Supermassive black holes: most powerful objects in the universe | Martin Gaskell | TEDxMeritAcademy
TLDRThis script narrates the historical journey of black holes' discovery, from Reverend John Mitchell's 1783 hypothesis to modern observations confirming supermassive black holes at galaxy centers. It explains how these cosmic phenomena, once thought to be invisible due to their gravitational pull, are now understood to emit intense light due to gas spiraling into them. The script also illustrates the role of accretion disks and viscosity in fueling and illuminating these celestial bodies, making them the universe's most potent energy sources.
Takeaways
- 🌌 The concept of black holes was first proposed by Reverend John Mitchell in 1783, suggesting objects with gravity so strong that not even light could escape them.
- 📜 Mitchell's theory was based on Isaac Newton's gravity theory, which is less accurate under extreme gravitational conditions.
- 🔬 In 1958, David Finklestein used Einstein's general theory of relativity to further support the existence of black holes and their detectability through gravitational influence.
- 👨🚀 William Herschel's observations in the 1780s unknowingly captured light from gas spiraling into a supermassive black hole at the center of distant galaxies.
- 🌌 Astronomers in the 20th century found evidence of active galactic nuclei, such as in NGC 55:48, where gas was moving at speeds approaching the speed of light.
- 🌌 The energy output from active galactic nuclei, like in Cen A, was calculated to be equivalent to 100 million supernovae, suggesting the presence of supermassive black holes.
- 🌐 The discovery of 3C 273, a distant active galactic nucleus, further confirmed the existence of supermassive black holes powering these bright phenomena.
- 🌌 Research has shown that every massive galaxy, including our Milky Way, has a supermassive black hole at its center.
- 🌀 The orbits of stars near the Milky Way's center, particularly the motion of star S2, indicate the presence of a 4 million solar mass black hole.
- 🔥 Black holes are not vacuum cleaners of the cosmos; instead, they accrete matter through the formation of an accretion disk due to viscosity and friction.
- ✨ The heat generated by the friction and viscosity within the accretion disk is responsible for the intense light emitted by objects like 3C 273, making them the most powerful energy sources in the universe.
Q & A
Who was the first person to postulate the existence of black holes?
-The Reverend John Mitchell, a British scientist and rector of a church in Fawn Hill, Yorkshire, was the first person to postulate the existence of black holes in his 1783 paper to the Royal Society in London.
What theory did John Mitchell use to argue for the existence of black holes?
-John Mitchell used Isaac Newton's theory of gravity to argue for the existence of black holes, although this theory is not entirely accurate when dealing with very strong gravity.
How did David Finkelstein contribute to the understanding of black holes?
-David Finkelstein used Albert Einstein's general theory of relativity to prove that black holes could indeed exist, demonstrating that their gravitational influence could be detected even though light cannot escape from them.
What role did William Herschel play in the early study of what we now recognize as galaxies?
-William Herschel, a composer and friend of John Mitchell, used large homemade backyard telescopes to discover objects that we now recognize as distant galaxies, including the detection of bright points of light in their nuclei.
What did astronomers at Lick Observatory discover about the nucleus of NGC 55:48?
-Astronomers at Lick Observatory discovered that the nucleus of NGC 55:48 contained hot, glowing gas that was moving very quickly, even up to a few percent of the speed of light.
What was the significance of the discovery of radio emissions from galaxies like Cen A?
-The discovery of powerful radio emissions from galaxies like Cen A led to the calculation by Jeffrey and Margaret Burbidge that the energy output from an active galactic nucleus was equivalent to 100 million supernova explosions, indicating the presence of a supermassive black hole.
What is the role of viscosity in the accretion disk around a black hole?
-Viscosity in the accretion disk, provided by tangled magnetic fields, causes the gas to spiral inward towards the black hole. It also generates heat through friction, similar to rubbing your hands together, which heats the gas to the point of emitting brilliant light.
How do supermassive black holes produce energy?
-Supermassive black holes produce energy as matter falls into them from great distances, converting gravitational potential energy into kinetic energy. The acceleration of this matter by the black hole's gravity results in the release of enormous amounts of energy.
What evidence supports the existence of a supermassive black hole at the center of our Milky Way galaxy?
-Observations of stars orbiting around an invisible point with a mass of over 4 million times that of the Sun, without any visible celestial body, provide the clearest proof of the existence of a supermassive black hole at the center of the Milky Way.
Why are black holes not considered to 'suck' in matter around them?
-Black holes are not considered to 'suck' in matter because, except when extremely close, their gravity is similar to any other gravity in the universe. Matter needs to be on a direct collision course to fall into a black hole, and even then, the black hole's small size means most matter will miss it.
What is the analogy used to explain how a supermassive black hole produces energy?
-The analogy of a hydroelectric dam is used to explain how a supermassive black hole produces energy. Just as water falling over a dam converts gravitational potential energy into kinetic energy, which drives turbines to generate electricity, matter falling into a black hole from vast distances is accelerated by the black hole's gravity, releasing large amounts of energy.
Outlines
🌌 The Birth of Black Hole Theory
In 1783, Reverend John Mitchell hypothesized the existence of celestial bodies with gravity so strong that not even light could escape, which we now refer to as black holes. He based his theory on Isaac Newton's theory of gravity. Later, in 1958, David Finkelstein utilized Einstein's general theory of relativity to provide further proof of black holes' existence. Mitchell's friend, William Herschel, observed bright points of light in the centers of galaxies, which we now understand to be supermassive black holes. Astronomers in the 20th century discovered that these bright nuclei contained hot, fast-moving gas spiraling into a black hole, providing indirect evidence of their existence.
🌠 The Energy of Supermassive Black Holes
The script explains the concept of energy production in supermassive black holes by comparing it to a hydroelectric dam. As matter falls into a black hole, it gains speed due to the immense gravitational pull, converting gravitational potential energy into kinetic energy. This process is analogous to water falling in a dam, which drives turbines to generate electricity. The script also discusses the discovery of distant active galactic nuclei, such as 3C273, which emit light brighter than entire galaxies, leading to the realization that these must be powered by supermassive black holes. The presence of supermassive black holes in nearby galaxies, including our own Milky Way, is supported by research showing stars orbiting around regions of concentrated mass that are invisible to the naked eye.
💫 The Dynamics of Black Holes and Accretion Disks
The script clarifies that black holes do not 'suck' in matter but rather matter falls into them due to gravity. It describes the process of gas falling towards a black hole and forming an accretion disk due to viscosity, similar to how smoke from fires swirls together. The inner parts of the accretion disk move faster than the outer parts, causing friction and heat, which in turn heats the gas to white-hot temperatures, emitting the brilliant light observed from active galactic nuclei. This process is how the black holes, initially postulated by John Mitchell, have become known as the most powerful energy sources in the universe.
🔥 The Viscosity and Friction in Accretion Disks
The final paragraph delves into the properties of viscosity and friction within accretion disks around black holes. It uses a demonstration with honey to illustrate how viscosity can slow down the motion of material, causing it to spiral inward. The script also explains that the differential motion of gas in the accretion disk, where the inner gas orbits faster than the outer gas, generates heat due to friction, similar to rubbing hands together. This heating effect is responsible for the intense luminosity of objects like 3C273, confirming the existence of supermassive black holes and their role as the universe's most potent energy sources.
Mindmap
Keywords
💡Black Hole
💡General Theory of Relativity
💡Supermassive Black Hole
💡Accretion Disk
💡Active Galactic Nucleus
💡Gravitational Potential Energy
💡Viscosity
💡Infrared Cameras
💡Nucleus of a Galaxy
💡Star Orbits
💡Differential Motion
Highlights
In 1783, Reverend John Mitchell was the first to postulate the existence of black holes based on Newton's theory of gravity.
David Finkelstein used Einstein's general theory of relativity in 1958 to prove the existence of black holes despite light's inability to escape.
William Herschel's observations in the 1780s unknowingly detected light from gas spiraling into a supermassive black hole.
Astronomers at Lick Observatory in the early 20th century found indications of high-velocity gas in the nuclei of galaxies.
Jeffrey and Margaret Burbidge calculated the immense energy output of active galactic nuclei, equivalent to 100 million supernovae.
Fred Hoyle and Edwin Fowler proposed in 1963 that supermassive black holes were the only plausible source of such energy in active galactic nuclei.
The discovery of the object 3C273 as an active galactic nucleus with a brightness exceeding entire galaxies was a significant milestone in astronomy.
Donald Lyndon Bell argued in 1969 that if distant galaxies like 3C273 were powered by supermassive black holes, then nearby galaxies must also contain them.
Astronomical research has confirmed that every massive galaxy, including our Milky Way, has a supermassive black hole at its center.
Observations of stars orbiting at high speeds around an invisible point in the Milky Way's center provide evidence for a supermassive black hole.
Black holes are not cosmic vacuum cleaners; they do not 'suck' in matter but rather matter falls into them due to gravity.
Gas falling into a black hole forms an accretion disk due to viscosity, spiraling and heating up due to friction.
The heating of gas in the accretion disk due to viscosity and friction is responsible for the brilliant light emitted by active galactic nuclei.
Black holes, once postulated as dark stars by John Mitchell, are now recognized as the most powerful sources of energy in the universe.
The concept of energy production by supermassive black holes is analogous to hydroelectric dams, where gravitational potential energy is converted into other forms of energy.
The time-lapse movie of the European Southern Observatory's Very Large Telescope captures the motion of stars orbiting the supermassive black hole at the Milky Way's center.
Transcripts
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