tag:blogger.com,1999:blog-2846514233477399562.post7362496029274809991..comments2024-01-08T09:37:04.406+01:00Comments on RÉSONAANCES: Black hole dark matterJesterhttp://www.blogger.com/profile/08947218566941608850noreply@blogger.comBlogger34125tag:blogger.com,1999:blog-2846514233477399562.post-37178284526657532342016-07-29T00:45:04.254+01:002016-07-29T00:45:04.254+01:00Today it was the H.E.S.S. Collaboration weighing i...Today it was the H.E.S.S. Collaboration weighing in after 10 years of looking for particle dark matter annihilations from the central 300 pc of the Galaxy. Paper at arxiv.<br /><br />After 10 years of effort: No-ShowRobert L. Oldershawhttps://www.blogger.com/profile/15396555790655312393noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-82888192269617651022016-07-24T22:49:01.442+01:002016-07-24T22:49:01.442+01:00PandaX experiment reports (7/22/16) yet another no...PandaX experiment reports (7/22/16) yet another no-show for particle dark matter.<br /><br />PBHs anyone?Robert L. Oldershawhttps://www.blogger.com/profile/15396555790655312393noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-56670834622692579482016-07-21T23:01:42.120+01:002016-07-21T23:01:42.120+01:00There is a very interesting new paper on the topic...There is a very interesting new paper on the topics of PBHs and the DM.<br /><br />http://arxiv.org/abs/1607.06077 <br /><br />Title: Primordial Black Holes As Dark Matter<br />Authors: B. Carr et al<br /><br />Take home lesson: It is difficult to put all the dark matter in PBHs if their mass function is monochromatic but this is still possible if the mass function is extended, as expected in many scenarios.<br /><br />And did you see the latest LUX report. Bye, bye "WIMPs"!<br /><br />RLO<br />http://www3.amherst.edu/~rloldershawRobert L. Oldershawhttps://www.blogger.com/profile/15396555790655312393noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-43769677458201410852016-07-10T13:27:03.927+01:002016-07-10T13:27:03.927+01:00Is the PBH scenario compatible with the lensing ef...Is the PBH scenario compatible with the lensing effect evidenced by the bullet cluster? Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-28953341906967226232016-07-01T03:35:42.887+01:002016-07-01T03:35:42.887+01:00I'm sure this is an obvious question but I'...I'm sure this is an obvious question but I'm curious. I get that the very early universe was a fog of hydrogen/helium, which started clumping together due to tiny primordial inhomogeneities, thus forming stars. Are we certain that the only outcome for such a clumping is a star, that it could not continue its runaway collapse and go all the way to a black hole without an intervening luminous step? Some process where fusion is not given time to take hold and counter the force of the collapse?<br /><br />If this is possible, there sure was a lot of matter just floating around available to turn into black holes ...Anonymoushttps://www.blogger.com/profile/10133900371827846947noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-81064853599244758912016-06-28T18:29:43.008+01:002016-06-28T18:29:43.008+01:00Hope this does not get annoying... Still wondering...Hope this does not get annoying... Still wondering about what would happen when a PBH gets stuck in macroscopic objects I tried to compute when a PBH could get destructive (i.e. absorbing more matter than it could release in energy)... so I computed when the radiation pressure of hawking radiation would cancel gravitational pull on infalling matter, and it turns out that it only really depends on specific weight of the surrounding matter and its optical depth using this very simplistic approach. Assuming earth core matter and an average optical depth of 10 cm (probably way too low for extremely high-energy gamma rays of such PBHs in question) this would be the case for a PBH of 10^10 kg. For comparison, the mass of a PBH that just evaporated by now would be about 10^11 kg. So I assume pretty much any PBH trapped inside earth would be dangerous, let's hope that there are none or they just eat too slowly or there are other effects reducing their appetite.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-1260840417479981272016-06-19T13:29:33.914+01:002016-06-19T13:29:33.914+01:00Data analysis takes time...
We'll probably se...Data analysis takes time...<br /><br />We'll probably see more at ICHEP, 3rd to 10th of August.mfbnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-11696604395732912682016-06-18T08:58:16.006+01:002016-06-18T08:58:16.006+01:00Any news on the 750GeV? By now the luminosity shou...Any news on the 750GeV? By now the luminosity should be enough to know something more. Right? Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-13260559926800703182016-06-16T16:30:46.471+01:002016-06-16T16:30:46.471+01:00Jester: I am aware that this (BH of right mass tra...Jester: I am aware that this (BH of right mass trapped in planet/sun/NS) is not a stable in the long term.<br /><br />I was rather wondering at which mass the turning point would be, assuming GR + Hawking radiation - i.e. between bigger BHs that would eventually accrete all the matter around and eventually consume most of the object they're embedded in and smaller BHs that would be harmless since they would radiate off more energy than they could consume and thus still eventually evaporate. Complicated by the fact that such strong Hawking radiation will probably heavily affect the rate of infalling matter just around that point...Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-24933966648674062572016-06-16T16:25:06.076+01:002016-06-16T16:25:06.076+01:00Concerning faster news, they could do what SNEWS d...Concerning faster news, they could do what SNEWS does for neutrinos: an automatic direct notification with position and time, some first approximate data quickly afterwards, then proper data analysis later. The proper data analysis will go faster once they did it a few times. At some point I also expect them to go to statistical analysis for not-that-significant events ("we observed 100, expected 10 background, ...").mfbnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-22812750443557644052016-06-16T14:59:11.965+01:002016-06-16T14:59:11.965+01:00@mfb, but sqrt(N) where N1 = mass of halo / mass o...@mfb, but sqrt(N) where N1 = mass of halo / mass of asteroid size BH (BH halo) vs N2 = mass of halo / mass of WIMP (WIMP halo) would be at least 5 orders of magnitude difference. What am I missing? Of course the momentum will have to be take into account too.RBShttps://www.blogger.com/profile/05190152376766693948noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-49528703193077872482016-06-16T11:22:14.256+01:002016-06-16T11:22:14.256+01:00The abstract of the PRL paper says that the signal...The abstract of the PRL paper says that the signal was initially identified within 70 seconds. They also alerted several observatories to search for EM counterparts within a day or so. So clearly, technically they could announce very quickly. I think I've read/heard somewhere (can't remember where) that they're planning to do that once detections become more common and they have more experience with the processing pipeline.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-6796699075450743422016-06-16T02:29:26.994+01:002016-06-16T02:29:26.994+01:00I guess they heard me.
So this new one was record...I guess they heard me.<br /><br />So this new one was recorded in December. Do you think they'll ever be able to report events right after they're recorded?Anonymoushttps://www.blogger.com/profile/09702349560231225588noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-88918429492647286752016-06-15T22:36:27.270+01:002016-06-15T22:36:27.270+01:00Right on cue a second gravitational wave event has...Right on cue a second gravitational wave event has been reported.<br /><br />http://www.nature.com/news/ligo-detects-whispers-of-another-black-hole-merger-1.20093<br /><br />Blurb from Nature piece: "this second event suggests that there is a large population of black hole pairs out there ..."<br /><br />This is getting interesting and I anxiously await news this summer from the new Kepler mission looking toward the Galactic center for microlensing events.Robert L. Oldershawhttps://www.blogger.com/profile/15396555790655312393noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-77355437421074896942016-06-15T19:44:35.438+01:002016-06-15T19:44:35.438+01:00After the direct detection of a transient gravitat...After the direct detection of a transient gravitational wave has been replicated thanks to GW151226, one may remark that the mass estimation for the merging compact objects involved relies on general relativity in the strong-field regime and it could be that the classical black hole binaries are not the best model for the source of these GW events, even if they are probably the most simple one! <br />May be GW events will become less boring astrophysical phenomena ;-) once an electromagnetic or neutrino counterpart will have been detected... cbhttps://www.blogger.com/profile/03349828290008437401noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-83784731243839358572016-06-15T19:43:23.153+01:002016-06-15T19:43:23.153+01:00A second binary black hole merger detected by LIGO...A second binary black hole merger detected by LIGO (>5 sigma again): journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.241103<br />14+8 solar masses, merged to a black hole with 21 (+1 solar mass as GW). Similar distance as the previous event.<br /><br />Two data points still make a poor statistics, but with two events in 3.5 months we should expect several events per year even at the current sensitivity, and a few events per week with the ultimate sensitivity goal. Plus tons of less significant events.<br /><br />@RBS: With trillions or orders of magnitude more black holes, I guess 1/sqrt(N) fluctuations are not that significant.mfbnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-59319886340354785512016-06-15T18:06:16.677+01:002016-06-15T18:06:16.677+01:00As per @mvb: if we take the volume of the occupied...As per @mvb: if we take the volume of the occupied part of our solar system on one hand; and the theory prediction for the mass/density of BH in a peripheral part of the galaxy disc on the other; we can get an estimate for the number of small BH which could wander within Solar system with a given mass range, e.g. from Pluto and above.<br />Now, if the result is around or greater than 1, it would mean that we should have observed the effects similar to that of a tiny invisible planet in the solar system dynamics. And the fact that we aren't seeing anything like that (fingers crossed) would provide the grounds for the exclusion of such mass/density BH in galaxies. How would it compare with the other limits described here?RBShttps://www.blogger.com/profile/05190152376766693948noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-24630989499322857582016-06-15T13:54:23.029+01:002016-06-15T13:54:23.029+01:00mfb, well for the same mass of the halo (that we s...mfb, well for the same mass of the halo (that we should be able to get from dynamics) black hole option would be far more "granular" - i.e. fewer granules and therefore more pronounced density fluctuations - not so?RBShttps://www.blogger.com/profile/05190152376766693948noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-67553276958282492912016-06-15T00:35:51.432+01:002016-06-15T00:35:51.432+01:00The black holes would be close to an ideal gas, th...The black holes would be close to an ideal gas, the particle mass does not matter.<br /><br />I wonder how often small black holes (in the asteroid-mass exclusion gap, in particular) would fall into planets or stars. And how can we find those events to set exclusion limits?mfbnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-48996344822624185492016-06-14T23:31:58.179+01:002016-06-14T23:31:58.179+01:00New LIGO announcement tomorrow:
http://news.mit....New LIGO announcement tomorrow: <br /><br />http://news.mit.edu/2016/wednesday-ligo-virgo-scientists-discuss-continued-search-gravitational-waves-aas-meetingAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-22481657437878665632016-06-13T14:42:06.243+01:002016-06-13T14:42:06.243+01:00Dynamically a bag of fine sand would behave quite ...Dynamically a bag of fine sand would behave quite differently from a sack of large rocks (the granule mass difference in this case would be in the 10^dozens). Should not we be able to detect such differences from observing movement of visible objects?RBShttps://www.blogger.com/profile/05190152376766693948noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-10932358511699811112016-06-13T13:09:26.825+01:002016-06-13T13:09:26.825+01:00I don't think there's a stable equilibrium...I don't think there's a stable equilibrium. As the black hole mass increases, Hawking radiation decreases, while accretion increases. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-61009353945516667612016-06-12T22:02:08.884+01:002016-06-12T22:02:08.884+01:00Just out of curiosity: imagine such a mini black h...Just out of curiosity: imagine such a mini black hole coming to rest in the middle of the sun or, more extremely, a neutron star. At what black hole mass would the mass loss due to Hawking radiation exactly outweigh mass gain due to infalling matter?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-42253071735033093472016-06-11T16:26:07.051+01:002016-06-11T16:26:07.051+01:00@ Robert Oldershaw,
Thanks, an intriguing idea in...@ Robert Oldershaw,<br /><br />Thanks, an intriguing idea indeed.<br /><br />Equally intriguing would be to consider that some of the promising non-baryonic models of Dark Matter (such as the superfluid Dark Matter model) and the PBH hypothesis share a common origin. What we currently view as incompatible theories may have a deeper physical foundation, rooted perhaps in the un-conventional geometry of spacetime in primordial times.Ervin Goldfainhttps://www.blogger.com/profile/07585008304556273617noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-3692008955368196732016-06-11T16:12:13.622+01:002016-06-11T16:12:13.622+01:00Supermassive black holes have to come from somewhe...Supermassive black holes have to come from somewhere - there have to be smaller black holes around, everything down to the mass scale where black holes form.<br /><br />Xezlec, the count is still at one highly significant event and one not that significant event because LIGO didn't publish the analysis of larger datasets yet. We have two events in 16 days, and the sensitivity is expected to improve by another factor 3 in the near future. The Einstein Telescope should then see too many events to look at all of them manually.<br /><br />@Chris: The system that can inject fake signals was not even operational at the time of detection. But even if it would have been: the people who operate it know extremely well when they use it.mfbnoreply@blogger.com