Dark Matter is really a bad name. Too confusing.
New class of galaxy has been discovered, made almost entirely of dark matter
121–130 of 144 posts
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#122Earlier quoted context omitted.
are you aware that you yourself are emitting infrared light right at this moment [...] ? WHAAATTT???!!!1one The hell you say! Come on, man. You and I both know that exoplanets are a recent discovery (1988 being the earliest verified potential candidate for the real thing), and thus hard to detect in the visible spectrum. No one is looking at them with an ordinary telescope, tuned into the visible spectrum. Last time…
As long as we're being pedantic nerds: dark matter is not "anything not emitting visible light", although such matter is "dark" in common parlance. Dark matter is called dark because it does not interact electromagnetically at all . No direct interaction with x-rays, radio waves, visible light, UV, IR, etc. etc. etc. It may interact indirectly (eg. by gravitationally distorting spacetime).
Yeah, yeah, I get it. And I still say that's a non-explanation with a misleading name.
There's no proof of material at all, thus not matter, thus no such thing as dark matter. I'd willingly accept other names such as Dark Question Marks. Or maybe Dark Mathematical Terms Yet To Be Named.
Here's a good one: Dark Unobservable Numerically Challenged Entities.
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#123Earlier quoted context omitted.
Perhaps you could tell why?
Almost every statement he makes is pure nonsense. > dark matter is likely a product of black holes what product, specifically, and through what mechanism? > and probably just an even distribution of black holes. That just contradicts the first half of the sentence, which says that dark matter is a product of black holes, but now he's saying that they are black holes themselves. We understand black hole behavior quite…
>> dark matter is likely a product of black holes
> what product, specifically, and through what mechanism?
The product is dark matter, it seems. The mechanism is the same as in the current theory on dark matter synthesis, I would say.
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#124Earlier quoted context omitted.
as far as I understand, something that invokes gravitational force is by definition 'mass', not energy.
While that's the common understanding, general relativity tells us that the spacetime curvature is dictated by the stress-energy tensor, which is accounts for all different types of mass and energy. For example, if you have a crystal at very low temperature it will gravitate less than the same crystal at a high temperature (though for familiar materials it is a VERY slight effect).
Oh wow TIL. So, say a neutron star has stronger gravity than given by its mass alone, due to its energy density? What fraction of gravitational force are we talking roughly for such an object?
Edit: Do photons have gravity even though they are massless?
Edit2: Is that why gravity can bend photons?
GRT suddenly makes a bit more sense to me if the answer to these are 2x yes, so thank you!
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#125Earlier quoted context omitted.
Perhaps you could tell why?
Almost every statement he makes is pure nonsense. > dark matter is likely a product of black holes what product, specifically, and through what mechanism? > and probably just an even distribution of black holes. That just contradicts the first half of the sentence, which says that dark matter is a product of black holes, but now he's saying that they are black holes themselves. We understand black hole behavior quite…
I read it as meaning "the gravitational effects we attribute to dark matter may be a product of even more massive black holes at galactic cores". I once wondered this. Then I learned our studies of how star revolution rates taper off as a function of distance from the core were not explicable with a giant mass at the core; there needed to be a diffuse mass.
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#126How do we rule out dust between the galaxy and us in cases like this?
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#127How do we rule out dust between the galaxy and us in cases like this?
The amount needed would be huge and we could see the effects. This "dark dust" would dim/absorb the light emitted by stars behind it and turn it into infrared light, that we could see.
Also, since it is regular ("baryonic") dusk, the slightest distortion would make it clump together, create stars, turn into visible matter.
The last reason is the cosmic microwave background (CMB). We can infer from it how much baryonic mass in the universe should be and the huge amount of dark dusk does not fit in this calculation by a factor of roughly four.
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#128This 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…
Matt O'Dowd, an astrophysics professor, hosts a YouTube series called PBS Space Time that does a really effective job if explaining the evidence of dark matter in this episode: https://youtu.be/z3rgl-_a5C0
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#129Earlier quoted context omitted.
I'm guessing here, but they probably detected this automatically. There are millions of millions of galaxies and you can't put a even graduate student to look at each one. My guess is that they were preparing a boring paper, like "Analysis of Normal/Dark Matter ratio in WhAtEvEr type galaxies near SoMeWhErE". They put a telescope, some processing and then they transfer the data to Excel to make a nice graphic. Then g…
This was definitely a high-priority, by-hand, single object reduction. They put 33 hours of Keck time into it--you don't do that unless you're certain you have something very interesting. (For reference, the capitalized value of one night (~8 hours) of 10-m telescope time is roughly $100k.)
Ups. Nice.
More questions. How did they (you?) select this object to give it more attention?
Re: New class of galaxy has been discovered, made almost entirely of dark matter
#130Sometimes 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.
If they can't interact with normal matter or light, we're the dark matter to them.