How much matter in the universe is composed of atoms

Unlike stars and galaxies, dark matter does not emit any light or electromagnetic radiation of any kind, so that we can detect it only through its gravitational effects. Even less is known about it than dark matter. This idea stems from the observation that all galaxies seems to be receding from each other at an accelerating pace, implying that some invisible extra energy is at work. The early universe All matter in the universe was formed in one explosive event The Big Bang In the American astronomer Edwin Hubble discovered that the distances to far-away galaxies were proportional to their redshifts.

Origins In the first moments after the Big Bang, the universe was extremely hot and dense. They seem to give out more X-rays than expected. These clusters of galaxies have changed their appearance with time, and calculations also show that in the past there were fewer galaxy clusters.

This indicates that the Universe must be a high-density environment, contradicting current ideas. The first observational hints of dark energy in the universe date back to the 's when astronomers were trying to understand how clusters of galaxies were formed. Their attempts to explain the observed distribution of galaxies were improved if dark energy were present, but the evidence was highly uncertain. In the 's, observations of supernova were used to trace the expansion history of the universe over relatively recent times and the big surprise was that the expansion appeared to be speeding up, rather than slowing down!

There was some concern that the supernova data were being misinterpreted, but the result has held up to this day. If Thus dark energy explains many cosmological observations at once.

Fast moving neutrinos do not play a major role in the evolution of structure in the universe. They would have prevented the early clumping of gas in the universe, delaying the emergence of the first stars, in conflict with the WMAP data.

However, with 5 years of data, WMAP is able to see evidence that a sea of cosmic neutrinos do exist in numbers that are expected from other lines of reasoning.

This is the first time that such evidence has come from the cosmic microwave background. Another Probe of Dark Matter By measuring the motions of stars and gas, astronomers can "weigh" galaxies. Candidates for the Dark Matter What is the nature of the "dark matter", this mysterious material that exerts a gravitational pull, but does not emit nor absorb light? There are a number of plausible speculations on the nature of the dark matter: Brown Dwarfs: if a star's mass is less than one twentieth of our Sun, its core is not hot enough to burn either hydrogen or deuterium, so it shines only by virtue of its gravitational contraction.

These dim objects, intermediate between stars and planets, are not luminous enough to be directly detectable by our telescopes. If the dark matter is made mostly of MACHOs, then it is likely that baryonic matter does make up most of the mass of the universe.

Supermassive Black Holes: these are thought to power distant "K" type quasars. Some astronomers speculate that dark matter may be made up of copious numbers of black holes.

These black holes are also potentially detectable through their lensing effects. New forms of matter: particle physicists, scientists who work to understand the fundamental forces of nature and the composition of matter, have speculated that there are new forces and new types of particles. One of the primary motivations for building "supercolliders" is to try to produce this matter in the laboratory.

Since the universe was very dense and hot in the early moments following the Big Bang , the universe itself was a wonderful particle accelerator. Cosmologists speculate that the dark matter may be made of particles produced shortly after the Big Bang. While a German supercomputer recently ran a simulation and estimated that around billion galaxies exist within range of observation, a more conservative estimate places the number at around billion.

Since the number of stars in a galaxy can run up to billion, then the total number of stars may very well be around 1. On average, each star can weigh about 10 35 grams. Since each gram of matter is known to have about 10 24 protons, or about the same number of hydrogen atoms since one hydrogen atom has only one proton , then the total number of hydrogen atoms would be roughly 10 86 — aka. Within this observable universe, this matter is spread homogeneously throughout space, at least when averaged over distances longer than million light-years.

On smaller scales, however, matter is observed to form into the clumps of hierarchically-organized luminous matter that we are all familiar with. In short, most atoms are condensed into stars, most stars are condensed into galaxies, most galaxies into clusters, most clusters into superclusters and, finally, into the largest-scale structures like the Great Wall of galaxies aka.

On a smaller scale, these clumps are permeated by clouds of dust particles, gas clouds, asteroids, and other small clumps of stellar matter. The observable matter of the Universe is also spread isotropically; meaning that no direction of observation seems different from any other and each region of the sky has roughly the same content.