28.1 Observations of Distant Galaxies
3 min read•june 12, 2024
Gazing at distant is like peering into the universe's past. As light travels billions of years to reach us, we see galaxies as they were long ago. This cosmic time machine reveals how galaxies have changed over billions of years.
Early galaxies were smaller, more irregular, and formed stars at a frantic pace. They had fewer heavy elements and looked quite different from the majestic spirals and ellipticals we see nearby. Studying these ancient galaxies helps us understand how the universe evolved.
Observations of Distant Galaxies
Information from distant galaxies
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- Light travel time enables observing the universe as it was in the past since light from distant galaxies takes billions of years to reach Earth ()
- occurs when light from distant galaxies is shifted towards longer, redder wavelengths due to the expansion of the universe, with greater redshift indicating more distant galaxies and observations further back in time ()
- expresses the relationship between a galaxy's distance and its redshift as , where is the galaxy's recessional velocity, is the , and is the galaxy's distance ()
- represents the time in the past when the light observed from a distant galaxy was emitted, calculated using the galaxy's redshift and the expansion rate of the universe ()
- is used to analyze the light from distant galaxies, providing information about their composition, temperature, and motion
Evidence of early star formation
- , an ultraviolet emission line produced by hydrogen atoms in star-forming regions, indicates the presence of young, massive stars in early galaxies ()
- Infrared emission suggests ongoing star formation in distant galaxies as dust in star-forming regions absorbs ultraviolet light and re-emits it in the infrared ()
- , a long-exposure image revealing thousands of galaxies in the early universe, shows many galaxies with blue colors, indicating young stellar populations and active star formation ()
- Spectroscopic observations revealing the presence of heavy elements, produced by stars, in distant galaxies confirm that stars had already formed and enriched the interstellar medium ()
- The provides unprecedented views of early galaxies, allowing for more detailed studies of their formation and
Early vs modern galaxy characteristics
- Size and morphology differ as early galaxies tend to be smaller and more irregular in shape compared to modern galaxies, with many classified as "proto-galaxies" or "galaxy fragments" ()
- Stellar populations in early galaxies are younger and more metal-poor compared to nearby galaxies, with the most distant galaxies potentially containing , the first generation of stars formed from pristine hydrogen and helium ()
- Star formation rates are higher in early galaxies compared to nearby galaxies, with the cosmic star formation rate peaking around 10 billion years ago and declining since then ()
- Chemical composition shows lower abundances of heavy elements in early galaxies compared to nearby galaxies, as the chemical enrichment of galaxies over cosmic time is driven by successive generations of stars ()
Large-scale structure and galaxy environment
- are the largest gravitationally bound structures in the universe, containing hundreds to thousands of galaxies
- The describes the large-scale structure of the universe, with galaxies arranged in filaments and sheets separated by vast voids
- are extremely luminous centers of galaxies, powered by supermassive black holes, and are more common in the early universe
- is believed to be responsible for the accelerating expansion of the universe, affecting the distribution and evolution of galaxies over cosmic time
Key Terms to Review (33)
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 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.
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.
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.
Evolution: Evolution in astronomy refers to the process by which galaxies form, change, and develop over time. It encompasses the physical processes that drive these transformations across billions of years.
Galaxies: Galaxies are vast systems composed of stars, stellar remnants, interstellar gas, dust, and dark matter, bound together by gravity. They vary greatly in size and structure and are fundamental building blocks of the universe.
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.
Globular clusters: Globular clusters are tightly bound groups of stars, typically containing hundreds of thousands to millions of members. They orbit the galactic core and are among the oldest objects in the universe.
Globular Clusters: Globular clusters are dense, spherical collections of tens of thousands to millions of old stars gravitationally bound together. They are found in the outer regions of galaxies, including the Milky Way, and provide insights into the formation and evolution of galaxies.
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.
Hubble constant: The Hubble constant is the rate of expansion of the universe, measured in kilometers per second per megaparsec (km/s/Mpc). It provides a relationship between the distance of galaxies and their recessional velocity due to cosmic expansion.
Hubble Constant: The Hubble constant is a fundamental parameter in cosmology that describes the rate of expansion of the universe. It represents the relationship between the distance to a galaxy and its recessional velocity, providing a measure of the expansion rate of the observable universe.
Hubble Sequence: The Hubble Sequence is a classification scheme for galaxies based on their visual morphology, which was developed by the astronomer Edwin Hubble. It provides a systematic way to categorize and understand the diverse shapes and structures of galaxies in the universe.
Hubble Space Telescope: The Hubble Space Telescope is a large, space-based observatory that has revolutionized our understanding of the universe. Launched in 1990, it orbits the Earth outside the distortion of the atmosphere, providing clear and detailed images of celestial objects. The Hubble Telescope's unique position above the Earth's atmosphere allows it to observe the cosmos in ways that ground-based telescopes cannot, making it a crucial tool for advancing our knowledge of astronomy and cosmology.
Hubble Ultra Deep Field: The Hubble Ultra Deep Field is an image of a small region of space in the constellation Fornax, constructed from Hubble Space Telescope data accumulated over many hours of observation. It is considered one of the most important deep-field images ever taken, as it provides a glimpse into the early universe and the formation of galaxies.
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.
James Webb Space Telescope: The James Webb Space Telescope (JWST) is a next-generation, large, infrared-optimized space observatory that will serve as the premier space-based observatory of the next decade. It is designed to study the earliest galaxies in the universe, observe the formation of stars and planets, and explore the mysteries of our solar system.
Lookback Time: Lookback time, also known as light travel time, is the time it takes for light to travel from a distant object to the observer. It represents the age of the observed object, as the light we see from it was emitted in the past. This concept is crucial in understanding the observations of distant galaxies and the consequences of the finite speed of light.
Lyman-alpha emission: Lyman-alpha emission is a type of ultraviolet radiation emitted when an electron in a hydrogen atom transitions from the second energy level to the first energy level. This transition releases a photon with a specific wavelength of 121.6 nanometers, which is known as the Lyman-alpha line. This emission is particularly important in the study of distant galaxies and the early universe.
Metallicity Gradient: The metallicity gradient refers to the variation in the abundance of heavy elements, or metals, within a galaxy or other astronomical object. This gradient is observed as a decrease in the concentration of metals from the center of the galaxy towards the outer regions.
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.
Population III Stars: Population III stars are the earliest generation of stars that formed in the universe, composed primarily of hydrogen and helium with little to no heavier elements. These stars played a crucial role in the evolution of the universe, providing the initial sources of light and energy that shaped the formation of the first galaxies and quasars.
Quasars: Quasars are extremely luminous active galactic nuclei powered by supermassive black holes at their centers. They emit massive amounts of energy, often outshining entire galaxies.
Quasars: Quasars are extremely luminous, compact objects at the centers of some distant galaxies. They are powered by supermassive black holes that are actively accreting matter, releasing enormous amounts of energy across the electromagnetic spectrum. Quasars are important for understanding the large-scale structure of the universe, the formation of spectral lines, the Doppler effect, evidence for black holes, observations of distant galaxies, and the composition of the universe.
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.
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.
Spitzer Space Telescope: The Spitzer Space Telescope is an infrared space observatory launched by NASA in 2003. It is designed to detect and study objects in the infrared spectrum, which is invisible to the human eye but can reveal important information about the composition and temperature of celestial bodies.
Starburst Galaxies: Starburst galaxies are a type of galaxy characterized by an extremely high rate of star formation, producing new stars at a much faster pace than normal galaxies. This intense burst of star-forming activity is typically triggered by events such as galaxy collisions or mergers, as well as the inflow of large amounts of gas and dust into the galaxy's central regions.
Very Large Telescope: The Very Large Telescope (VLT) is a state-of-the-art astronomical observatory located in Chile, operated by the European Southern Observatory (ESO). It is one of the world's most advanced ground-based optical and near-infrared telescopes, renowned for its remarkable imaging capabilities and ability to observe distant galaxies.