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LIGO detects probable black hole merger event
- civilian 7y agoCan anyone explain how I should be reading that graph? I'm surprised that the gravity anomaly is coming from a large region of space. And it's a curve. Is that expected? Why is it happening? A black hole merge is coming from a single point in space, so I would have expected there to be a single point. But I'm definitely missing something.
- petschge 7y agoIt does come from a single point but they can not tell where inside the shaded area of space the single point was. As far as I can tell from their website the event was seen by Virgo and only one of the Ligo detectors (Livingston), which makes localization in the sky rather uncertain. No clue at the moment why the second Ligo detector (Hanford) did not see it.
- turndown 7y agoFrom what I understand a lack of detection can also tell you something about where the point of origin is.
- petschge 7y agoIf you had a working detector taking good data than not hearing it also tells you something. But if the detector was not taking good data for whatever reason (local seismic event, high surface winds, technical glitch), then it doesn't help you. Also afaik (and I am not an expert) the first automatic pipeline doesn't use non-detections.
- SiempreViernes 7y agoIf not all of them see it and they have this shitty sky location, the one missing was either offline or its data was unusable for other reasons (ie someone left their phone on one of the mirrors and got a call).
- gus_massa 7y agoIt is easier to understand if you imagine that they are "hearing" the gravitational waves instead of "seeing" the gravitational waves. Analyzing how the waves affect both detectors and the delay, they can get a rough idea of the direction. The origin was in a single point that is probably in the dark zone in the bottom left. I'm not sure of the reason of the shape, but resolving equations in sphere usually give curved solutions, and then projecting it to a planisphere add more distortion. [I'm interested to read a more detailed explanation. Also, why the longitude is in hours?]
- petschge 7y agoThat's probably not longitude, but right ascension which is typically given in hours (and minutes and seconds).
- SiempreViernes 7y agoThe short version is "we heard something, but we don't know were from, somewhere over there probably waves at the sky"
- pfdietz 7y agoThe localization was particularly poor because LIGO Hanford apparently wasn't up(?), and didn't contribute data for this event.
- astro123 7y agoWith the caveat that I have nothing to do with ligo and so don't know much... I think that during this ligo run (it just turned back on in April-ish) they expect to find roughly 1 event per week. So this will be fairly common! [1] is a nice summary of what they have found so far. For people here interested in the engineering side of LIGO, it is absolutely mind blowing. The effect of the gravitational waves is tiny (fractions of the size of a proton change in length) and so there are so many things that need to be incredibly tightly controlled for. I went to a talk on this a year or so ago, but can't find the slides... Here's a summary [2] and the wikipedia page also has some info. 1 - https://www.sciencenews.org/article/ligo-virgo-made-5-likely-gravitational-wave-detections-month https://www.sciencenews.org/article/ligo-virgo-made-5-likely... 2 - https://www.engineering.com/Education/EducationArticles/ArticleID/14333/Engineering-the-LIGO-Gravitational-Wave-Detectors.aspx https://www.engineering.com/Education/EducationArticles/Arti...
- dreamcompiler 7y agoVeritasium has a good episode on the LIGO engineering challenges. https://youtu.be/iphcyNWFD10 https://youtu.be/iphcyNWFD10
- chrischen 7y ago> fractions of the size of a proton change in length ...less than a ten-thousandth the charge diameter of a proton.
- badosu 7y agoI wonder if, as we get to smaller scales, do things start quantizing? Are we far from it?
- viraptor 7y agoThere's some research suggesting that yes, it is. It plays nicely with the simulated universe theory. https://www.quora.com/Is-the-space-quantized-If-yes-then-are-the-size-of-quanta-also-increasing-with-the-expanding-universe https://www.quora.com/Is-the-space-quantized-If-yes-then-are...
- soulofmischief 7y agoBearing in mind how many universal systems seem to interact with each other, and how integral gravity is in life as we know it (required for basically every system from galaxy superclusters down to chemical reactions in our organelles) how crazy would it be if we found out at some point that gravitational waves are partly responsible for ensuring the dispersal of some kind of quantum entropy needed for a stable and evolving universe? Fractions of a proton don't mean much to us, but approaching the Planck scale it could mean a whole lot in terms of quantum probability.
- petschge 7y agoWhy do you say gravity is important for organelles? At those length scales other forces are MUCH more important than gravity.
- saagarjha 7y agoGravity is important for heavy elements to cluster in one place in sufficient concentrations to form organelles.
- krastanov 7y agoExcuse my language, but I want to stress how preposterous this statement is: this is complete and utter nonsense. Gravity is way more than 10^10 times weaker than electromagnetism at this scale. Unless you mean "gravity is important to make planets, and planets are where we have observed life", in which case you are stretching the meaning of this expression to a meaningless level.
- soulofmischief 7y agoHere you go: https://www.hindawi.com/journals/bmri/2015/863075/ https://www.hindawi.com/journals/bmri/2015/863075/ I am not being abstract. Beyond molecular chemistry, gravity and electromagnetism are the dominant ambient forces. We are still learning of the relationship between gravity and QM. What is complete and utter nonsense is refuting a hypothesis without understanding it.
- jeanlucas 7y agoOk, their twitter humor is on point: https://twitter.com/LIGO/status/1145427537629208577 https://twitter.com/LIGO/status/1145427537629208577 edit: actually all their replies are hilarious.
- mehrdadn 7y agoWow yeah, these are hilarious.
- macinjosh 7y agoThis is a pointless exercise. The money, brainpower, and effort being spent on this should go to fixing real problems we have here on earth. Children still go hungry, people are dying of thirst, and a bunch of nerds are spending millions to circlejerk over supposed cosmic events that have 0 impact on us. Hell, if we have to have a focus on space why aren't we doing something useful like space elevators, asteroid mining, or monitoring for potential incoming impacts. This is the definition of "Who cares?!"
- DiogenesKynikos 7y agoThis will sound cynical, but at this point, it's no longer news unless it's a binary neutron star merger. If there's an electromagnetic counterpart, then it's big news. If you have a gravitational wave detection with an EM counterpart, you can get a redshift and luminosity distance, which means that you can measure the Hubble constant (in a way that is completely independent from Type Ia Supernovae). Binary black hole mergers are not expected to give off any EM radiation. There should be a few binary neutron star mergers this run, and with some luck, there may be one with an EM counterpart.
- cperciva 7y agoPresumably if the location could be determined accurately enough and it was close to a galaxy, we could conclude that it was most likely in that galaxy, and thereby get a useful measurement though?
- DiogenesKynikos 7y agoNot with gravitational waves alone. People do want to correlate large numbers of binary black hole mergers with galaxy positions and come up with a statistical measurement of the Hubble constant, but no single BBH merger will be clearly identified with one galaxy under that scheme. You need lots of mergers, and the Hubble-constant determination is more model-dependent. Binary neutron stars with EM counterparts are much more straightforward.
- pfdietz 7y agoI'm waiting for a neutron star + black hole merger.
- stevespang 7y agoRemember that these signals are most likely events that occurred a very long time ago - - could have been billions of years ago even.
- gnufx 7y agoYes, the experimental details are stunning, particularly with an experimental physics background. As someone who had a narrow escape from a PhD working on resonant bar-type detection attempts, I've never understood how those were ever thought to be sensitive enough -- whether decent calculations just weren't available or what. Unfortunately, you're typically not in a good position to evaluate such things before starting the work.
- effie 7y agoWeber's initial calculations and experiments with bar detectors were a reasonable effort, because gravitational waves were something that nobody believed in. Bar detector has an advantage - it is cheap. A strong enough wave could excite it and it would have been great and cheap discovery. But later when nothing was being reliably detected, people turned to more expensive interferometric detector. Today it is believed the bar type detector could only detect extreme events nearby, which are very unlikely.
- idlewords 7y agoThis is so incredibly cool.
- Odenwaelder 7y agoI'm fascinated about the degree of automation. It seems that all the necessary computations are made and presented on that website. I would love to learn more about this and their tech stack.
- choeger 7y agoWas there not some severe doubt on the whole signal inference? I recall an article that critized them for some changes in the protocol and also questioned the statistical significance of their findings. How is the current state of that discussion?
- KnightOfWords 7y agoPretty much dismissed by later analysis I believe. Also, please bear in mind LIGO/VIRGO pinned down a neutron star merger with an optical counterpart, so there is independent confirmation the detectors can lift signal out of the noise.
- perlgeek 7y agoI love how that data is public, and viewable by anybody.
- Geenirvana 7y agoIs there anywhere that I can read up to understand the graphs?
- 7373737373 7y agoHow can black holes merge from our perspective, if something needs an infinite time to reach the event horizon from our perspective?
- delecti 7y agoThe event horizon itself isn't really a "thing". The event horizons can merge without any "somethings" reaching any event horizon.
- fsh 7y agoBecause it doesn't take infinite time from our perspective. The object falling into the black hole experiences strong time dilation due to the extreme gravitational field, but that doesn't affect a remote observer.
- 7373737373 7y agoIn the twin experiment, the observer sees his twin age slower, so it _does_ have a remote effect. From the perspective of the object falling into the black hole, the local conditions do not change, time is progressing normally etc.
- peter303 7y ago19 candidate events past 92 days since the improved system was turned on- about every five days. I am not sure what elevates a candidate to a confirmed event. Candidate events are posted quickly in hopes of observing associated photons.