Search For Dark Matters Essay Research Paper

Search For Dark Matters Essay, Research Paper

Looking for the Invisible: Search for the Dark Matter

There is perhaps no current problem of greater importance to astrophysics and cosmology than that of dark matter . The search for dark matter has dominated cosmology for half of the century. But one might ask, what is dark matter . What is it consisting of. And, how do we know that its there.

As much as 90 percent of the matter in the universe is invisible. Detecting this dark matter will help astronomers better comprehend the universe’s destiny. Eighty-four years after Albert Einstein introduced the world to his theory of general relativity, scientists are seeing that he was right all along about measuring what we now call dark matter. Astronomers supported by the National Science Foundation have found the first evidence of an effect called cosmological shear, a phenomenon predicted by Einstein s theory, in which light from distant cosmic objects bends due to gravitational forces. In Astronomy, as in all sciences, one can detect an object in one of two ways: either by observing it directly, or observing the effect that it has on other. It s always been known that there was matter in the night sky that we couldn t really directly see. So the question we have to ask is, what do we see in the night sky.

Well the answer to that question can be as simple as start and what people might call other stuff or as astronomers calls it stars and dark matters . So the question still stands as to what exactly is dark matter . And no one exactly know what it is, but we do have few guesses as to what it might be, and certain evidence that it is there.

What could the dark matter be. And what is it consisting of.

The dark matters are thought to be clusters of galaxies without light. Whatever dark matter turns out to be, we know for certain that the universe contains large amounts of it. For every gram of glowing material we can detect, there may be tens of grams of dark matter out there. Currently the astronomical jury is still out as to exactly what constitutes dark matter. In fact, one could say we are still at an early stage of exploration. Many candidates exist to account for the invisible mass, some relatively ordinary, others rather exotic.

Nevertheless, there is a framework in which we must work. Nucleosynthesis, which seeks to explain the origin of elements after the big bang, sets a limit to the number of baryons–particles of ordinary, run-of-the-mill matter–that can exist in the universe. This limit arises out of the Standard Model of the early universe, which has one free parameter–the ratio of the number of baryons to the number of photons.

From the temperature of the cosmic microwave background–which has been measured–the number of photons is now known. Therefore, to determine the number of baryons, we must observe stars and galaxies to learn the cosmic abundance of light nuclei, the only elements formed immediately after the big bang.

Without exceeding the limits of nucleosynthesis, we can construct an acceptable model of a low-density, open universe. In that model, we take approximately equal amounts of baryons and exotic matter (nonbaryonic particles), but in quantities that add up to only 20 percent of the matter needed to close the universe. This model universe matches all our actual observations. On the other hand, a slightly different model of an open universe in which all matter is baryonic would also satisfy observations. Unfortunately, this alternative model contains too many baryons, violating the limits of nucleosynthesis. Thus, any acceptable low-density universe has mysterious properties: most of the universe’s baryons would remain invisible, their nature unknown, and in most models much of the universe’s matter is exotic.

Evidences for Dark Matter

The way in which dark matter reveals its presence to us is through the gravitational effect it exerts on luminous matter in the universe. (”Luminous” matter is the matter we can see with our telescopes.) The most obvious example of the gravitational effects of dark matter can be observed when looking at the rotation of galaxies.

To study galactic rotation, astronomers look at the emission line spectra of stars in each part of the galaxy. When the light from a star is observed using a diffraction grating or a prism, the starlight is separated into its true colors, in much the same way ordinary sunlight can be separated into the full rainbow of colors known as the visible spectrum.

The true colors constituting starlight separate into a series of light and dark lines in the visible spectrum, with each colored line corresponding to a specific wavelength of light. The specific wavelengths at which these lines occur are characteristic of the elements the stars contain. Thus, they can be used as an elemental ”fingerprint” to identify a star’s composition.

When a star emitting these line spectra is moving away from us, all of the wavelengths of the spectral lines are shifted to higher values than they would have been were the star stationary or moving side to side (neither towards nor away from us). All of the spectral lines are thus shifted towards the long wavelength part of the spectrum, or to the red end of the spectrum.

This shifting of the lines, known as a Doppler shift, towards the red end of the