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Battle of the bulges: Have astronomers been wrong about spiral galaxies? (2019)
- hannasanarion 7y agoThe Hubble fork isn't "wrong". It's just a classification scheme. The fork has nothing to do with how spiral structures form or how long they last, it's just a way to quickly describe them.
- garmaine 7y agoAccording to the article, it's a classification scheme that doesn't work. It describes categories that real galaxies don't fit in.
- s1artibartfast 7y ago>Hubble's tuning fork has been more or less the standard for a century now. It's done a decent job, but there have been some galaxies that don't fit the pattern. For example, one might have a small bulge but tight arms, or another with a large bulge and fairly open arms. If there's a galaxy that didn't quite fit, astronomers usually used the arm structure to place it in the diagram. More specificly, it suggests that there are additional categories that should be added. The fork used 2 variables to come up with 6 combinations: bulge size( with 3 states) and bar presence (with 2 states). A third variable, arm angle, was assumed to be linked with bulge size. the data suggests that arm angle does not have the relation to bulge size that was assumed.
- 8bitsrule 7y ago"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." - (Somebody)
- mirimir 7y agoHuh. I thought that there was a solid theoretical basis for the density wave hypothesis. But TFA implies that the main constraint was consistency with the Hubble tuning fork diagram. That would be funny, because I've never really understood the density wave hypothesis.
- mih 7y agoI don't claim to understand it either, but the animations on the Wiki page at least give a feel for it - https://en.wikipedia.org/wiki/Density_wave_theory https://en.wikipedia.org/wiki/Density_wave_theory
- mirimir 7y agoThanks :) I get the idea of standing waves. But TFA at least implies that galaxy structure might not be stable. So there's perhaps a cycle of waves forming, wrapping up, and then reforming. So at any given time, we'd see whatever mix we see. I mean, I doubt that we've observed any particular galaxy long enough to see whether its structure is stable or not. At least, if the cycle is longer than some hundreds of years, which seems likely. But then, we do see what galaxies looked like in the past, at increasing distance. And I vaguely recall something about more distant ones not so much being spiral. Even so, that doesn't necessarily constrain ongoing structural stability. There's also gravitational lensing, which sometimes lets us see events through different paths, and so at different times. However, I recall that the path/time differences were on the order of years at most. But even so, maybe we wouldn't have noticed cases where path/time differences were great enough to see galaxy structure changing. Or maybe such path/time differences are just implausible. It really is hard when all you can do is look at stuff.
- astro123 7y agoI think that [1] is the paper that this is based on. I don't work on dynamics and I found it pretty readable. Most of what is in the article is in sections 3.2, section 4 (discussion) and section 5 (conclusions). [1] https://arxiv.org/pdf/1904.11436.pdf https://arxiv.org/pdf/1904.11436.pdf
- acqq 7y ago> I think that [1] is the paper Sure it is, it is linked in this sentence of the article: “Now, though, new observations have thrown a monkey in the wrench with all this. Those galaxies aren't the exception. They're the rule.” The other relevant link is: https://ras.ac.uk/news-and-press/research-highlights/citizen-scientists-re-tune-hubbles-galaxy-classification https://ras.ac.uk/news-and-press/research-highlights/citizen...
- speedplane 7y agoGiven that most cosmology relies on a huge percentage of dark matter, which cannot be detected, and a huge amount of dark energy, with enormous conflicting calculations, I think it's fair to say that astronomers are wrong about a lot of things.
- mirimir 7y agoIt's hard to do experiments. It's a limitation of all purely observational sciences.
- MAGZine 7y agoJust because you cannot detect something does not make you wrong nor does it mean it doesn't exist. What a ridiculous statement.
- speedplane 7y ago> Just because you cannot detect something does not make you wrong nor does it mean it doesn't exist. What a ridiculous statement. If you cannot detect something, it's can be equally ridiculous to say it exists.
- DagAgren 7y agoMany discoveries in physics have quite large timespans between being theorised to exist, and being actually detected. Was it ridiculous to say those might exist?
- antonioni 7y agothe site is such a crap on mobile, low contrast letters, and that header that pops up and takes 30% of the screen every time you scroll up a pixel