Caltech Astronomy Public Lecture Series - The Galactic Underworld: The Milky Way’s Sea of Dormant Black Holes - Kareem El-Badry - 12/08/2023

There are ~100 million black holes lurking throughout the Milky Way, but how do we detect them and how do they affect their surroundings? Join us for a 30-minute lecture investigating dormant black holes, followed by a panel Q&A consisting of several astrophysicists to answer your questions about astrophysics and space science. Timestamps below: 00:00 Announcements 06:29 Intro to Black Holes Presentation 07:52 Black Holes Presentation 38:45 Q&A for Black Holes Presentation 39:00 "Do you know the distribution of masses of black holes?" 40:32 "What is the theoretical minimum mass of a black hole?" 42:09 "Are black holes uniformly distributed through space?" 44:08 "How do black hole jets get ejected from black holes?" 46:00 "Does black holes have different orientations?" 48:33 Intermission 52:24 Q&A Panel Introductions 56:07 "What happens if a small black hole meets a big star?" 58:08 "What software do you use with black hole datasets?" 1:00:50 "How close would a rogue black hole get for us to detect it?" 1:03:30 "Are black holes preferentially located near our galactic center?" 1:05:04 "Why is Andromeda Galaxy's supermassive black hole so much bigger than ours?" 1:08:35 "How could we use Voyager's orbit to constrain nearby black holes?" 1:10:39 "Do we know of any galaxies that do not have supermassive black holes?" 1:12:48 "Are black holes just point masses? Are stars?" 1:14:50 "What is the relationship between supernovae and black holes?" 1:20:14 "Do the black holes orbit like the stars in the galaxy?" 1:22:20 "Are black holes dark matter?" 1:24:17 "What are the sizes of supermassive black holes?" 1:25:25 "How far out can black holes be kicked out of a galaxy?" 1:27:24 "What would it take for a human to see inside a black hole?" 1:28:42 "Why are supernova interesting?" 1:31:22 "How close of a supernova is dangerous for us?" 1:35:05 "When Milky Way and Andromeda merge, what will be our black hole's mass? 1:37:13 "How unstable are white holes if they exist?" 1:43:37 "Can merging black holes produce new elements?" 1:47:44 "Is Uranium the heaviest element observed in nature?" 1:49:11 "Can we observationally detect Hawking Radiation?" 1:51:19 "Does a black hole make a noise?" 1:54:58 "What made you want to go into astronomy?" 1:59:55 "Why are we able to observe black holes so much more frequently than before?" 2:06:14 Concluding Remarks *Apologies for the poor sound during the presentation. There were problems with the microphone being sensitive enough to pick things up. Please use the sub-title option in YouTube to get the full transcript. Title: The Galactic Underworld: The Milky Way’s Sea of Dormant Black Holes Speaker: Kareem El-Badry Abstract: About 100 million black holes are thought to lurk in the Milky Way. The vast majority of these black holes — which are corpses of long-dead generations of massive stars — emit no detectable light and only very rarely interact with their surroundings. I will describe how astronomers know this vast population of quiet black holes exists and how large-scale surveys of the Milky Way are beginning to detect the black holes' gravitational effects. I will also discuss relation between these nearby black holes and those being discovered by gravitational wave detectors. Poster Photo Credit: NASA Goddard