Скачать или смотреть Spiral Arms Explained: The Science Behind the Milky Way’s Structure

This video is part of a comprehensive series initially developed for William Paterson University and CUNY Hunter, aimed at supporting online classes and course materials for introductory astronomy. By engaging with all the videos within this series, you will effectively complete a full undergraduate course in astronomy, equipping yourself with the knowledge and skills necessary to navigate the night sky with confidence, learning all the basics and many advanced topics!

Now, we examine the Milky Way’s spiral arms, understanding their formation, appearance, and measurement. Like other spiral galaxies, the Milky Way has these majestic arms, but observing them from within is challenging. To comprehend them, we must acknowledge the difficulties. Traveling thousands of light years to view the Milky Way from above is impossible. Instead, we measure gas and dust clouds to trace the spiral structure. Spiral arms contain hot, young stars, particularly type O and B stars, which illuminate these regions. These short-lived stars indicate ongoing massive star formation. Notably, these arms cannot rotate with the galaxy because their structures are not fixed entities but patterns of star formation. The Sun takes about 260 million years to orbit the galaxy, completing about 50 orbits before dying, while O and B-type stars live for only about 1 to 10 million years. Hence, when we see an O star, it has not moved far from its birthplace. Walter Baade, a pioneering astronomer, described spiral arms as “beads on a string,” highlighting regions packed with intense star formation activity. These arms function as density waves, where gas and dust compress, leading to star formation, akin to a traffic jam of stellar material. The stars then continue their journey around the galaxy, giving the illusion of a rotating spiral. Examining nested elliptical orbits reveals that overlapping streams of gas create these stellar traffic jams, forming the spiral arms. This concept explains why we see bright star clusters and pink hydrogen glows concentrated in specific regions—these are the result of compressed gas clouds forming new stars. We have impressive visual evidence from galaxies like the Whirlpool Galaxy (M51). Dark lanes of gas, where star formation occurs, are followed by bright, hot stars moving out of these dense regions. The spiral structure becomes evident when gas compresses in these lanes, triggering star formation. The Spitzer Space Telescope’s infrared images of our galaxy show how star formation progresses from dark dust clouds to bright H2 regions. Radio astronomy, particularly the study of the 21-centimeter radiation, maps hydrogen gas in the Milky Way, helping us determine the locations and movements of gas clouds and create a map of the spiral arms. Examining the neutral hydrogen map and carbon monoxide emissions allows us to trace the spiral arms and understand their structure. Large-scale surveys like the Very Large Array (VLA) have confirmed spiral structures in nearby galaxies similar to the Milky Way. These methods and evidence reveal the active sites of star formation in the Milky Way, shaped by complex interactions of gas, dust, and gravitational forces.

0:00 Introduction
3:10 Spiral Arms are Sites of Active Star Formation
4:38 Galactic Spiral Arms
6:10 What are Spiral Arms?
8:23 Nested Elliptical orbits of stars...
14:03 M17 SWex Dark Star-Forming Cloud (younger)
15:57 Many eras of star formation
16:21 All-sky Milky Way in Hydrogen emission 21cm
17:18 21 cm radiation in our Milky Way Hydrogen atom
19:21 21cm Radiation of Neutral Hydrogen (HI)
22:23 Neutral Hydrogen Map of the Milky Way
23:17 All molecular clouds are found in HI regions
25:59 REVIEW QUESTIONS

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