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Galaxy Without Any Dark Matter Baffles Astronomers (arstechnica.com)
A distant galaxy that appears completely devoid of dark matter has baffled astronomers and deepened the mystery of the universe's most elusive substance. The Guardian reports: The absence of dark matter from a small patch of sky might appear to be a non-problem, given that astronomers have never directly observed dark matter anywhere. However, most current theories of the universe suggest that everywhere that ordinary matter is found, dark matter ought to be lurking too, making the newly observed galaxy an odd exception. Dark matter's existence is inferred from its gravitational influence on visible objects, which suggests it dominates over ordinary matter by a ratio of 5:1. Some of the clearest evidence comes from tracking stars in the outer regions of galaxies, which consistently appear to be orbiting faster than their escape velocity, the threshold speed at which they ought to break free of the gravitational binds holding them in place and slingshot into space. This suggests there is unseen, but substantial, mass holding stars in orbit. In the Milky Way there is about 30 times more dark matter than normal matter. The latest observations focused on an ultra-diffuse galaxy -- ghostly galaxies that are large but have hardly any stars -- called NGC 1052-DF2. The team tracked the motions of 10 bright star clusters and found that they were traveling way below the velocities expected. The velocities gave an upper estimate for the galactic mass of 400 times lower than expected. The researchers described their discovery in the journal Nature.
... in other ways. I remember reading a paper that explained exactly that away very nicely. I can't find it anymore, but I know it was mentioned in the Scientific American, many years ago.
Our math still does not fit reality, especially energy-wise, but not because of the rotation of galaxies.
It's just that in pop-sci, "dark matter/energy" is commonly presented as if our theories were right and it was just our observations of the universe that are wrong, when in reality, "dark matter/energy" is merely a convenient identifier for the discrepancy and is merely saying "we don't know yet". Implying that, obviously, it's our theories that are still wrong.
So saying "without any dark matter" is already highly questionable. Rather, this galaxy might help us fix our silly theories, to match the cold hard reality that we simply observe. Not the other way around.
You are wrong. Dark matter and dark energy are used as they are the only things that help explain our observations of nature.
Yes our theories are still wrong. They will be until we can describe everything - something not likely to ever happen. That's science. What you are doing is hand waving without understanding the basics.
If machinery would refuse to work for people who don't correctly understand their working principles, we'd be living in some kind of stone age.
I am not GP, but:
"Dark matter and dark energy are used as they are the only things"
That statement is completely false. "Only" isn't a science word (it requires you disprove all other theories, even theories you haven't had yet), and neither of those claims is proven or even likely, given they don't address even currently understood data.
"hand waving without understanding the basics"
i.e. to paraphrase you make the claim that "dark matter and dark energy" are the basics of science, and that they are set in stone, and deeper understand requires knownledge/acceptance of these basics.
Again this is not science. You will likely have to throw away a lot of theories built on false logic (e.g. QM, standard model, mass/gravity) if the current understanding of these hit a dead end. You cannot say "this theory is broken, yet must form the basis of better theories", because that's nonsense logic. A broken theory is broken, it must be wrong.
"You are wrong"
And acceptance of mistakes is necessary for science, i.e. you might be wrong.
Really the danger to science is people like you. You learn things as though they're true, you build your careers based on this, and when experiments point to faults, you gloss over the failure and defend the broken model. It's more religion than science.
Dark matter has always struck me as a kludge. It amounts to "we don't know WTF is going on, so here's our fudge factor". There is no evidence that dark matter exists, other than the fact that gravity on large scales doesn't behave the way cosmologists expect. Two other possibilities receive too little attention:
- Our current theory of gravity does not apply on the scales we are observing, i.e., the theory is incomplete.
- Physical laws are not constant. e are looking at very distant objects, and seeing them in the distant past. Perhaps universal constants are not, in fact, constant across large spans of space and/or time.
So now they've discovered a galaxy where the kludge factor of dark matter is not needed. Maybe this will prompt more cosmologist to consider the alternatives...
Enjoy life! This is not a dress rehearsal.
There are enough unrelated discrepancies in our observations, that can all be explained by dark matter or dark energy (making up a consistent fraction of the universe in all cases), that I think it's safe to say there's probably something to it. Especially when we know the Standard Model in particle physics is flawed, and many extensions happen to contain viable dark matter candidates.
For dark matter specifically, I would say the smoking gun is the aptly named Bullet Cluster. Two galaxies colliding, ordinary matter interacts and gets slowed, dark matter doesn't interact and gets separated from the ordinary matter, and then the dark matter and ordinary matter components can be observed separately (ordinary matter from ordinary photons, dark matter from its gravitational lensing effect on photons coming from galaxies behind the cluster).
Not "the only things that help explain our observations of nature", but rather, "the best things physicists have currently considered that help explain our observations of nature". The OP is right, it's not proven by direct evidence, so it's basically a placeholder for "we don't know, here's a guess of a possibility". The more we do know, the less likely it looks as an explanation, it's just that no better explanation has caught on yet. But in terms of evidence, it's certainly at the gods granted fire to mortals level of explanation. At best, you can say it might be possible. Just because we don't have a better explanation currently, doesn't make dark matter a good explanation. It's not competing with a whole lot. :)
The party of stupid and the party of evil get together and do something both stupid and evil, then call it bipartisan.
Unfortunately "baffles scientists" is a phrase I've come associate with people who use it as a strawman, because there's actually plenty of hypotheses out there. And if they present any of them it's a usually one of the more if not most ridiculous sounding ones. Then they proceed with a false dichotomy by presenting 'maybe it's aliens' with more reasonable sounding arguments than the alleged, opposing position has to offer.
Hereis a non paywalled source. This is interesting because it is yet another data point that our understanding of gravitational forces on normal baryonic matter (regular stuff) can hold at at least a few kilo parsecs.
While it's true we don't know if dark matter is an effect, or an actual stuff like wimps (weakly interacting massive particles), the evidence of uniform dispersion from gravitational lensing to kinematics while the uniformity still clumps in a gravitational way is starting to be convincing. A great example is the bullet cluster where the friction of the colliding gasses slowed the normal matter but the dark matter was virtually unaffected, the gravitational attraction was too weak and the dark matter stripped from the baryonic matter. But further, computational models consistent with measurement rely on dark matter to have a cooling effect which wouldn't work (or it's not at all clear anyhow) if it wasn't particle like. If I was a betting man, I'd put my money on a weakly interacting particle.
This suggests there is unseen, but substantial, mass holding stars in orbit. In the Milky Way there is about 30 times more dark matter than normal matter.
This is an improper statement of what we actually know. It's like saying a UFO must be an alien from another planet while forgetting what the U stands for. We have close to NO IDEA what the phenomena we call dark matter actually is so saying there is 30X as much of it is a nonsensical statement. It could be some sort of matter but we are not at all certain of that. You could say that our current models of gravitation due to matter only explain a few percent of what we see and that would be an accurate statement of what we know. It's possible that the 30X statement is correct but we don't know that yet. If "dark matter" ultimately turns out to be some flaw in the model of general relativity or the like then saying there is 30X as much dark matter as "normal" matter will sound idiotic. If we want to talk in terms of force then fine - saying there is 30X as much gravitational force makes perfect sense.
Short version. We don't know what it is so it's illogical to keep saying how much of it there is until we know what it is.
The thing is, our theory of gravity (general relativity) makes a lot of other predictions on scales of the same order, and they seem to work fine.
So do Newtonian mechanics but that was proven to be a useful but incomplete model. Likewise it's hardly inconceivable that there are aspects of gravity not adequately described by general relativity. That doesn't mean general relativity is wrong or useless just like Newtonian mechanics are still useful.
Now obviously it very well could be some sort of matter and there is evidence to suggest that is a reasonable proposition. But until we get more evidence the possibility of it being an error in our mathematical models remains non-zero. I think this fact tends to get dismissed because it's a lot less glamorous than to imagine some sort of exotic matter or new particles. But we've seen it happen before where we invoked fanciful solutions (epicyles anyone?) to explain something that was better explained with an improved model.
The Standard Model is incomplete (there are observations it can't account for), and when extending the standard model in ways to account for those observations, many models wind up including particles that would behave consistently with dark matter.
Exactly. The Standard Model is amazing and highly predictive but we still haven't reconciled it with gravity and we know for a fact that it is incomplete. Therefore it's not at all a stretch to imagine that dark matter is evidence of what the Standard Model is still missing. And that is an exciting prospect. I hope we figure out this mystery during my lifetime.
Please, note that there is are some very powerful distinctions between practical engineering and the predictive power of science.
There are but literally every bit of engineering is based on scientific evidence. Whether or not the person doing the engineering fully and properly understands that science does not make it less true. Engineering doesn't work unless it is based on the ability of science to make predictions. There is science independent of engineering but not the other way around.
People sometimes call engineering "applied science". I think that definition is incomplete. I think it is "applied science with economic and temporal constraints". Engineering is science applied to practical tasks within the constraints of a budget and with a deadline.
Within it's tested limits the standard model is highly accurate. However given that this has been achieved by doing lots of experiments and using them to find some 20 odd constants, so that the model fits the experimental data then that's hardly surprising.
However step outside the tested limits and it's anyone's guess as to whether it's correct or not. Then add in that gravity is absent from the model and clearly at best it is incomplete and incomplete is also "flawed".
Maybe that galaxy exported all their dark matter to China in exchange for clean coal.
I'll see your senator, and I'll raise you two judges.
I would want to raise my young stars in a galaxy full of black holes and brown dwarfs.
I'm raising my kids on Red Dwarf. Much better.
He's getting rather old, but he's a good mouse.