{"id":3110,"date":"2020-07-12T10:22:04","date_gmt":"2020-07-12T14:22:04","guid":{"rendered":"https:\/\/www.fas37.org\/wp\/?p=3110"},"modified":"2026-02-01T10:54:23","modified_gmt":"2026-02-01T15:54:23","slug":"dark-matter","status":"publish","type":"post","link":"https:\/\/www.fas37.org\/wp\/dark-matter\/","title":{"rendered":"Dark Matter"},"content":{"rendered":"\n

Young Astronomers Blog, Volume 28, Number 15.<\/strong><\/p>\n\n\n\n

In a previous article<\/a>, I explored the standard model of particle physics and discussed what ordinary matter is made of. All the matter that we can see and touch is composed of baryons (particles containing three quarks) and, as such, is referred to as baryonic matter. However, the universe is turning out to be much more mysterious (and darker).<\/p>\n\n\n\n

In the early 17th<\/sup> century, Johannes Kepler put forth his three laws of planetary motion. One of which states that the closer a planet is to the Sun, the faster it moves. This and much, if not all, of the motion of stars and galaxies is controlled by gravity. Isaac Newton published the first complete thesis on gravity in 1687 with his Philosophiae Naturalis Principia Mathematica<\/em> (Mathematical Principles of Natural Philosophy). In it he established the mathematical foundations for gravity and explained why Kepler\u2019s three laws work. Albert Einstein refined how we view gravity with his General Theory of Relativity<\/em> in 1915. Einstein viewed gravity as a something that curves space\/time rather than a force that attracts objects with mass.<\/p>\n\n\n\n

It was generally assumed that gravity associated with ordinary matter would account for the motion of the cosmos based on Newton\u2019s and Einstein\u2019s theories.<\/p>\n\n\n\n

The first indication that something might be missing from the universe came in 1932 from Jan Oort, who suggested that there must be more matter in the Milky Way that what is observed. Oort was followed by Fritz Zwicky, who studied the motion of the Coma galactic cluster and noticed that there was not enough mass to account for the movement of the cluster. He theorized that there might be hidden matter that, in 1933, he termed dunkle Materie (dark matter), although some say Oort was first to coin the term.<\/p>\n\n\n\n

In 1970, Vera Rubin and Kent Ford measured the rotational velocity of the Andromeda galaxy. They expected the galaxy to follow Kepler\u2019s laws and that matter should move slower about the galactic center the farther it is from the center. This did not turn out to be the case. They found that galactic material moved at the same rate regardless of the distance from the center. Over the next few years, this was confirmed with observations of other galaxies.<\/p>\n\n\n\n

In the 1970s, James Peebles and Jeremey Ostriker began to investigate the theoretical underpinnings of what Oort, Zwicky, Rubin and Ford had found. Their simulations indicated that galaxies acted as if they were enclosed within a halo of hidden matter. In 1982, Peebles published his theory of a \u201ccold dark matter (CDM)\u201d universe, which is the foundation for our modern view of the universe. Peebles recently was awarded the 2019 Nobel prize for this pioneering work in this field.<\/p>\n\n\n\n

Further evidence for dark matter comes through gravitational lensing. Light from distant galaxies is bent as it passes by nearby galaxies due to the interaction with the gravity of dark matter surrounding the galaxies.<\/p>\n\n\n\n

Other theories have been proposed to explain the evidence leading to the theory of dark matter. In 1983, Mordehai Milgrom offered MOND (Modified Newtonian Dynamics) suggesting that Newton\u2019s 2nd<\/sup> law of motion should be modified for large distances. MOND is still being discussed, although it hasn\u2019t been successful in replacing the dark matter hypothesis.<\/p>\n\n\n\n

In any event, dark matter remains elusive. it does interact with gravity, but not with light. Astronomers do think it accounts for around 85% of the matter in the Universe. Three types of particles have been proposed for dark matter.<\/p>\n\n\n\n