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
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.
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.
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.
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.
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.
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.
Dark matter seems more ghostly , like gravitational shadow of matter
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.
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.
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.