Musings from Jay (blog site permanently frozen 11/05/2024 morning)

A key reference is Space.com. This is largely an extract.  Dark matter is the mysterious stuff that fills the universe, but no one has ever seen it. It is believed to be 80% of the matter in the universe. We only assume it exists because, without it, the behavior of stars, planets and galaxies simply wouldn't make sense. Their observed motions do not match their detectable mass. If you include both matter and energy dark matter is 27% of the universe's content with normally detectable matter being 5% of the universe's content and dark energy being 68%. Both dark energy and dark matter are not understood. I wrote an essay on dark energy that covers that subject:  Dark Energy What we do know about dark matter is that if we look at a typical galaxy, take account of all the matter that we see (stars, gas, dust) and use Newton's Laws of Gravity and motion (or, more correctly, Einstein's General Relativity - GR), to try to describe the motions of that...

Two of the biggest mysteries in astrophysics is dark matter and dark energy. Neither are understood. 27% of the universe is estimated to be dark matter (this works out to 80% of matter in the universe) and 68% of the universe is estimated to be dark energy. That is a lot of the universe that is not understood!! We understand only the 5% remaining matter!! There are strong arguments in favor of the fact that a significant part of the matter in the Universe does not emit anything and is therefore invisible. The presence of such invisible matter can be found by its gravitational interaction with radiating matter. The study of galaxy clusters and galactic rotation curves indicates the existence of this so-called dark matter. So, by definition, dark matter is matter that does not interact with electromagnetic radiation, that is, it does not emit it and does not absorb it. Its nature is unknown.  Dark energy is a theoretically postulated repulsive force that counteracts gravity and cause...

Note: Much of this essay is a synthesis and summarization of lectures by Dr. Joshua N. Winn of Princeton University. The Incredible Scale of the Universe There are amazing things out in the universe that astronomers keep discovering, andastrophysicists keep analyzing and explaining. We are a small planet in the solar system and our sun is a modest star. We are on the edges of a modest galaxy called the milky way and we are in a quiet neighborhood of the galaxy. What is the scale at work here? To get a perspective on planet size, the radius of earth is 3963 miles. Jupiter has twelve times the diameter of Earth. An astronomical unit (AU) is the average distance of earth from the sun and is about 150 million km. Neptune is 30 AU from the sun. To get a perspective on star size, the sun has 109 times the diameter of earth. The largest known star in the milky way is UY Scuti whose radius is 1700 times that of our sun. It is 9500 light years away. A light year is the distance light travels in...