Date: September 9, 2011

Investigating the Darkness, Part 2

By Vinita Domier
Special to the Enterprise

Cosmological entities known as dark matter and dark energy will be the subject of the Davis Astronomy Club meeting this Saturday, September 10 at 7:30 p.m. at Explorit Science Center at 3141 5th Street.

Dark Matter was the subject of last week's article Investigating the Darkness, Part 1. This week's subject matter is dark energy.

Dark energy is a repulsive force in the universe even less understood than dark matter. According to Einstein's General Theory of Relativity, the rate of expansion of the universe that started after the Big Bang explosion should be gradually slowing down.

In 1998, however, two independent teams of astronomers studying distant supernovae discovered that the universe's expansion was actually speeding up. The anti-gravity force or repulsive energy causing this cosmic ballooning is known as dark energy, as like dark matter, it cannot be directly detected, but its existence is inferred from observations of its effects upon Type 1a supernovae.

A Type 1a supernova results when a white dwarf star in a binary star system explodes into a supernova. Matter is gravitationally attracted to the massive white dwarf from the much less massive normal star, until the white dwarf reaches critical mass at which point it undergoes a spectacular thermonuclear explosion known as supernova. As all white dwarf stars reach this critical explosive stage at the same critical mass, they achieve the same luminosity upon explosion, and hence can be used as standard candles to determine distances to Type 1a supernovae and hence how far back in time these explosions happened.

Also, the visible light from these supernovae undergo red-shifts in their spectrums proportional to the relative speeds at which the galaxies flee from each other due to the expansion of the universe. By analyzing the distance and red-shift data from many different Type 1a supernovae, the rate at which galaxies are moving away from each other is observed to be accelerating over time, resulting in a universe that is continually expanding rather than gradually contracting.

Hence, the conclusion is that the mysterious and undetectable dark energy is causing the detectable expansion of the cosmos.

This Saturday's meeting of the Davis Astronomy Club at Explorit will include a presentation on both dark matter and dark energy, followed by telescope viewing. These meetings are open to all ages and there are no dues to pay to be a member of the Davis Astronomy Club. If you are interested in Astronomy, please join us.

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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.

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Explorit Science Center is located at 3141 5th St. For more information call (530) 756-0191 or visit http://www.explorit.org, or ÒlikeÓ us on Facebook.