28.3 The Distribution of Galaxies in Space
3 min read•june 12, 2024
Galaxies aren't scattered randomly across space. They form groups, clusters, and , creating a vast . This structure follows the , which says the universe looks the same everywhere on large scales.
Our is part of the , a small cluster of about 50 galaxies. Beyond that, larger clusters and stretch across billions of light-years, separated by enormous . This layout shapes how galaxies evolve over cosmic time.
The Distribution of Galaxies in Space
Cosmological principle in large-scale structures
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- Universe appears uniform and looks the same from every location when viewed on vast cosmic scales ()
- Universe appears the same in all directions when observed on immense distances ()
- (CMB) radiation supports the with its nearly uniform distribution across the sky, exhibiting only minor fluctuations
- Galaxies and spread out evenly on scales exceeding 300 million light-years
- Cosmological principle enables cosmologists to create models of the universe assuming large-scale uniformity
Components of Local Group
- Local Group comprises a small cluster of galaxies, including our Milky Way
- Milky Way and (M31) dominate the Local Group as the two largest galaxies
- (M33), (LMC), and (SMC) represent other significant members of the Local Group
- Local Group encompasses around 50 known galaxies, primarily dwarf galaxies
- Region of space approximately 10 million light-years in diameter contains the Local Group
Groups vs clusters vs superclusters
- Groups of galaxies:
- Contain up to 50 galaxies
- Span diameters under 10 million light-years (Local Group)
- Clusters of galaxies:
- Contain 50 to thousands of galaxies
- Span diameters from 10 to 30 million light-years ()
- Observations of provide evidence for the presence of
- Superclusters of galaxies:
- Contain multiple galaxy clusters and groups, encompassing thousands of galaxies
- Span hundreds of millions of light-years (, which includes the Milky Way)
- Gravity binds groups, clusters, and superclusters together, forming the largest structures in the universe
Voids and cosmic structures
- :
- Enormous regions of space with few or no galaxies
- Span hundreds of millions of light-years ()
- :
- Elongated, narrow, and relatively dense regions of galaxies
- Link galaxy clusters and superclusters
- Create a cosmic web-like structure
- :
- Immense, flat structures made up of galaxies and galaxy clusters
- Span over a billion light-years in length ()
- Cosmic web of filaments, walls, and voids with galaxy clusters and superclusters at their intersections characterizes the large-scale structure of the universe
Cosmic Expansion and Dark Energy
- describes the relationship between a galaxy's distance and its recession velocity
- of distant galaxies provides evidence for the expansion of the universe
- is theorized to be responsible for the accelerating expansion of the universe
- helps astronomers study the distribution of matter in the universe, including dark matter
- is influenced by the large-scale structure and expansion of the universe
Key Terms to Review (37)
Andromeda Galaxy: The Andromeda Galaxy, also known as Messier 31 or NGC 224, is a spiral galaxy located approximately 2.5 million light-years from Earth. It is the largest and most massive galaxy in the Local Group, which includes our own Milky Way Galaxy. The Andromeda Galaxy's vast size, distance, and relationship to the Milky Way make it a crucial object of study in understanding the large-scale structure 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.
Cold dark matter: Cold dark matter (CDM) consists of slow-moving particles that do not emit, absorb, or reflect light, making them invisible and detectable only through gravitational effects. It plays a crucial role in the formation and clustering of galaxies in the universe.
Cosmic Microwave Background: The cosmic microwave background (CMB) is the oldest light in the universe, a faint glow that permeates all of space and is a remnant of the early stages of the universe's formation. It provides crucial information about the origins and evolution of the universe, as well as its large-scale structure and composition.
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.
Cosmological principle: The cosmological principle states that the universe is homogeneous and isotropic when viewed on a large enough scale. This means that the distribution of matter and energy is uniform, and the universe looks the same in all directions.
Cosmological Principle: The cosmological principle is a fundamental assumption in cosmology that states the universe is homogeneous and isotropic on large scales. This means that the properties of the universe are the same everywhere (homogeneous) and look the same in all directions (isotropic), regardless of one's location or orientation.
Dark energy: Dark energy is a mysterious form of energy that makes up about 68% of the universe and is responsible for its accelerated expansion. Its exact nature remains unknown, but it is a crucial component in cosmological models.
Dark Energy: Dark energy is a mysterious and pervasive form of energy that appears to be driving the accelerated expansion of the universe. It is a fundamental component of the universe that makes up approximately 68% of the total energy content of the cosmos.
The discovery of dark energy has revolutionized our understanding of the universe, as it challenges the traditional models of cosmology and the evolution of the universe. Dark energy is a crucial concept that helps explain the large-scale structure and dynamics of the universe, as well as its past, present, and future.
Dark Matter: Dark matter is a hypothetical form of matter that cannot be seen directly but accounts for the majority of the matter in the universe. It is believed to interact gravitationally with itself and with ordinary matter, but does not emit, reflect, or absorb light, making it invisible to traditional astronomical observations.
Filaments: Filaments are long, narrow, and bright features observed in the solar atmosphere, particularly in the chromosphere and corona. They are associated with the Sun's magnetic field and play a crucial role in understanding solar activity and the distribution of galaxies in space.
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.
Galaxy Evolution: Galaxy evolution refers to the study of how galaxies form, change, and develop over time. It encompasses the processes that shape the structure, composition, and properties of galaxies, from their initial formation to their present-day state and future evolution.
Geller: Geller is an astronomer known for her pivotal work in mapping the large-scale structure of the universe. Her research has significantly advanced our understanding of how galaxies are distributed in space.
Gravitational lens: Gravitational lensing is a phenomenon where light from a distant object is bent around a massive object between the light source and the observer. This effect can magnify and distort images of distant galaxies, providing valuable data about both the foreground and background objects.
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.
Homogeneous: Homogeneous describes a property of being uniform and consistent in composition or structure throughout. In astronomy, it often refers to the large-scale distribution of galaxies appearing similar when viewed from different regions of the universe.
Homogeneous: Homogeneous refers to something that is uniform or consistent in structure or composition throughout. In the context of the distribution of galaxies in space, homogeneous describes the large-scale distribution of galaxies as being statistically the same in all regions of the observable universe.
Hubble's Law: Hubble's Law is a fundamental principle in cosmology that describes the relationship between the distance of a galaxy from the Milky Way and its recessional velocity. It states that the farther a galaxy is from our own, the faster it is moving away from us, indicating an expanding universe.
Isotropic: Isotropic describes a property or phenomenon that is uniform in all directions. In astronomy, it often refers to the even distribution of galaxies and cosmic background radiation across the universe.
Isotropic: Isotropic refers to a property of something that is uniform and has the same value or characteristic in all directions. It is a concept that is often used in the context of the distribution of galaxies in space and the cosmic microwave background radiation.
Laniakea Supercluster: The Laniakea Supercluster is a vast collection of galaxies, including our own Milky Way, bound together by gravity. It is one of the largest known structures in the observable universe, spanning hundreds of millions of light-years across and containing the equivalent of tens of thousands of Milky Way-sized galaxies.
Large Magellanic Cloud: The Large Magellanic Cloud (LMC) is a satellite galaxy of the Milky Way, located approximately 163,000 light-years from Earth. It is one of the closest galaxies to our own and serves as an important laboratory for studying stellar evolution, variable stars, and the formation and distribution of galaxies in the universe.
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.
Milky Way: The Milky Way is the galaxy in which our solar system is located, comprising hundreds of billions of stars and vast amounts of gas and dust. It is a spiral galaxy, with a central bulge and a rotating disk of stars, gas, and dust. The Milky Way is an essential component in understanding the structure, formation, and evolution of the universe, as it provides a window into the larger cosmic landscape.
Milky Way Galaxy: The Milky Way Galaxy is the spiral galaxy that includes our Solar System, characterized by its barred structure and multiple spiral arms. It is one of billions of galaxies in the universe and contains over 200 billion stars.
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 Great Wall: The Sloan Great Wall is a large-scale structure in the distribution of galaxies, spanning hundreds of millions of light-years across the universe. It is one of the largest known structures in the observable universe and provides insights into the large-scale organization and evolution of matter on cosmic scales.
Small Magellanic Cloud: The Small Magellanic Cloud is a dwarf irregular galaxy that is a satellite of the Milky Way Galaxy. It is one of the closest galaxies to the Milky Way and provides valuable insights into the formation and evolution of galaxies.
Superclusters: Large-scale structures in the universe formed by groups of galaxy clusters bound together by gravity. Superclusters can span hundreds of millions of light-years and contain tens of thousands of galaxies.
Superclusters: Superclusters are the largest known structures in the universe, consisting of multiple galaxy clusters gravitationally bound together. They represent the highest level of organization in the large-scale structure of the cosmos, providing insights into the distribution and evolution of matter on the grandest scales.
Triangulum Galaxy: The Triangulum Galaxy, also known as Messier 33 or NGC 598, is a spiral galaxy located in the constellation Triangulum. It is the third-largest member of the Local Group of galaxies, after the Andromeda Galaxy and the Milky Way.
Virgo Cluster: The Virgo Cluster is a large, nearby galaxy cluster located in the northern constellation of Virgo. It is one of the most massive and densest concentrations of galaxies in the local universe, containing thousands of individual galaxies gravitationally bound together.
Voids: Voids are vast, empty regions in the universe with very few galaxies. They are significant in understanding the large-scale structure of the cosmos.
Voids: Voids are large, empty regions of space that contain very few galaxies. They are vast, underdense areas that stand in contrast to the filamentary structures and galaxy clusters that make up the large-scale structure of the universe.
Walls: Walls, in the context of the distribution of galaxies in space, refer to the large-scale structures that form the boundaries of cosmic voids. These walls are composed of galaxies and galaxy clusters, creating a web-like pattern across the observable universe.
The concept of walls is closely tied to the hierarchical structure of the cosmos, where matter is distributed in a complex network of filaments, sheets, and voids. Walls act as the dividing lines between these vast, relatively empty regions, serving as the scaffolding that supports the overall structure of the universe.