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Physicists argue that black holes from the Big Bang could be the dark matter
- mountainboy 6y agoWow, so many made-up things in one headline! now let me try... Unicorns from Oz could be the Tooth Fairy!
- SpikeDad 6y agoConfused because all of the stuff I've read and the videos from respected physicists say that there's no way the total mass of black holes could even be 5% of the predicted amount of dark matter that would have to be present to explain the motion of matter in the universe. Of course this is way above my pay grade.
- mturmon 6y agoI’ve heard the same claim, and the reason given was that microlensing surveys would have found more of these black holes. The article gets into this near the end: > For example, perhaps the strongest constraints on primordial black holes come from microlensing searches [...] In these efforts, astronomers monitor bright but distant sources, waiting to see if a dark object passes in front of them. These searches have long ruled out an evenly dispersed population of small black holes. > But if primordial black holes exist at a range of masses, and if they’re packed into dense, massive clusters, those results could be less significant than researchers thought, García-Bellido said. I heard about this most recently on Sean Carroll’s podcast: https://www.preposterousuniverse.com/podcast/2020/05/11/96-lina-necib-on-what-and-where-the-dark-matter-is/ https://www.preposterousuniverse.com/podcast/2020/05/11/96-l...
- speakeron 6y agoThe lack of microlensing evidence is one reason. The other is that there are constraints on the amount of baryonic matter in the universe from nucleosynthesis calculations in the Big Bang (i.e. the extra missing matter needed to account for galactic rotation curves can't be 'ordinary' matter). https://ned.ipac.caltech.edu/level5/March10/Garrett/Garrett3.html https://ned.ipac.caltech.edu/level5/March10/Garrett/Garrett3...
- jessriedel 6y agoPrimordial black hole would have formed before big bang nucleosynthesis and so would not contribute to the relevant amount of baryonic matter.
- Pet_Ant 6y ago> Primordial black hole would have formed before big bang nucleosynthesis and so would not contribute to the relevant amount of baryonic matter. What would they have been made up? Do quarks have mass, and there was enough of them? Or does energy through E=MC^2 mean that enough pure energy density can cause a black hole?
- pavel_lishin 6y ago> Or does energy through E=MC^2 mean that enough pure energy density can cause a black hole? Yes! https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics) https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)
- Enginerrrd 6y ago>What would they have been made up? Do quarks have mass, and there was enough of them? Or does energy through E=MC^2 mean that enough pure energy density can cause a black hole? I'm not sure exactly when primordial blackholes would have formed but I think it would have been sometime after inflation, though perhaps before baryogenesis. Here's the reasoning: I think it would be after the GUT epoch so gravity would have splintered off from the other forces and I think it would have been after inflation started so that inflation had a chance to exaggerate the scale of quantum fluctuations to create the necessary size & scale of density fluctuations for blackholes to form. Energy alone is enough to form a blackhole. However, it's not the energy density per se. That's sort of a necessary but not sufficient condition since you also need the surrounding spacetime to be at a low enough density relative to the region where you are expecting a blackhole to form. This, incidentally is a common source of confusion about the big bang. "Why didn't it just form a blackhole?" The answer is because ALL of the spacetime was at the same density.
- lmilcin 6y agoBlack holes are same as any other matter and the lensing is only dependent on mass. So if in a distant galaxy there is dark matter, the lensing will be exactly the same regardless fo whether this is in a form of cloud of particles or from billions of small black holes.
- T-A 6y agoMicrolensing surveys look for lensing of light from distant sources caused by relatively nearby masses.
- mturmon 6y agoThe reasoning appears to be that if the BHs are clumped, then the number of microlensing events will be lowered, as opposed to if the BHs are evenly dispersed. In other words, the number of concentrated masses intercepting rays of light from distant background sources would be given by the number of BH clusters as opposed to the number of BHs. The objects we're looking for are large masses in the space between us and the distant light source. Typically the light source would be in the LMC or in our own galactic center, and the BHs would be, for example, in our own galactic halo. We wouldn't expect to be finding BHs in a distant galaxy by microlensing. I'm describing (or trying to describe!) what seems to be the astrophysics consensus. Sean Carroll is a Caltech astrophysicist who was interviewing another astrophysicist, and my quote from the article gives the explanation from a third. Am I getting this wrong?
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- posix_compliant 6y agoWhat if dark matter is just the clumping up of particles that don’t interact?
- thisiscorrect 6y agoWhy would the clump if they don't interact?
- can16358p 6y agoI think that meant something like don't interact with our "ordinary matter" in a way that we know.
- rurban 6y agoGravity still attracts them. They do have mass
- magicalhippo 6y agoBut without interacting they have no means to shed the energy they gain when attracted to other matter, so they won't clump like normal matter.
- Google234 6y agoThey interact with normal matter and themselves via the force of gravity...
- magicalhippo 6y agoBut gravity is (effectively) a conservative force. For the most part a dark matter particle attracted to another particle will just convert all the kinetic energy it gained during the attraction back to potential energy as it whizzes past and away from the other particle. Normal matter particles can radiate away photons when they hit each other, ie friction, leading to a non-conservative interaction. This allows them to shed their energy and clump in a way dark matter can't.
- diminish 6y ago> the idea is appealing because it doesn’t invoke new particles or new physics theories. It just repurposes old elements. Hope was that, dark matter puzzle may bring new physics . Primordial black holes will be interesting to watch.
- moreteafather 6y agoWhat if the Big Bang Never Happened? https://www.youtube.com/watch?v=3KkhRibBllU https://www.youtube.com/watch?v=3KkhRibBllU
- DyslexicAtheist 6y ago> Lerner received a BA in physics from Columbia University[7] and started as a graduate student in physics at the University of Maryland, but left after a year due to his dissatisfaction with the mathematical rather than experimental approach there.[8][9] He then pursued a career in popular science writing. and > He wrote the 1991 book The Big Bang Never Happened, which advocates Hannes Alfvén's plasma cosmology instead of the Big Bang theory. He is founder, president, and chief scientist of Lawrenceville Plasma Physics, Inc. -- https://en.wikipedia.org/wiki/Eric_Lerner https://en.wikipedia.org/wiki/Eric_Lerner he couldn't grok the Math and so he took to writing and scientific-populism.
- Google234 6y agoWhile he does seem like tbe crackpot-type, your last point may not be fair. I don’t think you can get through a undergrad physics education without being able to handle a decent amount of math. It sounds like it was just unfortunate he couldn’t find a experimental physics group as a grad student. I am surprised about this though, while I don’t know how it was back then, UM has an amazing experimental physics program now.
- tus88 6y agoDoes dark matter emit hawking radiation?
- doublesCs 6y agoIf it did, it wouldn't be dark.
- V1ndaar 6y agoFor all reasonable sizes of black holes, the flux due to Hawking radiation would be _so ridiculously low_ that it wouldn't change anything about our usage of the term "dark matter". In fact most dark matter models do assume some form of extremely weak interactions with normal matter or dark matter decay, which is how we try to detect dark matter. The effective flux from such interactions is a lot larger than Hawking radiation would be.
- xefer 6y agoThis is going back many years, but I seem to recall that one of the arguments against primordial black holes is that - assuming Hawking radiation is correct - we should see evidence of black holes evaporating if they are of the correct size, but that hasn't been seen. https://www.nature.com/articles/248030a0 https://www.nature.com/articles/248030a0
- vivekd 6y agoI don't know physics very well, but I was under the impression that our current models said that the primordial black holes would have evaporated by now. Perhaps there was some explanation for this in the article that I missed?
- brainless 6y agoI think this is what you are referring to: https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_evaporation https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_e... "Hawking estimated that any black hole formed in the early universe with a mass of less than approximately 10^15 g would have evaporated completely by the present day."
- scott_s 6y agoAnd the relevant part from the article discussing it: > The original idea dates back to the 1970s with the work of Stephen Hawking and Bernard Carr. Hawking and Carr reasoned that in the universe’s first fractions of a second, small fluctuations in its density could have endowed lucky — or unlucky — regions with too much mass. Each of these regions would collapse into a black hole. The size of the black hole would be dictated by the region’s horizon — the parcel of space around any point reachable at the speed of light. Any matter within the horizon would feel the black hole’s gravity and fall in. Hawking’s rough calculations showed that if the black holes were bigger than small asteroids, they could plausibly still be lurking in the universe today. This theory proposes the black holes would be big enough to still be around.
- tremon 6y agoWould that evaporation be independent of matter accretion? Wouldn't a black hole of any size be able to sustain itself depending on the availability of matter in its catchment radius? Or would black holes of smaller size not be able to capture enough matter to sustain themselves?
- 02020202 6y agojust fyi, "dark matter" is not a matter at all. it is just a label for the leftovers in the mathematical equations that we use today to calculate "space stuff". scientists have made this up so they can keep using the math, even if the numbers don't add up. it's the same thing when large corporations use "good will" for differences in assets and liabilities in their accounting.
- V1ndaar 6y agoThat is being willfully ignorant. Yes, "dark matter" is a kind of catch all term for a bunch of phenomenon / experimental measurements we don't properly understand. There's a large number of different models trying to describe the seen behavior and make predictions to be able to detect it. And in most of those models, dark matter is indeed matter!
- rcxdude 6y agoThis is a view which is increasingly disfavoured by scientists. Theories which attempt to modify the mathmatics to explain dark matter have failed to hold up to observation, and more and more evidence is mounting that dark matter does in fact act like matter.
- sgt101 6y ago> mounting that dark matter does in fact act like matter. Apart from that the only way it interacts with anything else is via gravity...
- rcxdude 6y agoThere's nothing inconsistent with a form of matter which only interacts through gravity (plenty of matter does not interact with e.g. electromagnetism), especially if you weaken the statement to a form of matter which we can only currently detect through the gravitation effects it seems to have.
- Filligree 6y ago
- Lucasoato 6y agoLittle off topic: have you already found a way to exit the local group and access other galaxies? This should be our priority!
- holler 6y agoIf this were true, could the Earth ever collide with one of these asteroid-sized primordial black holes and what would happen? In theory would we even be able to detect the imminent rendezvous?
- Filligree 6y agoAn asteroid-mass black hole would be too small to interact much. It would go straight through the planet, and couldn't possibly capture enough mass to be e.g. captured, but it would register as something like a very high energy cosmic ray.
- nobrains 6y agoI am interested in knowing your reasoning on how/why this will happen? (would go straight through the planet + would register as something like a very high energy cosmic ray)
- vbarrielle 6y agoI suppose it has to do with the Schwarzschild radius of such a black hole being really small, I guess it would be something like 10^-8m according to https://en.wikipedia.org/wiki/Schwarzschild_radius https://en.wikipedia.org/wiki/Schwarzschild_radius which means almost nothing would fall inside its event horizon, and it probably would not collide with anything. However, the gravitational pull of an asteroid would not be negligible, so I guess it would have a big impact pulling things towards it.
- ben_w 6y agoI can answer the first question but not the second. The Schwarzschild radius of Vesta is 396.1 nm [0]; which means it a black hole with that mass would intersect 6.281 cm^3 [1] of material if it went through the center of the Earth. I have no idea why it might look like a cosmic ray. The surface gravity would be absolutely insane, so I would naïvely expect something like this look like an earthquake. [2] [0] http://www.wolframalpha.com/input/?i=event%20Horizon%20radius%20vesta http://www.wolframalpha.com/input/?i=event%20Horizon%20radiu... [1] http://www.wolframalpha.com/input/?i=%28396.1nm%29%5E2%20%2A%20pi%20%2A%20diameter%20of%20Earth http://www.wolframalpha.com/input/?i=%28396.1nm%29%5E2%20%2A... [2] http://www.wolframalpha.com/input/?i=gravity%202.67%C3%9710%5E20%20kg%20radius%20396.1%20nm http://www.wolframalpha.com/input/?i=gravity%202.67%C3%9710%...
- ngcc_hk 6y agoIt is shocking that 85% of matter is missing from our base model. Hope this solve it.
- avsteele 6y agoBut I thought dark matter candidates needed to not interact with EM radiation in the same way ordinary matter does. Black holes are perfectly capable of absorbing light, wouldn't this effect be seen? Perhaps they are so point-like that they can have sufficient density averaged out to account for the observed gravitational effects but a small enough cross-section that they contribute negligibly to light absorption?
- mabbo 6y agoGiven their mass would be, as the article says, the size of a large asteroid, the event horizon would be quite small. Ceres has a mass of 10^21kg, for example. This website[0] to calculate Schwartzchild radius estimates the event horizon for a black hole of that mass would be roughly 1 micro-meter (1 millionth of a meter). [0]https://www.omnicalculator.com/physics/schwarzschild-radius https://www.omnicalculator.com/physics/schwarzschild-radius
- hnuser123456 6y agoBlack holes this small would evaporate relatively quickly.
- knodi 6y agoBlackhole is a planet with enough mass to bend light.
- Sevrene 6y agoCould this be related at all to Generic Objects of Dark Energy (GEODEs)? https://en.wikipedia.org/wiki/Generic_object_of_dark_energy https://en.wikipedia.org/wiki/Generic_object_of_dark_energy
- MayeulC 6y agoWhat if antimatter, for some reason, clumped together more easily (weaker electric repulsion?). Wouldn't that cause more "anti-black holes" to form during the early period of the universe, explaining both matter/antimatter imbalance and part of the dark matter in the process? And now I wonder the same as holler: firstly, can you differentiate a black hole made of matter from one made of antimatter? The resulting energy couldn't leave it, AFAIK? Secondly, if there is any difference, what would happen to Earth in case of a collision?
- jdmichal 6y agoI think being able to tell the difference would have to be answered by solving the information loss problem. Because otherwise, every property is either dependent on or constrained only by the mass. And yes, even if they were antimatter black holes eating matter, it wouldn't matter because all the energy from the resulting annihilation would just stay in the black hole and due to mass-energy equivalence nothing would be different to the outside observer.
- Aerroon 6y agoCouldn't the accretion disk of a black hole give us a clue though? Likely not all of the material would've been beyond the event horizon. Some of it would've stayed outside of it in the accretion disk. It's likely that the antimatter that stayed out would at some point interact with the regular matter that falls towards the black hole, but even that might give us a clue based on how energetic the accretion disk is (how much it radiates for example). But I'm just guessing here.
- MayeulC 6y agoWell, probably not if we consider primordial black holes? Those can be quite light, and may have "cleared their orbit" a long time ago.
- Aerroon 6y agoI'm interested in antimatter too. There should be a lot of antimatter out there, but we can't seem to find it. It's possible that antimatter does interact gravitationally at a smaller magnitude with matter and/or other antimatter. As far as I know, we haven't even experimentally confirmed whether antimatter has the same sign for gravitational effects as regular matter (ie whether it's repulsive or attractive), but it seems very likely that it's the same as regular matter. The magnitude could be different though.
- jtolmar 6y agoI really appreciate how this theory makes testable predictions that already-planned experiments will be able to confirm or deny. Right or wrong (and most ideas are wrong), this is the gold standard of science.