Primordial Black Holes - Sixty Symbols

okay well we normally think of black holes as forming when stars collapse under the influence of their own gravity that pressure that tries to keep them up isn't enough to stop them from collapsing and then the inexorably fall down into a singularity and form an event horizon they have a mass of order at least as a mass of the Sun a solar mass it could be a few more tens of solar masses and even even the ones in the center of our galaxy the supermassive black holes of millions of solar masses but these are different these particular ones could have masses down as small as 10 to the minus 5 grams 10 to the minus 5 grams is the Planck mass but it's a probably the mass of a neuron also they were they could have formed extremely early on in the universe in the period which which we would associate with quantum gravity scales but they can leak we can have a range of matters we could have amassed that size of a golf-ball we could have a mass a particular interesting one that mass ranges around 10 to the 15 grams that's about the size of the mass of Mount Everest what is a primer your work okay well it's a black hole but it formed very early in the universe that's kind of where the primordial bit comes from you don't have to have a star to form a black hole I think that's the key thing here what you need is a region of high density of matter of material and then you need some big fluctuations which occurs over a region of the space in which you get an increased amount of matter such that it you've got so much matter that it falls within what we would call it Schwarzschild radius and then the event horizon can form and you've formed a black hole it didn't need to come from a collapsing star it can just be that there was some fluctuation which arose from something happening in the early universe which led to this formation what if you mishit you there's no star or anything no Liam yeah these could have formed where before stars formed they could form the some of those best probes we have as the very early universe the fact that these these massive objects are forming so early on and yet it is because there's a primordial soup of particles there that could have coalesced so for some reason some fluctuation occurred driven because I ended by lots of different subtypes of one of them is Indian during a period of inflation the universe expands exponentially fast that you have fluctuations of the energy density responsible for inflation in those situations can in regions of the universe cause these things to fall I suppose in the very early universe you're thinking of the quarks and the gluons that around is you know sub-sub a second time before a second when you might say the first nuclei form is a time of nucleosynthesis certainly where before 300,000 years after the Big Bang when you think of the first atoms forming so these are the building blocks if you like of our universe that are moving around in a plasma and I think you're coalescing these regions together they could have formed right of the plank here although you know you're very got to be very careful we don't really understand the physics of quantum gravity but they could form from then on in and associated with different time scales and as I said the one is particularly of interest for us today from constraining these would have formed about 10 to the minus 23 seconds after the Big Bang this is amazing right we're going to be using observations today to constrain and a physics event that could have occurred where before the first second expect the illness first atoms on a suit require a whole bunch of primordial black holes of various sizes form what happens next what's happening to the helmet so this is where the really cool stuff comes in the thing that makes them really potentially very interesting and it's thanks to Stephen Hawking lots of stuff is thanks to Stephen Hawking you realized that black holes don't remain black we evaporate thermal radiation photons if you like and as we evaporate this shrink and then mass decreases so quantum physics is coming in the evaporate because of quantum mechanics but what he showed was that the rate at which a black hole evaporates is inversely proportional to its mass so a light black hole evaporates very rapidly and as the associative temperature of this radiation is very high a massive black hole therefore evaporates very very slowly and it has an Associated very low temperature so in the early universe where you have very light black holes ten to the minus five grams 10 to the 17 grams these things are evaporating quite rapidly and in fact anything below 10 to the 15 grams the ones that form cluster 10 to the minus 23 seconds they have basically all evaporated by today the fact that they have evaporated actually places very important constraints on some of the models of our universe the ones that are evaporating today or how to have a mass of about 10 to 15 grams so they're coming to the end of their life now and they're emitting photons of orders 100 Giga electron volts and we can look for these they're looking for gamma rays we can look for these objects in the sky we can go and see are we finding any of them and the fact we don't see any of these gamma rays places constraints on the number of these black holes that could have been formed at this scale and that in turn places constraints on the its contribution to the overall mass of the universe so it turns out for a sort of black hole of a mass 10 to the 15 grams Mount Everest type black hole they have to contribute less than a hundredth of a millionth of the total mass of our universe energy density of our universe 10 to the minus 8 of the overall total and you can do the same for all these math scales by looking at what they produce and constraining them by the fact we're not seeing evidence of them and in particular in the early universe like the ones that we've apparated the ones that have gone when we do see you say well how on earth can you test for that we've got or what they'll have done of course is they produced radiation as they went though very hot the produced radiation they will have affected for example the time at which the first nuclei wanted to form it's called nucleosynthesis that occurred about about a second the process began if you've got lots and lots of very high-energy particles have been emitted by these black holes they will delay the onset of the formation of these as these new cloud because every time protons and neutrons try to combine together these photons will have come in and connect them apart again and so it would delay that onset so that's our legacy but we have very good bounds on when this occurred because we can measure the abundance of these of these nuclei and that in turn place is very calm tight constraints on the amount of primordial black holes that in turn places very tight constraints on the models the physics models which led to those primordial black holes forming and in fact you can rule out models based on the fact that you would have predicted they would have formed so many of these very small black holes they would have been injected so much radiation into the universe that would have delayed the onset of nuclear synthesis we don't see that so you were backwards and you've constrain any zone this is how it works not detecting them naturally sometimes can be quite useful with the problem of your black holes formed the world is no better oh yeah based on state embedded in the universe they're also they're all evaporating yeah just slowly so that massive ones are evaporated slower than the light on time but the ones that have another parade yeah but they just sort of stay embedded they're just like things left stuck in random parts yeah they're the I'm so for example those that have a mass bigger than 10 to the 15 grams there's a range of masses for which these in principle could act as Dark Matter candidate because they're there they're massive objects they're be very massive objects stuck in MIDI in the Centers of galaxies and there could be lots of them there and there are indeed mass ranges I think for example if they've got a mass range I think it's 10 to the 22 10 to the 26 grams we can't yet rule them out as dark matter candidates similarly if they've got masses in the range of I think it's 10 solar masses through a hundred solar masses they also can play roles of Dark Matter candidate they're different from your typical Dark Matter candidates which is subatomic particles that we associated in supersymmetry for example or wimp but they're still plausible candidates and the other sitting around and that's one of the goals is to try and search for these objects but also constrain them by looking for decay products as they evaporate so if we always talk about what is dark matter on all these time little interesting exotic particles there could be at the end of the day they could just be hulking aging old we can't rule them out yet yes and you know that says there are also possibilities that we actually don't really understand the endpoint of a black hole what actually happens is it evaporates one result is that perhaps they form a relic the evaporate evaporate evaporate down sort of around the Planck scale and then they just stop the stock is operating anymore of it and here's my relic and then you've got all these relics of about the Planck scale circling around the universe there are reasons people don't like it to do with information and storing of information but it's not ruled out as a totally ruled out as a model and we are picturing all these become sharp or floating exactly it's wonderful and then I mean looking you can go get further I mean you can because they could form all these different epochs right due to this situation those that correspond to a fluctuation at around a second the corresponding mass of those black holes would be ten to the five silver masses and that happens to be the type of mass scale that you find in the Centers of galaxies right these are the supermassive black hole scales a bit bigger one possibility is the the progenitor of these supermassive black holes are in fact primordial black holes for the second after the universe began that then can begin to accumulate matter surrounding that as far as I know hasn't been ruled out that's still a possibility it should be raining they're out of the radiation from these things it depends upon the the number of them out there right so and so what this is doing is placing tighter and tighter constraints from the allowed number nice I told you what the current bound is the current bound is their contribution to the overall energy budget has to be less than ten to the minus eight it still sounds like it could be reisel and radiation is ten to the minus four also today matter called that matter is about point three so these have to be negligible the reason they have to be negligible is precise what you say it hasn't been seen yet how long of not saying that how much more does that no separate item before you say hang on maybe these things to start there are that's a really good question I think if for you to be able to save that you would have to somehow rule out the mechanism by which they could form you would have to demonstrate that that mechanism isn't physically plausible or has been ruled out for some other reason if you can't rule out that mekin then there's no reason why they shouldn't form what what the bounds are telling you is that it that mechanism just obviously wasn't very efficient at forming them in the illumina or didn't occur very often ultimately it might be telling us something quite fundamental about our series if we don't see any we don't see any evidence of primordial black holes that indeed is going to be telling us something quite important about the very early universe and about the type of physics that went on there that we just haven't yet picked up on so the physics of nuclear synthesis is really quite well-established there's the process by which the protons and neutrons begin to combine and the rate at which they begin to combine it is quite well as it just requires an understanding of nuclear physics and local and thermodynamics in in regions the input of the black holes in this sense is that it changes if you like the temperature of the radiation that's around it determines the time scale at which nuclear synthesis should occur I agree completely that the physics of how the black hole's form and the physics of how many form is based on various assumptions about our understanding of how regions collapse how they break off from the expanding universe and collapse down to form these objects and then the number of density of these objects that form that depends upon some input parameter about the distribution of these of these black holes that is that's theoretical input that is either intuitive or ideally would come from some underlying theory but there's always assumptions made these are models we understand our universe as a model we're always testing the model and the idea is that we retest it till it breaks and then we see how what we have to change in the model to make it compatible again with observations it's important that the black holes that are evaporating right now that are coming to the end of their life and they are mountain mass black holes they're formed about 10 to the minus 23 seconds after the Big Bang those that forms a second after the Big Bang are already 10 to the 5 solar masses those that formed even later after that you know correspondingly bigger and yeah that pop of black holes now they're evaporating the ones that are evaporating you know that over ten to the five solar mass black holes are evaporating very very slowly they're very got a very low temperature so they're incredibly difficult to detect in fact Lee Hawking would undoubtedly win the Nobel Prize if they could directly detect Hawking radiation but the Provost Hawking radiation coming from these massive black holes is ten to the minus eight Kelvin ourselves incredibly lucky law could never created more mass yes yes oh wow welcome so one possibility with black holes is their form and then we know they evaporate but they also accretes of course when you're the accrete and so indeed it's a mechanism by which some black holes could actually grow so we're talking we're ballpark figures here right that's what I'm using you're quite right there's classes of black holes that would have formed and then depending on the vicinity that the stuff that was around and they would have started accreting faster than it would be evaporating but in terms of ballpark figures as to the timescale that a given mass black hole would evaporate on ones evaporating today corresponds to the interesting gram black holes it has secreted many many more grams of matter they operate correspondingly later on the probability of them forming now is extremely rare as we go fo no that's right that's right we'll take a ginormous fluctuation to Kozik whereas and the density basically has dropped so much I think that's the key thing that as you say we don't have that soup but the density of this soup is so so low now that you just need to have to have a massive bucket putting it all back together whereas in the early universe the density is much much higher and it's easier to learn a flip anyone oh yeah they were just popping up yeah there is a possible candidate for acquiring a primordial black old legend so this is an early early work but the amazing discovered by the LIGO team of the coalescing black hole these black holes have masses of around 30 solar masses and it's actually quite difficult to figure out a mechanism by which you form 30 solar mass black holes never mind and and having them in pairs and where how come this form in pairs a circling one another so it has led to a few papers suggesting actually maybe these are the seeds of these of primordial black holes which would a form suitably early in the universe you can then get a 30 solar mass black hole but once again it what's interesting you know the way science works once this discovery was announced no he surprised everybody within a few weeks the first sets of papers came out claiming this but you can but you know and I'm green here my colleague here nothing was able to show that actually is going to be very difficult to have this result explained in terms of the primordial black holes because of constraints that emerge from looking at the decay products of black holes and that constrains the density that you're going to get of them it doesn't mean they're not there and it doesn't yet mean it not this mechanism and it's a very intriguing mechanism I think but that's the way science works you come out with an idea then you test the idea against observation that could range from millions to trillions times the mass of our Sun and so it's important to consider this black hole even though physically compared to the size of the galaxy it's very very small

Channel: Sixty Symbols

Views: 284,050

Rating: 4.9575896 out of 5

Keywords: sixtysymbols, black holes, primordial black holes

Id: gs3mtZPySeM

Length: 16min 27sec (987 seconds)

Published: Tue Mar 21 2017

Reddit Comments

[u/spauldeagle]

Ah I love Ed Copeland. Brady hasn't had him on in a while and I really started to miss his font of knowledge about really interesting stuff. He obviously loves what he does, he gets so excited talking about it

[u/auviewer]

Isn't the argument for dark matter though for the behaviour of the spiral arms of galaxies? does this suggest primordial black holes are not a good candidate for dark matter? This video suggests primordial black holes are more around the centre of galaxies. But then wouldn't they become indistinguishable from typical stellar formed black holes?

[u/alpacalaika]

What would happen if a primordial black hole of small mass fell into a star? Would it turn into a large black hole?

[u/[deleted]]

How close could one get to a primordial black hole without becoming spaghetti?