Emily Levesque Public Lecture: The Weirdest Stars in the Universe
TLDRIn a fascinating public lecture at Perimeter Institute, Dr. Emily Levesque, an assistant professor of astronomy at the University of Washington, delves into the mysteries of the universe's most peculiar stars. She begins by introducing the Hertzsprung-Russell diagram, a fundamental tool in astronomy for plotting a star's temperature and brightness to understand its life cycle. The lecture takes the audience through the evolution of stars, from their birth to their dramatic deaths as supernovae, and the formation of neutron stars and black holes. Levesque also discusses her research on red supergiants and the discovery of the largest known stars, as well as the intriguing Thorne-Żytkow objects, which are red supergiants with a neutron star at their core. The talk is punctuated with anecdotes about the challenges and surprises of astronomical research, including the debunking of 'potassium flare stars' caused by match strikes and the discovery of fast radio bursts. The lecture concludes with a Q&A session, where Levesque's enthusiasm for astronomy is evident as she shares her journey to becoming a researcher and the excitement of potential future discoveries.
Takeaways
- 📍 Dr. Emily Levesque is an assistant professor of astronomy at the University of Washington in Seattle, known for her research on massive stellar astrophysics and cosmological tools.
- 🌟 The Hertzsprung-Russell (HR) diagram is a fundamental tool in astronomy for plotting stars according to their temperature and brightness, illustrating the life cycle and evolution of stars.
- 🔥 Massive stars, such as supergiants, go through distinct phases of life, starting as blue supergiants, transitioning to yellow supergiants, and ending as red supergiants, which are among the largest and coldest stars.
- 🌌 Dr. Levesque's research contributed to a better understanding of red supergiants' positions on the HR diagram by accurately measuring their temperatures using spectral lines from titanium oxide molecules.
- ✨ The discovery of extremely large stars, like KY Cygni, came unexpectedly from a project initially aimed at refining temperature measurements of red supergiants, highlighting the serendipity in scientific research.
- 💥 Supernovae are the explosive deaths of massive stars, resulting from the core collapse after the star has exhausted its nuclear fuel. They can briefly outshine entire galaxies and are crucial for the distribution of heavy elements in the universe.
- ⚫ Neutron stars and black holes are the remnants left after the supernova explosions of massive stars. Neutron stars are incredibly dense and supported by neutron degeneracy pressure, while black holes result from further core collapse.
- 🎓 Dr. Levesque's personal journey into astronomy was inspired by observing Halley's Comet at a young age and was further nurtured by science fiction and educational experiences, emphasizing the role of early inspiration in scientific careers.
- 🧬 The study of weird stars provides insights into the universe's history, evolution, and extremes, contributing to our understanding of stellar physics and the life cycles of stars.
- 📈 Observations of phenomena like supernovae, gamma-ray bursts, and gravitational waves are at the forefront of modern astronomy, often requiring rapid response and international collaboration to capture fleeting cosmic events.
- 🔬 The process of scientific discovery can involve both planned research and accidental findings, as illustrated by the stories of potassium flare stars and fast radio bursts, which showcase the importance of careful observation and the potential for unexpected results.
Q & A
What is the Hertzsprung-Russell (HR) diagram and how is it used in astronomy?
-The Hertzsprung-Russell diagram is a graphical tool used by astronomers to classify stars based on their temperature (plotted on the x-axis) and brightness or luminosity (plotted on the y-axis). It is primarily used to understand the life cycles of stars and how they evolve over time. By plotting a star on the HR diagram, astronomers can predict how it will change and eventually die.
What is a blue supergiant and how does it relate to the life cycle of a massive star?
-A blue supergiant is a massive star in the first phase of its life, characterized by high temperatures and large size. It fuses hydrogen into helium in its core and is represented on the HR diagram as being very hot and bright. As the star exhausts its hydrogen, it evolves and moves across the HR diagram, transitioning from a blue supergiant to a yellow supergiant and eventually to a red supergiant as it fuses heavier elements.
How does the size of a red supergiant like Betelgeuse compare to our solar system?
-Betelgeuse, a red supergiant, is incredibly large compared to our Sun. If Betelgeuse were to replace the Sun at the center of our solar system, its outer layers would extend well past the orbit of Mars and begin to approach the orbit of Jupiter. This immense size is a defining characteristic of red supergiants and contributes to their classification as 'weird stars'.
What is a luminous blue variable and how does it differ from a typical supernova?
-A luminous blue variable (LBV) is a type of star that is extremely bright, hot, and variable in its output. Unlike typical supernovae, which represent the end of a star's life in a single, dramatic explosion, LBVs undergo eruptions where they expel a significant amount of their mass. These eruptions can mimic the brightness of a supernova but the star remains intact afterward.
What is a neutron star and how does it form?
-A neutron star is the collapsed core of a massive star that has undergone a supernova explosion. It is incredibly dense and supported by neutron degeneracy pressure, a quantum mechanical principle. Neutron stars are the remnants of stars that were massive enough to collapse under gravity but not so massive as to form a black hole.
What is a gamma-ray burst and how are they detected?
-A gamma-ray burst (GRB) is an extremely energetic explosion that occurs in distant galaxies. It is thought to be caused by the collapse of a massive star into a black hole, which produces jets of high-energy particles. GRBs are detected using satellites and space telescopes designed to monitor the sky for these high-energy flashes. The Swift spacecraft, for example, is dedicated to detecting and studying GRBs.
How do astronomers determine the temperature of red supergiants?
-Astronomers determine the temperature of red supergiants by analyzing their spectra, particularly the absorption lines caused by molecules like titanium oxide. The strength and depth of these absorption lines can indicate the temperature of the star's atmosphere. The cooler the star, the stronger these lines appear in the spectrum.
What is a Thorne-Żytkow object and how is it formed?
-A Thorne-Żytkow object is a theoretical type of star formed when a neutron star merges with a red supergiant. The neutron star spirals into the red supergiant, replacing its core, and creating a star with a neutron star core surrounded by the red supergiant's envelope. These objects are predicted to have unique chemical signatures due to the extreme conditions at the core.
What is the significance of the discovery of a Thorne-Żytkow object candidate?
-The discovery of a Thorne-Żytkow object candidate is significant because it would provide empirical evidence for a theoretical model of a star that was proposed in the 1970s. It would also offer new insights into the behavior of binary star systems and the processes that occur within the cores of massive stars.
How do astronomers share and collaborate on new discoveries?
-Astronomers often share their findings through scientific publications, online forums, and by directly communicating with colleagues. They may post preliminary results or analyses, and there is an encouragement for collaboration rather than competition. Data and observations are often shared upon request to facilitate meta-analysis and further research.
What is the expected behavior of a supernova in our own galaxy?
-A supernova in our galaxy would initially cause some panic due to the sudden appearance of a bright object in the sky. However, once identified as a supernova, it would become a subject of great interest and curiosity. The supernova would be visible for a couple of weeks, gradually increasing in brightness before fading away. It would provide astronomers with a wealth of data to study the star's life cycle and the elements produced during its explosion.
Outlines
🌟 Introduction to Perimeter Institute and Dr. Emily Levesque
The video begins with a warm welcome to the Perimeter Institute's public lecture series in Waterloo, Ontario, Canada. Greg Dick, the director of educational outreach, introduces the event, explaining the lecture and Q&A format. Dr. Emily Levesque, an assistant professor of astronomy at the University of Washington, is introduced as the guest speaker. She is recognized for her research in massive stellar astrophysics and her accolades, including the Alfred P. Sloan fellowship. The lecture aims to discuss peculiar stellar phenomena and their significance in understanding the universe's history and extremes.
📈 The Hertzsprung-Russell Diagram and Stellar Evolution
Dr. Levesque delves into the Hertzsprung-Russell (HR) diagram, a fundamental tool in astronomy for plotting stars' temperatures and brightness. She explains how this diagram illustrates the life cycle of stars, from birth to death. The focus is on massive stars, particularly supergiants, which are highlighted on the HR diagram. Examples of such stars include Spica, a blue supergiant, and Polaris, a yellow supergiant. The lecture also touches on the end stages of massive stars' lives, as they transition from fusing hydrogen to helium and eventually become red supergiants, exemplified by Betelgeuse.
🔍 Understanding Red Supergiants and Their Spectra
The talk continues with an in-depth look at red supergiants, which are massive stars with extremely low temperatures. The speaker describes her first research project, which involved measuring the temperatures of red supergiants more accurately using titanium oxide absorption in their spectra. This led to a better understanding of these stars' positions on the HR diagram and a resolution of a long-standing discrepancy between observed temperatures and theoretical predictions.
🌌 The Discovery of the Largest Stars in the Universe
While re-measuring the temperatures of red supergiants, an accidental but significant discovery was made: the largest stars ever observed, including KY Cygni, which surpasses even Betelgeuse in size. This discovery was made possible by applying the Stefan-Boltzmann law to derive the stars' radii from their luminosities and temperatures. The newfound understanding of red supergiants' sizes and their placement on the HR diagram was a significant achievement in astrophysics.
💥 Supernovae: The Violent Deaths of Massive Stars
The lecture moves on to discuss supernovae, the explosive deaths of massive stars. Dr. Levesque explains the process leading up to a supernova, starting with the fusion of hydrogen into helium and progressing through the fusion of heavier elements until the star attempts to fuse iron, which cannot be fused without absorbing energy. The core collapse that follows results in a supernova. Historical and modern examples of supernovae are presented, including the Crab Nebula, which resulted from a supernova in 1054.
✨ Neutron Stars, Pulsars, and the Formation of Black Holes
Following the supernova, a neutron star or a black hole may form. Neutron stars are incredibly dense and supported by neutron degeneracy pressure. Some neutron stars, known as pulsars, emit beams of light as they rotate, creating a flashing effect. Black holes, an even more extreme outcome of massive star death, are also discussed. The lecture touches on gamma-ray bursts, a phenomenon associated with the formation of black holes, which are detected as brief, intense flashes of gamma rays from distant galaxies.
🚀 The Swift Spacecraft and the Detection of Gamma-Ray Bursts
The talk introduces the Swift spacecraft, designed to detect gamma-ray bursts. When a burst is detected, Swift triggers a rapid response from astronomers on Earth, who use ground-based telescopes to observe the event. This process is part of time-domain astronomy, which focuses on studying transient phenomena. The contrast between the Hollywood depiction of such discoveries and the actual, more meticulous scientific process is highlighted.
🌌 Gravitational Waves and Multi-Messenger Astronomy
The lecture concludes with a discussion on gravitational waves, ripples in space-time caused by the acceleration of massive objects. The detection of gravitational waves from colliding neutron stars, along with the accompanying gamma-ray burst and electromagnetic signals, marks a new era in multi-messenger astronomy. This discovery confirmed that gravitational waves and light can be emitted from the same cosmic event, providing a wealth of information about the universe.
🔬 The Thorne-Żytkow Object: A Neutron Star at the Heart of a Red Supergiant
Dr. Levesque describes the theoretical and now potentially observed Thorne-Żytkow object, a star with a neutron star core surrounded by the envelope of a red supergiant. These objects are predicted to have unique chemical signatures, and one candidate has been found based on its spectral lines indicating high levels of molybdenum, lithium, and rubidium. The discovery of such an object would have profound implications for our understanding of stellar interiors and the production of heavy elements.
🤔 Questions and Curiosity Drive Astronomy Forward
The lecture ends with a Q&A session where various topics are discussed, including the sharing of raw data in astronomy, the speed of gravitational waves compared to light, the lifecycle of stars like Polaris, and the personal journey of Dr. Levesque towards becoming an astronomer. The enthusiasm for astronomy is evident, and the importance of curiosity in driving scientific discovery is highlighted.
Mindmap
Keywords
💡Perimeter Institute
💡Hertzsprung-Russell Diagram
💡Supergiants
💡Spectral Analysis
💡Red Supergiant
💡Neutron Star
💡Gamma-Ray Bursts
💡Luminous Blue Variable
💡Supernova
💡Time Domain Astronomy
💡Thorne-Żytkow Object
Highlights
Dr. Emily Levesque discusses the strangest stellar phenomena in the universe, explaining how these unusual stars serve as a common thread for exploring the universe's history, evolution, and extremes.
The Hertzsprung-Russell diagram is used to plot normal stars and understand their evolution, with our Sun being a typical, unremarkable star.
Supergiant stars, which are at least eight times the mass of our Sun, evolve from blue supergiants to red supergiants, changing their position on the HR diagram.
Spica, a blue supergiant in the constellation Virgo, is used as an example of the first phase in the life of a massive star, fusing hydrogen into helium at extremely high temperatures.
Polaris, the North Star, is a yellow supergiant and a rare type of massive star with a short lifetime, surprising astronomers with its existence.
Betelgeuse, a red supergiant in the constellation Orion, is so large that if it replaced our Sun, it would extend past Mars' orbit.
Red supergiants have dramatic surface activity, with their entire surface boiling and roiling, unlike the small granules seen on the surface of our Sun.
Evolutionary tracks on the HR diagram represent the path a star takes during its lifetime, providing insights into stellar physics and theories of star evolution.
Dr. Levesque's research project at Kitt Peak National Observatory led to the accidental discovery of the largest known stars in the universe, including KY Cygni.
Supernovae are the dramatic deaths of massive stars, resulting from the core collapsing and causing an explosion that can outshine entire galaxies.
Luminous blue variables like the star that produced supernova 2009 IP are incredibly bright, undergo eruptions, and are not well understood, challenging traditional supernova theories.
Neutron stars, which can form from the core collapse of a massive star, are supported by neutron degeneracy pressure and are incredibly dense, with a teaspoonful weighing more than a mountain.
Pulsars are a type of neutron star that emit light from their magnetic poles, detected as a regular pulsing effect and first discovered by Jocelyn Bell Burnell.
Gamma-ray bursts are the most violent deaths of stars, occurring when a massive star's core collapses into a black hole, producing high-energy jets that emit gamma rays.
The discovery of gamma-ray bursts was accidental, originally detected by satellites monitoring for nuclear tests, and has led to dedicated telescopes like the Swift spacecraft for rapid detection.
Time domain astronomy focuses on studying fleeting and quick astronomical events, such as gamma-ray bursts, which require rapid response and analysis.
Gravitational waves were first detected in 2016 from colliding black holes, and later from colliding neutron stars, marking a new era in multi-messenger astronomy.
The detection of gravitational waves from colliding neutron stars on August 17, 2017, was accompanied by a flash of gamma rays and light across the electromagnetic spectrum, confirming theoretical predictions.
Thorne-Żytkow objects are theoretical stars with a neutron star core surrounded by a red supergiant envelope, and Dr. Levesque's team may have discovered the first candidate for such an object.
The potential existence of Thorne-Żytkow objects would have profound implications for understanding stellar interiors, binary star behavior, and element production in stars.
Transcripts
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