lecture08 - Stars Galaxies and the Universe Marua Brada AST...

Stars, Galaxies and the Universe Maru š a Brada č
AST 10G: Stars, Galaxies and the Universe
Lecture 8: What is our Universe made of? Our Galaxy

Stars, Galaxies and the Universe Maru š a Brada č
Today on AST 10G
Our Milky Way

Stars, Galaxies and the Universe Maru š a Brada č
Movie by B. Tully

Stars, Galaxies and the Universe Maru š a Brada č
Movie by B. Tully

Stars, Galaxies and the Universe Maru š a Brada č
The Light Side of the Universe
Our solar system - 1 star
The Milky Way contains about 2 × 10 11 stars

Stars, Galaxies and the Universe Maru š a Brada č
Milky Way: What Is It?

A river of stars? A pancake? Something else? Try counting stars
and their apparent brightnesses in various directions.

Herschels (1700's) and Kapteyn ( 1900): we are near the center of
a pancake.

Shapley (1910's): found distances of star clusters, came to very
different conclusion!

Stars, Galaxies and the Universe Maru š a Brada č
Shapley's Map: Where Are We?

Stars, Galaxies and the Universe Maru š a Brada č
Why Was Kapteyn Wrong?

Trumpler (1920's): star counts are deceptive because of
dust!

Now very well characterized with infrared and other
means.

Stars, Galaxies and the Universe Maru š a Brada č
“Spiral Nebulae”

known since 1700's

with telescopes of the time, not clearly different from planetary
nebulae and star-forming regions

Kant (1755): “island universes” like the Milky Way?

Shapley and Curtis debated this hypothesis in 1920...how would
you judge it?
M31

Stars, Galaxies and the Universe Maru š a Brada č

Argument in favor: This looks just like our model of the Milky Way,
so the Milky Way is just one of many.

Rebuttal: For something as large as the Milky Way to look this
small, the universe would have to be unimaginably, ridiculously
large
M31

Stars, Galaxies and the Universe Maru š a Brada č
Shapley-Curtis Debate

Argument opposed: a nova appeared in M31, which had a large
apparent brightness, proving that M31 is not distant.

Rebuttal: all other novae in M31 were much fainter than the one
Shapley cites. Who you gonna believe, the one or the many?
M31

Stars, Galaxies and the Universe Maru š a Brada č
Shapley-Curtis Debate

Argument in favor: why does M31 have so many novae anyway?
Possibly because it has billions of stars in it?

Rebuttal: we don't know what causes novae, so that doesn't prove
anything
M31

Stars, Galaxies and the Universe Maru š a Brada č
Shapley-Curtis Debate

Argument in favor: von Maanen detected M101 rotation in plane of
sky. If it were big, it would have to be rotating faster than speed
of light!