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David Butler #Space and Time

How Far Away Is It | 10 - The Milky Way

In this segment of our "How far away is it" video book, we cover the structure of the Milky Way galaxy.

After a brief history of what we thought going into the 20th century and how that changed, we give a high-level description of the three main components: the galactic center with its black hole, the galactic disk with its spiral arms, and the galactic halo stretching far out in all directions.

Using the full power of the Hubble, Spitzer, and Chandra space telescopes, we take a deep dive into the center of our galaxy with its central bulge. We detail the evidence for the existence of a supermassive black hole, Sagittarius A*, at the very center of the galaxy's core. We cover and illustrate the work done by the UCLA Galactic Centre Group in conjunction with the new Keck observatory on top of the Mauna Kea volcano in Hawaii, and the Max Plank Institute for Extraterrestrial Physics in Germany. This includes the obits of S0-2 and S0-102 as they approach Sag A*. A look at the G2 Gas Cloud as it approaches Sag A* is also included. 

Next, we go a level deeper into the nature of a Black Hole singularity. We review electron exclusion pressure and neutron exclusion pressure forces that hold back gravity for White Dwarfs and Neutron stars respectively. When that isn't enough, we get the collapse is total. We cover the Schwarzschild radius, event horizon, accretion disk and gamma-ray jets. In addition to the supermassive black hole Sag A*, we show a few of the solar mass black hole candidates including A0620-00, and GRO J1655-40. 

We then cover the structure of the galactic disk including: the bar core, the two 3 Parsec arms, Scutum-Centaurus, Perseus, Sagittarius with its Orion Spur, Norma and the Outer Arm. We review the locations of various celestial objects we've seen in previous Milky Way segments, to show how close to us they are. We also cover the disk's rotation and the Sun's orbit. We end the galactic disk coverage by illustrating how far one would have to go to take a picture that would include what we see in our illustrations.

Next, we cover the galactic halo. We start with Sharpley's globular cluster map that first showed that we were not at the center of the galaxy. We cover the size of the halo, the inner and outer halos orbital motion, and recent discoveries of massive amounts of Hydrogen in the halo and this findings impact on the Dark Matter debate. 

We conclude with another look at the distance ladder that took us across the galaxy.

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