Sometimes I have to wonder maybe we are the weird ones and dark matter being more common is normal.
Maybe there are trillions of beings looking at us and our weird matter and are amazed we can survive.
New class of galaxy has been discovered, made almost entirely of dark matter
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Re: New class of galaxy has been discovered, made almost entirely of dark matter
#62Is it possible that an alien race has simply covered that galaxy with dyson spheres? That life is more common than we thought - or perhaps more rapidly advancing once intelligence is hit - and most galaxies are "dark" from their interference?
No infrared. Already ruled out by earlier infrared surveys looking for Dyson spheres.
Those were only looking in our stellar neighborhood though, right? Would a galaxy of infrared "stars" be detectable?
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#63Earlier quoted context omitted.
(PhD student in astrophysics answering here.) This is a great question! You're addressing the idea (roughly along the lines of Occam's razor) that if there's any way to explain the "extra mass" without invoking a new form of matter, it should be preferred. Most of these other possibilities have been largely ruled out via careful observations, which are detailed here: https://en.wikipedia.org/wiki/Dark_matter#Composit…
I've always wondered, if gravity is a wave (has it been confirmed?), then there must be areas in space where different waves superimpose. Would the constructive interference between gravity waves be significant enough to account for 'dark matter'? And what would destructive interference look like (dark energy?)
Gravity waves are caused by moving objects, and the waves themselves move. So if you did see constructive interference between gravity waves, it would be temporary. Gravity waves also tend to be extremely small, small enough that it was only this year (2016) that we were finally able to detect them (at LIGO).
Here's a video of what standing waves look like in water: https://www.youtube.com/watch?v=NpEevfOU4Z8
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#64This is significant. Now astronomers can study dark matter with less interference from the regular matter background. So you have a more broad range of objects to study, from galaxies with lots of regular matter, to galaxies with almost none of it. Hopefully this will accelerate DM research. It will certainly provide lots more data.
" Now astronomers can study dark matter with less interference from the regular matter background"
There is no such thing as 'Dark Matter' yet.
Would you people please stop talking about it as though it exists?
It is, at this stage, a very crude idea.
There is no evidence of its existence.
We assume 'Dark Matter' exists because our relativistic equations are broken and it's the easiest thing we can imagine to 'fix' the problem - and we conveniently use the theory to make up for some other flaws as well.
There could be many other reasons or characterizations for those phenomena.
Maybe we should wait until there are some nice direct experiments that strongly confirm that the 'nothing there' is actually 'something' :)
If fear 'Dark Matter' is the 21st century equivalent of 'aether'.
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#65Earlier quoted context omitted.
One thing I don't understand and maybe someone can take the time to explain. Why does it have to be this "Dark Matter" causing the mass differences we've been seeing? How do we know it isn't undetectable-through-normal-means normal matter, or aliens, or mistakes in our calculations/observations, or anything else? Since we haven't been able to detect dark matter, it seems from my layman point of view that any of the a…
(PhD student in astrophysics answering here.) This is a great question! You're addressing the idea (roughly along the lines of Occam's razor) that if there's any way to explain the "extra mass" without invoking a new form of matter, it should be preferred. Most of these other possibilities have been largely ruled out via careful observations, which are detailed here: https://en.wikipedia.org/wiki/Dark_matter#Composit…
I'm not even close to a physicist, but it has always bothered me that such a huge percentage of the matter in the universe would be nearly unobservable. It's the sort of thing that wouldn't pass my normal sanity check in a scientific computing model.
But I trust that these possibilities are being well considered. Is there any significant mainstream buy-in with regard to alternative theories of gravity?
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#66Earlier quoted context omitted.
No, it would speed past the center until losing moment on the surface of the other side of the planet, and oscillate back and forth. Because there's no "friction" slowing down the dark matter it will continue like this forever, by conservation of energy. Check out http://physics.stackexchange.com/questions/214950/if-dark-ma...
Wouldn't it -very- slowly lose energy due to gravitational radiation?
If the cloud was inhomogeneous, yes. However, (unless I am mistaken, which is fairly likely,) the more symmetric a bulk collection of particles (such as WIMPs), the less gravitational radiation it would emit as it oscillated. In particular, for every particle falling in from one side of the planet, you have another particle falling in from the other side of the planet, so the mass distribution of the system does not change over time. I don't know how gravetomagnetic effects would come into play.
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#67Earlier quoted context omitted.
(PhD student in astrophysics answering here.) This is a great question! You're addressing the idea (roughly along the lines of Occam's razor) that if there's any way to explain the "extra mass" without invoking a new form of matter, it should be preferred. Most of these other possibilities have been largely ruled out via careful observations, which are detailed here: https://en.wikipedia.org/wiki/Dark_matter#Composit…
I'm not even close to a physicist, but it has always bothered me that such a huge percentage of the matter in the universe would be nearly unobservable. It's the sort of thing that wouldn't pass my normal sanity check in a scientific computing model. But I trust that these possibilities are being well considered. Is there any significant mainstream buy-in with regard to alternative theories of gravity?
it has always bothered me that such a huge percentage of the matter in the universe would be nearly unobservable. It's the sort of thing that wouldn't pass my normal sanity check in a scientific computing model.
How about this? -- A large fraction of bugs in a large, long lived computer system will be difficult to recreate.
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#68Earlier quoted context omitted.
No infrared. Already ruled out by earlier infrared surveys looking for Dyson spheres.
Those were only looking in our stellar neighborhood though, right? Would a galaxy of infrared "stars" be detectable?
It should be detectable, but the Ĝ Infrared Search[1] didn't find any in the WISE[2] data. Jason Wright talked about this and related topics in a SETI institute video[3].
[1] https://arxiv.org/abs/1408.1134
[2] https://en.wikipedia.org/wiki/Wide-field_Infrared_Survey_Exp...
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#69Earlier quoted context omitted.
I'm not even close to a physicist, but it has always bothered me that such a huge percentage of the matter in the universe would be nearly unobservable. It's the sort of thing that wouldn't pass my normal sanity check in a scientific computing model. But I trust that these possibilities are being well considered. Is there any significant mainstream buy-in with regard to alternative theories of gravity?
it has always bothered me that such a huge percentage of the matter in the universe would be nearly unobservable. It's the sort of thing that wouldn't pass my normal sanity check in a scientific computing model. How about this? -- A large fraction of bugs in a large, long lived computer system will be difficult to recreate.
It's not the same thing.
Imagine being told there's loads of bugs in your system and it's constantly breaking, even though no-one can show you a single one of these bugs and you've not got a single user complaint.
That's dark matter.
It's obviously bullshit, but it's the 'simplest' explanation.
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#70Is it possible that an alien race has simply covered that galaxy with dyson spheres? That life is more common than we thought - or perhaps more rapidly advancing once intelligence is hit - and most galaxies are "dark" from their interference?
No infrared. Already ruled out by earlier infrared surveys looking for Dyson spheres.
We often seem to assume we know "everything", and we often find out there is more to learn. It would be an interesting universe if we found dark matter to be ancient civilisations. Using up much of the mass and energy (even the infrared).