28.2 Galaxy Mergers and Active Galactic Nuclei
3 min read•june 12, 2024
Galaxy interactions shape the cosmic landscape, driving evolution and transformation. Collisions between galaxies cause structural changes, triggering starbursts and reshaping their forms. These cosmic dances redistribute stars, gas, and dust, ultimately determining the final merged galaxy's structure.
Supermassive black holes at galactic centers play a crucial role in this cosmic ballet. Their growth is linked to galaxy evolution, powering active galactic nuclei and influencing their hosts through feedback processes. This interplay between black holes and galaxies has shaped our universe's structure over billions of years.
Galaxy Interactions and Evolution
Galaxy mergers and structural changes
Top images from around the web for Galaxy mergers and structural changes
The Formation and Evolution of Galaxies and Structure in the Universe | Astronomy View original
Is this image relevant?
28.2 Galaxy Mergers and Active Galactic Nuclei | Astronomy View original
Is this image relevant?
28.2 Galaxy Mergers and Active Galactic Nuclei | Astronomy View original
Is this image relevant?
The Formation and Evolution of Galaxies and Structure in the Universe | Astronomy View original
Is this image relevant?
28.2 Galaxy Mergers and Active Galactic Nuclei | Astronomy View original
Is this image relevant?
1 of 3
Top images from around the web for Galaxy mergers and structural changes
The Formation and Evolution of Galaxies and Structure in the Universe | Astronomy View original
Is this image relevant?
28.2 Galaxy Mergers and Active Galactic Nuclei | Astronomy View original
Is this image relevant?
28.2 Galaxy Mergers and Active Galactic Nuclei | Astronomy View original
Is this image relevant?
The Formation and Evolution of Galaxies and Structure in the Universe | Astronomy View original
Is this image relevant?
28.2 Galaxy Mergers and Active Galactic Nuclei | Astronomy View original
Is this image relevant?
1 of 3
- Gravitational interactions between colliding galaxies cause tidal forces that distort and stretch their shapes
- Mergers disrupt the galaxies' original structures such as spiral arms or central bulges
- Stars, gas, and dust are redistributed within the galaxies during a
- Mergers trigger intense starbursts as gravitational disturbances compress gas clouds and initiate star formation
- Starbursts occur in the central regions of merging galaxies or in tidal tails created by the merger
- The final merged galaxy's structure depends on the initial properties of the merging galaxies (mass, gas content, morphology), their relative orientations and trajectories during the merger, and the presence of supermassive black holes in their centers
- , where larger galaxies consume smaller ones, is a common form of galaxy mergers
Influence of supermassive black holes
- Supermassive black holes (SMBHs) with masses of millions to billions of solar masses reside at the centers of most massive galaxies
- The formation and growth of SMBHs are closely linked to the evolution of their host galaxies
- ###active_galactic_nuclei_()_0### are extremely luminous central regions of galaxies powered by onto SMBHs and can outshine their host galaxies (quasars, Seyfert galaxies, radio galaxies)
- SMBHs and AGN influence their host galaxies through where intense radiation heats and ionizes surrounding gas, suppressing star formation
- AGN drive powerful outflows and jets that expel gas from the galaxy, limiting its ability to form new stars ()
- These feedback processes regulate the growth of both the SMBH and the host galaxy over time
- Galaxy mergers trigger AGN activity by providing fresh gas to the central SMBH, leading to enhanced AGN feedback that further influences the galaxy's evolution
- The relation suggests a tight link between the mass of the central SMBH () and the velocity dispersion of stars in the galaxy's bulge (), indicating co-evolution of SMBHs and their host galaxies
AGN Physics and Radiation
- of matter onto the SMBH powers the intense radiation observed in AGN
- , produced by relativistic electrons spiraling in magnetic fields, is a key emission mechanism in AGN jets
- The represents the maximum luminosity an AGN can achieve before radiation pressure overcomes gravity, setting a theoretical limit on black hole growth
Early vs present galaxy interactions
- Galaxy interactions and mergers were more common in the early universe due to higher density and closer proximity of galaxies
- The peak of activity occurred around 8-10 billion years ago (redshifts of ), coinciding with the peak of cosmic star formation history
- Frequent early universe mergers played a crucial role in shaping the galaxies we observe today
- In the present-day universe, galaxy interactions and mergers are less frequent due to lower density and wider separation of galaxies
- Galaxy clusters and groups still provide environments where mergers can happen more frequently in the present day
- The impact of galaxy interactions on galaxy evolution has changed over cosmic time:
- In the early universe, mergers were a primary driver of galaxy growth and morphological transformation, playing a key role in the formation of massive elliptical galaxies and the buildup of galaxy mass
- In the present day, while mergers still occur, other processes such as (internal processes like bar formation and development) and minor mergers are more dominant in shaping galaxies
- Studying the frequency and impact of galaxy interactions across cosmic time provides valuable insights into the formation and evolution of galaxies and the universe as a whole
Key Terms to Review (44)
$M_{BH}- ext{sigma}$ Relation: The $M_{BH}- ext{sigma}$ relation is an empirical correlation between the mass of the supermassive black hole (M$_{BH}$) at the center of a galaxy and the velocity dispersion ($ ext{sigma}$) of the stars in the galaxy's bulge. This relationship suggests a fundamental connection between the growth and evolution of supermassive black holes and the properties of their host galaxies.
Accretion: Accretion is the process by which particles in space stick together to form larger bodies, such as planets and stars. This occurs through collisions and gravitational attraction, leading to the growth of celestial objects.
Accretion: Accretion is the process by which matter, such as dust, gas, or smaller objects, accumulates over time to form larger bodies, like planets, stars, or galaxies. It is a fundamental mechanism underlying the formation and growth of many celestial objects in the universe.
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 nuclei (AGN): Active galactic nuclei (AGN) are extremely energetic regions at the centers of some galaxies, powered by supermassive black holes. They emit vast amounts of radiation across the electromagnetic spectrum, often outshining the rest of the galaxy.
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.
AGN: AGN, or Active Galactic Nuclei, refers to the extremely luminous and energetic centers of some galaxies, powered by supermassive black holes accreting matter. AGN are closely connected to the central regions of galaxies and the processes of galaxy mergers and evolution.
Andromeda-Milky Way Collision: The Andromeda-Milky Way collision refers to the predicted future merger of the Andromeda Galaxy, our closest major galactic neighbor, with the Milky Way Galaxy, which contains our solar system. This cosmic event is expected to occur in several billion years and will have significant implications for the structure and evolution of both galaxies.
Central Bulge: The central bulge, also known as the galactic bulge, is a prominent and densely packed region at the center of a galaxy, typically containing older stars and serving as the gravitational heart of the galaxy. This central component is a key feature in understanding the structure and evolution of galaxies, particularly in the context of galaxy mergers and active galactic nuclei.
Eddington Limit: The Eddington limit, also known as the Eddington luminosity, is the maximum luminosity that a star can reach before the outward radiation pressure overcomes the star's gravitational attraction, leading to the ejection of the star's outer layers. This concept is crucial in understanding the properties and evolution of various astronomical objects, particularly quasars and active galactic nuclei.
Elliptical Galaxy: An elliptical galaxy is a type of galaxy characterized by its smooth, featureless appearance and lack of distinct spiral arms. These galaxies are primarily composed of older, red stars and have a spheroidal or ellipsoidal shape, ranging from nearly circular to highly elongated.
Five-hundred-meter Aperture Spherical radio Telescope (FAST): The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the world's largest filled-aperture radio telescope, located in Guizhou, China. It is used for a variety of astronomical observations including pulsar discovery and interstellar communication research.
Galactic cannibalism: Galactic cannibalism occurs when a larger galaxy merges with and absorbs a smaller galaxy. This process significantly alters the structure and composition of both galaxies involved.
Galactic Cannibalism: Galactic cannibalism refers to the process by which a larger galaxy consumes and assimilates a smaller neighboring galaxy, incorporating its stars, gas, and dust into its own structure. This phenomenon is an important aspect of galaxy evolution and the formation of larger structures in the universe.
Galaxy Cluster: A galaxy cluster is a large group of galaxies bound together by gravity, containing hundreds to thousands of individual galaxies. These massive structures are some of the largest known objects in the universe and are important in the study of galaxy mergers and active galactic nuclei.
Galaxy collisions: Galaxy collisions are events where two or more galaxies pass through each other or merge due to gravitational attraction. These interactions can lead to the formation of new stars and active galactic nuclei.
Galaxy Merger: A galaxy merger is the process in which two or more galaxies collide and combine to form a single, larger galaxy. This event is a crucial aspect of galaxy formation and evolution, as it significantly shapes the structure and properties of galaxies over cosmic time.
Gravitational Interaction: Gravitational interaction is the attractive force between objects with mass that governs the motion and behavior of celestial bodies, from stars and planets to entire galaxies. This fundamental force is central to understanding various astronomical phenomena.
Gravitational Wave Detection: Gravitational wave detection is the process of observing and measuring the ripples in the fabric of spacetime caused by the acceleration of massive objects, such as colliding black holes or neutron stars. These waves carry information about the dynamics of their sources, providing a new way to study the universe.
Jet Formation: Jet formation is the process by which powerful, high-velocity streams of plasma and other matter are ejected from the vicinity of a supermassive black hole, often associated with active galactic nuclei or galaxy mergers. These collimated jets can extend for thousands or even millions of light-years from their source.
M87: M87, also known as Virgo A, is a giant elliptical galaxy located in the Virgo Cluster, approximately 55 million light-years from Earth. It is one of the most massive and luminous galaxies in the local universe and is notable for its active galactic nucleus and powerful jet of high-energy particles.
Mechanical Feedback: Mechanical feedback refers to the process by which the physical or structural changes in a system can influence and modify the driving forces behind those changes. It is a crucial concept in understanding the dynamics of galaxy mergers and active galactic nuclei, where the gravitational and kinetic interactions between components can significantly impact the overall system's evolution.
In the context of galaxy mergers and active galactic nuclei, mechanical feedback describes how the motion and distribution of matter, such as gas, dust, and stars, can create feedback loops that either amplify or dampen the processes driving the system's transformation.
Merger: A merger is the process where two or more galaxies collide and combine to form a single, larger galaxy. This event significantly influences the structure and evolution of the resulting galaxy.
Merger-Driven Evolution: Merger-driven evolution refers to the process by which the merging of galaxies can significantly shape and transform the properties and characteristics of the resulting galaxy. This phenomenon is closely linked to the topics of galaxy mergers and active galactic nuclei, as the gravitational interactions and energy released during these cosmic collisions can have profound impacts on the evolution of the participating galaxies.
Minor Merger: A minor merger is a type of galaxy merger where a smaller galaxy is absorbed by a larger, more dominant galaxy. This process is an important mechanism for the growth and evolution of galaxies over cosmic time.
Multi-Wavelength Observation: Multi-wavelength observation is the practice of studying celestial objects and phenomena by collecting and analyzing data across multiple regions of the electromagnetic spectrum, including radio, infrared, visible, ultraviolet, and X-ray wavelengths. This approach provides a more comprehensive understanding of the physical processes and properties of these cosmic entities.
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.
Radiative Feedback: Radiative feedback is a crucial concept in understanding the dynamics of galaxy mergers and active galactic nuclei. It refers to the process where the energy released from the accretion of material onto a supermassive black hole or the intense star formation in a galaxy merger can interact with and influence the surrounding environment, leading to further changes in the system.
Radio Telescope: A radio telescope is a specialized astronomical instrument designed to detect and analyze radio waves emitted by celestial objects. These telescopes are used to study a wide range of phenomena in the universe, from the structure of galaxies to the formation of stars and planets.
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.
Secular Evolution: Secular evolution refers to the gradual, long-term changes that occur in the structure and properties of galaxies over time, independent of periodic or cyclical variations. This concept is crucial in understanding the dynamic nature of galaxies and their evolution within the larger context of the universe.
Seyfert Galaxy: A Seyfert galaxy is a type of active galactic nucleus (AGN) characterized by a bright, compact core and emission lines in its spectrum, indicating the presence of a supermassive black hole at its center. These galaxies are known for their high levels of nuclear activity and luminosity, making them a subclass of AGNs.
Spectroscopy: Spectroscopy is the study of the interaction between matter and electromagnetic radiation, which provides valuable information about the composition, temperature, and motion of celestial objects. This technique is widely used in astronomy to analyze the properties of stars, galaxies, and other cosmic phenomena.
Spiral Arm: Spiral arms are the prominent, curving structures of stars, gas, and dust that extend outward from the center of a spiral galaxy. They are a defining feature of spiral galaxies and are closely associated with the formation of new stars.
Starburst: Starburst is a period of intense star formation in a galaxy, often triggered by a merger or interaction with another galaxy. During this phase, the rate of star formation can be up to 100 times higher than usual.
Starburst: A starburst is a region in a galaxy where stars are forming at an extremely rapid rate, much higher than the normal star formation rate in the galaxy. This intense burst of star formation is typically associated with galaxy mergers and active galactic nuclei, where the collision of gas-rich galaxies or the accretion of material onto a supermassive black hole provides the necessary fuel to ignite the starburst activity.
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.
Tidal Force: Tidal force is the differential gravitational pull exerted by a massive body, such as the Moon or a galaxy, on different parts of another object. This uneven gravitational attraction can lead to distortions, stretching, or even the breakup of the affected object.
Tidal Tail: A tidal tail is an elongated stream of stars, gas, and dust that extends from a galaxy, often as a result of gravitational interactions during a galaxy merger or close encounter. These tails can provide valuable insights into the dynamics and evolution of interacting galaxies.
Unified Model: The unified model is a comprehensive theoretical framework that seeks to unify and explain the diverse phenomena observed in active galactic nuclei (AGN) and quasars. It proposes a common underlying structure and mechanism to account for the wide range of properties and behaviors exhibited by these celestial objects.