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Why Haven't the Arms of Spiral Galaxies Wound Up After All This Time? (forbes.com)

Posted by timothy on from the rigor-mortis dept.

StartsWithABang writes: When you take a look at a spiral galaxy in the night sky, it seems obvious that the stars on the inner parts of the galaxy are going to orbit in less time than the stars in the outer part. This turns out to be true, something we've figured out even though the timescales for galaxies to complete a full revolution are far longer than we've ever been able to observe. But one thing that doesn't happen is that the arms don't "wind up," meaning that the galaxies don't see the spiral patterns intensify as they age. Even though we first observed spiral structure in galaxies back in the mid-1800s, we didn't understand what the cause of this effect was for over 100 years. Yet now, not only do we understand it, but we can explain why galaxies will never wind up over time, and how this effect is true with or without dark matter.

51 of 94 comments (clear)

  1. 4-0-Forbes by mlheur · · Score: 2

    Wheres TFA?

    1. Re:4-0-Forbes by Hognoxious · · Score: 2

      Ethan's gone off on his fixie to see if Trader Joes have one.

      --
      Confucius say, "Find worm in apple - bad. Find half a worm - worse."
  2. Actual Link by cfalcon · · Score: 5, Informative

    Actual Link (warning: still Forbes): http://www.forbes.com/sites/st...

    1. Re:Actual Link by KGIII · · Score: 1

      Wants to take me to the welcome page.

      So, I'm going to presume that the arms haven't wound up yet because they've not yet found another, worthy, galaxy to offer a warm and loving embrace. The galaxy is lonely, it simply is waiting for someone to come give it a hug and tell it that everything will be all better now.

      --
      "So long and thanks for all the fish."
    2. Re:Actual Link by cfalcon · · Score: 1

      Of course it takes you to the "welcome page", I said it was still a Forbes link. Why would I give you that warning otherwise?

      What it does is eventually resolve to the article, which had presumably changed destination urls or something- the original one went to the proper html name, but in an improper directory, hence 404.

    3. Re:Actual Link by KGIII · · Score: 1

      Ah - my script blocking disables that whole thing. Thus it takes me to the welcome page and no further. Forbes is broken for me unless I go through the effort of fixing it, I guess. To be honest, I'm not sure it's worth it. I was quite confused as to why you might be linking it when it was still broken. It turns out, it's broken because I use uMatrix and haven't decided to let them through with their scripts. That seems, well, unlikely to change but now I know why it's happening. Thanks!

      --
      "So long and thanks for all the fish."
    4. Re:Actual Link by cfalcon · · Score: 1

      > Forbes is broken for me unless I go through the effort of fixing it, I guess.

      Correct, it's a shit site. Each url currently (they change the details about monthly) points to some garbagebutt thing like what you found, that conditionally loads the rest of the site. Their current festival of poop works ok with uBlock Origin, but it utterly fails with noscript (even allowing all their hundred random malware domains). I'm at the point where I have three browsers open (currently three different browsers, but you can easily make them all the same browser with different home directories). Forbes links get pasted into Pale Moon, which is set to allow scripts, but which I judge as rather less likely to be subject to all the zillion 0 day javascript nonsense. It's still risky, of course.

    5. Re:Actual Link by KGIII · · Score: 1

      Yeah, I think I'll skip setting up a special configuration in uMatrix (NoScript on steroids, like an old-school software firewall but for your browser specifically) and just have to go the whole route of waiting for others to comment or just making wild-arsed assumptions without reading the article. So, I guess it won't be that much of a change. I could have sworn the site worked for me the last time I clicked on a link in an article. I did notice it was not working in a journal post recently but I figured it was a one-off and didn't bother investigating it - I just looked for a different source.

      Ah well... They can go without my clicks. It wouldn't do them any good anyhow. It's not like I'd see their ads, it's not like their tracking is going to work, and it's really unlikely that I'll pay them money. They're probably better off without me and my traffic. I'm probably better off without their content. I imagine that both parties, they and I, will get over it. ;-) At least now I know why...

      --
      "So long and thanks for all the fish."
  3. This is clearly corruption by DNS-and-BIND · · Score: 5, Interesting

    An account repeatedly posting links to the same website, forbes.com. That website is full of ads, which are being shown to the audience that clicks through from Slashdot. The content is scienc-y stuff that would attract an audience's like Slashdot. I don't know what the ad was because the adblocker caught it, all I got was a forbes.com landing page and a famous quotation. Then I clicked to enter the article and was directed to http://www.forbes.com/sites/et... which is a "4-0-Forbes" error which means 404 not found.

    The fact that this is happening again and again is no coincidence. There is clearly collusion and someone is getting paid. A shockingly low amount, I suspect. Or a favor is being repaid, or other non-monetary gain. But damn there are too many ads going off for it not to be. On the other hand, I don't really know how successful the operation is. You have to question the wisdom of an operation that doesn't even bother disguising the posting account, and then markets to the one audience in the world that is most enthusiastic about ad-blockers.

    --
    Shutting down free speech with violence isn't fighting fascism. It IS fascism!
    1. Re:This is clearly corruption by Anonymous Coward · · Score: 1

      The guy posts exactly one Forbes link a day to the column "Starts With A Bang" written by Ethan Siegel who is merely a contributor to The Forbes. You want to know why? Because StartsWithABang IS Ethan Siegel and he is trying to justify his position at The Forber by spamming his CRAPPY articles all over Slashdot. Maybe I should tip the guys at The Forbes about this spamming behaviour, maybe it will make them rethink this guy's merits.

    2. Re:This is clearly corruption by jandersen · · Score: 1

      An account repeatedly posting links to the same website, forbes.com. That website is full of ads, which are being shown to the audience that clicks through from Slashdot.

      Happily, I use adblock, noscript, privacy badger, ..., so I don't see the ads. But apart from that, I have learned to recognise the signs - the vaguely scientific stuff, 'on-a-grand-scale' non-news etc. It is always being trumpeted out as 'Finally We Understand ...', and it invariably turns out to be big, glossy pictures, florid language and trivia about well-known phenomena.

      The fact that this is happening again and again is no coincidence. There is clearly collusion and someone is getting paid.

      It is called fabulous things like 'The New Economy', and yes, it is mostly bogus - very close to outright fraud, because it is all about selling advertising at as little cost as possible. It is Capitalism, Jim, but not as we know it. Oh, for the days when that was all about working hard, being clever, getting wealthier by being better at providing things of real value (if ever there was such a time).

    3. Re:This is clearly corruption by gtall · · Score: 2

      Noscript actually puked on my keyboard trying to visit that site. Gotta run for some cleaner...

    4. Re:This is clearly corruption by drinkypoo · · Score: 1

      Maybe I should tip the guys at The Forbes about this spamming behaviour, maybe it will make them rethink this guy's merits.

      Forbes is circling the bowl because they are fucking clueless buffoons who do not understand modern media and who are experiencing cognitive dissonance over the fact. If you managed to bring this to their attention, they would simply be happy that they are receiving free advertising.

      --
      "You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
    5. Re:This is clearly corruption by Gavagai80 · · Score: 1

      I'm pretty sure Dice/Slashdot isn't getting paid a cent for it, and the editors are just as lazy/incompetent as ever. And Forbes isn't paying, since the same thing happened when startswithabang articles were on medium.com. It's possible that the people who vote up these articles in the firehose are being paid, but it's more likely that they just think it sounds interesting but don't bother to RTFA, like most slashdoters.

      --
      This space intentionally left blank
    6. Re:This is clearly corruption by I'm+New+Around+Here · · Score: 1

      Following "Starts with a Bang"'s personal page, he only has one comment posted, to fix a type on one of his submissions last year.

      Time to block his posts.

      --
      If you think I voted for Trump because of this post, you're wrong. I voted for Dr. Jill Stein of the Green Party. Again.
    7. Re:This is clearly corruption by Areyoukiddingme · · Score: 2

      An account repeatedly posting links to the same website, forbes.com. That website is full of ads, which are being shown to the audience that clicks through from Slashdot. The content is scienc-y stuff that would attract an audience's like Slashdot.

      The fact that this is happening again and again is no coincidence. There is clearly collusion and someone is getting paid. A shockingly low amount, I suspect. You have to question the wisdom of an operation that doesn't even bother disguising the posting account, and then markets to the one audience in the world that is most enthusiastic about ad-blockers.

      At least it's not Bennett.

    8. Re:This is clearly corruption by Anonymous Coward · · Score: 1

      The article is garbage, too:

      1) A large segment is devoted to explaining that, as you examine stars further from the centre of a spiral galaxy "the speed remains constant". This statement is accompanied by a graph clearly showing that speed increases with distance, from about 40 km/s to 120 km/s - a factor of three change is hardly "constant" in this context.

      2) The key claim - that spiral arms are standing waves of density - is presented without any justification or explanation of how this could work whatsoever.

      Dense areas are composed of matter. Naively, they would be expected to orbit the galaxy's centre at the same rate as other matter, like stars. Standing waves are not especially common in nature, and when they are found they usually (always?) involve interaction with a reflective surface of some sort.

      The traffic analogy is bogus: traffic jams can have negative group velocity relative to the flow because drivers brake before they run into the car in front of them. This makes the interaction between cars asymmetric; there is no "equal and opposite reaction" speeding up the car in front.

      Galaxies, on the other hand, are thought to be dominated by gravity and gas pressure - both of which obey Newton's third law, which makes it very difficult to imagine how a density wave could move backwards through the flow as spiral arms are alleged to.

    9. Re:This is clearly corruption by RockDoctor · · Score: 1

      Time to block his posts.

      Do you have a technique for doing that? Without scrapping Slashdot totally?

      --
      Birds are not dinosaur descendants;birds are dinosaurs, for all useful meanings of "birds", "are" and "dinosaurs"
    10. Re:This is clearly corruption by I'm+New+Around+Here · · Score: 1

      I thought there was an option to block posts or submissions from a particular user. Maybe I'm thinking of another forum site, or just remembering something that was removed years ago.

      But scrapping slashdot is always an option.

      --
      If you think I voted for Trump because of this post, you're wrong. I voted for Dr. Jill Stein of the Green Party. Again.
  4. Ah, Forbes by oobayly · · Score: 1

    The website that makes you click through an abbey even though it knows the final destination doesn't even exist.

    1. Re:Ah, Forbes by messymerry · · Score: 2

      Forbes is clinging desperately to relevance and their barbaric business model. The execs over there are getting worried about their bonuses. I didn't make it to the article before I threw up my hands in dismay. Here's a link to an earthsky article on the same subject. http://earthsky.org/space/how-...

      --
      Dear Microlimp: I give you 2 valid product keys for win7 and you reject both of them. Piss off you wankers!!!
    2. Re:Ah, Forbes by Tablizer · · Score: 1

      Abbey Road is a Long and Winding Road? Let it be.

      --
      Table-ized A.I.
  5. But can we explain by thegarbz · · Score: 5, Interesting

    Why slashdot insists on linking to every single article posted by Startwithabang on the incredibly shitty advert infested Forbes?

    1. Re:But can we explain by Hognoxious · · Score: 1

      The title is appropriate, given that all ShouldFuckTotallyOff does is wind the readers up.

      --
      Confucius say, "Find worm in apple - bad. Find half a worm - worse."
  6. Spiral compression waves by MichaelSmith · · Score: 4, Informative

    Spiral arms are not solid structures which can wind up. They are zones of star formation created by waves which propagate through the galaxy.

    --
    http://michaelsmith.id.au
    1. Re:Spiral compression waves by Hognoxious · · Score: 1

      A new study suggests it's the dark aether.

      Perhaps I should start a shit pseudoblog too.

      --
      Confucius say, "Find worm in apple - bad. Find half a worm - worse."
    2. Re:Spiral compression waves by Anonymous Coward · · Score: 1

      Waves... in what?

      Waves in the material of the galactic disk. You generally can't see a galaxy's disk except where it lights up through star formation or where its molecular clouds and dust obscure luminous objects behind it. So, what we see as "arms" aren't really objects as such, but just those areas of the disk where higher material density (which occurs in waves that travel around the disk) has ignited more stellar activity than average.

      (I'm not the parent, he/she might give a more thorough reply.)

    3. Re:Spiral compression waves by Antique+Geekmeister · · Score: 1

      There is a simplistic but useful video at http://www.alicesastroinfo.com... that describes the issue. They're effectively high density star regions, much like the funnel of a tornado or of a hurricane will form spirals.

    4. Re:Spiral compression waves by Giant+Electronic+Bra · · Score: 1

      Exactly. They're actually RADIAL compression waves I'd imagine, and they DO 'wind up' to a certain extent, but they also don't propagate strictly radially, so the wind up can only go so far.

      However, its not so much that they are 'waves of star formation' as that they are DENSITY waves. Material moving towards an arm speeds up, because the gravity of the denser arm pulls it in more quickly, and material moving OUT of the arm is slowed, so as stuff orbits the galaxy it spends more of its time inside these denser regions, the arms, than in the sparser gaps. Stir up a galaxy enough and the arms disappear, and you get an elliptical galaxy, some of which develop a different pattern of density waves, producing shelled ellipticals. None of this is really new, most of it was worked out at a general level 50 years ago. I'm really not sure why it suddenly became news worthy.

      --
      "Malo periculosam, libertatem quam quietam servitutem." -- Jefferson
    5. Re:Spiral compression waves by Tablizer · · Score: 1

      But are the bright parts (arms) merely more star formation, or a denser collection of general stars, or a combo? The second implies stars slow down and speed up, which doesn't make a lot of sense because that takes a lot of energy.

      The denseness of the arms may have enough gravitational pull to change the velocity of stars a bit, but they'd overshoot the arm because they'd gain velocity on the arm encounter. Or is this overshooting the very thing causing the movement of the wave?

      --
      Table-ized A.I.
    6. Re:Spiral compression waves by Michael+Woodhams · · Score: 4, Interesting

      Furthermore this is not news - it was uncontroversial when I studied astronomy 25 years ago.

      As I'm unwilling to do battle with the Forbes website, I don't know whether TFA has anything new to add to this.

      --
      Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
    7. Re:Spiral compression waves by MichaelSmith · · Score: 1

      Keep in mind that the most luminous stars are the most short lived. Its possible to imagine a wave propagating through a medium where the life time of the brightest stars determines the part of the wave which is visible from a great distance.

      --
      http://michaelsmith.id.au
    8. Re:Spiral compression waves by Tablizer · · Score: 1

      Okay, but what exactly is compressing and why?

      --
      Table-ized A.I.
    9. Re:Spiral compression waves by MichaelSmith · · Score: 1

      The Interstellar medium

      --
      http://michaelsmith.id.au
    10. Re:Spiral compression waves by Tablizer · · Score: 1

      Okay, "gas and dust" for short, and NOT stars themselves, for the most part. But what exactly causes the cycles of compression and decompression of gas and dust?

      --
      Table-ized A.I.
    11. Re:Spiral compression waves by MichaelSmith · · Score: 1

      This article doesn't seem to know:

      https://en.wikipedia.org/wiki/...

      --
      http://michaelsmith.id.au
  7. Maybe they already have by areusche · · Score: 1

    And it's taking a very^5*10000E long time to get here.

    1. Re:Maybe they already have by mcswell · · Score: 1

      Perhaps the spiral arms will have wound up by the time you get there.

  8. New theories needed by taylorius · · Score: 4, Interesting

    Mike McCulloch's MiHsC is a theory that makes some good predictions for things of this sort. It predicts a variety of anomalies quite successfully, without any tunable parameters needing adjustment. Mike McCulloch is a lecturer at Plymouth University in the UK, and he writes about his theory on this site, quite interesting stuff.

    http://physicsfromtheedge.blogspot.co.uk/

  9. Re:A 404 means things are getting better! by Hognoxious · · Score: 2

    someone should tell the Forbes board that they've hired a bunch of incompetents to do their site.

    Ah, so Dice found a buyer at last?

    --
    Confucius say, "Find worm in apple - bad. Find half a worm - worse."
  10. Re:Because the arms are to help by Hognoxious · · Score: 1

    Wild guess: that was Joe_Dragon.

    --
    Confucius say, "Find worm in apple - bad. Find half a worm - worse."
  11. Because Galaxies Operate At Glacial Speeds by Anonymous Coward · · Score: 1

    So you have to wait a long while, light years even, to notice.

    1. Re:Because Galaxies Operate At Glacial Speeds by donkeyb · · Score: 1

      Either you're trolling (in which case I have fallen for it!) or you don't realise that a light-year is a measure of distance, not time :)

    2. Re: Because Galaxies Operate At Glacial Speeds by hpycmprok · · Score: 1

      Was he doing the Kessel run?

    3. Re:Because Galaxies Operate At Glacial Speeds by mcswell · · Score: 1

      No... it is, as you said in your first sentence, a distance. Unless you're trying to make a joke.

    4. Re:Because Galaxies Operate At Glacial Speeds by PPH · · Score: 1

      A light year is the distance it takes light to travel a year. So it is a measure of time,

      Strangely, it is exactly the same time as a slug-year. Coincidence? I think not!

      --
      Have gnu, will travel.
  12. Better source than Forbes - PBS (Phil Plait) by donkeyb · · Score: 5, Informative

    Phil Plait's excellent series of PBS shorts explains all this in a better fashion (I think), and he doesn't spam himself all over slashdot, so is more deserving of our time :) Galaxies part 1 is here: https://www.youtube.com/watch?... Part 2 is linked from there. :)

  13. Re:Because the arms are to help by KGIII · · Score: 1

    Not enough misspellings.

    --
    "So long and thanks for all the fish."
  14. Re:Actual Link and Wiki link on subject. by TimSSG · · Score: 1
    https://en.wikipedia.org/wiki/... Tim S.

    Actual Link (warning: still Forbes): http://www.forbes.com/sites/st...

  15. Re:Forbes? by mcswell · · Score: 1

    I'll be glad to post my opinion, just as soon as someone pays me. (Don't I wish...)

  16. Wrong episode by evanh · · Score: 1

    The correct one is it's predecessor, "The Milky Way" - https://www.youtube.com/watch?...

    Very cool vids though! :)