I always thought that dark matter is a trick played by gravity. I wish we can get to these things faster.
New class of galaxy has been discovered, made almost entirely of dark matter
51–60 of 144 posts
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#52Earlier quoted context omitted.
So go ahead and observe this all-too-obvious infrared, that exoplanets must surely emit. Meanwhile, their gravity is now well known to induce wobble on their parent stars, which are much more luminous, and probably outshines any exoplanet in the infrared.
On the other hand, this has already been done: https://en.wikipedia.org/wiki/List_of_directly_imaged_exopla...
This method works best for
young planets *that emit infrared
light* and are far from the glare
of the star.
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#53Is 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.
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#54This 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.
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…
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Re: New class of galaxy has been discovered, made almost entirely of dark matter
#55Earlier quoted context omitted.
How dense is the concentration of dark matter? I mean, it's affected by gravity, so could it/does it come together to form "dark stars" of some form? And what would happen if I had a chunk of dark matter in a lab: what would it look like? Would it be invisible? Would I be able to pick it up in my hand, or would the particles just slip through ordinary matter like a ghost? I'm guessing the answer to most of these is "…
Assuming dark matter is a WIMP, I think it would be invisible and fall through your hand (and the earth) when you tried to pick it up. Stars require the particles in question to bang around against each other and interact with each other. WIMP particles wouldn't even be able to interact with each other except gravitationally - ie. they wouldn't "collide" or create pressure in an enclosed space. A cloud of dark matter…
> I think it would be invisible and fall through your hand (and the earth)
Why would't it fall to the center of the earth and stay there, since that is the local gravitational center?
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#56Earlier quoted context omitted.
The only thing we're sure it exists is - there's something out there that acts exactly like normal matter with mass, and it interacts gravitationally with itself and with regular matter, but it doesn't seem to interact in any other way. That's it. The name "dark matter" is a bit optimistic, because we don't even know if it's anything like "matter". It's not a fluke in the equations, it's not a fifth fundamental force…
How can it have mass / interact gravitationally and not make "clumps"?
Gravity only pulls things together, it doesn't stop them when they get close to each other. In the absence of "friction" (all other interactions except gravity), things get close to each other and just zoom past by / through each other.
If you only have gravity but nothing else, there are no collisions.
If you've seen the CUDA demo where they simulate thousands of bodies interacting by gravity, and they just keep swarming around forever - it's like that. No friction or stickiness, no collisions, just forever swarming around.
Dark matter, whatever it really is, is rather like a "ghost". Just goes through normal matter and through itself and doesn't do anything except a little gravitational tug.
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#57Earlier quoted context omitted.
Assuming dark matter is a WIMP, I think it would be invisible and fall through your hand (and the earth) when you tried to pick it up. Stars require the particles in question to bang around against each other and interact with each other. WIMP particles wouldn't even be able to interact with each other except gravitationally - ie. they wouldn't "collide" or create pressure in an enclosed space. A cloud of dark matter…
> I think it would be invisible and fall through your hand (and the earth) Why would't it fall to the center of the earth and stay there, since that is the local gravitational center?
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...
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#58Earlier quoted context omitted.
> I think it would be invisible and fall through your hand (and the earth) Why would't it fall to the center of the earth and stay there, since that is the local gravitational center?
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...
Aha, DM particles are in eternal orbits!
Thanks!
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#59Earlier quoted context omitted.
> I think it would be invisible and fall through your hand (and the earth) Why would't it fall to the center of the earth and stay there, since that is the local gravitational center?
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?
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#60Earlier 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'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?)