19 ms·
The fastest pulsar spins at 716Hz; its equator spins at 24% the speed of light
- joezydeco 13y agoLemme guess, you caught this from http://xkcd.com/1331/ http://xkcd.com/1331/ too?
- almost 13y agoYep, I saw that little guy blinking away and had to know more...
- lifeisstillgood 13y agoI could not take my eyes off "One Birth" / "One Death" Fascinating - and I think humanity is "winning"
- darklajid 13y agoSecond kid since yesterday. Fighting for humanity here.. ;-)
- bch 13y agoAt that rate, better stock up on diapers. http://xkcd.com/605/ http://xkcd.com/605/
- lifeisstillgood 13y agoTwins? Congratulations - the battle is worth it :-)
- einrealist 13y agoIt makes me sad because most of the births are in underdeveloped countries, where people have no access to clean water and healthy food. And as more people of countries like China enter middle class, the resources we depend on, will diminish faster and faster.
- lifeisstillgood 13y agoPlease watch anything by Hans Rosling for an entertaining and educational counter-balance to your fears, ; while having some validity, over population is it one of humanities most pressing problems.
- lifeisstillgood 13y agotypo: over population is not one of humanities most pressing problems
- einrealist 13y agoThanks, I will.
- sanoli 13y agoI couldn't take my eyes off of the fact that everytime wikipedia is edited someone dies. How 'bout that for the correlation=causation folks!
- nakkiel 13y agoYou certainly know how to choose your battles..
- return0 13y agoDamnit you guys, stop editing!
- justinpombrio 13y agoHuh, I was more surprised that every time someone dies Wikipedia is edited.
- bautez 13y agoI found it quite eerie and fascinating that the "heartbeat" and "one death" categories are so alike in rhythm.
- dredmorbius 13y agoIf you keep winning like that for too long you lose.
- lifeisstillgood 13y agowhat's the timescale here ? Still on the same planet? Yeah maybe, but there is a lot of land here anyway.
- dredmorbius 13y agoIt's not land that's the problem, strictly speaking. Look up Leibig's Law of the Minimum. The historical preindustrial peak human population was around 500-800 million. Maybe we'd be lucky and be able to sustain somewhat more than that, say 2 billion. I have a hard time seeing much more given energy and resource limitations. Prediction's hard, especially about the future, but I suspect we're looking at a crisis well within 100 years. Possibly a few decades out, if that. Look up Limits to Growth.
- doorhammer 13y agoI stared at the 'my turn signal' and 'car in front of me' signal together for way too long. I went into the same trance I do sitting behind cars at a real red light.
- joezydeco 13y agoI caught that too! That was a bit of icing on a really clever cartoon.
- doorhammer 13y agoalso, obligatory secondary xkcd reference "Turn Signal": http://xkcd.com/165/ http://xkcd.com/165/
- fsiefken 13y agodoes this mean that time flows significantly faster on the outside of the pulsar then on the inside, if so does this significantly impact the pulsar dynamics?
- darkmighty 13y agoIt doesn't affect the dynamics, but it might affect the radiation emitted by it as seen from the outside. All particles in the dilated reference experience the same dilation (approximately - it does vary radially, not sure if significant).
- deletes 13y agoThere is not much difference. The relativistic factor is 1.030107, that is a ~3% change. EDIT: My amateur physics say that the gravitational well adds 9.7% to that. I tried the same calculation for earth and it gave a sensible result: a change of 6.95 * 10^-10. Here is an answer from physics exchange which gets the same result: http://physics.stackexchange.com/questions/10089/gravitational-time-dilation-at-the-earths-center http://physics.stackexchange.com/questions/10089/gravitation...
- Zikes 13y agoThat's about 11 days per year, or 43 minutes per day.
- InclinedPlane 13y agoKeep in mind that differences in gravity will also affect time dilation.
- ars 13y agoAnyone feel like calculating the energy embodied in just the rotation of this star?
- throwaway_yy2Di 13y agoAbout 10^46 J? In the classical approximation (1/2 Iω^2), assuming a uniform sphere of 2.0 solar masses and r=16 km. That's about 3% of the mass-energy (mc^2 = 3e47 J). This could be way off.
- Crito 13y agoWolfram Alpha has 10^46 J as 100x the energy given off by a supernova. I don't know if that means your numbers are off, or if this star is just mind-bendingly insane.
- breischl 13y agoWA also puts the mass-energy of two solar masses at 3.574 x 10^47 J. So the initial calculation seems about right. My very-amateur-physicist guess is that the difference is because a supernova only converts a small fraction of the star's mass into energy - the remaining mass is thrown outwards to form planets and such. [1] - http://www.wolframalpha.com/input/?i=mass-energy+of+two+solar+masses http://www.wolframalpha.com/input/?i=mass-energy+of+two+sola...
- throwaway_yy2Di 13y agoWikipedia suggests 10^44 J for type Ia, but 10^46 J for a more energetic core collapse: https://en.wikipedia.org/wiki/Supernova https://en.wikipedia.org/wiki/Supernova
- saalweachter 13y agoYou can pack a lot of energy into a rotating system. You have similar problems with ring worlds or terraforming Venus (which barely rotates at all). Transporting in the extra hydrogen and all the rest is trivial compared to spinning it up to a decent period.
- tsotha 13y agoThis is sort of the ultimate demonstration of the spinning ice skater who seems to be in every eighth grade science book.
- NAFV_P 13y agoYou can see round the back of a neutron star: http://en.wikipedia.org/wiki/Neutron_star#Properties http://en.wikipedia.org/wiki/Neutron_star#Properties
- jurjenh 13y agoWow, that page led me to the fact that there is such a thing as centrifugal force... And all these years spent trying to correct people. Oh well, you live, you learn. http://en.wikipedia.org/wiki/Photon_sphere http://en.wikipedia.org/wiki/Photon_sphere
- twic 13y agoSince we're already talking XKCD: http://xkcd.com/123/ http://xkcd.com/123/
- jjoonathan 13y agoThe "war on centrifugal force" is pedagogical. If you sit in an inertial frame, all forces you intend to teach are due to interactions between objects. This lets teachers introduce the interactions one at a time in a way that presents minimal opportunity for the "no, that equation doesn't work here for XYZ reasons which you won't understand until after you've taken vector calculus" problem. If you allow rotating reference frames then you've got to talk about transformation rules in gory detail. Everyone understands centrifugal force, but what about the coriolis and euler forces? Our intuition doesn't tell us when they apply and when they don't, so we have to be systematic about it, and that means "gory details". And guess what "being systematic about it" involves? Moving to an inertial frame of reference and taking derivatives! You can't be intuitively correct or systematic about rotating frames without thoroughly understanding inertial frames, so that's what you learn first, along with strongly worded advice to stay away from non-inertial frames (e.g. defining frame-dependent forces as "fictitious"). Anyone doing general relativity is comfortable enough with coordinate transformations that they can understand the caveats that come with frame-dependent forces and even take advantage of them to simplify calculations or definitions (the process of going from a "global" to a "local" coordinate system is highly nontrivial in GR). That's why the Coriolis, Euler, and Centrifugal forces are called "fictitious" while gravity isn't.
- angelbar 13y agoWhen I try to get on my head a "sun" spinning 716 times on a second I feel my stomach sick... Lousy astronaut here :-(
- agonz253 13y agoDropping something the mass of a tennis ball into this pulsar(assuming 2 solar masses for it) would generate approximately the same amount of energy upon impact as that of 12 atomic bombs like the one tested in New Mexico, and it would reach the surface at 60% the speed of light...relativistic effects aside
- saalweachter 13y agoWhich is to say: the escape velocity is 60% of the speed of light! So even starting from 24% of the speed of light at the equator you need to go 10,000x faster than on Earth to escape.
- hackaflocka 13y agoWhy do planets, stars and moons spin? Are there any that don't?
- wellboy 13y agoMy armchair attempt would say that a star/moon would only NOT spin if at their creation, the clouds of material came 100% from all sides equally. Normally though, stars or planets are caught from clouds catching and revolving around each other for a couple of million years until the condense to a solid object. Thus the spin.
- teamonkey 13y agoClassically, mathematically, the answer is conservation of angular momentum. As matter falls on to the body the body needs to rotate faster to conserve the energy of the system. A rotation happens if there is even a tiny asymmetry in the accreting matter. In the case of our own Moon, one side is more massive than the other and over the course of millions of years became tidally locked so that the heavier side always points towards the Earth.
- TheCoreh 13y agoIt has to do with the total angular momentum of a system composed of multiple smaller bodies. (Like the dust/debris cloud during solar system formation) This minute physics video (about the shape of the solar system) explains it probably better than I can put into words myself: http://www.youtube.com/watch?v=tmNXKqeUtJM http://www.youtube.com/watch?v=tmNXKqeUtJM The relevent part starts at about 1:03, but I recommend watching the whole thing.
- dfc 13y agoLinking to wikipedia pages with titles like this = Today I Learned on HN Yet another reason I like the "don't change the title; the title is not for editorializing" policy on HN.
- Kell 13y agoSo what are you proposing in this case, that the original poster had kept the Wikipedia title? Or that the linked Wikipedia article shouldn't have been posted at all ? Because hn's anti editorialization policy is useless in both cases. For, in the first case, without editorialization, the title is completely useless except for experts on the subject. And for the second case, it has nothing to do with title editorialization, but with content.
- dfc 13y agoThe policy is: "Do not change the title." What is it that you are having trouble understanding?
- hangonhn 13y agoThey also spin so regularly that you can build a clock out of their signals: http://en.wikipedia.org/wiki/Pulsar_clock http://en.wikipedia.org/wiki/Pulsar_clock
- privong 13y agoNow someone just needs to build an API and and app for the Pebble so there can be a pulsar wristwatch.
- MichaelDickens 13y agoNot only are they regular enough to make clocks, but they're 5 times more accurate than atomic clocks.
- dfc 13y agoI am assuming you are repeating the claim on the wikipedia page. Or maybe (hopefully) you have another source? I saw the claim on the wiki article and my first reaction was bullshit. My second reaction after stumbling across dead links in two of the three the citations was bullshit. After re-reading the article and the one functioning citation without seeing a accuracy/precision/stability figure my third reaction was also bullshit. The strontium clock at Boulder loses one second in five billion years. [1][2][3] Does anyone have any information supporting the pulsar clock claim? I have a sneaking suspicion that the author of this claim --just like the catalog in the chair pocket on airplanes--thinks my radio clock that syncs to WWVB/DCF77 is "an atomic clock." [1] http://www.theverge.com/2014/1/22/5333324/nist-atomic-clock-keeps-precise-time-for-5-billion-years http://www.theverge.com/2014/1/22/5333324/nist-atomic-clock-... [2] http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12941.html http://www.nature.com/nature/journal/vaop/ncurrent/full/natu... [3] http://www.colorado.edu/news/releases/2014/01/22/jila-strontium-atomic-clock-sets-new-records-both-precision-and-stability http://www.colorado.edu/news/releases/2014/01/22/jila-stront...
- MichaelDickens 13y agoSome atomic clocks are considerably less accurate. I can't find a citation, but IIRC, older cesium atomic clocks are accurate to about 1 second every 300 years.
- aragot 13y agoHoly cow: We can detect an object 16km large at 18,000 light-years from Earth!
- robnite 13y agoThe core of a Pulsar has never been directly observed. Their makeup is hypothetical. Perhaps an alternative explanation for the observed behaviour would be less astounding... https://www.thunderbolts.info/tpod/2004/arch/040920pulsar.htm https://www.thunderbolts.info/tpod/2004/arch/040920pulsar.ht...
- nikster 13y agoI like that theory. Generally the problem with science is that it's turned into a belief system almost akin to a religion by many people. Strangely, even by very smart physicists. They seem to overlook the fact that we don't know anything; compared to what is out there our knowledge might approach a millionth of a millionth percent of all knowable things; but even that is just for illustration because if you only take into account the scale of the known universe it's going to be a number so small as to approach 0. We know literally nothing. It's fine to come up with grand theories of how things work - human imagination is a wonderful thing. Just don't mistake it for facts.