25.2 Spiral Structure
3 min read•june 12, 2024
Spiral galaxies fascinate astronomers with their stunning arms and complex structures. Radio and infrared observations reveal the distribution of gas, dust, and stars, painting a comprehensive picture of these cosmic beauties.
and shape , triggering as gas compresses. Over time, gas depletion and galactic interactions transform spiral structures, leading to the diverse array of galaxies we observe today.
Mapping and Evolution of Spiral Structure in Galaxies
Mapping of Milky Way's spiral structure
Top images from around the web for Mapping of Milky Way's spiral structure
Scutum-Centaurus Arm Archives - Universe Today View original
Is this image relevant?
Spiral Structure | Astronomy View original
Is this image relevant?
The Architecture of the Galaxy · Astronomy View original
Is this image relevant?
Scutum-Centaurus Arm Archives - Universe Today View original
Is this image relevant?
Spiral Structure | Astronomy View original
Is this image relevant?
1 of 3
Top images from around the web for Mapping of Milky Way's spiral structure
Scutum-Centaurus Arm Archives - Universe Today View original
Is this image relevant?
Spiral Structure | Astronomy View original
Is this image relevant?
The Architecture of the Galaxy · Astronomy View original
Is this image relevant?
Scutum-Centaurus Arm Archives - Universe Today View original
Is this image relevant?
Spiral Structure | Astronomy View original
Is this image relevant?
1 of 3
- detect emissions from neutral atomic hydrogen (HI) allowing mapping of in the galaxy
- Radio observations also detect emissions as carbon monoxide (CO) is a tracer of molecular hydrogen (H2) revealing the distribution of molecular clouds ()
- Infrared observations penetrate dust obscuration as dust absorbs visible light but allows infrared to pass through revealing the location of young, massive stars often associated with ()
- Infrared observations allow mapping of the stellar distribution
- Combining radio and infrared data provides a comprehensive view of the revealing the distribution of gas, dust, and stars in the galaxy
Differential rotation and spiral arms
- Inner regions of the galaxy rotate faster than outer regions leading to the winding up of material in the galactic disk
- Spiral arms are regions of higher density where stars and gas move in and out of as they orbit the galaxy
- Spiral arms are not material structures but rather patterns that rotate at a different speed than the stars and gas (density waves)
- As gas enters the higher density spiral arm region, it gets compressed triggering
- Newly formed stars are more concentrated in the spiral arms and young, massive stars ionize the surrounding gas making the arms more prominent ()
- Massive stars in spiral arms explode as supernovae with shock waves compressing nearby gas triggering further star formation helping maintain the spiral arm structure ()
Galactic Rotation and Interstellar Medium
- affects the distribution of stars and gas in spiral galaxies
- The , consisting of gas and dust, plays a crucial role in shaping spiral structure
- Star formation is enhanced in regions where the is compressed, often occurring in spiral arms
Evolution of galactic spiral structure
- Spiral galaxies in the early universe had higher gas content and star formation rates with more prominent and well-defined spiral arms
- Gas depletion over time from star formation reduces the gas content available for forming new stars affecting spiral structure evolution
- Mergers and interactions through gravitational forces can disrupt or enhance spiral structure with major mergers transforming spiral galaxies into elliptical galaxies
- involves internal processes that slowly change the galaxy's structure over time
- Bar formation from redistribution of angular momentum can lead to the formation of a central bar driving gas inflows and affecting spiral arm structure
- from stellar encounters and minor mergers can increase the velocity dispersion of stars leading to a thickening of the disk and a reduction in spiral arm prominence
- Present-day spiral galaxies have lower gas content and star formation rates compared to the early universe with less prominent spiral arms and increased prevalence of barred spiral galaxies (, )
Key Terms to Review (28)
21 cm Hydrogen Line: The 21 cm hydrogen line, also known as the HI line, is a spectral line emitted by neutral hydrogen atoms in the universe. This line is caused by the transition between the two hyperfine levels of the ground state of the hydrogen atom and has a wavelength of 21.106 cm, or a frequency of 1420.406 MHz.
21-cm line: The 21-cm line is a spectral line emitted by neutral hydrogen atoms due to the hyperfine transition. It is a crucial tool in radio astronomy for mapping interstellar gas and studying galactic structures.
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.
Carina Nebula: The Carina Nebula is a large, complex star-forming region located in the southern constellation of Carina. It is known for its stunning visual appearance and its significance in the study of stellar formation and the structure of our Milky Way galaxy.
CO Molecular Line: The CO (carbon monoxide) molecular line refers to the spectral line emitted by the carbon monoxide molecule, which is commonly used as a tracer for studying the structure and dynamics of the interstellar medium, particularly in the context of spiral galaxies.
Density Wave Theory: Density wave theory is a model that explains the formation and maintenance of spiral structures in spiral galaxies. It proposes that the spiral arms are not made up of the same stars over time, but rather are regions of higher density that propagate through the galactic disk, causing the stars to bunch up and appear as spiral arms.
Density Waves: Density waves are spiral-shaped patterns of increased density that rotate through the disks of spiral galaxies, including our own Milky Way. These waves of higher density trigger star formation and are responsible for the distinctive spiral arm structure observed in many galaxies.
Differential galactic rotation: Differential galactic rotation is the phenomenon where different parts of a galaxy rotate at different speeds. In spiral galaxies, such as the Milky Way, stars closer to the center rotate faster than those in the outer regions.
Differential rotation: Differential rotation is the phenomenon where different parts of a rotating object, like a star or planet, rotate at different speeds. In stars like the Sun, this means the equator rotates faster than the poles.
Differential Rotation: Differential rotation is a phenomenon where different parts of a rotating body, such as a star or a planet, rotate at different angular velocities. This non-uniform rotation is a crucial concept in understanding the solar cycle and the spiral structure of galaxies.
Disk Heating: Disk heating refers to the process by which the velocity dispersion of stars in a galaxy's disk increases over time. This leads to a thickening of the disk and a more random, less organized motion of the stars within it.
Galactic Rotation: Galactic rotation refers to the circular motion of stars and other celestial bodies within a galaxy around the galaxy's center of mass. This rotation is a fundamental feature of the architecture and structure of galaxies, including the Milky Way in which our solar system resides.
HI Distribution: The HI (neutral atomic hydrogen) distribution refers to the spatial distribution and density of neutral hydrogen gas in a galaxy. This distribution is a crucial component in understanding the structure and evolution of spiral galaxies, as it provides insights into the dynamics and composition of the interstellar medium.
HII Regions: HII regions are large, diffuse clouds of ionized hydrogen gas found in star-forming regions of galaxies. These regions are characterized by the presence of hot, young, and massive stars that emit intense ultraviolet radiation, which ionizes the surrounding hydrogen gas, creating a glowing, emission-line nebula.
Interstellar medium: Interstellar medium (ISM) is the matter that exists in the space between star systems within a galaxy. It consists of gas (both ionized and neutral) and dust, playing a crucial role in the life cycle of cosmic material.
Interstellar Medium: The interstellar medium refers to the vast expanse of gas and dust that fills the space between stars within a galaxy. It is the material that exists in the space between solar systems and plays a crucial role in the formation and evolution of stars, as well as the overall structure and dynamics of galaxies.
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.
Orion Nebula: The Orion Nebula is a vast, luminous cloud of gas and dust located in the Milky Way galaxy, situated in the constellation of Orion. It is one of the most well-known and extensively studied star-forming regions in our galaxy, providing valuable insights into the processes of stellar birth and early stellar evolution.
Radio observations: Radio observations involve detecting and analyzing radio waves emitted by astronomical objects. These observations provide critical information about the structure and dynamics of celestial entities.
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.
Self-Propagating Star Formation: Self-propagating star formation is a process where the formation of one star can trigger the formation of additional stars in the surrounding region. This phenomenon is particularly relevant in the context of spiral structure in galaxies, as it can contribute to the maintenance and evolution of the spiral pattern.
Spiral arms: Spiral arms are regions of a spiral galaxy that extend from the center and wind outward in a spiral pattern. They are sites of high star formation activity and contain young, hot stars, gas, and dust.
Spiral Arms: 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 the Milky Way and many other galaxies, and play a crucial role in the architecture and evolution of these galactic systems.
Spiral Structure: Spiral structure refers to the distinctive pattern of rotating, elongated arms that emanate from the center of certain galaxies, particularly spiral galaxies. This structure is characterized by the presence of young, hot, and massive stars that trace out the spiral arms, giving these galaxies their iconic appearance.
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.