PHYS 183 Chapter Notes - Chapter 22: Elliptical Galaxy, Spiral Galaxy, Gravitational Lens
Document Summary
22: dark matter, dark energy and the fate of the universe. Astronomers don"t know what the universe is made of. Have good reason to think the vast majority of the universe isn"t composed of atoms, but rather dark matter & dark energy. Nature of dark matter & dark energy is unknown. Dark matter: a name given to whatever unseen influence is causing observed gravitational effects. Dark energy: a name given to whatever unseen influence is causing the universe expansion to accelerate. Evidence for dark matter in galaxies: distribution of mass in milky way. Use orbital motion of a star to measure mass of milky way within star"s orbit could do the same thing with orbits of stars at every distance from galactic centre. Velocity hard to determine due to interstellar dust obscuring view but can use. Most mass in milky way not concentrated at centre orbits of progressively more distant gas clouds encircle more & more mass.
