Astronomy - Dark Matter - Essay Example

23 percent is dark matter, which we cannot observe and is invisible to us and 73 percent is dark energy which is countering the effects of gravity and hence driving the expansion of the universe. The idea of dark matter came after observing the motion of spiral galaxies like our own Milky Way. Motion of the stars in Andromeda Galaxy, which is our nearest, was observed. In case of spiral galaxy, it was expected that the stars at the outer layer or arms of the galaxy would move faster than the ones on the inside to keep up with the shape of the galaxy.

The observations, however, were contradicting this notion and readings showed stars at the outside moving with almost the same speed as the inner stars. Since gravity depends on mass of the object, it was calculated that the visible mass of the galaxy was not enough to keep it together. The anomaly in the motion of spiral galaxy suggested that the mass of the galaxy might be more than it seems. We see circular motion all around us in the universe from the motion of our planets around the sun and in a similar way motion of stars around galactic center.

Calculations suggested that the visible mass of the galaxy did not have enough gravitational force to overcome the centrifugal force in spiral galaxies and with the mass of visible matter; the galaxies would lose their spiral shape and break away. Since, this is not the case and we see spiral galaxies all around us; there must be invisible matter that seems to have a gravitational effect but does not interact with visible matter. This invisible matter is called dark matter and it has mass which in turn gives it gravitational force.

An explanation for this missing mass was given that red dwarfs or remnants of supernovas which are difficult to observe because they are low light sources, could account for this missing mass; but, the idea was soon ruled out because the missing mass discrepancy could not be justified with even dwarf galaxies. Dark matter may not be visible to us, but, there are strong observations pointing towards its existence. Gravitational lensing is an effect which points towards existence of dark matter.

As per Einstein’s theory, light bends with the gravitational effect of massive objects. Dark matter does not interact with light, but, because it has mass, light from distant galaxies bend around areas with dark matter. The area of dark matter in between the telescope and the galaxies, act as a giant lens and distorts the image, magnifies some galaxies and even causes circular lines distortions typical with common lenses (Kleingrothaus and Arnowitt 27). It is further observed that galaxies form within clumps of dark matter.

Dark matter is thought to be the skeleton aiding in formation of galaxies. It is still not completely understood how the galaxies form, but when computer simulations are run for creation of galaxies with only the visible matter, the result point towards a failed galaxy that could not hold itself together. However, with the inclusion of dark matter or extra mass, the evolution of galaxies as per the computer simulations line up with the images we observe in the universe (Clavin 2). Visible matter joins in the clumps of dark matter and stars initially form because of increased effect of gravity.

Over time galaxies evolve from elliptical to circular disks and eventually in their present form that is spiral galaxies. The mystery of dark matter questions