8.3 Quasars and Their Host Galaxies
2 min read•august 9, 2024
Quasars are super bright centers of distant galaxies, powered by massive black holes gobbling up matter. They're so bright, they outshine entire galaxies, and their light travels billions of years to reach us.
Studying quasars helps us understand how galaxies grow and change over time. Their light also acts like a cosmic flashlight, revealing clues about the stuff between galaxies and the early universe.
Quasar Properties
Defining Characteristics of Quasars
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Top images from around the web for Defining Characteristics of Quasars
Frontiers | Active Galactic Nuclei at All Wavelengths and from All Angles View original
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- Quasars represent extremely luminous and active galactic nuclei found in distant galaxies
- indicates quasars are moving away from Earth at high velocities, often exceeding 0.1c
- of quasars surpasses that of entire galaxies, typically ranging from to ergs per second
- Spectral energy distribution of quasars spans a wide range of wavelengths, from radio to X-rays
- Emission lines in spectra reveal information about the physical conditions and chemical composition of the surrounding gas
Variability and Energy Output
- in quasar brightness occurs on timescales ranging from hours to years
- Rapid variations in brightness constrain the size of the emitting region to be relatively small
- of quasars primarily originates from the accretion of matter onto a supermassive black hole
- Quasars emit radiation across the electromagnetic spectrum, with peaks in the ultraviolet and X-ray regions
- of relativistic particles often accompany quasars, contributing to their radio emission
Quasar Environment
Host Galaxy Interactions
- of a quasar typically appears as a faint, diffuse glow surrounding the bright central source
- between quasars and their host galaxies suggests a symbiotic relationship in their growth and development
- Quasar activity can significantly impact the evolution of the host galaxy through (outflows, radiation pressure)
- and interactions with other galaxies may trigger quasar activity by funneling gas towards the central black hole
Intergalactic Medium and Quasar Absorption Lines
- consists of numerous absorption lines in quasar spectra caused by intervening neutral hydrogen in the
- Analysis of the Lyman-alpha forest provides insights into the distribution and evolution of matter between galaxies
- allow astronomers to study the chemical composition and physical conditions of gas in the early universe
- in quasar spectra reveal the presence of heavy elements in the intergalactic medium, tracing
Key Terms to Review (22)
Active Galactic Nucleus: An active galactic nucleus (AGN) is a region at the center of some galaxies that emits an extraordinary amount of energy, often outshining the entire galaxy. This immense energy output is primarily caused by accretion of material onto a supermassive black hole, which generates intense radiation across various wavelengths, including visible light, X-rays, and radio waves. AGNs are crucial for understanding galaxy formation and evolution, as they can influence their host galaxies' properties through feedback mechanisms.
Co-evolution: Co-evolution is the process by which two or more species influence each other's evolutionary development through reciprocal adaptations. In the context of quasars and their host galaxies, co-evolution describes how the growth of a supermassive black hole at the center of a galaxy can impact the galaxy's structure and star formation rates, while simultaneously, the properties of the galaxy can influence the black hole's growth and activity.
Cosmic Chemical Evolution: Cosmic chemical evolution refers to the process through which the chemical elements in the universe are formed and distributed over time, significantly influenced by stellar processes, supernovae, and the dynamics of galaxies. This evolution plays a crucial role in understanding the formation of stars, planets, and the overall chemical makeup of the universe, linking the lifecycle of stars to the cosmic abundance of elements.
Donald Lynden-Bell: Donald Lynden-Bell is a prominent astrophysicist known for his significant contributions to the understanding of quasars and their host galaxies. His work has greatly influenced the study of active galactic nuclei, particularly through the development of models that explain the dynamics and evolution of these energetic astronomical objects. Lynden-Bell's research helps bridge the connection between quasars and their surrounding environments, revealing insights into galaxy formation and evolution.
Doppler Effect: The Doppler Effect is the change in frequency or wavelength of a wave in relation to an observer moving relative to the source of the wave. This phenomenon is essential for understanding how we perceive the motion of celestial objects, allowing astronomers to determine their velocities and distances through shifts in the wavelengths of light they emit or absorb.
Energy output: Energy output refers to the total amount of energy produced by an astronomical object, such as a quasar, over a specific period of time. This concept is crucial in understanding the luminosity of quasars, which are among the brightest and most energetic objects in the universe, indicating the immense power generated by their supermassive black holes as they consume surrounding matter.
Feedback mechanisms: Feedback mechanisms are processes that help systems maintain stability or drive change by using outputs to influence future behavior. These mechanisms can be positive, amplifying effects that lead to growth or acceleration, or negative, counteracting changes to restore balance. In the context of astrophysics, these mechanisms play a crucial role in the life cycle of stars and galaxies, influencing processes like star formation and the dynamics of supermassive black holes.
Gravitational Lensing: Gravitational lensing is the bending of light from distant objects due to the gravitational field of a massive object, such as a galaxy or cluster, located between the observer and the light source. This phenomenon allows astronomers to study the distribution of mass in the universe, providing insights into various cosmic structures and the nature of dark matter.
Host galaxy: A host galaxy is the galaxy in which a celestial object, such as a quasar or active galactic nucleus, resides. The characteristics of the host galaxy can influence the formation and behavior of these objects, revealing important information about the relationship between galaxies and their active nuclei.
Intergalactic medium: The intergalactic medium is the matter that exists in the space between galaxies, primarily composed of hot ionized gas, cold gas clouds, cosmic dust, and dark matter. It plays a critical role in the universe's structure and evolution, acting as the reservoir for gas that can fuel star formation in galaxies and influencing the dynamics of galaxy interactions.
Jets: Jets are highly collimated streams of gas and plasma that are ejected from the regions around young stars and supermassive black holes. They are formed through the interaction of magnetic fields and accretion processes, playing a crucial role in transporting energy and material away from these cosmic objects. Jets can affect their surroundings significantly, impacting star formation in nearby regions and influencing the dynamics of host galaxies.
Luminosity: Luminosity is the total amount of energy emitted by a star, galaxy, or other astronomical object per unit time, typically measured in watts. This fundamental property allows for the comparison of different celestial objects and plays a crucial role in understanding their behavior, evolution, and classification. By knowing the luminosity, astronomers can infer distances and the physical characteristics of these objects, which is essential for grasping the dynamics of the universe.
Lyman-alpha forest: The Lyman-alpha forest refers to a series of absorption lines in the spectra of distant quasars caused by intervening hydrogen gas in the intergalactic medium. These absorption lines occur at the wavelength of the Lyman-alpha transition, which is a specific electromagnetic radiation emitted by hydrogen atoms. The presence of the Lyman-alpha forest allows astronomers to study the distribution and evolution of hydrogen in the universe, revealing important information about the structure of the cosmos and the processes involved in galaxy formation and evolution.
Martin Schmidt: Martin Schmidt was an American astronomer known for his pioneering work in the discovery of quasars, which are extremely bright and distant objects powered by supermassive black holes. His research significantly advanced our understanding of the early universe and the nature of these enigmatic objects, particularly in relation to their host galaxies. Schmidt's identification of the first quasar in 1963 marked a turning point in astrophysics, as it opened up new avenues for exploring cosmic evolution and the formation of galaxies.
Mergers: Mergers refer to the process where two or more galaxies combine to form a single, larger galaxy. This process is a key mechanism in galaxy evolution and has significant implications for the development of quasars, the interaction of galaxies, and the broader cosmic structure.
Metal Absorption Lines: Metal absorption lines are specific wavelengths in a spectrum where light from a celestial object is absorbed by metal ions, resulting in dark lines that indicate the presence of these elements. These lines provide vital information about the composition, temperature, density, and motion of distant astronomical objects, particularly in the context of quasars and their host galaxies, allowing astronomers to analyze the physical conditions and chemical makeup of the universe.
Quasar: A quasar is an extremely luminous active galactic nucleus powered by a supermassive black hole at its center, which emits enormous amounts of energy as matter falls into it. These cosmic phenomena are significant for understanding the early universe and the formation of galaxies, as they serve as indicators of cosmic evolution due to their high redshifts and distant nature.
Quasar Absorption Lines: Quasar absorption lines are dark features in the spectra of quasars, caused by the absorption of specific wavelengths of light by intervening gas clouds between the quasar and the observer. These lines provide critical information about the composition, temperature, density, and velocity of the absorbing gas, which is often located in the host galaxy or intergalactic medium. By analyzing these absorption lines, astronomers can better understand the physical conditions surrounding quasars and their host galaxies.
Redshift: Redshift refers to the phenomenon where light from an object in space is shifted towards longer wavelengths, making it appear more red. This effect is primarily observed in astronomical objects moving away from us, allowing scientists to measure the velocity and distance of these objects, and providing crucial insights into the expansion of the universe and the nature of cosmic phenomena.
Spectroscopy: Spectroscopy is the study of the interaction between light and matter, allowing scientists to analyze the composition, structure, and physical properties of astronomical objects. This technique reveals information about temperature, density, mass, luminosity, and chemical composition by examining the spectrum of light emitted, absorbed, or scattered by materials.
Supermassive black hole theory: Supermassive black hole theory proposes the existence of extremely massive black holes, typically millions to billions of times the mass of the Sun, located at the centers of galaxies. These black holes play a crucial role in galaxy formation and evolution, influencing the motion of stars and gas in their vicinity and contributing to phenomena like quasars.
Variability: Variability refers to the changes or fluctuations in the brightness or other observable properties of astronomical objects over time. In the context of quasars and their host galaxies, variability is a crucial characteristic that helps astronomers understand the underlying processes occurring in these distant and energetic systems. The study of variability can reveal information about the size, structure, and activity levels of quasars, as well as the nature of their interactions with surrounding galaxies.