The Hidden Mass: Dark Matter’s Influence on the Milky Way

#DarkMatter #MilkyWay #GalaxyRotation #Astronomy #CosmicMysteries #GalacticDynamics #SpaceScience #Astrophysics #GravitationalLensing #SpaceExploration

In this video, we continue our exploration of the Milky Way by delving into its rotation and the intriguing discovery of dark matter. After examining the Milky Way’s spiral arms, we now ask a fundamental question: how fast is the Milky Way rotating? This takes us back to the foundational work of Newton and the heliocentric model proposed by Copernicus. Newton’s laws of motion and gravity allow us to understand the rotational dynamics of galaxies. By examining the rotation curves of the Milky Way, we notice something peculiar. Using Doppler shifts to measure the speed of gas clouds and stars, we observe that the inner parts of the galaxy rotate as if they are a solid body. However, the outer parts exhibit what is known as differential rotation, where the orbital speed remains roughly constant regardless of the distance from the galactic center. This defies the expected Keplerian drop-off, where objects farther from the center should orbit more slowly. This discrepancy led astronomers to propose the existence of dark matter—an unseen and mysterious form of matter that exerts gravitational influence, accounting for the flat rotation curves observed in the Milky Way and other spiral galaxies. The only way to maintain a constant rotational speed at greater distances is for the mass of the galaxy to increase proportionally with the radius. This implies the presence of significant mass beyond the visible stars and gas. We use numerous methods to study dark matter, such as analyzing the rotation curves of external galaxies, looking for microlensing events, and observing gravitational lensing by galaxy clusters. These approaches collectively indicate that dark matter is ubiquitous, extending well beyond the luminous parts of galaxies. Evidence for dark matter extends beyond individual galaxies to galaxy clusters. Figures like Fritz Zwicky and Vera Rubin demonstrated that clusters of galaxies also require substantial amounts of dark matter to explain their dynamics. Observations of X-ray emitting gas within clusters, gravitational lensing, and the behavior of galaxy clusters during collisions support the notion that dark matter constitutes about 90% of the total mass in these systems. We explore the various candidates proposed for dark matter, such as Machos (massive compact halo objects) and WIMPs (weakly interacting massive particles), along with more exotic particles like axions and sterile neutrinos. While none of these candidates have been definitively detected, ongoing research continues to refine our understanding. The significance of dark matter reshapes our comprehension of the universe, indicating that most of the mass in the cosmos is non-luminous and interacts primarily through gravity. Understanding dark matter is critical for unraveling the full story of our galaxy and the broader universe. Join me in this deep dive into the mysteries of dark matter and the rotational dynamics of the Milky Way. We’ll explore the evidence, theories, and ongoing research that continues to push the boundaries of our knowledge in astronomy.

This is part of my complete intro Astronomy class that I taught at Willam Paterson University and CUNY Hunter.

0:00 Introduction
0:01 The Link to Newton's Gravity
4:41 Circular Motion due to a Central Force
6:16 Circular Motion due to Gravity
7:16 Measuring Rotation Speed of Galaxies
8:54 The Rotation of the Galaxy's Disk
13:30 The Mass of the Milky Way Galaxy
16:56 Example: Milky Way
19:56 Dark Matter in the Milky Way
21:43 Rotation Curves of Other Galaxies
23:20 23% is Dark Matter
26:38 The Dark Matter of the Milky Way Galaxy
30:31 Dark Matter Halos
31:27 Dark Matter in Galaxy Clusters
38:45 The Musket Ball Cluster
42:43 REVIEW QUESTIONS

[book]

I don't have the math, yet, but doesn't dark matter smell a little bit like luminiferous aether?

[LuciFeric]

Very interesting. Thank you professor.

[butHomeisNowhere___]

Am I correct in saying that, given the data, it looks like the dark matter density increases with the distance from the nucleus? Sort of like how a mattress will lift up around your body when you lay on it, the dark matter increases *around* baryonic matter?

[elijaguy]

I wonder why Zwicky didnt call it transparent matter. Dark interacts with light: it absorbs it. therefore it becomes dark, therefore it is opaque. While Dunkles Materie is invisible, absolutely transparent, and this quality is what haunts the scientists and also us, the laymen.

[christopherreed]

Not all of us with dyslexic learning disorder I put a lot of time into listening to you your very smart 😉 I thank you for speeding up my learning rather than learn 🙂 something not followed

[HotPinkst]

Stellar black holes are hard to directly detect, couldn't dark matter just be a mix of all the hard to detect objects in greater than expected quantity? If our tech can't 'see' it then it must be dark matter doesn't seem like a scientific explanation for making the extraordinary claim of a new substance all that strongly.