ASTR 107 Lecture Notes - Lecture 9: Dark Matter Halo, Elliptical Galaxy, Spiral Galaxy
ASTR 107 Lecture 9 Dark Matter
-We estimate the amount of mass in a spiral galaxy by how much light it gives off. More light =>
more stars => more mass
-According to Hepler’s laws, rotation speeds should decrease with larger radius- they do not
-There must be an additional source of gravity that oes not make light, called dark matter
-luminous matter (normal matter) cannot produce all the gravity in a galaxy
-90-95% of the mass of a spiral galaxy is dark matter, it is located in a larger dark matter halo
around the galaxy
-dark matter dominates elliptical galaxies as well
-in 1998 astronomers studying Supernova in a very distant galaxies expected the expansion to
be slowing down but instead the data indicated that the expansion is speeding up and they
found that that universe is expanding at an accelerated rate
Matter and Energy in the universe:
-negative gravity or repulsive gravity, vacuum of space can have non-zero energy
-The fate of the universe depends on mass; stop expanding →then collapse(Big crunch), not
enough mass to reverse but expands more slowly(Big chill), or it will expand forever at ever-
increasing speed(Big rip) The big rip is the current fate of the universe with our current ideas
so far
-in 10^39 years, normal matter will decay and leave only black holes
-10^100 years, even the largest black holes will evaporate
-an ever expanding universe is filled with photons and elementary particles
find more resources at oneclass.com
find more resources at oneclass.com
