what is dark matter?

Answer 1

In the 19th Century astonomers insisted that there had to be another planet closer to the sun than Mercury, in order to explain inconsistencies in Mercury's orbit, and some even maintained that they had actually seen this planet, which, in fact, does not exist at all. Nowadays, some astromers insist dark matter has to exist because... well, you probably see where I'm going with this.

Answer 2

From the size and rate of expansion of the universe we observe (and also the size and rate of rotation in galaxies and clusters), we can calculate how much matter is in the universe. Trouble is, we observe only a small fraction of that amount. So we infer that there is some other kind of matter that we can't observe and we call it dark matter. We don't yet know what it is, but particle physicists and astronomers are looking. Another possibility is that we don't understand gravity as well as we think we do and there's a discrepency between reality and general relativity.

Answer 3

Scientists using different methods to determine the mass of galaxies have found a discrepancy that suggests ninety percent of the universe is matter in a form that cannot be seen. Some scientists think dark matter is in the form of massive objects, such as black holes, that hang out around galaxies unseen. Other scientists believe dark matter to be subatomic particles that rarely interact with ordinary matter.

The dark matter hypothesis aims to explain several anomalous astronomical observations, such as anomalies in the rotational speed of galaxies (the galaxy rotation problem). Estimates of the amount of matter present in galaxies, based on gravitational effects, consistently suggest that there is far more matter than is directly observable. The existence of dark matter would also resolve a number of inconsistencies in the Big Bang theory, and is crucial for structure formation.

If dark matter does exist, it vastly outmasses the "visible" part of the universe . Only about 4% of the total mass in the universe (as inferred from gravitational effects) can be seen directly. About 23% is thought to be composed of dark matter. The remaining 73% is thought to consist of dark energy, an even stranger component, distributed diffusely in space, that probably cannot be thought of as ordinary particles. Determining the nature of this missing mass is one of the most important problems in modern cosmology and particle physics.

The first to hypothesize dark matter was Fritz Zwicky, of the California Institute of Technology (Caltech) in 1933. He applied the virial theorem to the Coma cluster of galaxies and obtained evidence of unseen mass.

Hope that helps~

Answer 4

In astrophysics and cosmology, dark matter is matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. According to present observations of structures larger than galaxy-sized as well as Big Bang cosmology, dark matter accounts for the vast majority of mass in the observable universe

Answer 5

In astrophysics and cosmology, dark matter is matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter.

Answer 6

matter means a thing and dark means black so which objects are black things those are dark matters.

Answer 7

For questions like this, wikipedia's a far better place to look. Read the first couple lines of my source, or the whole thing if you're really interested in it.

Answer 8

That stuff that collects under your toenails.

Answer 9

the material in space? like why space is black.