1.3 Overview of the universe and its constituents
4 min read•july 25, 2024
The universe is a vast tapestry of cosmic objects, from to . These components form a hierarchy of scales, from our solar system to the spanning billions of light-years.
and energy play crucial roles in shaping the universe's structure and evolution. While invisible, their effects are seen in galaxy rotations, , and the accelerating expansion of space itself.
Components and Structure of the Universe
Components of the universe
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- Planets
- consist of rocky compositions found in inner solar system (Mercury, Venus, Earth, Mars)
- contain primarily hydrogen and helium located in outer solar system (Jupiter, Saturn, Uranus, Neptune)
- orbit other than our Sun discovered through various detection methods (radial velocity, transit)
- Stars
- fuse hydrogen in cores represent majority of observable stars (Sun)
- expand and cool as hydrogen fuel depletes in core (Aldebaran, Arcturus)
- form from collapsed cores of low-mass stars after red giant phase (Sirius B)
- result from supernova explosions of massive stars with extremely dense cores (Crab Pulsar)
- possess gravitational fields so strong that nothing can escape their event horizons (Cygnus X-1)
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- Spiral galaxies feature distinct arms rotating around a central bulge (Milky Way, Andromeda)
- have smooth, featureless appearances with ellipsoidal shapes (M87)
- Irregular galaxies lack defined structure or symmetry often due to gravitational interactions (Large Magellanic Cloud)
- contain fewer stars and less mass than larger galaxy types (Fornax Dwarf)
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- contain small collections of gravitationally bound galaxies (Local Group)
- comprise large collections of galaxies held together by gravity (Virgo Cluster)
- Superclusters consist of multiple galaxy clusters and groups forming largest known structures (Laniakea Supercluster)
Scales of cosmic organization
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- Sun occupies central position with planets orbiting in elliptical paths governed by gravity
- located between Mars and Jupiter contains numerous small rocky bodies
- extends beyond Neptune's orbit harboring icy bodies and dwarf planets (Pluto)
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- Nearest star systems found within few light-years of Sun (Alpha Centauri, Barnard's Star)
- consists of gas and dust between nearby stars
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- structure includes spiral arms, central bulge, and extended halo
- contains majority of stars, gas, and dust concentrated in relatively flat plane
- orbit in galactic halo as ancient spherical collections of stars
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- Milky Way and Andromeda galaxies dominate as largest members of Local Group
- orbit larger galaxies due to gravitational attraction (Magellanic Clouds)
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- Gravitationally bound collections of galaxies interact and move collectively
- fills space between galaxies with hot, diffuse gas emitting X-rays
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- Laniakea Supercluster encompasses our local cosmic neighborhood including Milky Way
- and form large-scale structure resembling cosmic web spanning vast distances
Cosmic web in structure
- Network-like structure of matter distribution spans observable universe
- Components of cosmic web
- Filaments form thread-like structures of galaxies and gas connecting larger structures
- occur at intersections of filaments often containing massive galaxy clusters
- create sheet-like structures of galaxies forming boundaries between voids
- Voids represent nearly empty regions between filaments and walls with few galaxies
- Formation process
- Initial density fluctuations arise in early universe
- Gravitational collapse of matter occurs over cosmic time
- Denser regions attract more matter, forming filaments and nodes
- Less dense regions become increasingly empty, forming voids
- Observational evidence
- Galaxy redshift surveys reveal filamentary structure on large scales (Sloan Digital Sky Survey)
- Weak gravitational lensing maps dark matter distribution confirming cosmic web predictions
Dark matter and energy influence
- Dark matter
- Non-luminous matter detected through gravitational effects on visible matter
- Evidence supports existence
- Galaxy rotation curves show unexpectedly flat velocity profiles
- Gravitational lensing observations reveal more mass than visible matter alone
- anisotropies indicate presence of non-baryonic matter
- Facilitates structure formation by providing additional gravitational attraction
- Shapes cosmic web by influencing matter distribution on large scales
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- Unknown form of energy causing accelerated expansion of universe
- Evidence supports existence
- observations show universe expanding faster than expected
- Cosmic microwave background measurements indicate flat geometry of universe
- Counteracts gravity on large scales pushing galaxies and clusters apart
- Drives accelerated expansion of universe affecting its long-term evolution
- Universe composition
- Ordinary matter comprises ~5% including familiar protons, neutrons, and electrons
- Dark matter accounts for ~27% providing additional gravitational influence
- Dark energy dominates at ~68% causing accelerated expansion
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- Standard model of cosmology incorporates dark matter (CDM) and dark energy (Lambda)
- Successfully explains various observations including cosmic microwave background and large-scale structure
Key Terms to Review (42)
Asteroid belt: The asteroid belt is a region in space located between the orbits of Mars and Jupiter, containing a vast number of rocky bodies known as asteroids. This region is significant because it represents the remnants of the early solar system, with these asteroids being leftover building blocks that never coalesced into a planet. The asteroid belt provides insights into the formation and evolution of planetary systems, including our own.
Black holes: Black holes are regions in spacetime where gravity is so strong that nothing, not even light, can escape from them. They form from the remnants of massive stars after they undergo gravitational collapse, and their unique properties challenge our understanding of physics, particularly in relation to the universe's structure and the fundamental laws governing it.
Clusters of galaxies: Clusters of galaxies are large-scale structures in the universe that consist of a group of galaxies bound together by gravity. These clusters can contain anywhere from a few dozen to thousands of galaxies, along with hot gas and dark matter, forming the largest known gravitationally-bound structures in the universe. They are essential for understanding the distribution of matter and the evolution of cosmic structures over time.
Cosmic microwave background: The cosmic microwave background (CMB) is the remnant radiation from the Big Bang, filling the universe with a nearly uniform glow of microwave radiation. It serves as a snapshot of the universe when it was just 380,000 years old, providing vital clues about its early conditions, structure, and expansion. The CMB plays a crucial role in understanding the universe's constituents, its expansion over time, and influences our comprehension of dark matter and dark energy.
Cosmic web: The cosmic web is the large-scale structure of the universe, characterized by a vast network of interconnected filaments of dark matter and galaxies. This structure forms a complex pattern of voids, filaments, and clusters, shaping how matter is distributed throughout the universe. Understanding the cosmic web is crucial for studying galaxy formation, the behavior of dark matter, and the overall evolution of cosmic structures.
Dark energy: Dark energy is a mysterious force that is driving the accelerated expansion of the universe. It constitutes about 68% of the total energy density of the universe and affects how galaxies, galaxy clusters, and large-scale structures behave over cosmic timescales. This concept connects to many aspects of astrophysics, including the formation and evolution of the universe, the cosmic microwave background radiation, and our understanding of Hubble's law.
Dark Matter: Dark matter is a mysterious and invisible form of matter that does not emit, absorb, or reflect light, making it undetectable by traditional astronomical methods. Despite being unseen, it makes up about 27% of the universe's total mass-energy content and plays a crucial role in the structure and evolution of galaxies, influencing gravitational interactions in the cosmos.
Dwarf Galaxies: Dwarf galaxies are small galaxies that contain only a few billion stars, which is significantly less than the hundreds of billions found in larger galaxies like the Milky Way. Despite their size, dwarf galaxies are vital constituents of the universe as they help astronomers understand galaxy formation, dark matter distribution, and the overall structure of the cosmos.
Elliptical galaxies: Elliptical galaxies are a type of galaxy characterized by their ellipsoidal shape, smooth light distribution, and lack of significant structure. These galaxies primarily contain older stars and very little gas or dust, leading to minimal new star formation. Their simplicity in structure and stellar population makes them an essential component in the broader understanding of the universe and its constituents.
Exoplanets: Exoplanets are planets that exist outside of our solar system, orbiting stars other than the Sun. They are crucial for understanding planetary systems and the potential for life beyond Earth. The discovery of exoplanets has expanded our knowledge of the universe, revealing a diversity of planetary types and environments that challenge our previous notions about how planets form and evolve.
Filaments: Filaments are vast, thread-like structures in the universe that form the backbone of the cosmic web. They consist of galaxies, dark matter, and gas that are interconnected, creating a large-scale structure that influences the distribution of matter and energy in the universe. Understanding filaments helps explain how galaxies are organized and how they interact with one another.
Galactic Disk: The galactic disk is a flattened, rotating region of a galaxy that contains stars, gas, and dust, often forming spiral structures. This area is where most of a galaxy's star formation occurs, making it crucial for understanding the life cycle of stars and the dynamics of the galaxy as a whole.
Galactic scale: Galactic scale refers to the vast distances and structures that define the organization and composition of galaxies, encompassing everything from individual stars to clusters of galaxies. This term highlights the immense size of the universe, where galaxies can span hundreds of thousands of light-years and contain billions of stars, as well as the various constituents that make up these colossal systems, such as dark matter and interstellar gas.
Galaxies: Galaxies are vast systems composed of stars, stellar remnants, interstellar gas, dust, and dark matter, all bound together by gravity. They are fundamental building blocks of the universe, with each galaxy containing millions to trillions of stars, and they come in various shapes and sizes such as spiral, elliptical, and irregular. Understanding galaxies is crucial for comprehending the larger structure of the universe and the formation of cosmic structures.
Galaxy cluster scale: Galaxy cluster scale refers to the vast regions in the universe that contain groups of galaxies bound together by gravity, often including dozens to thousands of individual galaxies. These clusters represent one of the largest structures in the universe and are critical for understanding cosmic evolution, large-scale structure formation, and the distribution of dark matter.
Galaxy clusters: Galaxy clusters are large groups of galaxies held together by gravity, containing anywhere from a few dozen to thousands of galaxies, along with gas and dark matter. They are the largest known gravitationally-bound structures in the universe, playing a critical role in understanding the large-scale structure of the cosmos and the distribution of matter, including dark matter, across different scales.
Galaxy Groups: Galaxy groups are collections of galaxies that are held together by gravity and typically contain a few to several dozen galaxies. These structures play a crucial role in the large-scale organization of the universe and are fundamental in understanding how galaxies interact, evolve, and form larger structures like galaxy clusters.
Gas Giants: Gas giants are large planets primarily composed of hydrogen and helium, with deep atmospheres and no well-defined solid surface. They are significant features in the universe, often found in the outer regions of planetary systems, and play a crucial role in understanding planetary formation and the dynamics of celestial bodies.
Globular Clusters: Globular clusters are densely packed groups of older stars, typically containing thousands to hundreds of thousands of stars bound together by gravity. These clusters are found in the halos of galaxies and play an important role in understanding the formation and evolution of galaxies and their stellar populations.
Gravitational Lensing: Gravitational lensing is the bending of light from a distant object, such as a galaxy or quasar, by the gravitational field of a massive object, like a galaxy cluster or black hole, situated between the observer and the distant source. This phenomenon provides crucial insights into the distribution of mass in the universe, including dark matter, and influences our understanding of cosmic structures and the evolution of galaxies.
Intracluster Medium: The intracluster medium (ICM) is the hot, diffuse gas that exists in the vast spaces between galaxies within galaxy clusters. This medium contains a significant amount of baryonic matter and plays a crucial role in the dynamics and evolution of galaxy clusters. The ICM is primarily composed of ionized hydrogen and helium, along with traces of heavier elements, and its properties influence the formation of galaxies and large-scale structures in the universe.
Kuiper Belt: The Kuiper Belt is a vast region of the solar system that extends beyond the orbit of Neptune, populated by small icy bodies and dwarf planets. This area plays a critical role in our understanding of the solar system's formation and the distribution of its constituents, as it contains remnants from the early solar system and helps explain the characteristics of other celestial objects.
Lambda-CDM Model: The Lambda-CDM model is the standard model of cosmology that describes the evolution of the universe from the Big Bang to its current state, incorporating the effects of dark energy and dark matter. This model explains how the universe is structured and how it expands over time, providing a framework that aligns with observations of cosmic microwave background radiation, large-scale structure, and galaxy formation.
Local Group Scale: Local group scale refers to a specific level of astronomical study that focuses on the Local Group, a collection of more than 50 galaxies, including the Milky Way and its neighboring galaxies. This scale allows astronomers to analyze the structure, dynamics, and interactions of these galaxies, which are gravitationally bound together. Understanding the Local Group is essential for grasping larger cosmic structures and the overall evolution of the universe.
Local Interstellar Medium: The local interstellar medium refers to the region of space immediately surrounding our solar system, composed of gas, dust, and cosmic rays that exist between stars. This medium plays a critical role in the formation of stars and planetary systems and influences the overall chemical composition and physical characteristics of the Milky Way galaxy.
Main sequence stars: Main sequence stars are a category of stars that are in a stable phase of stellar evolution where they fuse hydrogen into helium in their cores. This process generates a significant amount of energy, producing the light and heat we observe from these stars. Main sequence stars represent the longest phase in a star's lifecycle and are crucial in understanding stellar evolution, nucleosynthesis, and the broader characteristics of the universe.
Milky Way Galaxy: The Milky Way Galaxy is a barred spiral galaxy that contains our solar system and is one of the billions of galaxies in the universe. It has a diameter of about 100,000 light-years and is estimated to contain 100 to 400 billion stars, along with gas, dust, and dark matter, forming a vast cosmic structure that plays a crucial role in understanding the universe and its components.
Neutron stars: Neutron stars are the remnants of massive stars that have undergone a supernova explosion, leading to the collapse of their cores primarily composed of neutrons. These compact objects are incredibly dense, with a mass greater than that of the Sun packed into a sphere only about 20 kilometers in diameter. Their extreme properties make them fascinating subjects in the study of stellar evolution and the fundamental forces of nature.
Nodes: In astrophysics, nodes refer to specific points in the orbit of celestial bodies, such as planets and moons, where their orbital planes intersect with the plane of another celestial reference, like the ecliptic or the equatorial plane. These nodes are crucial in understanding orbital mechanics, eclipses, and the dynamics of celestial movements.
Planets: Planets are large celestial bodies that orbit a star, such as the Sun, and are characterized by their spherical shape due to self-gravity. They come in various types, including terrestrial planets like Earth and gas giants like Jupiter, each exhibiting unique features and atmospheres. The study of planets is essential to understanding the structure and dynamics of solar systems and the broader universe.
Red Giants: Red giants are large, luminous stars that have expanded and cooled after exhausting the hydrogen fuel in their cores. As they evolve, these stars enter a phase where they exhibit a reddish hue due to lower surface temperatures, typically ranging from 3,000 to 5,000 Kelvin. This phase is significant in the life cycle of stars, showcasing the transition from main sequence stars to more advanced stages of stellar evolution.
Satellite Galaxies: Satellite galaxies are smaller galaxies that orbit a larger galaxy, held together by the gravitational pull of the larger galaxy. These smaller galaxies provide important insights into the formation and evolution of galaxies, as they interact gravitationally with their host galaxies, influencing their structure and behavior over time.
Solar system scale: Solar system scale refers to the relative distances and sizes of the various celestial bodies within our solar system, as well as how these dimensions compare to the vastness of space beyond it. Understanding solar system scale helps in visualizing the enormous gaps between planets, moons, asteroids, and the Sun, which are often hard to grasp due to their immense distances and sizes compared to everyday objects.
Stars: Stars are massive celestial bodies composed mainly of hydrogen and helium, undergoing nuclear fusion in their cores to produce energy and light. They are fundamental building blocks of the universe, forming galaxies and influencing cosmic structures and processes. Stars vary in size, temperature, brightness, and life cycle, which can include stages like main sequence, red giant, and supernova, making them critical for understanding the evolution of the universe.
Stellar neighborhood scale: The stellar neighborhood scale refers to the spatial dimension in which stars and their surrounding environments, such as star clusters and nearby galaxies, interact and evolve. This scale encompasses regions of space typically extending from several light-years to a few hundred light-years, providing insight into the local structures and dynamics within the broader context of the universe.
Supercluster scale: Supercluster scale refers to the large-scale structure of the universe, where galaxy clusters come together to form vast, interconnected regions called superclusters. These superclusters can span hundreds of millions of light-years and consist of numerous galaxies, clusters, and dark matter, showcasing the distribution of matter in the universe and its influence on cosmic evolution.
Superclusters: Superclusters are vast groups of galaxies that are among the largest known structures in the universe, typically containing dozens to thousands of galaxies bound together by gravity. They play a crucial role in understanding the large-scale structure of the universe and the distribution of matter, as they are formed from smaller clusters and groups of galaxies that have merged over billions of years.
Terrestrial planets: Terrestrial planets are the rocky, inner planets of our solar system that include Mercury, Venus, Earth, and Mars. They are characterized by solid surfaces, relatively high densities, and the presence of rock and metal composition, distinguishing them from the gas giants found further out in the solar system. Understanding terrestrial planets helps in studying planetary formation and the conditions that support life.
Type Ia Supernovae: Type Ia supernovae are powerful explosions that occur in binary star systems when a white dwarf star accumulates enough matter from its companion star to ignite nuclear fusion. These events are crucial for understanding the universe's expansion, as they serve as standard candles for measuring astronomical distances and play a significant role in the evolution of galaxies.
Voids: Voids are large, relatively empty regions in the universe that contain very few galaxies or other matter compared to the average density of the cosmos. They are significant for understanding the large-scale structure of the universe, revealing how matter is distributed and the dynamics of cosmic evolution. Voids play a critical role in shaping the arrangement of galaxies and clusters, serving as gaps in the intricate web of matter that composes the universe.
Walls: In the context of the universe, walls refer to large-scale structures that delineate vast cosmic voids, acting as boundaries between different regions filled with matter. These walls are composed of galaxy clusters and superclusters, forming a web-like structure that defines the large-scale organization of the universe. Their existence highlights how matter is distributed unevenly across space, leading to areas of dense galaxies surrounded by vast empty regions known as voids.
White Dwarfs: White dwarfs are the remnants of medium-sized stars that have exhausted their nuclear fuel and undergone a process of shedding their outer layers, leaving behind a hot, dense core primarily composed of carbon and oxygen. These stellar remnants play a significant role in understanding stellar evolution, as they mark the final stages of a star's life cycle and contribute to the chemical enrichment of the universe.