17 ms·
All disk galaxies rotate once every billion years: study
- mrfusion 9y agoIs it strange that it’s a round human number like one billion? Why not 883,259,631 years?
- ralusek 9y agoTo be clear it's not a human number, because a year is not arbitrary, like an hour or a minute. It is still weird that it would be a clean decimal (arbitrary) figure based off of our solar system's year.
- samstave 9y agoThe universe breathes at a set rate
- em3rgent0rdr 9y agoWell a year is still a human-centric number, because it is related to the planet humans live on. However, it is not weird and most likely it means nothing but a simple coincidence. When you look at the number of time units that it could be a power of n multiple of, then such a coincidence becomes less surprising.
- 8note 9y agothe article say "about one billion years" humans probably rounded it to one billion so they can talk about it more easily
- ben509 9y agoBenford's law shows that leading digits of measured values are not evenly distributed, and tend to be smaller.
- Retra 9y agoHow is that relevant? A bias in a distribution does nothing to prohibit the existence of outliers.
- JoBrad 9y agoFTA > "It’s not Swiss watch precision," said Gerhardt Meurer, an astronomer from the International Centre for Radio Astronomy Research (ICRAR), in a press release. "But regardless of whether a galaxy is very big or very small, if you could sit on the extreme edge of its disk as it spins, it would take you about a billion years to go all the way round."
- 1053r 9y agoThis is extremely suspicious for various theories of dark matter, right? How is it that all disk galaxies have just enough dark matter in just the right distribution to make up for the various radii and distributions of visible matter and end up rotating at the same rate? I have no answers, but as they say, the most interesting words in science are, "Huh, that's funny..."
- mikeash 9y agoIsn’t it just as suspicious absent dark matter? Seems just plain weird regardless.
- hammock 9y agoIf you accept the notion that all disc galaxies are oriented on exactly the same plane (which is current scientific consensus I believe), then it doesn't seem that far-fetched to think that they all rotate the same way as well.
- poopchute 9y ago"If you accept the notion that all disc galaxies are oriented on exactly the same plane (which is current scientific consensus I believe)" That is easily disprovable, no? We can see many many different angles of disc galaxies. A simple google search will show tons and tons.
- muthdra 9y agoI agree. It looks pretty random. Its probably even more random since we can't reliably eyeball the chirality in most of photographed galaxies so half the angles in one of the axis are practically mirrored at first glance.
- eximius 9y agoI feel like they might have noticed if it was that simple.
- 9y ago
- OrganicMSG 9y agoThis is strikingly scale invariant. I know it seems insane to ask it of something that big, but could it possibly be an effect that is bootstrapping up from the smallest scales?
- JeremyBanks 9y agoWhat do you mean?
- OrganicMSG 9y agoThese are galaxies of very different sizes but yet sharing an oddly similar time signature which have another similarity, that is that they have developed without a major collision since the big bang, given they are disk galaxies. I am asking whether there could be a scale invariant function acting here that makes the rotation of the galaxy more dependent on age rather than size, that got started when the vortices that ended up as galaxies were much closer together and at much smaller scales.
- lawlessone 9y agois this not normal? Like how planets will orbit a mass of star or black hole at a certain distance depending on their speed?
- samschooler 9y agoI’d actually love to get an explanation for this. Do galaxies work similar to solar systems in that all objects are in orbit around a central mass or is it a different phenomenon that binds matter together into a galaxy?
- Merad 9y agoI believe the current theory is that most (all?) galaxies have a supermassive black hole at their heart.
- muthdra 9y agoYeah, or so I heard. What's the cause and effect order for galaxies and their corresponding supermassive black holes?
- kwoff 9y agoPlanets orbit around the center of mass. It's coincidental that the center of mass is (at least in our case) at the sun's location, because the sun has most of the mass.
- mutagen 9y agoThe mass of the central black hole is a tiny fraction of the mass of the galaxy, it might be more correct to say that the objects in a galaxy orbit the common mass (including dark matter) of the galaxy. For example, the black hole at the center of the Milky way is estimated at 4.1×10^6 M (solar mass) and the total Milky Way mass is estimated at 0.8–1.5×10^12 M (figures from Wikipedia). Some interesting articles found while digging for these numbers: https://ned.ipac.caltech.edu/level5/Merritt/Merritt1.html https://ned.ipac.caltech.edu/level5/Merritt/Merritt1.html https://academic.oup.com/mnras/article/420/4/3621/975383 https://academic.oup.com/mnras/article/420/4/3621/975383 https://academic.oup.com/mnras/article/414/3/2446/1042117 https://academic.oup.com/mnras/article/414/3/2446/1042117
- amelius 9y agoI'd like to see a time-lapse video of that :)
- kakarot 9y ago> However, the researchers note that further research is required to confirm the clock-like spin rate is a universal trait of disk galaxies and not just a result of selection bias Exactly, and that's why the article's title is misleading and clickbaity. The article also basically copies the press release [0] line for line. Still, if this is true that's a pretty groundbreaking discovery. Perhaps we are witnessing a previously undetected force at work, one that operates on much larger scales with much larger masses. [0] https://www.icrar.org/cosmic-clocks/ https://www.icrar.org/cosmic-clocks/
- fooker 9y agoCould be an artifact of the preconditions required for the formation of disk galaxies.
- isostatic 9y agoMilky Way is every 200 million years, as every school child knows: "The sun, and you and me, and all the stars that we can see Are moving at a million miles a day In an outer spiral arm at forty thousand miles an hour Of the galaxy we call the Milky Way Our galaxy itself, contains a hundred billion stars It's a hundred thousand light years side-to-side It bulges in the middle, sixteen thousand light years thick But out by us its just three thousand light years wide We're thirty thousand light years from galactic central point We go round every two hundred million years And our galaxy is only one of millions of billions In this amazing and expanding universe" - The Galaxy Song.
- crispyporkbites 9y agois this a thing? please make this a thing
- petewailes 9y agoIt's a thing. Monty Python
- cl0ckt0wer 9y agohttps://www.youtube.com/watch?v=buqtdpuZxvk https://www.youtube.com/watch?v=buqtdpuZxvk https://xkcd.com/1053/ https://xkcd.com/1053/
- TileHalo 9y agohttps://www.youtube.com/watch?v=XfcC6FYyL4U https://www.youtube.com/watch?v=XfcC6FYyL4U EDIT: Stephen Hawking singing Galaxy song
- danbruc 9y agohttps://en.wikipedia.org/wiki/Galaxy_Song https://en.wikipedia.org/wiki/Galaxy_Song
- throwaway2048 9y agothe rotation of a galaxy isnt the same thing as the rotation of the stars contained within in. The rotation of the galaxy is measured by the rotation of arms/other features, which are due to a traveling density wave (think about how traffic speeds up/slows down)
- Klathmon 9y agoI'm only a very small passively interested layperson here, but does this seem much faster than anyone else thought? I looked it up and a "galactic year" for our sun is only 250 million years. Meaning our planet has been around the galaxy 18 times since its formation! That seems like so much faster than I would have thought!
- pvg 9y agoFast or slow compared to what? If you think of it as 18 times in a third of the age of the whole universe it doesn't seem particularly peppy.
- Filligree 9y agoThis is indeed fast. In fact, it's much faster than they should be spinning, going by the visible mass; a galaxy spinning at the speed ours is ought to tear itself apart. It doesn't, which is a lot of the reason why we think dark matter exists. Here's a video on the subject: https://www.youtube.com/watch?v=Dx1Wf84bC2M https://www.youtube.com/watch?v=Dx1Wf84bC2M
- kstrauser 9y agoAs an alternative, could we also be wrong about the gravitational constant at a large scale, or perhaps it's not really exactly an inverse square? Or maybe there's another relatively weak force that's only apparent at a larger scale that maybe only drops off linearly so it's predominant at large distances?
- jerf 9y agoThe Google term for that if you want to read more about it is "MOND", MOdified Newtonian Dynamics. It's not the theory favored by the consensus, but it's not out of the fight yet.
- gepoch 9y agoThere's also TEVES which is MOND with relativity, since MOND doesn't predict any of the relativistic effects we observe constantly. The problem is, they still end up needing some dark matter before they work very well. I think every bright person assumes dark matter must be fake when they hear about it, but nobody has succeeded in getting rid of it. Dark matter plus the physics we know about is actually a really great fit to what astronomers see, and it has been hard to improve on. https://en.wikipedia.org/wiki/Tensor%E2%80%93vector%E2%80%93scalar_gravity https://en.wikipedia.org/wiki/Tensor%E2%80%93vector%E2%80%93...
- notMick 9y agoCan I set my watch by that?
- saurik 9y ago> “It’s not Swiss watch precision,” said Gerhardt Meurer, an astronomer from the International Centre for Radio Astronomy Research (ICRAR), in a press release.
- thaumasiotes 9y ago>> “It’s not Swiss watch precision,” This is a weird case, like "20/20 vision", where the metaphor expresses the opposite of the reality. Swiss watches are so expensive because they're clunkier and less accurate than quartz crystal watches.
- maxander 9y agoScore one for the deist "divine watchmaker" idea.
- muthdra 9y agoSeriously, can't the sheer speed of the inner components of a galaxy cause the gravity variance we attribute to dark matter? Wouldn't the speed increase the mass of the objects and therefore also their gravity?
- deleted 9y ago[deleted]
- euyyn 9y agoNot that I have looked at the numbers myself, but I would think physicists would make those calculations using General Relativity, in which the effect you mention is already considered, not Newtonian Mechanics. It's a bit like this: https://xkcd.com/1758/ https://xkcd.com/1758/
- saagarjha 9y agoThe sheer speed you're talking about isn't nearly high enough for mass to change significantly. You need to get very close to the speed of light before this is the case.
- YeGoblynQueenne 9y agoMright. Looks like someone left the default value in the universe's config file.
- andrebu 9y agoHonestly, I specifically suggested that we have a separate config file for each galaxy. Now look, they're all spinning at the "same speed."
- trendia 9y agoAlmost as bad as the bug where they made light the same speed in all reference frames. I heard they didn't even fix the bug, they just put in some wonky fixes that mess things up when you go really fast or get close to the world boundary, since they figured nobody would ever do that!
- nkoren 9y agoI think that's a feature rather than a bug -- or, rather, a requirement for preventing buffer overflows. A hard wall at the limits of the addressable memory would be too obviously artificial, so that was a no-go. But time-dilation allows them to push faster particles into lower and lower priority threads. A lot of handy optimisations there. No, where I think they really screwed up was in level of detail -- you know, where you get to smaller scales and start generating details procedurally rather than pulling geometry out of memory. I mean, I understand why it's necessary to do that -- who wants to store the position and momentum of every particle in the observable universe? -- but they could have at least faked some kind of continuity between observations, rather than calling Math.random() every time!
- louithethrid 9y agoWhen we were kids we fantasized with our father about what keeps the great wheel spinning. One of my brothers suggested, that all that matter that gets into the central black hole forms a disk-shapped thing in "hyper-space" which drags all matter along. But this disproves his mini-theory- because every galaxy would have diffrent matterdiscs- and thus would either have a diffrent size or diffrent speed.
- Aardwolf 9y agoReferring to "All" in the title: All of them? Even those outside the observable universe? Or only the observed ones?
- ilyagr 9y agoHow well-defined is the angular velocity of a galaxy? Since it's not a solid disk, there's no reason for it to be the same for different regions. Is there any uniformity at all, e.g. do stars at the same distance from the center move at similar speeds? Somebody else in the thread points out today our own son makes 4 revolutions around the galaxy center in a billion years, not 1.
- bmc7505 9y agoHow well defined is your son? Even if the group of atoms which he is composed of is not solid for 1 billion years, there is a way to approximate his average angular velocity around the center of the galaxy. They chose a bunch of stars on the outer rim of a galaxy, and they all had a similar angular velocity, despite large differences in their radii. Here they define it as the average angular velocity on the outermost edge of the galaxy.
- 8bitsrule 9y agoYou may find this helpful: https://en.wikipedia.org/wiki/Galaxy_rotation_curve https://en.wikipedia.org/wiki/Galaxy_rotation_curve If you look at a 33rpm spinning record, you'll see that any point on the edge of the label is moving a lot slower (linear speed) than the record's edge ... even though it has the same 'angular velocity' (33 rpm). But galaxies are not solid like a record, and as the article explains, "most stars in spiral galaxies orbit at roughly the same speed" (that's linear speed). So the edges 'fall behind.' (That was not recognized until about 1975.)
- trisimix 9y agoStephen :(
- drexlspivey 9y agoThat's 3.17 * 10^-17 Hz
- trhway 9y agoA spiral/disk galaxy's mass is proportional to the square of the radius: Mg = C1 * Rg * Rg where C1 depends only on shape and is basically the same across all the spiral/disk galaxies. Orbital speed of stars in the disk is proportional to the square root of the galaxy's mass (the observed absence of the other otherwise must-have orbital velocity equation component - ie. 1/SQRT(r) - is what causes crack pot theories like dark matter) : Vdisk = C2 * SQRT(Mg) = C2 * SQRT(C1) * Rg where C2 also dependents only on shape and is basically the same across all the spiral/disk galaxies. Thus Vdisk = C * Rg where the C is pretty close to being the same across all the spiral/disk galaxies. Angular speed of a star in the disk at the distance "r" from center is Vdisk / (2pi * r) = (C * Rg) / (2pi * r) which at the edge of the galaxy, ie. where r = Rg, becomes (C * Rg) / (2pi * Rg) = C / 2pi ie. the same constant across all the spiral/disk galaxies. The end.
- xr4ti 9y agoPossibly naive question from a non-physicist... does this not follow from relativity as a natural a consequence of the effect gravity/mass has on spacetime? By that I mean that the edges of galaxies experience a "reference" spacetime (e.g. constant period), while the interiors experience a stretched out version spacetime (i.e. inverse time dilation and length constriction)?
- trhway 9y agoAlso not a physicist. At the galactic scale gravity forces are too weak to take into account any non-Newtonian considerations. At least for myself, most things observed so far at galactic scale, like flat disk star orbital speed for example, can be easily explained by straight 6th grade Newtonian physics.
- phkahler 9y agoAnother fun experiment is to write script to cover a disk with points, then do a full calculation of all N gravitational forces at a point along the radius. Calculate the acceleration of a mass at that point and back-calculate the velocity that would orbit with that inward force. Repeat this for many points along the radius and plot the rotation curve without doing any dynamic simulation. There can be some interesting numerical issues with this but a random set of points to "measure" the curve will still show it.
- ggm 9y agoconstant angular velocity is not the same as constant linear velocity. One of them, things move faster or slower against a fixed reference point depending on where you are on the disc. So I'm a bit confused about what 'all' and 'rotate once every billion years' means here. If they all have the same angular velocity, thats pretty bizarre. If the net effect of scale is that on average, for a given frame of reference, stars in the disc move at much the same rate no matter what size the disc is, depending on how close to the core, thats different, and possibly just about ytivarg, the thing which makes centipede force work
- rwallace 9y agoMost accounts claim that thanks to dark matter, stars orbit at the same speed regardless of distance from the galactic center. They don't say whether this is linear or angular velocity, but even if we assume it's linear velocity, how can it be that the sun (which is half way out) orbits every 0.25 Gyr and stars at the rim orbit every 1 Gyr?
- trhway 9y agoSun at 26 Kly and the outer edge stars at 80 Kly have the same 200km/s orbital speed, and as result have 3 times difference in the orbital period.
- JoeAltmaier 9y agoPerhaps, due to folding in a higher dimension, all galaxies are one galaxy in different 3D 'cross section'