Which of the following best summarizes what we mean by dark matter? matter for which we have theoretical reason to think it exists, but no observational evidence for its existence. matter that we have identified from its gravitational effects but that we cannot see in any wavelength of light. matter that may inhabit dark areas of the cosmos where we see nothing at all. matter consisting of black holes.

Dark matter is a type of matter, whose composition is unknown and which corresponds to 80% of the matter in the universe. Its name refers to the fact it does not emit or interact with any type of electromagnetic radiation, being completely transparent throughout the electromagnetic spectrum.  

However, it interacts with the known matter through gravity.  

This means that, like gravity, dark matter can not be observed directly, however its existence is inferred through the movement of the stars and the cosmic dust within the galaxies.

jupiter is the largest planet in our solar system, having a mass and radius that are respectively, 318 and 11.2 times that of earth. suppose that an object falls from rest near the surface of each planet and that the acceleration due to gravity remains constant during the fall. each object falls the same distance before striking the ground. determine the ratio of the time of fall on jupiter to that on earth.