4 ms·

The closest good candidates for stellar black holes are thousands of light-years away from Earth. There is one possible candidate at about 1.1 kly, but there a

The closest good candidates for stellar black holes are thousands of light-years away from Earth. There is one possible candidate at about 1.1 kly, but there are good reasons to think that it (QV Telescopii) will turn out to be something else, as seems to be the case for LB-1 *. V616 Monocerotis at ~ 3.3 kly <https://en.wikipedia.org/wiki/A0620-00 https://en.wikipedia.org/wiki/A0620-00> is the closest thing that is virtually certain to be a black hole. Given measurements of the Local Standard of Rest and star surveys of the LSR neighbourhood, it is unlikely that there are any stellar-mass black holes at all within about 300 light-years of Earth (and X-Ray astronomy and microlensing/MACHO-hunting surveys each gives even more pessimistic nearby black hole numbers) so the prospects of getting a signal from an Earth probe dispatched to close to a black hole within a millennium is, pardon the pun, faint. There could be only some thousands up to a few (~10) million in the Milky Way, a galaxy of hundreds of billions of stars at this point in its evolution. There may be as many as ten billion stellar black holes in and around Milky-Andromeda five or so billion years in our future. I note you also say "creating ones experimentally", but that is in the realm of science fiction at this stage, barely hard s.f. even for microscopic masses, and it gets decidedly soft as one climbs up the mass scale from nanograms.

ramraj07 5y ago
Fair, is it still theoretically possible that primordial black holes of mediocre sizes are floating around? Also of course experimental black hole creation is in the realm of science fiction but so was going to the moon 150 years back. Question is if there’s a fundamental theoretical block , similar to FTL , in achieving it?
- raattgift 5y ago
  Primordial black holes may be floating around, but they are very unlikely to be any to be closer to Earth than stellar black holes, given the kinematic evidence. (There could be faint hope for an isolated one of a fairly small handful within the Milky Way. FWIW, I don't think there are small PBHs. There might be gargantuan ones in the universe. There definitely isn't one of those hiding in our galaxy though, but maybe in our galaxy cluster near the centre of mass, wherever that is (millions of light years away, at least). There are some huge central black holes in some local galaxies that may have been seeded as primordial black holes -- the mechanism of growth of such ginormous black holes is not fully understood yet)). So they aren't really going to help you reach your thousand-year deadline, absent FTL travel. Some researchers have proposed semi-seriously that there could be a small black hole lurking at the outer margins of our solar system. That obviously could be reached within a thousand years in principle (depends on how far out it is, although it must be considerably beyond Neptune's orbit), but we are perhaps decades out from a detection of it, if it even exists. The idea is, however, one of many reasons to build telescopes that are mainly to be aimed at objects in our star's immediate neighbourhood, to do very sensitive mapping of the metric the solar system sources (or, in Newtonian terms, our sun's gravitational field and the disturbances planets, asteroids, and other objects impose on it), and to do "nanolensing" observations on objects at a variety of distances. The Vera C. Rubin Observatory's Legacy Survey of Space and Time is a step in that direction, and will eliminate many possible hiding spaces for a nearby black hole. There is an upper limit on proper acceleration proportional to mc^3/h-bar for massive subatomic particles like electrons, from Caianiello (1984) <https://doi.org/10.1007/BF02748378 https://doi.org/10.1007/BF02748378> (free PDF <https://link.springer.com/content/pdf/10.1007/BF02748378.pdf https://link.springer.com/content/pdf/10.1007/BF02748378.pdf>) arising from uncertainty relations. We have no hope of producing that kind of acceleration as even with the best possible superconductors an Earth-bound accelerator can manage much less than a millionth of that <https://arxiv.org/abs/quant-ph/0407115 https://arxiv.org/abs/quant-ph/0407115>, and we need to be much closer in order to make a black hole out of small charged particles. Large particles are even harder to accelerate extremely. We also have a power-density problem: what fuels such an accelerator? Alternatively, accelerating less extremely means much longer linear accelerators, or nearly equivalently, less curvature in a ring accelerator. I think we're looking at a ring about the diameter of the orbit of Jupiter, or a linear accelerator crossing a large chunk of the inner solar system, but that's just a guess (someone has probably worked out some comparable size for ultrarelativistic heavy ions (lead or gold) though). So the tl;dr is that it's not impossible, and it's easier than trying to throw large stars at one another, but neither is really plausible within your 1000 years. And neither is easier than sending a probe to V616 Mon. and waiting several thousand years. And we might do better by making really good observatories in and around Earth. Technically we could do all three, I guess, but we're more likely to live long enough to see improvements on the results from the <https://eventhorizontelescope.org https://eventhorizontelescope.org>. And of course, what I said about your three-digit timeframe goes double (if you pardon the expression) for your two-digit one.
  - raattgift 5y ago
    This line of thinking led me to a paper I had not read before (even though it has a tremendous number of citations and is reference (2) in his famous Black Hole Explosions? (evaporation) letter of 1974[1]), by Hawking (1971) <https://academic.oup.com/mnras/article/152/1/75/2604549 https://academic.oup.com/mnras/article/152/1/75/2604549> (PDF freely available there). In this paper he considers the possibility that the universe is almost dominated by tiny (~ micrograms) black holes formed in the very early universe, persisting to the 1970s and leaving tracks in sufficiently large and sufficiently numerous cloud chamber detectors given sufficient time. (This was also decades before optical detectors like at SNOLAB, but incongruously after the Nobel prize for bubble chambers, although it was on the cusp of the activation of <https://en.wikipedia.org/wiki/Gargamelle https://en.wikipedia.org/wiki/Gargamelle> and the Big European Bubble Chamber -- he would have been aware of how close they were to activation, and results from smaller predecessors). Fascinatingly, several years after publication, conceptually similar papers were put forward for hunts for dark matter, even though it is impossible to extract from this Hawking 1971 paper that he was thinking of galactic rotation curves. The paper also pre-dates evidence for the acceleration of the expansion of the universe, and contains the curious sentence: "An upper bound on the number of these objects can be set from the measurments by Sandage (7) of the deceleration of the expansion of the Universe." However, the excellent Allan Sandage paper of 1961 <https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1961ApJ...133..355S&db_key=AST&page_ind=0&plate_select=NO&data_type=GIF&type=SCREEN_GIF&classic=YES https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_que...> does not really let one take sides ("It suffices to say that no uncontested evidence is presently available [to choose between steady-state and expanding universe]") like Hawking 1971 seems to. Nevertheless, Hawking raises an interesting and slightly spooky premonition of dark matter at super-galactic scale, keeping clusters of galaxies looking like clusters over long periods of time, rather than separating into individual isolated galaxies: "This extra density could stabilize clusters of galaxies which, otherwise, appear mostly not to be gravitationally bound." In context Hawking was clearly thinking about a universe that grows into some very long term non-expanding/non-contracting configuration which includes clumps of galaxies. Hawking 1971 tl;dr is "good luck actually observing these small weakly-interacting things, if they exist". Which is appropriate for 21st century particle dark matter experimentalists too. :^) Penultimately, some patience with google scholar has found that a small handful of the many articles citing Hawking 1971 explore the idea of primordial black holes as dark matter. (but see below). And finally, sometimes asking questions like yours (how does one build a very small black hole?) and taking them seriously leads to some very early, vague, ideas about how the universe might work in bulk, which is probably very very similar to what provoked Hawking's letter about 52 years ago. - -- [1] https://sci-hub.se/https://doi.org/10.1038/248030a0 https://sci-hub.se/https://doi.org/10.1038/248030a0 The relevant part of his evaporation letter: "There might, however, be much smaller black holes which were formed by fluctuations in the early Universe². Any such black hole of mass less than 10^15 g would have evaporated by now." In that context, I think a very low motivation for someone not terribly interested in the history of primordial black hole research to have previously hunted down a 1971 note whose idea was shortly thrown under the bus by its author is fairly understandable. :^) Hawking 1971 is however an early note on primordial black holes (the only obvious earlier one in the literature is from Zel'dovich and Novikov in 1966), and that seems to be behind many of the citations I briefly sampled. Practically all also cite the more extensive follow-up Carr & Hawking 1974 "Black holes in the early Universe" <https://ui.adsabs.harvard.edu/abs/1974MNRAS.168..399C/abstract https://ui.adsabs.harvard.edu/abs/1974MNRAS.168..399C/abstra...> which is very close in submission date to the publication date of Hawking's "Black hole explosions?" yet does not appear to consider evaporation.

ramraj07 5y ago

Fair, is it still theoretically possible that primordial black holes of mediocre sizes are floating around? Also of course experimental black hole creation is in the realm of science fiction but so was going to the moon 150 years back. Question is if there’s a fundamental theoretical block , similar to FTL , in achieving it?

raattgift 5y ago
Primordial black holes may be floating around, but they are very unlikely to be any to be closer to Earth than stellar black holes, given the kinematic evidence. (There could be faint hope for an isolated one of a fairly small handful within the Milky Way. FWIW, I don't think there are small PBHs. There might be gargantuan ones in the universe. There definitely isn't one of those hiding in our galaxy though, but maybe in our galaxy cluster near the centre of mass, wherever that is (millions of light years away, at least). There are some huge central black holes in some local galaxies that may have been seeded as primordial black holes -- the mechanism of growth of such ginormous black holes is not fully understood yet)). So they aren't really going to help you reach your thousand-year deadline, absent FTL travel. Some researchers have proposed semi-seriously that there could be a small black hole lurking at the outer margins of our solar system. That obviously could be reached within a thousand years in principle (depends on how far out it is, although it must be considerably beyond Neptune's orbit), but we are perhaps decades out from a detection of it, if it even exists. The idea is, however, one of many reasons to build telescopes that are mainly to be aimed at objects in our star's immediate neighbourhood, to do very sensitive mapping of the metric the solar system sources (or, in Newtonian terms, our sun's gravitational field and the disturbances planets, asteroids, and other objects impose on it), and to do "nanolensing" observations on objects at a variety of distances. The Vera C. Rubin Observatory's Legacy Survey of Space and Time is a step in that direction, and will eliminate many possible hiding spaces for a nearby black hole. There is an upper limit on proper acceleration proportional to mc^3/h-bar for massive subatomic particles like electrons, from Caianiello (1984) <https://doi.org/10.1007/BF02748378 https://doi.org/10.1007/BF02748378> (free PDF <https://link.springer.com/content/pdf/10.1007/BF02748378.pdf https://link.springer.com/content/pdf/10.1007/BF02748378.pdf>) arising from uncertainty relations. We have no hope of producing that kind of acceleration as even with the best possible superconductors an Earth-bound accelerator can manage much less than a millionth of that <https://arxiv.org/abs/quant-ph/0407115 https://arxiv.org/abs/quant-ph/0407115>, and we need to be much closer in order to make a black hole out of small charged particles. Large particles are even harder to accelerate extremely. We also have a power-density problem: what fuels such an accelerator? Alternatively, accelerating less extremely means much longer linear accelerators, or nearly equivalently, less curvature in a ring accelerator. I think we're looking at a ring about the diameter of the orbit of Jupiter, or a linear accelerator crossing a large chunk of the inner solar system, but that's just a guess (someone has probably worked out some comparable size for ultrarelativistic heavy ions (lead or gold) though). So the tl;dr is that it's not impossible, and it's easier than trying to throw large stars at one another, but neither is really plausible within your 1000 years. And neither is easier than sending a probe to V616 Mon. and waiting several thousand years. And we might do better by making really good observatories in and around Earth. Technically we could do all three, I guess, but we're more likely to live long enough to see improvements on the results from the <https://eventhorizontelescope.org https://eventhorizontelescope.org>. And of course, what I said about your three-digit timeframe goes double (if you pardon the expression) for your two-digit one.
- raattgift 5y ago
  This line of thinking led me to a paper I had not read before (even though it has a tremendous number of citations and is reference (2) in his famous Black Hole Explosions? (evaporation) letter of 1974[1]), by Hawking (1971) <https://academic.oup.com/mnras/article/152/1/75/2604549 https://academic.oup.com/mnras/article/152/1/75/2604549> (PDF freely available there). In this paper he considers the possibility that the universe is almost dominated by tiny (~ micrograms) black holes formed in the very early universe, persisting to the 1970s and leaving tracks in sufficiently large and sufficiently numerous cloud chamber detectors given sufficient time. (This was also decades before optical detectors like at SNOLAB, but incongruously after the Nobel prize for bubble chambers, although it was on the cusp of the activation of <https://en.wikipedia.org/wiki/Gargamelle https://en.wikipedia.org/wiki/Gargamelle> and the Big European Bubble Chamber -- he would have been aware of how close they were to activation, and results from smaller predecessors). Fascinatingly, several years after publication, conceptually similar papers were put forward for hunts for dark matter, even though it is impossible to extract from this Hawking 1971 paper that he was thinking of galactic rotation curves. The paper also pre-dates evidence for the acceleration of the expansion of the universe, and contains the curious sentence: "An upper bound on the number of these objects can be set from the measurments by Sandage (7) of the deceleration of the expansion of the Universe." However, the excellent Allan Sandage paper of 1961 <https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1961ApJ...133..355S&db_key=AST&page_ind=0&plate_select=NO&data_type=GIF&type=SCREEN_GIF&classic=YES https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_que...> does not really let one take sides ("It suffices to say that no uncontested evidence is presently available [to choose between steady-state and expanding universe]") like Hawking 1971 seems to. Nevertheless, Hawking raises an interesting and slightly spooky premonition of dark matter at super-galactic scale, keeping clusters of galaxies looking like clusters over long periods of time, rather than separating into individual isolated galaxies: "This extra density could stabilize clusters of galaxies which, otherwise, appear mostly not to be gravitationally bound." In context Hawking was clearly thinking about a universe that grows into some very long term non-expanding/non-contracting configuration which includes clumps of galaxies. Hawking 1971 tl;dr is "good luck actually observing these small weakly-interacting things, if they exist". Which is appropriate for 21st century particle dark matter experimentalists too. :^) Penultimately, some patience with google scholar has found that a small handful of the many articles citing Hawking 1971 explore the idea of primordial black holes as dark matter. (but see below). And finally, sometimes asking questions like yours (how does one build a very small black hole?) and taking them seriously leads to some very early, vague, ideas about how the universe might work in bulk, which is probably very very similar to what provoked Hawking's letter about 52 years ago. - -- [1] https://sci-hub.se/https://doi.org/10.1038/248030a0 https://sci-hub.se/https://doi.org/10.1038/248030a0 The relevant part of his evaporation letter: "There might, however, be much smaller black holes which were formed by fluctuations in the early Universe². Any such black hole of mass less than 10^15 g would have evaporated by now." In that context, I think a very low motivation for someone not terribly interested in the history of primordial black hole research to have previously hunted down a 1971 note whose idea was shortly thrown under the bus by its author is fairly understandable. :^) Hawking 1971 is however an early note on primordial black holes (the only obvious earlier one in the literature is from Zel'dovich and Novikov in 1966), and that seems to be behind many of the citations I briefly sampled. Practically all also cite the more extensive follow-up Carr & Hawking 1974 "Black holes in the early Universe" <https://ui.adsabs.harvard.edu/abs/1974MNRAS.168..399C/abstract https://ui.adsabs.harvard.edu/abs/1974MNRAS.168..399C/abstra...> which is very close in submission date to the publication date of Hawking's "Black hole explosions?" yet does not appear to consider evaporation.