How Can We Predict What Happens at an Event Horizon?
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00:00
LightKopfstützeAerodynamicsBlack holeRadiationOrder and disorder (physics)Musical ensembleGround (electricity)Me 323 GigantJet (brand)MaterialWeatherGasWolkengattungMeteorologyElectric power distributionGalaxyOrbitDensityUniverseFahrgeschwindigkeitHandwagenSpare partShip classLastNyquist stability criterionSubwooferMassCrystal structureSteckverbinderDrehmasseStarHot workingRegentropfenSizingYearHose couplingQuantumRadio telescopeCombined cycleMechanicPhase (matter)Lecture/ConferenceMeeting/Interview
Transcript: English(auto-generated)
00:04
The research question deals with one of the most fascinating objects which we have in astrophysics, which are black holes. Black holes are strange objects because they are a place where space and time begin to mix up and mess up. And a combination of gravity and quantum mechanics becomes important.
00:26
And they are very fascinating because every galaxy seems to have a very massive black hole in the very center. And the black hole seems to know about the properties of the galaxy, which nobody can understand. So the black hole gives us insight into a very strange world which seems to be
00:45
important in order to understand the rest of the universe and where we know nothing about it. The black hole is defined as a black hole because inside a certain region nothing can escape, not even right. That's why it is black. But there's a last stable orbit, which we call the event horizon, outside of which gas can still radiate away.
01:08
We see the light and then inside this event horizon radiation can't make it out. It's called event horizon because it's also the horizon where space and time change their properties.
01:20
So events change in their sequence of what happens. So this is something very, very funny and unexpected from general relativity. So this event horizon is the holy grail in order to understand black holes. And we want to resolve the event horizon and see what happens there, which means we have to wait for an event at that horizon.
01:46
We use the same method as meteorologists use on Earth to calculate how the weather is evolving. We simulate the physics of a gas cloud or a gas using hydrodynamic equations, which are known on Earth.
02:09
Navier-Stokes equations, which is solved iteratively on a computer. So we go step by step and so the weather pattern and the density distribution and the velocity distribution is changing with time.
02:23
We have a problem. The galactic center is a very complex place. And so we do not really know all the environment, which is very important if you want to understand how the weather evolves. And so we do a simulation of a cloud moving around a black hole. And then we go to our observer friends, which sit fortunately next door because at the
02:46
Max Planck Institute we are in this fortunate situation to have the theorists and the observers together. And only if you work together, always interact with the observers and tell you whether you're right or wrong, can you work the complexity of the universe out.
03:00
So it should be there. It should be something like that. It should exist everywhere. Unfortunately, it's not everywhere like this. But here we are in Gaussian when the fortunate situation that observers and theorists are strongly interacting. And so we are always kind of being corrected by the observations and by the observers and that helps us to tune our models so that we get the conditions right.
03:21
And then we calculate iteratively what happens if this gas cloud moves around a black hole in the hope that we will predict when gas creates a black hole, when an observer has to look carefully to see what happens close to this last stable orbit, close to the event horizon.
03:43
So our key findings was evolving as a function of time. In 2012, this gas cloud was discovered and was still very compact and spheroidal. And then we immediately started calculating that and we predicted the cloud will become a spaghetti.
04:02
By the gravity of the black hole, it will be torn apart into a very long object. It will not fall directly into the black hole. It will move around the black hole, but the strong gravity of the black hole will tear it apart. And that should happen around 2014-15. And indeed, observers were looking and they found something like that.
04:22
They found the spaghettification of this gas cloud. So we were quite happy because we saw that indeed meteorology works in the universe, which we were sure before. Then we predicted now comes an exciting moment. The gas will fall back and accrete onto the black hole.
04:41
And if you look carefully, you see the event horizon, which has never ever been seen before. And the observers then told us, no, the cloud after becoming a spaghetti is now actually compactifying again. So we were rather puzzled about this silly gas cloud not doing what our meteorological equations would predict to do.
05:03
And we found a reason for this, which is connected to that the cloud has a magnetic field and also that it is consisting of lots of little droplets. So it does not only behave like a gas cloud, it has also some substructure. And including the substructure, we are right now recalculating everything.
05:24
And we predict that this infall will still happen, but it will happen at a later phase in a couple of years. And that is what the observers now can use to really understand what happens when gas falls in.
05:44
The black hole is special because it has an event horizon. The event horizon is the place where light can still disappear from the black hole and a little farther in, light is stuck. And the event horizon is a fascinating place. It's a prediction of general relativity, but at the same time it's a quantum object.
06:05
Its size is so small that quantum mechanics matters. Now, general relativity and quantum mechanics cannot be unified because general relativity is not part of quantum mechanics. And quantum mechanics predicts that everything is extended. And general relativity says the event horizon is infinitely thin.
06:23
So we expect when gas enters this last stable orbit in the event horizon, we'll see new phenomena, which combine general relativity and quantum mechanics in a new theory of quantum gravity. And we might learn something about this new and yet unknown theory just when this event happens.
06:47
The journey is very fascinating because on the observational side, and I told you we are always connecting to the observers, we now have the event horizon telescope, which is a combination of lots of radio telescopes.
07:00
You combine them to get a radio telescope as big as the Earth. And with this telescope, once you resolve the event horizon, that's what you can do. You will see all kinds of phenomena that will arise at this event horizon. You might get gigantic jets of material being blown out of the center of the galaxy close to the event horizon.
07:21
That's something we can predict when we simulate the gas falling towards the black hole, maybe including new theory, which we have learned about from this first event. These jets are enormously important because they are bigger than a whole galaxy, and they might affect the dynamics of the whole galaxy.
07:40
And that brings us to this fascinating connection between the mass of a black hole and the mass of the galaxy, which is strongly correlated. The kinematics of the galaxy is correlated to the black hole in the center. And at the moment, we don't understand how these tiny objects can mess up a whole galaxy. So we'll learn a lot about how galaxies evolve, maybe even how stars evolve in the galaxies.
08:03
And we might learn something about these supermassive black holes in the first place. They are so massive that they cannot have formed out of a collapsing star. So we have no idea where these black holes come from, how they got all this material they seem to have. And that is a very, very bright future in the next 10 years.