28.5 The Formation and Evolution of Galaxies and Structure in the Universe
4 min read•june 12, 2024
Galaxies form and grow through gravitational collapse, mergers, and gas accretion. Dark matter plays a crucial role, providing the gravitational scaffolding for structure formation. These processes shape the of filaments, clusters, and voids we observe today.
Elliptical and spiral galaxies follow different evolutionary paths. Ellipticals form through major mergers, while spirals grow more gradually. Environmental factors and ongoing processes like and feedback continue to influence galaxy evolution over cosmic time.
Galaxy Formation and Evolution
Describe the main processes by which galaxies form and grow over cosmic time
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- Gravitational collapse of matter in the early universe
- form first providing a gravitational well for baryonic matter (gas and dust) to fall into
- Gas cools and condenses within dark matter halos forming stars and galaxies (Milky Way)
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- Smaller galaxies merge to form larger galaxies over time ()
- Major mergers can disrupt galaxy structure and trigger bursts of
- Minor mergers contribute to galaxy growth without significantly altering morphology (Sagittarius Dwarf Spheroidal Galaxy merging with the Milky Way)
- occurs when larger galaxies consume smaller ones
- Accretion of gas from the
- Cold gas flows along filaments of the cosmic web into galaxies (Magellanic Stream)
- Accreted gas fuels ongoing star formation (Orion Nebula)
- Feedback processes
- Stellar winds and supernovae can expel gas from galaxies regulating star formation (Crab Nebula)
- (AGN) feedback can heat and expel gas suppressing star formation in massive galaxies (M87)
Explain how dark matter and gravity shape the large-scale structure of the universe
- Cosmic web
- Dark matter and gravity form a network of filaments and nodes on large scales (Sloan Great Wall)
- Galaxies and form along these filaments and at the nodes (Virgo Cluster)
- Dark matter halos
- Invisible halos of dark matter surround galaxies and
- The gravitational influence of dark matter halos helps to hold galaxies and clusters together (Bullet Cluster)
- The extends far beyond the visible part of a galaxy
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- Small density fluctuations in the early universe are amplified by gravity over time
- Overdense regions collapse to form galaxies clusters and the cosmic web ()
- Voids
- Underdense regions expand and become largely empty of matter ()
- Voids are surrounded by sheets filaments and nodes of the cosmic web ()
Compare the formation and evolution of elliptical versus spiral galaxies
- Elliptical galaxies
- Form through major mergers of galaxies ()
- Mergers disrupt the ordered motion of stars resulting in a smooth ellipsoidal shape
- Contain mostly old red stars with little ongoing star formation (M87)
- Gas is depleted or heated preventing further star formation
- Spiral galaxies
- Form through more gradual processes such as gas accretion and minor mergers
- Maintain a disk structure with spiral arms ()
- Contain a mix of young blue stars and old red stars (Andromeda)
- Ongoing star formation occurs in the disk particularly in the spiral arms ()
- Environmental effects
- Elliptical galaxies are more common in dense environments such as galaxy clusters (Coma Cluster)
- Spiral galaxies are more common in less dense environments such as the outskirts of clusters or in the field ()
- Evolution
- Spiral galaxies can transform into elliptical galaxies through major mergers ()
- Elliptical galaxies can grow larger through subsequent mergers with other galaxies ()
Cosmic Structure and Dark Matter
Explain how dark matter and gravity shape the large-scale structure of the universe
- Density fluctuations in the early universe
- Quantum fluctuations in the early universe created small variations in density
- These density fluctuations were amplified by a period of rapid expansion
- Growth of structure
- Overdense regions attract more matter through gravity becoming even more dense (Galaxy clusters)
- Underdense regions become less dense as matter flows away from them (Voids)
- Role of dark matter
- Dark matter interacts gravitationally but not electromagnetically
- It forms the scaffolding for the large-scale structure of the universe (Cosmic web)
- Baryonic matter follows the distribution of dark matter forming galaxies and clusters
- Cosmological simulations
- Computer simulations model the evolution of the universe from early density fluctuations ()
- These simulations reproduce the observed large-scale structure including the cosmic web
- Observational evidence
- Galaxy surveys map the distribution of galaxies in the universe ()
- The observed large-scale structure matches the predictions of dark matter models ()
- measurements help determine the distances and velocities of galaxies
Cosmic Expansion and Structure Formation
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- Rapid expansion of the early universe that amplified quantum fluctuations
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- Sound waves in the early universe that left imprints on the large-scale structure
- Star formation
- Process by which gas collapses to form new stars, driving galaxy evolution
Key Terms to Review (32)
2dF Galaxy Redshift Survey: The 2dF Galaxy Redshift Survey was a large-scale spectroscopic survey of galaxies that aimed to map the large-scale structure of the Universe. It provided crucial insights into the formation and evolution of galaxies, as well as the distribution of matter on cosmological scales.
Active Galactic Nuclei: Active galactic nuclei (AGN) refer to the extremely luminous and energetic centers of some galaxies, powered by supermassive black holes that are actively accreting matter. These galactic nuclei emit radiation across the entire electromagnetic spectrum, from radio waves to high-energy gamma rays, making them some of the most energetic phenomena in the universe.
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.
Baryon Acoustic Oscillations: Baryon acoustic oscillations (BAOs) are the remnants of sound waves that propagated through the early universe, imprinting a characteristic scale on the distribution of matter and galaxies. These oscillations provide important information about the composition and evolution of the universe.
Boötes Void: The Boötes Void is a large, approximately spherical region of space containing relatively few galaxies compared to the universe as a whole. It is located in the northern celestial hemisphere, near the constellation of Boötes, and is one of the largest known voids in the observable universe.
Centaurus A: Centaurus A is a prominent elliptical galaxy located approximately 12 million light-years from Earth. It is one of the closest and most studied active galactic nuclei, known for its distinctive radio lobes and jets emanating from a supermassive black hole at its center. Centaurus A is a key object of study in the fields of galaxy properties, formation, and evolution.
Coma Cluster: The Coma Cluster is a large cluster of galaxies located in the northern constellation of Coma Berenices. It is one of the nearest and richest galaxy clusters to our Milky Way galaxy, providing important insights into the large-scale structure and evolution of the universe.
Cosmic Inflation: Cosmic inflation is a theory that describes an extremely rapid exponential expansion of the universe in the first fraction of a second after the Big Bang. This rapid expansion is thought to have smoothed out irregularities and set the stage for the universe we observe today.
Cosmic Web: The cosmic web is a large-scale structure of the universe, composed of galaxies, galaxy clusters, and filaments of matter that are separated by vast empty spaces called voids. It is a complex network that describes the distribution and organization of matter on the largest scales in the universe.
Dark Matter Halos: Dark matter halos are vast, spherical regions of invisible, gravitationally dominant matter that surround and envelop galaxies. They are a crucial component in the formation and evolution of galaxies, as well as the overall structure of the universe.
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.
Galactic Halo: The galactic halo is a spherical or ellipsoidal region surrounding the disk and bulge of a galaxy, consisting of diffuse gas, stars, and other matter not concentrated in the galactic plane. It is a crucial component in understanding the architecture, mass, stellar populations, formation, and evolution of galaxies.
Galaxy clusters: Galaxy clusters are large groups of galaxies bound together by gravity, typically containing hundreds to thousands of member galaxies. They represent the largest gravitationally bound structures in the universe and provide crucial insights into cosmic evolution and distribution.
Galaxy Clusters: Galaxy clusters are massive, gravitationally bound groups of galaxies that can contain hundreds or even thousands of individual galaxies. They are the largest known structures in the universe held together by their mutual gravitational attraction.
Gravitational Instability: Gravitational instability is a fundamental concept that describes the process by which matter in the universe, from the formation of the solar system to the evolution of galaxies, becomes organized into structures under the influence of gravity. It is a critical mechanism that drives the formation and evolution of celestial bodies and large-scale structures in the cosmos.
Hercules A: Hercules A is a powerful radio galaxy located in the constellation Hercules. It is one of the brightest and most luminous radio sources in the sky, emitting a vast amount of energy across the electromagnetic spectrum. This active galactic nucleus is a key example of the complex structures and processes that shape the formation and evolution of galaxies in the universe.
Hierarchical Merging: Hierarchical merging is a fundamental concept in the formation and evolution of galaxies and the large-scale structure of the universe. It describes the process by which smaller structures, such as dark matter halos and galaxies, gradually combine and merge to form larger, more massive structures over cosmic time.
Inflation: Inflation is a sustained increase in the general price level of goods and services in an economy over time. It is a key concept in understanding the formation and evolution of galaxies, the age of the universe, the beginning of the universe, and the inflationary universe.
Inflationary universe: The inflationary universe is a theory that proposes a period of extremely rapid exponential expansion of the universe immediately following the Big Bang. It explains several key cosmological observations such as the uniformity of the cosmic microwave background radiation and the large-scale structure of the cosmos.
Intergalactic Medium: The intergalactic medium (IGM) refers to the diffuse gas and plasma that fills the space between galaxies within a galaxy cluster or the larger-scale structure of the universe. It is the matter that exists outside of galaxies and stars, permeating the vast empty spaces between them.
Local Group: The Local Group is a small cluster of galaxies that includes the Milky Way Galaxy and the Andromeda Galaxy, along with about 50 other smaller galaxies. It is the closest major concentration of galaxies to the Milky Way and provides important insights into the structure and evolution of galaxies on a larger scale.
Local Void: The Local Void is a large, relatively empty region of space in the local universe, located in the direction of the constellations Boötes and Corona Borealis. It is a significant feature of the large-scale structure of the universe, characterized by a lower density of galaxies compared to the surrounding areas.
Mice Galaxies: Mice Galaxies, also known as interacting galaxies, are a class of galaxies that are gravitationally bound and in the process of merging or colliding with each other. This phenomenon is a key aspect of the formation and evolution of galaxies, as well as the structure of the universe on larger scales.
Millennium Simulation: The Millennium Simulation is a large-scale computer simulation of the formation and evolution of the universe, focusing on the properties and structure of galaxies. It provides a comprehensive model of the cosmic structure formation process, allowing researchers to study the complex interactions between dark matter, gas, and stars that shape the observable universe.
Orion Arm: The Orion Arm is a minor spiral arm of the Milky Way galaxy, situated between two major spiral arms known as the Perseus Arm and the Sagittarius Arm. It is the solar system's location within the Milky Way, and it plays a crucial role in understanding the structure and evolution of our galaxy.
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.
Sloan Digital Sky Survey: The Sloan Digital Sky Survey (SDSS) is a major multi-year project that has created the most detailed three-dimensional maps of the universe. It uses a specialized telescope and camera system to observe and analyze the properties of celestial objects, providing valuable data for studying the colors of stars, the evolution of quasars, the formation and evolution of galaxies, and the overall structure and model of the universe.
Star formation: Star formation is the process by which dense regions within molecular clouds in interstellar space collapse to form stars. This often results in the creation of a cluster of stars rather than a single star.
Star Formation: Star formation is the process by which dense regions within molecular clouds in space collapse under their own gravitational attraction to form stars. This is a fundamental process that shapes the structure and evolution of galaxies, including the Milky Way, and is closely tied to the topics of spiral structure and the formation and evolution of galaxies and large-scale structure in the universe.
Whirlpool Galaxy: The Whirlpool Galaxy, also known as Messier 51a or NGC 5194, is a prominent spiral galaxy located approximately 23 million light-years away from Earth in the constellation Canes Venatici. It is one of the most famous and well-studied galaxies in the night sky, known for its distinctive spiral structure and ongoing interactions with a neighboring galaxy.