Dark Matter
Two people have been credited for determining the need for dark matter. The first was astronomer Jan Oort, who back in 1932 measured the perpendicular motions of nearby stars relative to the disk of our galaxy. By studying the gravitational influence of the disk on these stars he was able to calculate the mass of the disk. The value he determined was twice as much as that inferred by the visible stars and nebulae in that region. A year later in 1933 astronomer Fritz Zwicky estimated the mass of a group of galaxies by measuring their brightness. When Zwicky used a different method of calculating the mass of the cluster he found it to be 400 times the value from directly inferring the mass from the brightness of the cluster. In both cases Oort and Zxwicky came to the conclusion that the visible galaxies only accounted for 10% of the mass needed to keep them gravitationally in the cluster. Based on 70 years of accumulated observations of the motions of galaxies and the expansion of the universe, most astronomers believe that as much as 90% of the stuff constituting the universe may be objects or particles that cannot be seen. In other words, most of the universe's matter does not radiate - it provides no glow that we c
For every gram of glowing material we can detect, there may be tens of grams of dark matter out there. Black Holes on the other hand have an over abundance of matter. Again, we need about 5 times more matter than we can see via electromagnetic radiation. Red dwarf stars are an accumulation of hydrogen which has collected under it's own gravity. The first group is made up of Massive Compact Halo Objects (MACHOs). But it is also theorized that within an individual galaxy, you can measure the rate of rotation of the stars about the galactic center of rotation. But most astronomers would agree that MACHOs alone do not make up enough accountable mass. The outer stars in the galaxies seem to rotate too fast for the amount of matter that we see in the galaxy. It occurs when a red dwarf or black hole passes between a star or galaxy and an observer on Earth. Machos are non-luminous objects, meaning they do no reflect light, that make up halos around galaxies. From NASA's Hubble telescope, astronomers have been able to estimate that red dwarfs comprise of only 6% of the mass making up galactic halo matter. Exactly what dark matter is really composed of is purely theoretical at this time. Therefore they are non-luminous, but they do have a large enough mass which can account from gravitational effects. These results can be explained by assuming that there is a "dark matter halo" surrounding every galaxy.
Common topics in this essay:
Zwicky Oort's,
WIMPs Particle,
MACHOs Machos,
Oort Zxwicky,
Earth MACHO,
Black Holes,
Jan Oort,
NASA's Hubble,
Fritz Zwicky,
Holes Red,
dark matter,
black holes,
normal matter,
red dwarfs,
red dwarf,
red dwarf stars,
matter galaxy,
matter halo,
it's own,
gravitational field,
motion galaxies,
dark matter halo,
black holes red,
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Acceptance Essays
