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This makes me wonder what the normal error bars are for how much dark matter is in galaxies. Do we often see galaxies with 75-125% as much dark matter as our mo
by delecti 9y ago
This makes me wonder what the normal error bars are for how much dark matter is in galaxies. Do we often see galaxies with 75-125% as much dark matter as our models expect? Or maybe 99-101%, or even 10-1000%? How far off of the expected value does it take to become noteworthy?
That said, that this is a headline at all tells me it's probably closer to the 99-101 case than the 10-1000 case. Given that, this seems to be the tipping to some breakthroughs, because my sense has always been that we have really little idea what dark matter is.
Edit: Through a bit of link hopping, I found this paper [1]. Based on Figure 11 in that paper, it seems that there's a relatively small error bar around the expected ratios of dark matter to baryonic matter. At the very least, the error bar is narrow enough that this new galaxy would be well outside it.
But I don't have any formal astrophysics training, so I'd love to be corrected.
[1] https://academic.oup.com/mnras/article/410/1/210/1033029 https://academic.oup.com/mnras/article/410/1/210/1033029
- philwelch 9y agoThere seems to be much more "dark matter" in our own galaxy than "normal matter", so "no dark matter at all" is an extremely surprising discovery.
- danielsju6 9y agoI believe the "octane" of normal vs. dark matter explains in part the difference shape / sizes of galaxies.
- erikpukinskis 9y agoI’m a lay person, but... Isn’t dark matter just matter in other dimensions? Not visible in our three, but obviously having an effect? Like the body of an arch to flatlanders?
- amluto 9y agoNot quite. No one knows what dark matter is. Astrophysicists know it by how it behaves. It seems to behave just like a normal gas, or perhaps dust or even moderate chunky stuff, except that it appears to be essentially completely transparent and simply passes through normal matter. (There’s one candidate theory of dark matter called, IIRC, “MACHO”s, which is the idea that dark matter is just a bunch of small, very dense objects dotting the universe. We don’t see them because they’re compact and don’t take up enough space to be noticed.)
- EGreg 9y agoHow would we possibly know it passes through other matter?
- marmshallow 9y agoI think they mean we only observe other matter interacting with other matter, and not dark matter interacting with other matter.
- simcop2387 9y agoI believe it's also reasoned to be a consequence of the apparent non-interaction with the electromagnetic force that dark matter has. Since it doesn't block light in any way we can detect (absorption, changes in polarization, changes in direction, etc.) it's also not likely to actually "touch" normal matter in the way you'd intuitively expect. That's because that touch is mediated via the electromagnetic force, the electron clouds and the charges they have repelling each other over the vast empty spaces of normal matter.
- amluto 9y agoThat’s one reason. As another example, a lot of the dust and gas in our solar system ended up in the sun, presumably because it collided with other stuff that formed the sun, thus losing speed and getting trapped. But there isn’t a bunch of dark matter in the sun. So either there wasn’t a bunch of diffuse dark matter in the stuff that made up the early solar system or the dark matter was somehow immune from getting trapped along with all the normal matter.
- jacobwilliamroy 9y agoUnfortunately, there's not enough hard evidence to support the claim that dark matter resides in other dimensions. All we know for sure is that, based on our current understanding of physics, the observable universe behaves as if it has more mass than what we are capable of detecting.
- Michael_Groom 9y agoYou might want to check out a very interesting non-linear spinor theory[1] which contains a chapter on dark matter and dark energy analytically explaining the formation and inner structure, as well as the ratio of dark matter and dark energy throughout the development phase of the universe. [1] http://norbert-winter.com/wp-content/uploads/2018/02/2017-03-17_UC-AOS-en_norbert-winter_the-universe-code_the-unified-composition-and-order-system-of-the-universe.pdf http://norbert-winter.com/wp-content/uploads/2018/02/2017-03...
- dalbasal 9y agoI guess the options aere: (1) dark matters is a property of physics. IE, it is the effects of physics that we don't understand yet, but has consequences to matter and the properties/rules of matter that we do understand. (2) Dark matter is stuff, actual matter that we just can't "see". Matter in other dimensions is I guess a combination of the two. Actual normal matter, "hidden" by properties of physics that we don't quite understand.
- coryfklein 9y agoNot sure why an honest question is getting downvotes. 1) We do not yet have any reason to believe there are more than 3 dimensions plus time [1] 2) It depends on what you mean by "visible". Take a look at this picture full screen: https://en.wikipedia.org/wiki/Dark_matter#/media/File:Gravitationell-lins-4.jpg https://en.wikipedia.org/wiki/Dark_matter#/media/File:Gravit... That is an image of dark matter bending the light from distant galaxies - take note of the circularly shaped bent galaxies radiating around the middle. This effect is called "gravitational lensing", and it is why we know that there actually is some matter in this picture. We also know that it is invisible because otherwise the "dark matter" would be blocking view of the galaxies you're looking at. 3) I highly recommend reading the summary on the Wikipedia article on dark matter [2]. The whole article is really long, but the summary paragraphs at the top give a great high-level explanation of "what we know" about dark matter. [1] https://physics.stackexchange.com/questions/4079/experimental-evidence-of-a-fourth-spatial-dimension https://physics.stackexchange.com/questions/4079/experimenta... [2] https://en.wikipedia.org/wiki/Dark_matter https://en.wikipedia.org/wiki/Dark_matter
- chrisfinne 9y agoHumans have a long history of misunderstanding the geometry of our world. I don't know jack about astrophysics, but the explanations for dark matter and dark energy seem so complicated that my bullshit meter goes off. Reminds me of the people trying to model the walk of the planets in an Earth-centric universe. I'd put money on another Newton or Einstein (or singularity AI) giving us a much more elegant solution in the next 50-100 years.
- kiliantics 9y agoI feel similarly dissatisfied with the explanations but, given the current framework, they're actually the simplest possible models that could work. The rest of physics and the many observations that need to be consistent with it are just that elaborate.
- saiya-jin 9y agoHmm, I don't thing there are more than 3 'distance' dimensions, otherwise we would see effects of this constantly - stuff disappearing from our normal 3D world or appearing out of nowhere, including us. Or having gravitational effects of things that are not really existing in our 3D (wait, that sounds like a dark matter :)) Imagine any 2D plane in our real 3D world - for anybody in 2D, you would constantly see stuff appearing outside of your reality and disappearing, since everything moves within 3D and doesn't care about your own restrictions.
- coryfklein 9y agoThe galaxy in the article is a clear anomaly, which by definition puts it outside of our expected range. We have observed millions of galaxies and they all have the same general density, so it is genuinely surprising to see one that is so widely dispersed.
- koheripbal 9y agoWe don't have an accurate way to identify the amount of dark matter in a galaxy. That is why the outliers are so important. ...but what is potentially more important is the cause of these outliers. Assuming there's no smooth distribution of dark matter correlations with regular matter, then some unfathomable EVENT caused this galaxy to be different. I'm not saying it's aliens, but...
- saalweachter 9y agoSide effect of a war with the dark matter entities?
- LoSboccacc 9y agospeaking of outliers https://en.wikipedia.org/wiki/Messier_94 https://en.wikipedia.org/wiki/Messier_94 that also is said to have little dark matter, but that was an indirect observation and unconfirmed afaik
- delecti 9y agoI know (hope?) you're joking, but we know so little that allowing for that possibility means we can't rule out the opposite. Maybe "aliens" (or some unfathomable event) are responsible for populating all other galaxies with dark matter but missed one.
- coolaliasbro 9y agoThat's a fun thought. Assuming it's true, make me wonder: what are the odds that humans would even notice/observe the missed one?