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Things are happening out there that affect the Earth every day that we have no clue about unless we make a point to seek to know. One of the phenomenons in the universe is dark matter--a mass of unknown, undetected matter that neither admits nor reflects light. Dark matter is undetectable by the radiation it admits, but it's postulated to exist in the universe because of observed gravitational effects.

Astronomers have found a wealth of other evidence that some force is causing the expansion of the universe to speed up, and how much of it there is. There's a crucial fact in all of this: it seems to be neither weakening or strengthening as space enlarges. This phenomenon is called "dark energy"; it is called that for a lack of a better term.

Most of the stuff in clusters of galaxies is invisible, and these are the largest structures in the Universe held together by gravity. (What is this gravity holding the universe together....?) It is interesting to conclude that most of the matter in the entire universe is invisible.

The universe is vast and fascinating. The earth that we humans inhabit is within and apart of the functioning universe. There are lots of things happening out there in the universe that we are totally oblivious to here on earth........

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Interestingly enough, the nature of dark matter remains one of the most profound unsolved mysteries in science until this day. Our Milky Way shines with the brilliant light of hundreds of billions of stars. It also contains giant clouds of gases, and numerous planets; and a supermassive black hole at its core. What's interesting to astronomers is that everything in our galaxy that can see with the most powerful telescopes constitutes just a small fraction of the Milky Way's gravitational mass. Most of that mass is in some kind of dark form, which is identified as "dark matter".

One of the greatest surprises in the history of astronomy was discovering that all the things we see in space amounts to less than 1% of the universe's total matter and energy. There is hard to detect gas between galaxies, and all other forms of ordinary matter--consisting of some kind of exotic, invisible particles that don't form atoms. Dark matter's gravity dominates the universe, shapes its history, and provides the gravitational pools in which normal matter could accumulate to make galaxies.

About 10 or more years ago, astronomers discovered that the expansion of the universe is accelerating; the opposite of what was expected. This revelation was made known because of the ability to measure the distances of far galaxies by the apparent brightnesses of theType-Ia supernovae within them. This tells how much the universe expanded, while the light was in transit. Astronomers were able to see how the expansion rate has changed over long stretches of cosmic time.

A team led by Russian astronomer Igor Karachentsev, analyzed recent Hubble Space Telescope observations of Local Group galaxies motions (radial velocities). Studying how galaxies move with respect to the gravitational center of the Local Group, they could find the boundary where the Local Group's gravity gives way to dark energy's (anti-gravity) effect on larger scales, and that Dwarf galaxies beyond this boundary are moving outward.