Spinning Black Holes

Spinning Black Holes


On November 22, 2014 a burst of x-rays was detected by ASASSN that’s the All Sky Automated Survey for Super Novae but this was no supernova the signal came from the center of a galaxy around 290 million light-years away and what we now belive happened was a star came too close to a supermassive black hole with a mass millions of times that of our Sun and it was eaten The black hole fed on the star and yes, this is the actual termenology astrophysicists use to describe it Events like these are thought to be rare occurring maybe once every 10,000 to 100,000 years in a galaxy they’re called Tidal Disruption Events, or Tidal Disruption Flares as the star approached the side closest to the black hole experienced a much gravitational pull than the other side, ripping the star to shreds matter spiraling into the black hole formed an accretion disk an annular ring of gas and dust that’s accelerating and heating up emitting visible light UV and X-rays observable from Earth Now what’s remarkable about this event is that it transformed a dormant or quiescent black hole one that wasn’t really feeding into one that we can observe thanks to the matter falling in from that star and is what it looked like Okay if you’re disappointed, check out these artists renditions of the same event but if you’re cynical you might say “Well how do we know that’s what really happened? what if the scientists are just making this up to get more grant funding or to inspire people to go into science” well I’ll explain how we know this is actually what went down but first things got wierder scientists trained three X-ray telescopes to observe this part of the sky for years after the event and what they found was a strong and regular pulse of X-rays brightening and dimming every 131 seconds and it shows up in the data from all three telescopes they observed periodically over 450 days but the pulse maintained this rhythm and didn’t get weaker in fact as time went on the relative strength of the pulse got stronger modulating the X-ray signal by around 40% and what was causing these periodic flashes of X-rays and what could it tell us about the black hole well let’s back up because black holes are some of the simplest objects in the Universe by that I just mean that they are characterized by only two attributes Mass and Spin Okay, there’s also charge but since black holes should essentially be neutral mass and spin are the two that count mass is relatively easy to determine far away from a black hole, you can even use Newtonian physics. By measuring the gravitational effects of the black hole on other bodies, you can estimate the mass of of the black hole this has been done and black holes been found with masses ranging from just few times our Sun, stellar-mass black holes, up to billions of solar masses — supermassive black holes it’s generally accepted that there is a supermassive black hole at the centers of most galaxies, including our own. But what about spin? since black holes form from collapsing stars and all known starts rotate, all black holes should also be rotating I mean, what are the chances that a bunch of matter just collapses into a point perfectly with no rotation? It’s just not going to happen. And then additional matter falling into the black hole contributes its angular momentum. So like a figure skater pulling their arms into a… point object, You can imagine black holes get spinning pretty fast. But spin is harder to measure because unlike mass, it only affects objects relatively close to the black hole. But there is a way to do it. Actually, 3 ways. To understand all of them, you have to understand isco. In Newtonian physics, around a compact mass, you can place an object in a circular object at any radius and it will be stable. It doesn’t matter how close you get. This is not the case according to general relativity. Here, there is an innermost stable circular orbit, With a radius know as r-isco. Closer than this, and no orbits are stable: they all fall into the black hole. So when you’re looking at a black hole that is feeding, the innermost edge of the accretion disk is at r-isco. What’s useful for our purposes is that r-isco depends on the spin of the black hole. The faster it’s spinning, the smaller r-isco becomes. Assuming it’s spinning in the same direction as the matter in the accretion disk. The rotation enables particles to orbit closer to the black hole, than they’d be able to for a non-spinning black hole. So you can kind of think of it as though the spin is supporting the particles against the relentless pull of gravity. Now spin is normally discussed in terms of a dimensionless parameter that ranges from 0, no spin, to 1, maximum spin. Though I guess you could also have spins down to -1 if the black hole is spinning in the opposite direction from the accretion disk. Now, as spin increases, r-isco decreases. by a factor of 6, shrinking down to the size of the event horizon. And this sets what many scientists think is the maximum spin a black hole can have. Because if the minimum stable orbit were the size of the event horizon, Then light could escape from the black hole, allowing us to see into the singularity. This is called a naked singularity, and it makes a lot of scientists uncomfortable. As yet, there isn’t a strong theoretical reason why a black hole can’t exceed this maximum spin, It’s just that we haven’t seen one, and the thought of an exposed singularity just kind of… feels wrong. Most suspect the maximum real-world spin parameter is around 0.998. So how can you use r-isco to measure the spin of a black hole? Well first, let’s think of how we measure the size of anything far away from us in deep space, like the radius of a star Most stars are so far away that they’re simply point objects in our telescopes. So how can you figure out their radii? Well, first, look at the spectrum of their light. By seeing how red-shifted absorption lines are, you can determine how far away the star is. The spectrum also tells you the temperature of the star — Because it should approximate a black-body curve. And now the power radiated per unit area is strongly dependent on its temperature. So if you know how bright the star appears from Earth, how far away it is, and how much power its radiating per unit area, Well, then you could work out its area and hence its radius. You can actually so something very similar for a black hole’s accretion disk. Just instead of estimating the radius of a glowing sphere, you’re estimating the radius of the dark circle, r-isco, in the middle of the glowing accretion disk. Then you can use r-isco to find the spin parameter. This has been done for a number of black holes, revealing spin parameters from around 0.1 up to close to the maximum. But this method only works if the radiation from the black hole is dominated by black-body radiation from the accretion disk. which, often, it’s not. Another approach involves looking at x-rays emitted by iron around a black hole. Some black holes show a distinct iron emission line. But instead of the single frequency you’d expect, the line is broadened by factors like the Doppler shift due to the high velocity of the iron in the accretion disk. and gravitational redshift, due to the extreme gravitational fields close to the black hole. By looking at the low-energy limit of the iron emission line, you can determine how close the black hole it was emitted. And hence, r-isco. But what if there is no bright iron emission line? Well, luckily, there is a third way. And that, is to look for periodic oscillations in the data. Like the repeated x-rays observed every 131 seconds. The thinking is, these cycles must be caused by clumps of matter orbiting the black hole. And at frequencies that high, they must be orbiting very close in, probably near r-isco. Even that close, they’d be going half the speed of light. But what kind of clumps or objects would these be? Well the study’s authors argue that the best candidate involves an unlikely scenario: Years before the tidal disruption event, they propose that there was a white dwarf start in orbit around this black hole. Now, it might be stable, orbiting in this way, for perhaps one or two hundred years. By itself it wouldn’t be visible from Earth. But then the other star wondered by, and was ripped apart in the tidal disruption event. Its mass fell in towards the black hole forming an accretion disk. With the addition of this stellar debris, the white dwarf was cloaked in glowing matter, creating an x-ray hotspot orbiting the black hole, and its period would directly relate to the spin of the black hole. In this case, the measured spin parameter turned out to be at least 0.7 and possibly as high as the theoretical maximum of 0.998, meaning objects in the accretion disk were going at least half the speed of light. This is the first measurement of spin made possible by a tidal disruption event. The implication is that this could provide a method for determining the spin of black holes. Particularly ones that have been dormant, which is about 95% of supermassive black holes. If they shred a star, we get insight into their spin. Now why is this important? Well, because it helps us understand the origins of black holes. If supermassive black holes grow in size mainly by feeding on a steady stream of matter from within their own galaxy, You’d expect their spins to be very large, because the angular momentum of that matter would be more or less aligned. so it would add up over time. But if instead, supermassive black holes grow predominantly by merging with other black holes, You might expect their spins to be lower, because the spins of two black holes are likely to be randomly oriented rather than aligned. As we are able to measure the spins of more black holes in different ways, farther out and therefore further back in time, We should be able to better understand their growth. And since supermassive black holes lie at the center of most galaxies, They also lie at the center of an understanding of how those galaxies have formed and evolved over billions of years.

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  1. Im fast to hate on any other YouTuber just like THE REST IF YOU! But this kids videos are smart. Fast and well created. Why the DIS LIKES!? It it because you may or may not think he is gay. And rather you hate that or not? I my self: IF YOU ARE NOT BOTHERING ME? You are not BOTHERING me! See how EASY THAT IS!

  2. Oh yeah buddy MY SUPPER MASSIVE BLACK HOLE IS QUITE WIDE! I’ll show YOU how to evolve over billions of years pal!

  3. 825 thumbs down. WHY? probably some hyper-sensitive social justice dimwits think it's racist to name these phenomena 'black' holes. what about red dwarfs? oh my he said what?!

  4. Great job love your videos, in respect to Black Holes do they spin in any particular direction or are they subject to forces Such as we would understand here on earth ie: the coriolis effect which we understand here in the North South hemispheres.

  5. Even in presence of dark energy where everything is moving apart, how can a star (or solar system) can be fed to black hole??? Black hole is not near to any star in sky……

  6. While watching the video,in the beginning I said to my self physics is not so difficult after all…and then the math comes in…

  7. 白矮星繞黑洞旋轉的示意圖好像是錯的,理論上來說應該能看到整個“白矮星繞黑洞公轉”的軌跡

  8. If twp black holes of exact opposite spin merge, does the spin cancel each other and become stellar black hole?

  9. How can we measure the the mass of the Black Holes, since we don't know about the gravity of it, may be gravity will be infinity???

  10. If it was millions of light years away, how were we seeing it every 131 seconds then? It would be having to go faster than the speed of light

  11. The scientists arent making anything up. They're just clueless as to the mechanism which cause a black holes existence. Black holes don't feed on anything first off. Secondly, they spin and do not suck. Unfortunately this means nothing is violently ripped apart and swallowed up. Spectroscopy is also completely misinterpreted by scientists. a Although very thorough, and well explained, this explanation is completely off. Through no fault of his own of course. The blame lies with his professors.

  12. Say a space traveler orbits black hole 1m away from it's event horizon. When he will look into the window, what will he see? Say the window looks away from the black hole.

  13. If rotating mass is pulled all the way down to the singularity, shouldn't it angular momentum become infinite?

  14. So if this thing is 290 million light years away, does that mean the black hole ate the star 290 million years ago?

  15. All this sounds electrically based, not mechanically. Periodicity, oscillation, flickering of the stars, etc. Perhaps they are plasmoids and the center of galaxies? Moreover it would explain magnetic fields of stars and planets. Gravity may merely be an extension of electricity. But, astronomers need their big paychecks and fancy equipment.

  16. Este gran vídeo confirma nuevamente al gran Stphen Hawkings y una de sus frases "Los agujeros negros no son tan negros"

  17. Love your videos … All the time …. BTW how was it that specifically 4.5B years ago that the collision happened??

  18. Very interesting indeed Derek. Thank you. Here is a question I've been asking on several channels and so far got no convincing answer. If a black hole is that region of space where matter is so dense that gravity becomes extremely strong that to escape it, we need matter to travel faster than the speed of light (which as far as we know is impossible), and since black holes are a tiny part of the universe, then how come the universe as a whole could come into being? If all matter and energy of the entire universe was condensed into singularity, then it should be impossible for any object to escape it because it should me much stronger than any known blackhole, yet the whole universe came into being. Can you please shed some lights?

  19. If this happened 290 million light-years away, doesn't that mean it happened 290 million years ago and we only received the light in 2014?

  20. This is utterly ridiculous. How can anyone observe anything falls into blackhole? They freeze on the surface of blackholes.

  21. It still amazes me how strong black holes are because they emit no light. But it is still there because if they were to explode it’s a massive firework

  22. Big stars I mean I know they exist
    Black holes they are super rare
    Spinning black holes I don't think that exists so stop saying

  23. "For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." – Richard Feynman, the finest man that ever lived.

  24. how much time does it take for a black hole to eat a star .. and we have a technology of a hundred years or so . how can we observe it . in just 10 or a 100 years . i believe it will take thousand or a million years for a black hole to do its process .

  25. I'm not 100% agree with a black hole theory and also I don't have a batter explanation ether, just the feeling. In science, the feeling has no place but also have a place?

  26. Why is r-isco not the event horizon?

    Also, does the Earth have an r-isco (satellites orbiting too close get pulled in by gravity/atmosphere)? If so, we could tell Newtonian physics is wrong simply from objects orbiting too close to planets

  27. If the gravitational force of a black hole is so great that light can't escape, I wonder what the inside of one looks like.

  28. 3:16 – Oh so its not possible for matter to collapse perfectly and create a black hole without spin, but its possible for a "big bang" to line things up perfectly to form humans – extremely complicated organism…This is just outrageous and I call bs

  29. So black holes eat stars and that’s how galaxies are born…. looks like you guys kinda got this whole thing figured out. Pack up, the day is over.

  30. How much you wanna bet a black hole is dark matter and that black hole have you guys seen a white hole it's amazing

  31. 0:34
    I think it is not rare.
    Only for us with the limited sight.
    Our technology is not good enough to scan the whole univers at the same time.

  32. if dwarf star is rotating around black hole then intensity of light by the star should varying due to bending of light?

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