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Chapter 22

Chapter 22 Summary Cosmic Perspective

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Astronomy 1021
Chris Racknor

CHAPTER TWENTY TWO Dark Matter Dark Energy and the Fate of the Universe Dark matter and dark energy sound very similar but they are each hypothesized to explain different observations dark matter is thought to exist because we detect its gravitational influence dark energy is a term given to the source of force that may be accelerating the expansion of the universe Either dark matter exists or we do not understand how gravity operates across galaxy sized distances there are many reasons to be confident about our understanding of gravity leading many to conclude that dark matter is real Dark matter seems by far to be the most abundant form of mass in the universe we still do not know what it is but we suspect is it largely made up of some type of as yet undiscovered subatomic particles If dark matter is indeed the dominant source of gravity in the universe then it is the glue that binds together galaxies clusters superclusters and other large scale structures in the universe all this structure has probably grown from regions in the early universe where the density of dark matter was slightly enhanced The fate of the universe depends on whether gravity can ever halt the current expansion the total strength of gravity seems to weak to do so even when we account for dark matter and the evidence indicating that the expansion is accelerating only reinforces the idea that expansion will never cease What We Mean by Dark Matter and Energy Dark matter and energy have never been directly observed but each has been proposed to exist because it seems the simplest way to explain a set of observed motions in the universe dark matter is the name given to the unseen mass whose gravity governs the observed motions of stars and gas clouds dark energy is the name given to what ever may be causing the expansion of he universe to accelerateEvidence for Dark Matter in Galaxies The orbital velocities of stars and gas clouds in galaxies do not change much with distance from the centre of the galaxy applying Newtons laws of gravitation and motion to these orbits leads to the conclusion that the total mass of a galaxy is far larger than the mass of its stars because no detectable visible light is coming from this matter we call it dark matterEvidence for Dark Matter in Clu
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