Episode Summary: "Super-Duper Novas with Michael Shara" on StarTalk Radio
In this engaging episode of StarTalk Radio, host Neil deGrasse Tyson teams up with co-host Chuck Nice and esteemed astrophysicist Michael Shara to delve deep into the explosive lives of stars. Titled "Super-Duper Novas with Michael Shara," the episode offers a comprehensive exploration of novas, supernovas, and their profound impact on the universe.
1. Introduction of Guest: Dr. Michael Shara (02:24)
The episode kicks off with a warm welcome to Michael Shara, a renowned astrophysicist and a pivotal figure at the Department of Astrophysics. Chuck Nice highlights Shara's longstanding relationship with the Hubble Space Telescope Institute, noting, “[03:07] Michael Shara: I was there more than 40 years ago... the first scientific hire without tenure who got tenure at the Space Telescope Institute.” This establishes Shara's deep roots and expertise in the field of stellar explosions.
2. Understanding Novas and Supernovas (03:51 - 05:53)
Shara begins by clarifying the fundamental differences between novas and supernovas. “[04:07] Michael Shara: They are completely different things,” he asserts, emphasizing that despite their similar nomenclature, the phenomena are distinct. He further elaborates on the various types of novas, including micronovas, dwarf novas, and recurrent novas, each with unique characteristics and behaviors.
Neil chimes in humorously, “[04:30] Michael Shara: They’re all,” prompting a light-hearted exchange about the complexities of stellar terminology. The discussion underscores that while both events involve stellar explosions, their underlying mechanisms and outcomes differ significantly.
3. Binary Star Systems and Novae Explosions (06:35 - 09:05)
A pivotal point in the conversation revolves around the nature of binary star systems in relation to novas. Shara explains, “[06:35] Michael Shara: Every nova is a binary star,” highlighting that these explosive events typically involve two stars in close proximity. Neil probes further, asking if one star feeds another, to which Shara responds, “[06:44] Michael Shara: That’s exactly right. And feeding may not be exactly the right word. You might think of it as a kind of cannibalism. Oh, involuntary.”
This segment delves into the dynamics of mass transfer between stars, illustrating how one star can accrete material from its companion, leading to repeated explosive outbursts characteristic of recurrent novas.
4. Classification of Supernovas: Type I and Type II (13:57 - 16:57)
The conversation transitions to supernovas, with Shara distinguishing between the two primary types. “[14:01] Michael Shara: It used to be thought that there were two kinds of supernovas,” he begins, confirming Chuck's guess, “[14:02] Chuck Nice: Let me guess. Type one and type two.”
Shara elaborates on the classifications:
- Core Collapse Supernovas (Type II): Result from massive stars (20-100 solar masses) whose cores collapse under gravity, leading to a catastrophic explosion.
- Degenerate Supernovas (Type I): Arise from white dwarf stars in binary systems that accumulate mass beyond their Chandrasekhar limit (~1.4 solar masses), leading to an uncontrollable energy release.
He notes, “[15:54] Michael Shara: So we know that in very, very first, from very first principles, the broadest way of looking at these supernovas are that they're either what we call core collapse supernovae... or singular double degenerate supernovae.”
5. The Role of Supernovas in Creating Heavy Elements (23:41 - 25:19)
Shara addresses the origin of heavy elements in the universe, explaining, “[23:45] Michael Shara: Probably a combination of them.” He discusses how different types of supernovas contribute to the synthesis of elements like iron, silicon, and nickel. “[24:27] Michael Shara: And then there are things that are 10 to 100 times brighter than that, and those are the hypernovas.”
Neil interjects with enthusiasm, “[23:11] Neil deGrasse Tyson: So I love the idea that I've never heard it put before when you say the Pacific Ocean amount of hydrogen...”
This segment underscores the critical role supernovas play in seeding the cosmos with the elements essential for life and planet formation.
6. Pre-Supernova Detection and Betelgeuse’s Impending Explosion (20:47 - 54:08)
A highlight of the episode is the discussion on predicting supernovae, particularly focusing on Betelgeuse. “[20:47] Chuck Nice: Yep... Why can't we study this to kind of know what's happening inside of a black hole?”
Shara outlines the challenges and current methodologies in detecting pre-supernova signals:
- Neutrino Detection: “[48:21] Michael Shara: And a gorgeous detector right near Sicily, a huge underwater detector.”
- Gravitational Waves: “[50:07] Michael Shara: We have several detectors, at least three up and operating now, that are going to detect those gravitational waves.”
They discuss the theoretical timeline of Betelgeuse’s supernova, with Shara estimating, “[46:56] Michael Shara: Probably a million years to go, but it might be tomorrow.” The conversation touches on the potential visibility and impact of such an event, assuring listeners that while spectacular, it poses no immediate threat to Earth.
7. Historical Supernovas and the Star of Bethlehem (54:08 - 59:59)
Shara and the hosts explore historical records of supernovas, referencing the Crab Nebula’s 1054 AD supernova. “[56:07] Michael Shara: So we have the technology, astronomers now have the technology to once and for all answer the question.”
They examine ancient astronomical records from China, Japan, and Korea, seeking correlations with biblical accounts like the Star of Bethlehem. Shara concludes, “[57:55] Michael Shara: And there is no good candidate,” suggesting that the biblical event lacks astronomical evidence as a recorded supernova.
Neil reflects, “[58:51] Michael Shara: So we now have the technology, astronomers now have the technology to once and for all answer the question.”
This dialogue emphasizes the interplay between astronomy, history, and mythology in understanding celestial events.
8. Type Ia Supernovas as Standard Candles (60:37 - 67:17)
The episode delves into the significance of Type Ia supernovas in measuring cosmic distances. Shara explains, “[60:37] Michael Shara: These are the so called type 1A supernovae.” He describes how these supernovas serve as “standardizable candles” due to their consistent peak luminosity, allowing astronomers to gauge vast intergalactic distances accurately.
Chuck adds, “[66:37] Chuck Nice: They actually calibrate themselves for you. There you go. That's amazing.”
This segment highlights the pivotal role Type Ia supernovas played in the discovery of dark energy and the accelerated expansion of the universe, underscoring their importance in modern cosmology.
9. Closing Remarks and Future Prospects (69:00 - 70:16)
As the episode wraps up, the panel reflects on the advancements in astrophysics and the exciting possibilities ahead. Shara mentions ongoing research to better understand supernovas and their remnants, while Neil encourages listeners to continue exploring the cosmos.
Notable Quotes:
- “[04:07] Michael Shara: They are completely different things.”
- “[06:35] Michael Shara: Every nova is a binary star.”
- “[14:01] Michael Shara: It used to be thought that there were two kinds of supernovas.”
- “[23:45] Michael Shara: Probably a combination of them.”
- “[46:56] Michael Shara: Probably a million years to go, but it might be tomorrow.”
- “[60:37] Michael Shara: These are the so called type 1A supernovae.”
- “[66:37] Chuck Nice: They actually calibrate themselves for you. There you go. That's amazing.”
This episode of StarTalk Radio masterfully blends scientific rigor with accessible explanations, offering listeners a detailed understanding of the life cycles of stars, the mechanisms behind their explosive deaths, and their indispensable role in shaping the universe. Michael Shara's expertise provides clarity on complex topics, making this episode a must-listen for astronomy enthusiasts and curious minds alike.