27.2 Supermassive Black Holes: What Quasars Really Are
3 min read•june 12, 2024
Supermassive black holes lurk at the hearts of galaxies, powering the brightest objects in the universe: quasars. These cosmic beacons shine with the intensity of billions of stars, fueled by matter spiraling into the black hole's immense gravitational pull.
Quasars reveal the early universe, their light traveling billions of years to reach us. Their extreme brightness, rapid variability, and high-energy emissions stem from the incredible forces at play near the black hole's , where physics takes a wild ride.
Supermassive Black Holes and Quasars
Key features of quasars
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- Extremely bright, point-like sources of light
- Luminosities can exceed that of an entire galaxy (Milky Way)
- Appear star-like in telescopic images despite vast distances
- High redshifts indicate they are very distant objects
- Implies quasars are some of the most distant objects in the universe (billions of light-years away)
- Light from quasars originates from the early universe
- Broad emission lines in their spectra suggest presence of hot, fast-moving gas
- Gas moves at speeds up to 10% the speed of light
- Indicative of high-energy processes occurring near the
- Rapid variability in brightness on timescales of days to weeks
- Suggests the energy-producing region is very compact (solar system-sized)
- Rapid changes not possible if emission region were galactic scales
Supermassive black holes in quasars
- Supermassive black holes reside at the centers of galaxies
- Can have masses ranging from millions to billions of solar masses ( in Milky Way)
- Surrounded by an , beyond which nothing can escape
- Matter falling towards the black hole forms an
- Gravitational energy converted to heat and radiation as matter spirals inward
- Accretion disk can reach temperatures of millions of degrees, glowing brightly
- of high-energy particles may be launched perpendicular to accretion disk
- Powered by twisting of magnetic fields near the black hole
- Can extend for thousands of light-years beyond the galaxy ()
- Combination of luminous accretion disk and jets produces enormous energy output of quasars and active galactic nuclei
Energy generation in quasars
- Matter is drawn towards the
- Can come from nearby stars, gas clouds, or even entire galaxies
- As matter falls towards black hole, it forms an accretion disk
- Gravitational potential energy converted to kinetic energy and heat
- Friction and viscosity in disk cause it to heat up to millions of ℃
- Hot accretion disk radiates energy across the electromagnetic spectrum
- Produces thermal radiation from infrared to X-rays
- Also generates non-thermal radiation through synchrotron and inverse Compton processes
- Some infalling matter may be ejected in the form of jets
- Powered by twisting of magnetic fields near black hole
- Jets can accelerate particles to near the speed of light ()
- Interaction between jet particles and surrounding matter produces additional radiation
- Total energy output of a can be watts or more
- Equivalent to luminosity of hundreds of average galaxies ()
- Most of this energy released in a very small region around the ()
- Limited by the , balancing radiation pressure and gravity
Observational effects
- can distort and magnify light from distant quasars
- When a quasar's jet is aimed directly at Earth, it appears as a , exhibiting extreme variability and polarization
Key Terms to Review (27)
Accretion Disk: An accretion disk is a rotating disk of dense, accreting material surrounding a central object, such as a star, black hole, or neutron star. It is formed by the gravitational attraction and conservation of angular momentum of material falling towards the central object.
Active Galactic Nucleus: An active galactic nucleus (AGN) is the bright, central region of a galaxy that is powered by a supermassive black hole actively accreting matter. AGNs are some of the most luminous and energetic objects in the universe, emitting intense radiation across the electromagnetic spectrum.
Andromeda: Andromeda is the nearest major galaxy to the Milky Way, located approximately 2.5 million light-years away. It is a spiral galaxy similar in structure and size to our own Milky Way galaxy, and it is a prominent feature in the northern night sky, visible to the naked eye under clear conditions.
Andromeda galaxy: The Andromeda Galaxy, also known as M31, is the closest spiral galaxy to the Milky Way and is on a collision course with it. It is approximately 2.537 million light-years from Earth and is the largest galaxy in the Local Group.
Blazar: A blazar is a type of active galactic nucleus (AGN) where a supermassive black hole at the center of a galaxy is powering a relativistic jet of plasma that is pointed directly towards the Earth. Blazars are among the most luminous and energetic objects in the known universe.
Eddington Luminosity: Eddington luminosity is the maximum luminosity that a star can achieve before the outward radiation pressure from the star's core exceeds the inward gravitational force, causing the star to become unstable and potentially expel material. This concept is particularly relevant in the context of supermassive black holes and the nature of quasars.
Emission Line: An emission line is a specific wavelength of light that is emitted by an atom or molecule when it transitions from a higher energy state to a lower energy state. Emission lines are a crucial feature in the study of supermassive black holes and the nature of quasars.
Event horizon: The event horizon is the boundary surrounding a black hole beyond which nothing, not even light, can escape. It marks the point at which the gravitational pull becomes so strong that escape velocity exceeds the speed of light.
Event Horizon: The event horizon is the boundary around a black hole, beyond which nothing, not even light, can escape the immense gravitational pull of the black hole. It marks the point of no return, where the gravitational forces become so strong that they overcome all other forces, including the speed of light.
Gravitational Lensing: Gravitational lensing is the bending of light by the gravitational field of a massive object, such as a galaxy or a black hole. This phenomenon occurs because the presence of matter distorts the fabric of spacetime, causing light to follow a curved path as it travels through this warped spacetime.
Infalling material: Infalling material refers to matter that is being pulled towards and ultimately accreted by a massive object, such as a supermassive black hole. This process often results in the emission of significant amounts of energy.
Inverse Compton Scattering: Inverse Compton scattering is a process in which a high-energy photon interacts with a low-energy electron, causing the electron to gain energy and the photon to lose energy. This phenomenon is a key mechanism behind the production of high-energy radiation in various astrophysical environments, including quasars.
Jets: Jets are high-speed streams of ionized matter ejected from the regions around supermassive black holes. They travel at nearly the speed of light and can extend across thousands or even millions of light-years.
M87 jet: The M87 jet is a prominent jet of plasma emanating from the supermassive black hole at the center of the elliptical galaxy Messier 87 (M87). This jet is one of the most studied astrophysical jets and provides valuable insights into the processes occurring around supermassive black holes, which are believed to power the energetic phenomena observed in quasars.
Quasar: A quasar is an extremely luminous active galactic nucleus, powered by a supermassive black hole at its center. Quasars emit enormous amounts of energy, often outshining the entire galaxy in which they reside.
Quasar: A quasar is an extremely luminous active galactic nucleus (AGN) powered by a supermassive black hole at the center of a distant galaxy. Quasars are among the most energetic and distant objects in the observable universe, emitting vast amounts of electromagnetic radiation across the spectrum, from radio waves to X-rays and gamma rays.
Quiescent: Quiescent describes a state in which an astronomical object, such as a galaxy or black hole, is inactive or exhibits minimal activity. It contrasts with active states where significant energy emission and other dynamic phenomena occur.
Redshift: Redshift is the phenomenon where the wavelength of light emitted from a distant object is shifted towards longer, or redder, wavelengths compared to the original wavelength. This shift in the observed wavelength is caused by the relative motion between the object and the observer, as well as the expansion of the universe.
Relativistic Jet: A relativistic jet is a powerful, highly collimated beam of plasma that is ejected from the vicinity of a supermassive black hole at a significant fraction of the speed of light. These jets are associated with active galactic nuclei, such as quasars, and are a key feature in understanding the nature of these energetic phenomena.
Sagittarius A: Sagittarius A* (Sgr A*) is a supermassive black hole located at the center of the Milky Way Galaxy. It is approximately 4 million times the mass of the Sun and plays a crucial role in the dynamics of our galaxy.
Sagittarius A*: Sagittarius A* (Sgr A*) is a supermassive black hole located at the center of the Milky Way galaxy. It is a key feature in understanding the architecture, dynamics, and evolution of our galaxy, as well as the nature of black holes and their role in the universe.
Schmidt: Schmidt telescopes, also known as Schmidt cameras, are wide-field telescopes that use a spherical primary mirror and a corrector plate to reduce spherical aberration. They are particularly useful for astronomical surveys and capturing images of large areas of the sky.
Schwarzschild Radius: The Schwarzschild radius is a critical distance around a massive object, such as a black hole, within which the object's gravitational pull is so strong that nothing, not even light, can escape. It represents the boundary at which the object's escape velocity equals the speed of light.
Supermassive black hole: Supermassive black holes are extremely dense regions at the centers of galaxies with masses ranging from millions to billions of times that of the Sun. They exert immense gravitational forces that can influence entire galaxies.
Supermassive Black Hole: A supermassive black hole is an extremely dense and massive black hole at the center of most, if not all, galaxies, including our own Milky Way. These black holes have masses millions to billions of times greater than that of the Sun and exert a powerful gravitational influence on the surrounding galaxy.
Synchrotron radiation: Synchrotron radiation is electromagnetic radiation emitted when charged particles travel at near-light speeds in curved paths. This phenomenon is often observed in the magnetospheres of giant planets due to their strong magnetic fields.
Synchrotron Radiation: Synchrotron radiation is a type of electromagnetic radiation emitted by charged particles, typically electrons, when they are accelerated in a curved path by a strong magnetic field. This radiation is observed in various astrophysical phenomena, including gamma-ray bursts, supermassive black holes in quasars, and active galactic nuclei.