Spiral nebulae: back in the earlytelescope days when astronomers were calling everything fuzzy a nebula, the spiral nebulae were those where they could detect a faint spiral pattern.
Island Universes: some astronomers thought the spiral nebulae were whirlpools or new stars, others thought they were far away universes.
The Great Debate: When the National Academy of Sciences sponsored a debate between Shapley and Curtis about the scale of the universe. Both men were wrong. Edwin Hubble discovered the truth.
In 1921 Hubble studied the Andromeda Nebula after the 100-inch Hooker telescope was built at Mt. Wilson in California. He discovered a cepheid variable in the nebula. Found the nebula to be a million miles away. What with all the doubt on cepheid variables after the debate he was reluctant to come forward. Russell presented the paper for him in 1925. It was easily accepted. The universe was expanded tenfold. The nebula became a galaxy.
Edwin Hubble looks like Hank Azaria in this photo.
I think barred spiral galaxies are the prettiest.
Lenticular means convex on both sides, or lentil-shaped.
Spiral galaxies have higher net rotation speed than ellipticals. They have more evidence of new star formation than ellipticals. Spiral galaxies have a mix of old and new stars in general. Elliptical galaxies have mostly very old stars and little dust for new ones. Spiral galaxies are the brightest, but elliptical galaxies are the most numerous.
Spiral galaxy arms are caused by a compression wave. Super-massive stars go supernova. The supernovae send out shock waves. The waves cause new condensations. One way or another you get arms. The exact cause and why they persist is still a mystery, though.
Small, old Population II stars are at the center of our galaxy. The Milky Way is pretty typical, all told. Population I stars are found in hot, blue open clusters on the spiral arms. Along with supernovae and nebulae. The small, yellow/orange, old Population II stars are in the halo and the center.
M87, an elliptical, is one of the largest we know of. It is 1000x as massive as the Milky Way. It's nearly spherical and is symmetrically surrounded by globular clusters. It has a huge jet of gas coming from its core. There is a vortex of gas in the center there swirling around a black hole. The jet comes from ionized atoms or charged particles getting caught in a strong magnetic field. The jet extends 8000 light years. The M87 is surrounde by other galaxies, and even has a hold on us. It and its entourage form the Virgo super-cluster of galaxies.
Elliptical galaxies are like globular clusters, spiral galaxies are like solar systems.
Comments