primary lens.
고급 망원경은 대물렌즈(1차 거울)의 지름을 표시한다. 배율을 강조하는 망원경은 저급 망원경이라고 봐도 좋다.
For instance, our telescope at the University of Alberta has a huge 14 inch diameter mirror. Sorry about the imperial units, they're still common among telescope manufacturers. The 14 inch mirror can collect much more light than smaller telescopes revealing dim structures in the night sky like the Ring Nebula in the constellation of Lyra.
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Large ground-based research telescopes like the two gemini telescopes in Chile and Hawaii have mirrors that are eight meters in diameter.
지상의 대형 연구용 망원경으로 직경이 8m인 제미니(쌍둥이) 망원경이다. 칠레와 하와이에 설치되었다.
But that's a drop in the bucket compared to some ongoing construction projects like the extremely large telescope or ELT which will have the largest compound mirror of any telescope in history. The ELT's compound mirror will have an effective diameter of 39 meters. Itself made up of a collection of smaller mirrors that can be aimed independently.
역사상 가장큰 망원경이 건설중인데 ELT 다. 여러개의 반사거울로 구성된 망원경이다. 유효 직경이 39m가 될 것이다. 이렇게 큰 거울을 깍기는 불가능하다. 작은 반사거울을 여러개 조함하여 한곳으로 빛을 모으는 방식이다.
Scientists call this independent motion adaptive optics because the mirrors need to move in order to cancel out the turbulence of earth's atmosphere. Often, they measure these disturbances using powerful lasers.
여러개의 개별 거울을 각각 조절하여 한곳으로 모으는 기술을 적응광학이라 한다. 거울을 각각 조절하여 지구 대기의 흔들림(고도별 온도차에 따른 대류 현상이 원인이다)을 상쇄시킬 수 있다.
Here's the Subaru telescope calibrating its optics. The earth's atmosphere is turbulent and the rapid motion of air pockets in the atmosphere smears out the light from stars which makes them appear blurry.
지구 대기의 흔들림의 정도를 측정하기 위해 강력한 레이저를 사용한다.
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What would be the best place to construct these massive telescopes? Of course, you'd want to build them near the top of a mountain. This is not to get them closer to the stars. By situating the telescope on the top of a mountain, we decrease the amount of atmosphere between the telescope and the stars, which improves the seeing.
대형 망원경은 산곡데기에 건설하는 이유는 별에 더가갑게 가려는 것이 아니다. 온도차로 인한 대류현상이 심한 지표면보다 온도변화가 적은 (건조하고) 높은 아지랑이가 없는 곳으로 가려는 것이다.
Seeing is actually a technical term used by astronomers. If the atmosphere is calm and the images seen through the telescope are crisp and steady, we say "the seeing is good tonight".
'씨잉(seeing)'은 천문학자들이 사용하는 전문용어다. 대기가 안정되어 선명한 간측 영상을 얻을 수 있을 때 '씨잉이 좋다' 라고 한다.
There's an obvious way to avoid the blurring effects of earth's atmosphere. Launch a telescope into space. Of course, you're probably already familiar with the Hubble Space Telescope, but did you know about its successor, the James Webb Space telescope?
관측영상을 흐리게 하는 주된 원인인 대기를 피해 우주로 망원경을 올려 보내기도 한다. 유명한 허블 우주망원경이 있다. 허블 우주망원경의 대를 이어 제임스 웹 우주망원경이 준비중이다.
* 우주로 망원경을 올려 보내면 이상적이긴 하나 너무 비용이 많이 들고 관리가 어렵다. 적응광학 같은 제어 기술이 발달 함에 따라 대기영향을 최소화 할수 있게 되었다. 이에따라 지상에 초거대 망원경의 설치가 차라리 유용하다고 주장된다. 그래서인지 제임스 웹 우주망원경을 쏘아올리는 계획이 계속 지연되고 있다.
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The telescopes that we've just looked at are all visible light telescopes also called optical telescopes. These are telescopes that can detect light visible to our eyes along with some neighboring wave-lengths in the infrared and ultraviolet light. This type of telescope is capable of viewing stellar companions of black hole binary systems.
광학 망원경은 넓은 전자기 대역 중 가시광과 인접한 적외선과 자외선으로 극히 일부 영역을 관측한다. 광학 망원경은 쌍성계 블랙홀의 별 구성을 관측할 때 사용된다.
However, since most of the energy emitted by a black hole is in parts of the electromagnetic spectrum that our eyes can't see, we need to investigate other types of telescopes capable of detecting light that is invisible to our biological eyes
블랙홀 계에서 방출되는 에너지는 대부분 전자기 스펙트럼중 우리가 볼 수 없는 영역이다. 따라서 이런 빛을 검출하기 위해서 다른 종류의 망원경이 필요하다.
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Black hole jets emit radio waves. Part of the spectrum emitted by hot plasma within the jet. So, a radio telescope is an important tool for black hole astronomers. Remember that radio waves are the lowest energy and thus the longest wavelength part of the electromagnetic spectrum. Since radio waves are electromagnetic waves or photons, they still travel from the black hole towards us at the speed of light.
블랙홀의 제트는 전파를 방출한다. 스펙트럼의 일부인 전파는 제트내에 뜨거운 프라즈마에서 방출된다. 전파망원경은 블랙홀을 연구하는 천문학자에게 아주 중요한 관측도구다. 가장 낮은 에너지를 나르는 전파는 전자기 스펙트럼중 가장긴 파장을 갖는 축에든다. 전파도 빛과 마찬가지로 전자기파 이므로 블랙홀에서 빛의 속도로 날아온다.
Radio waves have long wavelengths that range from millimeters to meters in length, which is the reason why radio antenna have to be very long. You might be familiar with radio waves that you receive when listening to a radio station. For example, if you were listening to a station at 102.9 on the dial, meaning that you're capturing photons with frequencies of 102.9 megahertz. They would have a wavelength of approximately 2.92 meters. Recall, a green laser have tiny wavelengths measured around 532 nanometers.
전파의 파장은수미터에서 수 밀리미터에 이르기 때문에 안테나의 크기가 아주 커진다. 예를 들어 주파수가 102.9Mhz 인 방송국 신호의 파장은 2.92미터가 된다. 녹색 레이저의 파장이 532나노미터인 것에 비하면 엄청 길다.
Radio telescopes like the ones that make up the very large array, which was featured in the movie Contact, are usually large dishes instead of antenna. Light waves from neighboring radio telescopes in an array can be combined using a technique called interferometry which allows the whole group of telescopes to act as one large one. The effective size of a radio array is similar in size to the distance between the dishes.
전파 망원경으로 영화 콘택트에 나오는 거대한 접시형 안테나가 배열이 안테나 대신 이용된다. [매우 미약한 전파 신호를 잡아내려면 한개의 안테나로는 부족하다.] 간섭계 기술을 적용하여 배열된 전파 망원경에서 인접한 망원경에서 수신한 신호를 모아 하나의 거대한 망원경의 효과를 낸다. 접시 망원경이 떨어진 거리가 바로 망원경의 대물경 유효 직경이 된다.
The largest single-dish telescope called FAST, the 500 meter aperture spherical telescope is 500 meters in diameter and located in China. If you've seen the James Bond movie "GoldenEye", you might recognize the Arecibo radio telescope in Puerto Rico where Bond defeats Stravalion.
단일 전파 망원경으로 가장 큰 것은 중국에서 건설한 FAST로 접시의 직경이 500미터다. 그 이전에는 푸에르토리코에 건설된 300미터 접시가 가장 컸었다.
Radio telescopes located at different parts of the earth as shown on this map are being used as one earth-sized radio telescope called the Event Horizon Telescope. It's observing Sagittarius A-star, the supermassive black hole at the center of our galaxy. We'll discuss the Event Horizon Telescope's observations in Module 10.
전파망원경의 크기를 극단적으로 넓힌 경우로 지구 대륙에 전파망원경을 배치하고 한데 묵은 사건지평선 망원경이 있다. [전파 망원경은 간섭계 기법으로 대물 직경을 엄청나게 늘릴수 있어서 감도는 좋지만 해상력이 떨어진다.] 이 망원경으로 우리은하의 중심에 있는 초거래블랙홀인 궁수자리 A별을 관측하고 있다. 사건지평선 망원경에 대해서 10주차 강의에서 다시 살펴볼 것이다.
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On the other end of the electromagnetic spectrum at high energies, black hole accretion disks produce x-rays. So, an x-ray telescope would be the best tool in our hunt for black holes, but there's one problem, earth's atmosphere absorbs x-rays. Actually, that's a really good feature for our atmosphere.
If x-rays could make it through the atmosphere to the ground, we would constantly be irradiated. X-rays have even more energy than ultraviolet light. The light that causes sunburns. So, tanning under the x-ray light from a black hole would burn you to a crisp. Don't worry though, x-rays used in doctors offices and dentists offices are produced in safe quantities. Radiation therapy used to treat cancers are a good example of the damage x-rays can do to the cancers of course.
Since the earth's atmosphere protects us from cosmic x-rays, an x-ray telescope needs to be launched above the atmosphere and into space. This diagram shows how much of the earth's atmosphere blocks light with different wavelengths.
Visible light and radio waves can penetrate through the earth's atmosphere. However, gamma rays, x-rays, ultraviolet and infrared radiation are blocked by the atmosphere. So, telescopes that can observe light at these wavelengths usually orbit the earth.
The Chandra x-ray telescope is an important black hole detecting telescope. It allows astronomers to view x-ray images and spectra of black holes. Chandra is named after the Indian physicist Chandrasekhar, who is famous for his theoretical work on black holes, neutron stars, and white dwarf stars. He also prefer to be called Chandra.
Another orbiting x-ray telescope is called the XMM-Newton. Although, Chandra is a better telescope for creating detailed x-ray images, XMM-Newton is a better telescope for determining the wavelength of those x-rays.
A new telescope called Athena with a planned launch date in the year 2028 will combine the best features of these two telescopes.
Nustar is another x-ray telescope that orbits the earth, but the long length of this telescope allows astronomers to view much higher energy x-ray photons than the Chandra observatory. This allows Nustar to detect processes taking place very close to the black hole's event horizon.
A nice x-ray telescope called NICER was recently mounted on the International Space Station and is orbiting the earth on the ISS. Nicer is designed to accurately give the time of every x-ray photon that strikes it. This allows NICER to detect rapid changes in x-rays that are emitted by black holes and neutron stars.
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Astronomy that makes use of the accurate photon timing is sometimes called time domain astronomy. This is just a small selection of some of the telescopes that are used to study black holes. A completely different way to detect a black hole is through gravitational radiation. Of course, we'll learn more about gravitational radiation in module 10.
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[인터뷰] [커세라 페이지]
Why are X-ray telescopes useful for studying black holes?
X선 망원 경이 블랙홀 연구에서 유용한 이유는 무엇입니까?
Interview with Dr. Daryl Haggard, Professor at McGill University
맥길 대학교 교수 대릴 해거드 박사와 인터뷰
And I was sort of a training junior astronomer at the time that the Chandra X-ray Observatory launched, but that was in 1999 and started to kind of giving us data as a scientific community in 2000. And so my first introduction to doing observational astronomy was through the X-ray lens of the Chandra X-ray Observatory, which still is a major workhorse in a major part of the research I do today.
So the beautiful thing about X-rays is that they're so high energy that they penetrate through a lot of dust and gassed. So think about what you're trying to do when you want to study the black hole at the center of the Milky Way galaxy. You're in the Earth or sitting on the surface of the Earth, and you're in this big spiral galaxy and you're looking through the galaxy to try to see this object that's at the center of the galaxy.
So you've got to look through all of that junk, like all those stars, all that gas, all that dust. So the beautiful thing about X-rays is that they're really high energy, they just penetrate right through all of that stuff not all of it, but most of it in the same way that they penetrate through your own flesh and they're only stopped by your bones, right?
So you know X-rays are really good at penetrating stuff.
So X-rays are great for studying accretion disks of objects partly because they penetrate all this stuff, and also because those accretion disks I keep saying they're really, really, really, really hot. So the temperatures that you need are millions to billions of Kelvin. That's a really hot.
I forget what the conversion is to centigrade, but anyway 10 to the 8 Kelvin is the temperature on average of hot X-ray emitting gas. And so that's a great way to study these extremely hot environments near the supermassive black hole, plus it has this added advantage that doesn't get absorbed easily by the material along your line of sight.
[X-선 천문학 관련 강좌] Analyzing Universe
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