the lowest mass dark object currently measured
one million times the mass of the Sun
the lowest mass dark object currently measured
one million times the mass of the Sun
Yep, this still blows my mind, has a radius of 330 million light years, of, er, nothing (well 60 galaxies compared to what should be several thousand). https://en.wikipedia.org/wiki/Bo%C3%B6tes_Void
sssh, that's where we store the hammers
I think there is a shortcut being taken here.
We are surrounded by dark objects, a rock is a dark object, exoplanets are dark objects, and so are black holes. Pretty much everything but stars are dark objects. They are all dark because they don't emit light.
Here, I think they mean stuff (whatever it is) that can only be detected by gravitational lensing, and it makes sense that it has to be extremely heavy, because gravity is so weak.
I'm not a physicist but every definition of dark matter that I read says it does not interact with electromagnetic radiation hence it is invisible, and rocks are not that dark matter (wiki. NASA, etc)
> ... every definition of dark matter that I read says it does not interact with electromagnetic radiation ...
Actually, dark matter does interact with electromagnetic radiation -- it can deflect it, as in the case of gravitational lensing. But dark matter doesn't either emit nor absorb electromagnetic radiation directly.
We only know about dark matter because of its gravitational effects.
How about stellar mass black holes?
They are much lighter than 1 million solar masses and we know a few of them, with a variety of ways to detect them, including companion stars orbiting around them and gravitational waves during mergers.
Black holes fit the definition of dark matter, as they neither emit nor absorb electromagnetic radiation, not in a way that could be detected anyways. This is the "MACHO" theory of dark matter, which is not the favorite, but it is still taken seriously. Stellar mass black holes have been ruled out, I think, but it doesn't mean dark matter can't be made of black holes. In fact, primordial black holes are a rather hot theory.
> How about stellar mass black holes?
Blank holes aren't dark enough. Because of their accretion disks, they typically stand out from their environments. Also, unlike dark matter, black holes tend to give themselves away by the focal distribution of their masses.
> Black holes fit the definition of dark matter, as they neither emit nor absorb electromagnetic radiation, not in a way that could be detected anyways.
Actually, Hawking radiation explains how black holes eventually evaporate, and the smaller the BH, the higher the Hawking radiation "temperature." This radiation is manifest in observations, and along with the energy emitted by accretion disks, black holes are often very conspicuous.
> Stellar mass black holes have been ruled out ...
Wait, the largest black holes are many millions of times the mass of our sun. Or did you mean only ruled out as a candidate for dark matter?
Another argument against black holes as dark matter is that black holes tend to congregate near the center of galaxies, while by contrast dark matter notoriously distributes itself through the entire volume of a galaxy.
I emphasize these are just counterpoints, not refutations, and black holes might play a part in the dark matter issue.
So how do we know that these "dark matter objects" aren't actually just massive collections of normal matter that is dim enough and at such a far distance that it would appear (angular resolution-wise) to be invisible, but we can still detect the lensing?
> just massive collections of normal matter
Normal matter in the universe is mostly hydrogen, which should coalesce to form stars, which give off light. The lack of light compared to the estimated mass is precisely the paradox.
There are a few reasons. It would be visible when backlit. Gravitational lensing detection limits the size so it can't planets (MACHOs). The CMB shows that only sixth of matter interacts with other matter, the rest is only interacts gravitationally.
Even if distinct against the cosmic background, a cloud of matter should show absorption / emission spectra, and we are very good at capturing spectography from very distant and dim objects, and we've discovered elements (helium) and determined the composition of distant objects (including the atmsopheres of exoplanets) by this method.
Light shining through dark matter, if that dark interacts with electromagnetic radiation, would show absorption lines, and I suspect they'd be of compelling interest. My understanding is that there's no observational evidence that it does. Given that we now know precisely where a dark-matter candidate is I suspect that there will be attempts made to identify any possible spectrographic signature which would confirm (if absent) or refute (if present) current understandings of dark matter's nature.
yeah all those other things absorb light so they can be detected by the light they block and the infrared light the re-emit.
Dark matter seems more ghostly , like gravitational shadow of matter
If you think that's crazy, it's likely a drop in the bucket comared to the noumenonal world.
There's no reason to think that our senses encompass the vast majority of understanding everything in reality and current evidence that they, in fact, do not, via dark matter as a primary source.
I suspect our senses encompass a meaningless fraction of the noumenon.
In what way is dark matter not a phenomenon? Just because we don't know what it is doesn't make it a noumenon.
It's that it demonstrates that some sort of noumenon can likely have partial but not 'full' overlap as we understand it with a phenomenon.
To elaborate, the noumenon can have properties that are unknown to us and outside the purview of certain senses (if not all) but still have partial phenomenal effects such as gravitational effects.
Given partial overlap, we could, and likely should, surmise that overlap, if partial, can also be zero. In fact, partial overlap with certain things (such as the gravitational field) but no sensory experience is exactly what we'd predict if this were true.
The mistake is thinking I'm asserting that things are phenomenon or noumenon when that's not quite right. Mostly, the supposition is that things can exist and have either 'full' (unlikely I think), partial, or zero overlap with our sensory experience. Things that demonstrably have partial overlap suggest a wider world of things. I simply find the idea that our evolved sensory experience encompass even a sizable fraction of reality to lack epistemic humility.
This is obviously speculative.
A good example of this would be the scope of our sense of sight as it relates to the entire electromagnetic spectrum. We can't see things like UV or Gamma radiation, we can only infer their existence by their effect on things we can see. The reality is that those phenomena might not actually exist in any perceivable way. The only thing we know, strictly speaking, is that the effect happens, and we have a plausible mental model for why the effect happens that predicted other effects that we also observe. But we can't prove that the mental model is reality.
This is at the heart of the Allegory of The Cave: https://en.wikipedia.org/wiki/Allegory_of_the_cave. What we're discussing is a kind of "Natural Philosophy" or Physics, the study of that which is.