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Investigating the Darkness Part 1

This article appeared in the September 2, 2011 edition of the Davis Enterprise.

By Vinita Domier

Special to the Enterprise

 Everyone is invited to the Saturday, September, 10, 2011 meeting of the Davis Astronomy Club at Exploit’s 3141 5th Street location starting at 7:30pm. You do not have to pay any dues to be a member of the Davis Astronomy Club. If you are interested in astronomy, you are welcome to attend. Telescope viewing will be available after the presentation.

 This month we will discuss two little understood cosmological entities - dark matter and dark energy. Together they make up about 95% of the cosmos. Dark matter accounts for 25%, and dark energy 70%.

 The remaining 5% of the universe is comprised of ordinary matter – atoms in everything on earth, stars, and galaxies. As matter and energy are interrelated (by Einstein’s famous equation, E=mc2, where E represents energy, m represents mass of matter, and c represents the speed of light), matter and energy can be added together to determine the present mass-energy composition of the universe.

 Dark matter is an invisible and as of yet undetermined form of matter that only manifests itself gravitationally. Dark matter can be inferred from its gravitational effects on visible (or normal) matter and gravitational lensing effects on background cosmological radiations.

 As dark matter does not emit, reflect or scatter electromagnetic radiations, it cannot be detected directly.  Fritz Zwicky coined the name “dark matter” in the 1930s to explain the missing mass in the universe.

 Matter in the universe was smooth and featureless when the universe was young soon after the Big Bang explosion. Gradually, matter became organized into stars, stars into galaxies, and then galaxies into clusters.

 These clusters of galaxies include all the stars in their individual galaxies and also the gases between the galaxies. The immense gravitational compressing of these gases, due to the massive galaxy cluster, causes the gases to heat up and emit detectable X-rays.

 These X-rays indicate the distribution and temperature of the hot gases.  Scientists use this information to deduce the total mass or matter in that cluster that is interacting gravitationally with the gases.

 Surprisingly, it turns out there is 5 times more gravitational effect on the gases than can be accounted for by the visible or detectable mass in any galaxy cluster. Hence, the conclusion is that there is a lot of dark matter in the universe that is not directly detectable, but is indirectly detectable by its gravitational effects.

 Check back next week for a discussion of dark energy, and save the date for the Astronomy Club’s September 10 meeting.  Also, be sure to check out Explorit’s facebook page.

Explorit’s coming events:

Astronomy Club Meeting, Saturday, September 10, 2011 at 7:30 p.m.  Presentation on Dark Matter and Energy.  Telescopes will be set up for viewing, weather permitting, after the presentation.


Explorit Science Center is located at 3141 5th St. For more information call (530) 756-0191 or visit, or “like” us on Facebook.

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