Stellar mass black holes are most easily identified when they are accompanied by a companion. The gravitational effect of a black hole on it's companion star can help give us a location where the black hole might be hiding.
항성질량급 블랙홀은 동반성을 관찰하여 수월하게 찾아낼 수 있다. 블랙홀이 동반성에 미치는 중력효과는 숨어있는 블랙홀을 찾는데 도움이된다.
If the black hole is actively feeding on the companion star, we will be able to see this clearly in the X-ray portion of the spectrum. In fact, because these systems are so bright in X-rays, they are often referred to as X-ray binaries. We should note however, that this term refers to systems containing a star and a compact object.
만일 블랙홀이 동반성에서 물질을 활발히 흡입하고 있다면 [강착원반이 고온이므로] 스펙트럼의 X선 영역에서 강한 빛이 관측된다. 실제로 이런 쌍성계는 X 선 영역에서 매우 밝으므로 X선 쌍성계라 불린다. 단, 이 X선 쌍성계가 별과 밀집천체의 쌍을 지칭한다는 점에 주목하자.
As we're aware, compact objects can be either neutron stars or black holes. As such, it is important that when we observe these systems we try and find the mass of the compact object. If the mass of the compact object is more than three solar masses, it must be a black hole. If it's lighter than that, it's likely a neutron star.
이 밀집천체란 블랙홀일 수도 있고 중성자 별일 수도 있다. 이런 쌍성계의 관측에서 밀집천체의 질량을 파악하는 것이 중요하다. 밀집천체가 태양질량의 세배를 넘으면 블랙홀이고 넘지 않을 경우 중성자별일 가능성이 높다.
In some cases though, it can be very hard to tell the mass of the compact object. When astronomers are unsure of the characteristics of systems like this, they list them as a black hole candidate.
하지만 밀집천체의 질량을 알아내기는 어려운 경우도 있다. 그래서 천문학자들은 블랙홀 후보군이라고 분류한다.
There are two types of X-ray binaries: high-mass X-ray binaries and low-mass X-ray binaries. But this classification is not based on the mass of the compact object. It may seem strange to you at first, but X-ray binaries are classified by the mass of the companion star, not the compact object.
X선 쌍성계는 두가지 종류로 분류된다. 고질량 X선 쌍성계와 저질량 X선 쌍성계다. 하지만 이런 분류는 밀집천체의 질량에 따른 분류가 아니다. 동반성의 질량에 따른 분류다.
The companion stars in low-mass X-ray binaries have masses that are the mass of the Sun or smaller. High-mass X-ray binaries have companion stars that are at least 10 times more massive than the Sun.
저질량 X선 쌍성계의 동반성은 태양 혹은 그이하의 질량을 갖는다. 고질량 X선 쌍성계의 동반성은 최소한 태양질량의 10배 이상이다.
Any time astronomers come up with a classification like this, you'll find that some objects don't quite fit. So, we also have an in-between group that is sometimes called intermediate-mass X-ray binaries. But their properties are usually pretty similar to the low-mass X-ray binary group.
이런 분류에 맞지 않은 경우도 있다. 두 종류 사이에 낀 경우 중간급 X선 쌍성계라고 한다. 이 급의 특성은 저질량 X선 쌍성계에 가깝다.
Why would astronomers choose to classify binary systems based on the type of companion star, rather than the type of compact object?
쌍성계를 밀집천체 대신 동반성으로 분류하는 이유가 뭘까?
The reason for this classification is that the properties of the system depend more on the type of donor star than the type of compact object. What this means is that observations of these systems vary more dramatically if you compare high-mass and low-mass X-ray binaries than if you were to compare stellar-mass black holes and neutron stars that are both feeding on, say, a low-mass star.
쌍성계의 특성이 동방성의 형에 더 명확하기 때문이다. [블랙홀은 판별할 어떤 것도 보여주지 않는다.] 고질량 X선 이중성과 저질량 X선 이중성의 관측한 자료를 비교해보면 저질량 별로부터 물질을 공급받는 항성급 블랙홀과 중성자별의 차이보다 매우 극명한 차이를 보여주고 있다.
저질량 동반성을 가진 블랙홀과 중성자별은 관측자료상 구분이 어렵다. 이에 비해 동반성의 크기에 따른 쌍성계의 밀집천체에서 방출되는 X선의 차이는 매우 크다.
When their companion is a low-mass star such as in a low-mass X-ray binary, the gas from the companion star flows to the black hole via Roche lobe overflow that we studied in an earlier module.
X선 쌍성계의 동반성의 질량이 작은 경우 동반성에서 블랙홀로 흡수되는 가스 흐름은 로슈로브 넘침을 통해 이뤄진다.
Also, recall high-mass stars tend to have larger outflows of material in the form of powerful stellar winds. In high-mass X-ray binaries the mass loss through wind ends up being accreted onto the black hole. This is called wind fed accretion. However, we should note that high-mass stars can also feed black holes via Roche lobe overflow. Typically, low-mass companions are small in size, while high-mass companions are large.
고질량 동반성의 경우 항성풍을 통해 대량의 물질 흐름이 일어난다. 물론 고질량 별에서도 로슈로브 넘침은 일어나며, 저질량 동반성보다 규모도 훨씬 크다.
-------------------------------------
Small stars can orbit closer to the black hole than large stars can. Kepler's laws of motion tells us that stars with small orbital separations orbit with faster speeds and take shorter amount of time to orbit. Low-mass X-ray binaries typically have short orbital periods that can range from less than an hour to many hours.
블랙홀 쌍성계에도 케플러 행성궤도 법칙이 적용된다. 저질량 X선 쌍성계의 경우 공전 주기는 수시간 가량이다.
Meanwhile, the larger companions in high-mass X-ray binaries orbit further away from the center of mass of the system and can take a few days to complete one orbit. This means that the feeding or mass transfer mechanism, and so the rate of mass transfer along with the orbital period, can be greatly impacted by the type of companion star.
이에반해 큰 동반성을 가진 X선 쌍성계의 경우 궤도 반경이 길어 공전주기는 몇일 가량된다. 따라서 블랙홀이 덩치를 불리는 물질 전달 비율은 동반성의 종류에 따라 크게 영향을 받는다.
------------------------------------
Stars are usually classified by observing their color in visible light, since this is the portion of the spectrum where they are usually the brightest. We've already learned that accretion disks around black holes will also emit some visible light. This means that if we want to view the companion star of the black hole, we'll have to wait until a black hole was finished eating a major meal so that the disk isn't emitting light which would otherwise pollute our image.
별이 내는 빛 중 가시영역 스펙트럼에서 가장 강한 파장[스펙트럼 형]에 따라 별을 분류해왔다. 강착원반 역시 가시광 영역의 빛을 낸다. 따라서 동반성을 관측 하려면 블랙홀이 물질을 다 빨아들여 더이상 강착원반이 관측 영상에 방해를 주지 않을 때까지 기다려야 한다.
* 모든걸 빨아들이는 블랙홀 대신 동반성을 관측해야 한다. 멀리있는 쌍성계 블랙홀을 관측할때 동반성과 함께 블랙홀의 강착원반에서 방출되는 빛이 포함 되므로 동반성 만을 정확하게 관측하여 판단하기 어렵다.
When astronomers want to classify a star, they look at it using different filters to determine the star's properties. Low-mass stars with masses less than the Sun's mass are dim and have colors that range from yellow to orange to red. High-mass stars are bright and are blue in color.
천문학자들이 별을 분류하기 위해 다양한 종류의 필터를 사용하여 별의 특성을 알아낸다.
태양보다 작은 질량의 별은 어둡기도 하고 황색에서 적색계통의 빛을 낸다. 높은 질량의 별은 밝고 청색빛을 낸다.
Since low-mass stars are dim, they can be difficult to detect. So, sometimes we have trouble detecting the companion in a low-mass X-ray binary, and the binary is classified based on its X-ray emission instead. The companion stars in high-mass X-ray binary systems are usually easier to see since they are so bright, meaning that in many cases we can also obtain a detailed spectrum of the star.
어두운 저질량 별은 발견하기 어렵다. 따라서 저질량 X선 이중성에서 동반성을 찾기는 곤란하다. 그대신 X선 방출로 분류한다. 고질량 X선 이중성계에서 동반성은 아주 밝기 때문에 비교적 찾기 쉽다. 그리고 대부분 해당 별의 상세한 스펙트럼을 얻을 수 있다.
So, it isn't at all surprising that the first confirmed black hole, Cygnus X-1 has a bright blue high-mass companion star. However, accretion disks can also look very blue, bluer in fact than hot blue stars. This means that when the disk is bright, it can be incredibly hard to work out what kind of star is feeding the compact object.
청색 고질량 동반성을 가진 시그너스 X-1이 블랙홀로 확인된 것은 놀랄일도 아니다. 실제로 강착원반은 보통의 별보다 더 청색을 띄었다. 원반이 너무 밝아서 어떤 종류의 별이 밀집천체로 공급되는지 밝혀내기는 굉장히 어렵다.
X-ray images of black holes are not quite as impressive to look at as some of the other types of images we've seen in this course. They can be fairly featureless with just a series of dots scattered in a black section of the sky, except, of course, when they suddenly change.
블랙홀의 X선 영상은 이 강좌중에 봐왔던 다른 영상들보다 더 인상적이진 않다. 급격한 변화를 보였던 점을 제외하면 검은 하늘에 그저 특징없는 몇개의 흩어진 점일 뿐이다.
The left-hand image shows an X-ray image of the sky near our old friend, Cygnus X-1. In the left image taken before June 2015, we see full bright, X-ray point sources. Cygnus X-1 is the brightest X-ray source in Cygnus and a high-mass X-ray binary.
왼편의 사진은 시그너스 X-1 인근의 X선 관측상이다. 2015년 6월 이전에 찍은 사진으로 X선 광원들이 밝게 보인다. 시그너스 X-1은 백조자리에서 밝은 가장 밝은 X선 광원으로 고질량 X선 이중성 이다.
Cygnus X-3 was the third X-ray source discovered in Cygnus and is a low-mass X-ray binary. At this moment, it is unknown whether there is a neutron star or a black hole in Cygnus X-3. 3A 1954+319 is also a low-mass X-ray binary, most likely harboring a neutron star. Cygnus A is a supermassive black hole, but it looks dim because it's in a galaxy far, far away, while the other sources are in our own galaxy.
시그너스 X-3는 백조자리에서 세번째 밝은 X선 광원으로 저질량 X선 이중성이다. 현재까지 블랙홀인지 중성자 별인지 확인되지 않았다. 3A 1954+319 역시 저질량 X선 이중성인데 중성자별로 추정된다. 시그너스 A는 초거대 블랙홀로 아주 멀리 떨어져 있는 은하여서 어둡게 보인다.
-----------------------------------------------
A small X marks the spot where the low-mass X-ray binary, V404 Cyg, suddenly became as bright as Cygnus X-1 and Cygnus X-2 in June 2015. V404 Cyg is close to 8,000 light-years away from us. The companion is a type K star, which means that it's orange in color and has a mass that is just 40 percent of our Sun's mass. The black hole has a mass that is seven times our Sun's mass. So, there is no danger that this could be a neutron star masquerading as a black hole.
작은 십자표시는 저질량 X선 이중성으로 V404 Cyg다. 2015년 6월에 갑자기 시그너스 X-1과 X-2보다 밝게 관측되었다. V404 Cyg는 지구로부터 약 8천광년 떨어져 있다. 동반성은 K형 별로 태양질량의 40% 로 오렌지색을 띈다. 이 쌍성계의 블랙홀은 태양질량의 7배다. 따라서 블랙홀을 가장하지만 여지없이 중성자별이다.
In this movie, the black hole and it's accretion disk are the bluish white light at the center of the image. The accretion disk suddenly erupted on June 26th, 2015, emitting X-rays in all directions. These X-rays form a spherical shell front that expands and collides with dust clouds far away from the black hole. The red rings are X-rays that are reflected off the dust that lies between the black hole and the Earth. Although the wave front is a sphere, we see circles since the dust clouds are a series of surfaces between the black hole and the Earth.
관측 동영상에서 보면 중심의 청백색이 블랙홀과 강착원반이다. 이 강착원반은 2015년 6월 26일 갑자기 X-선을 전방향으로 분출 하였다. 분출된 X-선이 전방향으로 퍼져나가 블랙홀과 멀리 떨어진 먼지구름들과 충돌하였다. 영상에서 붉은 환은 블랙홀과 지구 사이의 먼지에 부딧쳐 반사된 X선의 모습이다. 분출된 X선은 전방향의 구형으로 퍼져나갔으나 원형으로 관측된 것은 블랙홀과 지구사이에 놓인 먼지 구름이 일련의 띄를 이루기 때문이다.
Another example of a low-mass X-ray binary is the X-ray source, X9 in the globular cluster named 47 Tuc. A globular cluster is a dense star cluster that can have many millions of stars. Since the stars are closer to each other than in part of the galaxy where we live, the stars can easily hook up with other stars to form binary systems through dynamical formation.
So, if you were to randomly choose a globular cluster to look at with an X-ray telescope, you'd have a good chance of finding an X-ray binary. The X-ray binary X9 is still classified as a candidate black hole, since its mass has not yet been measured, but the orbital period is very small, only 25 minutes, and the companion star is most likely a white dwarf.
The companion star to the black hole Cygnus X-1 is easily seen as the bright star in the very center of this visible light image of the constellation, Cygnus. Since this is a visible light image, we can't see the accretion disk of the black hole. The red light is coming from glowing hydrogen gas in a nearby star forming region.
Cygnus X-1's companion star is named HDE 226868. But for obvious reasons, we normally call it Cygnus X-1's companion star. The companion is a type O supergiant that has a larger mass than the black hole. The companion star's mass is 19 times larger than the Sun while the black hole's mass is 15 times the Sun's mass.
The two objects orbit their common center of mass, which is closer to the companion once every 5.6 days. Both high-mass and low-mass X-ray binaries are spotted scattered throughout galaxies. They're relatively easy to spot because the black holes have their dinner sitting right there next to them in the binary system.
What happens when we switch up to other size scales? What are the alternative diets for supermassive black holes?
-------------------------------------------------
[인터뷰] [커세라 페이지]
What is a black hole outburst?
Interview with Dr. Aarran Shaw, Astronomer at the University of Alberta
But outburst is a sudden increase in luminosity of a source. A source will go from bubbling around in what we call this low quiescent state, where you either don't see it because it's just not giving off enough x-rays, or optical lights, or it's existing at a lowish luminosity that we can't see. Then, it will increase its luminosity or its brightness by a factor of 1000, and that's what we call an outburst. Then it will start to decay back to this level that is known to be normal for this source. There are a few black holes that jump out or you are being extremely cool, I guess is the word. So two years ago or 2.5 years ago now, there was a very bright outburst of an X-ray binary called V404 Cyg, and this was the first time this source had been seen in outburst for 26 years. So outburst in 1989,
Play video starting at 1 minute 14 seconds and follow transcript1:14
is one of the most famous black holes in the galaxy. The great thing about outbursting in the modern era of astronomy is that, we have a huge array of facilities our disposal. So back in 1989, we looked at it with optical telescopes, and maybe an x-ray telescope. There weren't many around, but now we have all sorts of facilities that we can coordinate via the power of the Internet essentially to look at this thing at the same time. So we have optical telescopes looking at it at the same time as radio telescopes, and all the x-ray observatories that are currently in orbit around the Earth. From the simultaneous astronomy, we can actually find out how the different wavelengths of light interact with each other, what the interplay is there. So that was fascinating. Somewhere that I was involved with, we found that we could measure the base of the jet. So there's a jet that is coming out of the top of the black hole, and coming out of the poles of the black hole, and we can use this simultaneous x-ray and optical view to look at what the interplay is between the x-ray light and the optical light. We can see that the x-ray light, and the optical light are delayed by around 0.1 seconds. This gives us an idea of the size of the base of this jet. I thought that was absolutely fascinating, so that's really cool stuff that happened very recently.
-----------------------------------
댓글 없음:
댓글 쓰기