Qquestion: We now hear the terms “dark matter” and “dark energy”. What is that? (Asked by a curious space cadet.)
Answer: These are fairly new terms in astronomy or cosmology, and are quite complicated and theoretical. I’ll do my best to explain them.
Analysis of the orbital speed of stars in the Milky Way indicates that it contains much more matter which is explained by the stars and the gas they contain. (The speed of the orbit is proportional to the mass of the orbiting body.) Almost everywhere astronomers are watching – the Milky Way, other galaxies, or a cluster of galaxies – most of the material needed to cause gravitational behavior to occur. the galaxy (like the orbital speed of stars) appears to be invisible to telescopes using light, radio waves, x-rays, or other electromagnetic radiation.
Oddly enough, it seems that only about 5% of the universe is considered normal matter. Invisible matter was originally called missing mass, but a better term, “dark matter”, is now used. (Dark because we can’t see it.) Apparently, the Milky Way’s disk is embedded in a “halo” of dark matter that extends perhaps 150,000 light-years from the center of the Milky Way.
Regardless of how scientists think it is, even as gravity pulls inward, the universe continues to expand outward faster and faster. To explain this, it is proposed that something invisible counteracts gravity by separating the universe. This is called “dark energy”, which gives rise to negative pressure that separates space. As space expands, more space is created, and with it, more dark energy. Based on the observed expansion rate, scientists estimate that the sum of all dark energy must be more than 70% of the total content of the universe.
However, no one could put their finger on it. All of this has to do with modern relativistic cosmology – a difficult subject.
CPS (Curious Postscript): “It always looks the darkest right before it goes totally black.” – Charlie Brown
Curious about something? Send your questions to Dr Jerry D. Wilson, College of Science and Mathematics, Lander University, Greenwood, SC 29649, or email [email protected] The selected questions will appear in the curiosity corner. For the background of the corner of curiosity, go to curiosity-hornner.net.