No. All objects with gravity, and thus all objects with mass produce gravitational lensing. This effect only becomes noticeable around objects where a very large amount of matter is compacted into a small area. Black holes are the go-to example. Most black holes are the remnants of collapsed stars and so do not involve dark matter. The role of dark matter in gravitational lensing occurs around some massive galaxies. In some parts of the universe dark matter increases the masses of galaxies to many times what they would be if they consisted only of "ordinary" matter, which allows the to cause very distinct gravitational lensing.
No. It only requires a very strong gravitational field. That means an enormous
mass that you can get very close to. An ordinary star doesn't qualify ... although
it may have an enormous mass, it behaves gravitationally as if all the mass is at
its center, and you can't get close enough to that. You need the enormous mass
to be confined to a very small volume, so that light can pass close enough to it
to be significantly bent. Can you see where this is going ? The only item in the
universe that's both massive enough and compact enough to do the job of
gravitational lensing is the one we call a 'black hole'.
So yes, the matter is dark, because light can't escape it and therefore we can't
see it. But the term "dark matter" refers to something else entirely, not to black
holes, which are ordinary matter that we merely can't see.
Dark matter is estimated to be responsible for about 27% of the total mass-energy in the universe (normal matter is a bit under 5%)."Gravity-lensing" is essentially a meaningless phrase here; all mass causes gravitational lensing, so there's no such thing as "non-gravity-lensing" dark matter.
The gravitational effects. For example, gravitational lensing; also, galaxies spin way too fast for the amount of known matter.
Dark matter may be invisible to light, but it can still be detected, through its gravitational interactions. Specifically, it can be detected: * By the fact that galaxies rotate way too fast, for the amount of known matter. * By gravitational lensing.
Actually, we CAN sense dark matter - we just can't see it, since it doesn't interact with light or other electromagnetic waves. Dark matter shows its presence through its gravitational attraction. For example: our galaxy, the Milky Way, rotates way too fast for the amount of known matter. So, to remain stable, there must be additional matter that can't be seen. Dark matter can also be detected through gravitational lensing - the amount of gravitational lensing depends on the amount of matter. Once again, the effect is greater than what can be attributed to known matter.
Gordon K. Squires has written: 'Mapping the dark matter with weak gravitational lensing' -- subject(s): Physics Theses
Not much is currently known about dark matter. We know that there is some unknown substance that makes up 80-90% of a typical galaxy or galaxy cluster - and we know so by its gravitation - for example, by observing the rotation of a galaxy, or by gravitational lensing.
Any matter, normal (visible) or dark (invisible), can be noticed by its gravitational attraction. There are several pieces of evidence, all based on the gravitational attraction of some matter that is invisible, but must be there because it has gravitational effects. These include the fact that galaxies rotate way too fast for the amount of known matter, studies on gravitational lensing, and several other pieces of evidence.
we can observe its gravitational influence on visible matter.
Dark matter is matter that is inferred to exist from gravitational effects on visible matter and background radiation, but is undetectable by emitted or scattered electromagnetic radiation.
Dark matter.
There are several pieces of evidence for dark matter. For example: * Our galaxy, and many other galaxies, rotate way too fast for the amount of known matter. * Evidence from gravitational lensing.
Dark matter can be detected by its gravitational effect on nearby stars, causing them to very slightly alter their relative motions.