Distant Galaxies In The Dark

Star-blazing galaxies outline mysterious and enormous web-like filaments composed of weird invisible dark matter whose identity we do not know. However, we strongly suspect that the dark matter is composed of so-far undiscovered exotic particles that do not interact with light, and are therefore invisible. All of the majestic galaxies, glistening with billions and billions of incandescent stars, seem to gather like swarms of bees around the perimeters of immense empty (or almost-empty) Voids. These great cavities can be as much as 150 light-years across, and they are quite black because they contain very little luminous matter. One light year is the distance that light can travel in a vacuum, which is 5,850,000,000,000 miles! The prevailing theory of galaxy formation suggests that small galactic embryos, or protogalaxies, formed first in the ancient Cosmic gloom that was swathed in starless darkness. These protogalaxies eventually collided and merged together in early times to create the majestic, enormous galaxies that we see today. This so-called bottom-up theory, indicates that large galaxies were a rarity in the very early Universe, and that they eventually grew to their magnificent size by way of the bonding together of smaller, protogalactic globs. The galaxies were born in cradles of the invisible dark matter, which are termed halos. In the early Universe, it is believed that the dark matter and "normal" atomic matter clumped and danced together to create an intricate web of thin and intertwining filaments. "Normal" matter, of which stars, planets, moons, and people are made, is the stuff of atoms, and it composes a mere 4% of the matter-energy content of the Universe. The dark matter is not atomic matter, and it is far more abundant in the Universe. The most abundant gas in these ancient filaments was hydrogen--the most plentiful "normal" atomic element in the Universe, as well as the lightest. "Normal" atomic matter composes all of the elements that we find in the Periodic Table. Hundreds of millions of years later, the hydrogen condensed to create galaxies and clusters and superclusters of galaxies along the twisting filaments of the Cosmic Web. For many, many years, astronomers assumed that the greatest quantity of mass contained in a galaxy dwelled where the galaxy was most luminous--in its heart where there are the greatest number of incandescent stars. However, in the early 1980s, observations of remote spiral galaxies surprisingly indicated that this is not the case. If it were, stars further out from the galactic hidden wiki would be circling more slowly in their orbits around the core than stars closer to the heart of the galaxy. This expected motion of stars orbiting within a galaxy is analogous to the way planets in our Solar System circle the Sun. The outer planets--Jupiter, Saturn, Uranus, and Neptune--circle more slowly in their orbits around the Sun than the inner planets--Mercury, Venus, our Earth, and Mars. The closer a planet is to our Star, the swifter its orbit. This was what scientists expected to see when they applied Sir Isaac Newton's law of gravity to the way they thought stars would behave in a typical spiral galaxy.