Glossary

6.5 Starburst galaxies

10 min read•august 20, 2024

are cosmic powerhouses, experiencing star formation rates far beyond normal galaxies. These intense bursts of stellar creation shape galaxy evolution and offer a glimpse into the early universe when star formation was more common.

Studying starbursts reveals the triggers and impacts of extreme star formation. From to extended bursts, these galaxies come in various types, each providing unique insights into the processes that drive rapid stellar birth and galactic transformation.

Starburst galaxies overview

  • Starburst galaxies are galaxies experiencing an exceptionally high rate of star formation compared to typical galaxies
  • These galaxies are important for understanding the processes that drive extreme star formation and the impact of these events on galaxy evolution
  • Studying starburst galaxies provides insights into the conditions prevalent in the early universe when star formation rates were generally higher

Definition of starburst galaxies

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  • Starburst galaxies are defined as galaxies with star formation rates significantly higher than the average rate for galaxies of similar mass and type
  • The star formation rate in starburst galaxies can be tens to hundreds of times higher than in normal galaxies
  • Starbursts are often triggered by specific events such as galaxy mergers or interactions, leading to a rapid increase in star formation activity

Characteristics of starburst galaxies

  • High star formation rates, often exceeding 10-100 solar masses per year
  • Intense emission from young, dominating the galaxy's spectrum
  • Presence of numerous star-forming regions and stellar clusters
  • Increased dust content due to the high rate of star formation
  • Strong infrared emission from dust heated by young stars
  • Galactic outflows driven by stellar winds and supernovae

Star formation in starburst galaxies

  • Star formation in starburst galaxies is characterized by its extreme intensity and the presence of numerous young, massive stars
  • The high star formation rates in these galaxies have significant implications for their evolution and the surrounding interstellar medium

Extreme star formation rates

  • Starburst galaxies exhibit star formation rates that are significantly higher than those observed in normal galaxies
  • These rates can range from a few solar masses per year to hundreds of solar masses per year, depending on the galaxy's size and the intensity of the starburst
  • The extreme star formation rates are often concentrated in specific regions within the galaxy, such as the nucleus or extended star-forming regions

Triggers for starburst activity

  • Galaxy mergers and interactions are common triggers for starburst activity
    • The gravitational tidal forces during mergers can compress gas clouds and induce intense star formation
  • Galactic bars can channel gas into the central regions of galaxies, fueling nuclear starbursts
  • Accretion of gas from the intergalactic medium can also provide the necessary fuel for enhanced star formation

Duration of starburst phase

  • The starburst phase in galaxies is relatively short-lived compared to the overall lifetime of the galaxy
  • Typical durations of starburst activity range from a few million years to a few hundred million years
  • The duration depends on factors such as the available gas supply, the efficiency of star formation, and the feedback processes that can regulate or suppress further star formation

Stellar populations in starbursts

  • Starburst galaxies are characterized by a high proportion of young, massive stars
  • These stars emit intense ultraviolet radiation and have short lifetimes, typically a few million years
  • The presence of numerous young stellar clusters and associations is a hallmark of starburst galaxies
  • The stellar populations in starbursts also include older stars formed before the onset of the starburst event

Interstellar medium in starburst galaxies

  • The in starburst galaxies is significantly impacted by the high rate of star formation
  • The ISM plays a crucial role in regulating star formation and is, in turn, shaped by the feedback processes associated with young, massive stars

Gas content and distribution

  • Starburst galaxies typically have higher gas fractions compared to normal galaxies
  • The gas is often concentrated in dense, compact regions where star formation occurs
  • Molecular gas, particularly H2, is abundant in starburst galaxies and serves as the fuel for star formation
  • The distribution of gas can be affected by galaxy interactions, mergers, and galactic outflows

Dust content and obscuration

  • Starburst galaxies contain significant amounts of dust, which is produced by the intense star formation activity
  • Dust grains absorb and scatter ultraviolet and optical light, leading to obscuration of the starburst regions
  • The dust is heated by the intense radiation from young stars and re-emits the energy in the infrared wavelengths
  • can make it challenging to study starburst galaxies in visible light and often requires observations at infrared or radio wavelengths

Feedback from star formation

  • The high rate of star formation in starburst galaxies leads to strong feedback effects on the ISM
  • Stellar winds from massive stars and explosions inject energy and momentum into the surrounding gas
  • This feedback can trigger turbulence, heat the gas, and drive galactic outflows
  • Feedback processes can also regulate star formation by disrupting gas clouds and suppressing further collapse

Galactic winds and outflows

  • Starburst galaxies often exhibit driven by the collective effect of stellar feedback
  • These outflows can carry gas, dust, and heavy elements out of the galaxy and into the intergalactic medium
  • Galactic winds can have velocities reaching hundreds to thousands of kilometers per second
  • Outflows can have a significant impact on the evolution of starburst galaxies by removing gas and regulating future star formation

Types of starburst galaxies

  • Starburst galaxies can be classified into different categories based on their physical properties, the spatial extent of the starburst, and their luminosity
  • Understanding the different types of starburst galaxies helps in studying their characteristics and the mechanisms driving their star formation

Nuclear starbursts vs extended starbursts

  • Nuclear starbursts are characterized by intense star formation concentrated in the central regions of the galaxy, typically within a few hundred parsecs of the nucleus
  • have star formation activity distributed over larger scales, often spanning several kiloparsecs
  • The spatial extent of the starburst can provide insights into the triggering mechanisms and the gas distribution within the galaxy

Luminous infrared galaxies (LIRGs)

  • LIRGs are galaxies with infrared luminosities between 101110^{11} and 101210^{12} solar luminosities
  • The high infrared luminosity is attributed to dust heated by intense star formation activity
  • LIRGs are often associated with galaxy mergers and interactions, which can trigger the starburst activity
  • Examples of LIRGs include Arp 220 and NGC 6240

Ultraluminous infrared galaxies (ULIRGs)

  • ULIRGs have even higher infrared luminosities, exceeding 101210^{12} solar luminosities
  • These galaxies are among the most luminous objects in the universe and are predominantly powered by intense starbursts
  • ULIRGs are almost always associated with galaxy mergers and exhibit highly concentrated star formation in their central regions
  • Examples of ULIRGs include Markarian 231 and IRAS F10214+4724

Blue compact dwarf galaxies

  • are small, gas-rich galaxies undergoing intense star formation
  • These galaxies have low metallicities and are characterized by their blue colors, indicating a young stellar population
  • The starburst activity in blue compact dwarfs is often triggered by the accretion of gas from the surrounding environment
  • Examples of blue compact dwarf galaxies include I Zwicky 18 and NGC 1705

Observational properties of starburst galaxies

  • Starburst galaxies exhibit distinct observational properties across different wavelength regimes
  • These properties provide valuable information about the physical conditions, star formation activity, and the interstellar medium in these galaxies

Optical and UV emission

  • Starburst galaxies are characterized by strong optical and ultraviolet emission from young, massive stars
  • The spectra of starburst galaxies show prominent emission lines from hydrogen (Hα, Hβ) and other ionized species, indicating the presence of H II regions
  • The UV continuum emission is enhanced due to the contribution from hot, young stars
  • Dust obscuration can significantly attenuate the optical and UV emission, especially in the most extreme starbursts

Infrared emission and dust heating

  • Starburst galaxies emit a significant fraction of their energy in the infrared wavelengths
  • The intense star formation activity heats the dust grains in the interstellar medium, which then re-emit the energy in the infrared
  • The infrared emission provides a measure of the total star formation rate, as it is less affected by dust obscuration compared to optical and UV wavelengths
  • The infrared spectra of starburst galaxies often show strong emission features from polycyclic aromatic hydrocarbons (PAHs) and silicate dust grains

Radio emission and supernovae

  • Starburst galaxies are strong radio emitters due to the presence of synchrotron radiation from relativistic electrons accelerated in supernova remnants
  • The radio emission is a tracer of the recent star formation activity, as it is linked to the rate of core-collapse supernovae
  • The radio continuum emission can also arise from free-free emission in H II regions surrounding young, massive stars
  • Radio observations provide a dust-unbiased view of the star formation activity in starburst galaxies

X-ray emission and hot gas

  • Starburst galaxies can emit X-rays from various sources, including hot gas, X-ray binaries, and supernova remnants
  • The intense star formation activity can heat the interstellar gas to temperatures of millions of degrees, producing diffuse X-ray emission
  • X-ray binaries, formed by the collapse of massive stars into compact objects (neutron stars or black holes), are abundant in starburst galaxies and contribute to the X-ray emission
  • Supernova remnants can also emit X-rays as the expanding shock waves heat the surrounding gas

Evolution of starburst galaxies

  • Starburst galaxies undergo significant evolution during and after the starburst phase
  • Understanding the evolutionary processes in starburst galaxies is crucial for tracing their impact on galaxy growth and the formation of large-scale structures

Starburst-AGN connection

  • There is a close connection between starburst activity and the presence of active galactic nuclei (AGN) in some galaxies
  • The intense star formation in the central regions of starburst galaxies can fuel the growth of supermassive black holes, leading to AGN activity
  • AGN feedback, in the form of outflows and radiation pressure, can also impact the star formation activity in the host galaxy
  • The interplay between starbursts and AGN is important for understanding the co-evolution of galaxies and their central black holes

Post-starburst galaxies and E+A galaxies

  • , also known as E+A or K+A galaxies, are galaxies that have recently undergone a starburst phase but show no ongoing star formation
  • These galaxies exhibit strong Balmer absorption lines, indicating the presence of a significant population of A-type stars formed during the starburst
  • The lack of ongoing star formation suggests that the starburst was rapidly quenched, possibly due to the exhaustion of gas or feedback processes
  • Post-starburst galaxies provide insights into the transitional phase between starbursts and quiescent galaxies

Impact on galaxy evolution

  • Starburst events can have a profound impact on the evolution of galaxies
  • The intense star formation can rapidly consume the available gas, leading to a depletion of the fuel for future star formation
  • Galactic outflows driven by the starburst can remove gas and metals from the galaxy, affecting its chemical evolution and ability to form new stars
  • Starbursts can also contribute to the growth of the stellar mass and the formation of globular clusters

Starbursts in the early universe

  • Starburst galaxies were more common in the early universe when the overall star formation rate density was higher
  • High-redshift starburst galaxies, such as Lyman-break galaxies and submillimeter galaxies, provide insights into the conditions and processes that shaped galaxy formation in the early universe
  • Studying starburst galaxies at different cosmic epochs helps in understanding the evolution of star formation rates and the buildup of stellar mass over time

Starburst galaxies as probes of galaxy formation

  • Starburst galaxies serve as valuable probes for understanding the processes of galaxy formation and evolution
  • By studying starburst galaxies at different redshifts and in various environments, we can gain insights into the history of star formation and the assembly of galaxies

Insights into star formation history

  • Starburst galaxies provide snapshots of intense star formation episodes throughout cosmic history
  • By comparing the properties of starburst galaxies at different redshifts, we can trace the evolution of star formation rates and the factors that influence them
  • Studying the stellar populations and chemical abundances in starburst galaxies helps in reconstructing the star formation history of galaxies

Constraints on galaxy merger rates

  • Galaxy mergers are a primary trigger for starburst activity, especially in the most luminous infrared galaxies
  • The frequency and properties of starburst galaxies can provide constraints on the galaxy merger rate as a function of redshift
  • By comparing the observed merger rates with theoretical models, we can test our understanding of the hierarchical growth of galaxies

Role in chemical enrichment of galaxies

  • Starburst galaxies play a significant role in the chemical enrichment of galaxies and the intergalactic medium
  • The intense star formation in starbursts leads to the production of heavy elements through stellar nucleosynthesis
  • Galactic outflows driven by the starburst can transport these newly synthesized elements into the surrounding environment
  • Studying the chemical abundances in starburst galaxies and their outflows helps in understanding the chemical evolution of galaxies and the distribution of metals in the universe

Implications for reionization and first galaxies

  • Starburst galaxies in the early universe may have contributed to the reionization of the intergalactic medium
  • The intense UV radiation from young, massive stars in starburst galaxies could have provided a significant fraction of the ionizing photons needed to reionize the universe
  • Studying the properties of high-redshift starburst galaxies, such as their star formation rates and escape fractions of ionizing radiation, can help constrain models of reionization
  • Understanding the role of starburst galaxies in the early universe is crucial for unraveling the formation and evolution of the first galaxies

Key Terms to Review (30)

Astrophysics: Astrophysics is a branch of astronomy that focuses on understanding the physical properties and underlying processes of celestial objects and phenomena. It combines the principles of physics and astronomy to study the universe's structure, evolution, and behavior, including how stars form, evolve, and end their life cycles. This scientific field connects deeply with concepts such as cosmic expansion, the formation of galaxies, and theoretical frameworks that propose multiple universes.
Blue compact dwarf galaxies: Blue compact dwarf galaxies are small, low-mass galaxies characterized by intense star formation and a blue appearance due to the presence of young, hot stars. They typically have high surface brightness and a compact size, making them distinct in the universe, especially when compared to larger, more evolved galaxies. Their rapid star formation is often associated with interactions or mergers with other galaxies.
Cosmology: Cosmology is the scientific study of the large-scale properties and evolution of the universe as a whole. It encompasses understanding the origins, structure, and dynamics of the cosmos, including theories on its expansion and the nature of celestial objects. Key areas such as starburst galaxies and the Friedmann equations provide critical insights into the fundamental processes that govern cosmic evolution and shape the universe's large-scale structure.
Dust Lanes: Dust lanes are dark, elongated features found in galaxies, primarily composed of interstellar dust that absorbs and scatters light. These lanes are often visible in spiral galaxies and are significant indicators of star formation regions, marking areas where new stars are being born from the dense material within them. They play a vital role in the structure and appearance of galaxies, influencing how we perceive their morphology.
Dust obscuration: Dust obscuration refers to the phenomenon where interstellar dust absorbs and scatters light from stars and galaxies, significantly affecting the observed brightness and color of astronomical objects. This effect is particularly important in starburst galaxies, where intense star formation can lead to substantial amounts of dust being produced, thereby impacting how we perceive these galaxies and their associated phenomena.
E+a galaxies: e+a galaxies, or 'post-starburst' galaxies, are a category of galaxies that exhibit both early-type galaxy characteristics and a recent burst of star formation. These galaxies show features typical of elliptical galaxies, like smooth, featureless light profiles, alongside spectral signatures indicating a burst of star formation that has occurred relatively recently, often within the last 1 billion years. This unique combination makes them key to understanding galaxy evolution and the star formation processes occurring in different environments.
Elliptical Galaxies: Elliptical galaxies are a type of galaxy characterized by their smooth, featureless light profiles and an elliptical shape. They generally contain older stars, little to no gas or dust, and exhibit minimal star formation compared to spiral galaxies. Understanding their formation and evolution provides insights into the processes that govern galaxy development and structure.
Extended starbursts: Extended starbursts refer to periods of intense star formation in galaxies that last longer than typical starburst events, often spanning tens of millions of years. These extended periods of activity can produce large numbers of stars and can significantly alter the structure and evolution of the galaxy, contributing to the formation of new stellar populations and the enrichment of interstellar medium with heavy elements.
Galactic winds and outflows: Galactic winds and outflows refer to the streams of gas that are expelled from a galaxy, often as a result of intense star formation or the activity of supermassive black holes. These processes can have significant impacts on the galaxy's evolution, influencing star formation rates, the distribution of gas, and the overall chemical enrichment of the intergalactic medium. Such winds can carry energy and material away from the galaxy, effectively shaping its structure and future development.
Gas inflow: Gas inflow refers to the process by which gas, often in the form of hydrogen and helium, moves into a galaxy from its surroundings, typically triggered by gravitational interactions or collisions. This inflow is critical for fueling star formation, particularly in starburst galaxies, where rapid star formation occurs due to an abundance of gas being available. The influx of gas can lead to a significant increase in the rate of star production and influence the overall evolution of the galaxy.
Hierarchical Structure Formation: Hierarchical structure formation is a cosmological model that describes how the universe evolves from small, simple structures to larger, more complex ones, often involving the merging of smaller entities to form bigger systems. This process plays a vital role in shaping the formation and distribution of galaxies, leading to the diversity of galaxy types and their environments. As smaller structures collapse under gravity, they create gravitational wells that attract more mass, eventually resulting in the formation of galaxy clusters and large-scale structures in the universe.
High star formation rate: A high star formation rate refers to the rapid creation of new stars within a galaxy, often indicated by a significant amount of gas and dust being converted into stars over a short period. This phenomenon is closely associated with various types of galaxies, particularly those that experience intense gravitational interactions or possess abundant star-forming materials. It highlights the dynamic processes at play in galactic environments where conditions are ripe for stellar birth, leading to vibrant, often chaotic cosmic scenes.
Hubble Space Telescope Observations: Hubble Space Telescope observations refer to the data and images collected by the Hubble Space Telescope, a powerful space-based observatory launched in 1990. These observations have revolutionized our understanding of the universe by allowing astronomers to study celestial objects and phenomena in unprecedented detail, particularly starburst galaxies that exhibit intense star formation activity. Hubble's unique position above Earth's atmosphere eliminates atmospheric distortion, providing clearer images and insights into the processes occurring in these vibrant galaxies.
Interstellar medium (ISM): The interstellar medium (ISM) is the matter that exists in the space between stars in a galaxy, composed of gas, dust, and cosmic rays. It plays a critical role in the life cycle of galaxies by acting as the material from which new stars form and influencing the dynamics of star formation. The ISM is not uniform; it contains regions of varying density, temperature, and composition, which can lead to phenomena such as starburst activity in certain galaxies.
Joan E. McGowan: Joan E. McGowan is a prominent astrophysicist known for her research on starburst galaxies, which are regions of intense star formation within galaxies. Her work has contributed significantly to the understanding of the processes that drive starbursts and their implications for galaxy evolution. By studying the characteristics and environments of starburst galaxies, McGowan has helped illuminate how these phenomena influence the broader structure and behavior of the universe.
Lambda cold dark matter model: The lambda cold dark matter model, often abbreviated as \( \Lambda CDM \), is the prevailing cosmological model that describes the large-scale structure and evolution of the universe. It combines the effects of a cosmological constant, denoted by \( \Lambda \), which represents dark energy, with cold dark matter, a non-baryonic form of matter that interacts only through gravity, playing a crucial role in shaping cosmic structures like galaxies and clusters.
Luminous Infrared Galaxies (LIRGs): Luminous Infrared Galaxies (LIRGs) are galaxies that emit a significant portion of their energy in the infrared spectrum, typically having luminosities greater than 10^{11} L☉, where L☉ is the luminosity of the Sun. These galaxies are often characterized by intense star formation activity, which is fueled by gas and dust, leading to the rapid production of stars. This vigorous starburst activity results in large amounts of dust that absorb the visible light and re-emit it as infrared radiation.
Lyman-alpha emission: Lyman-alpha emission refers to a specific wavelength of ultraviolet light emitted by hydrogen atoms when their electrons transition from the second energy level to the first. This emission is significant in astrophysics, especially in the study of starburst galaxies, where intense star formation leads to abundant ionization of hydrogen and results in strong Lyman-alpha signals.
Massive Stars: Massive stars are those with a mass greater than about eight times that of the Sun. These stars are significant in the universe due to their rapid evolution and their role in creating heavy elements through nuclear fusion, ultimately leading to supernova explosions that enrich the interstellar medium. Their intense luminosity and short lifespans contribute to the dynamics of starburst galaxies, where they can trigger bursts of star formation.
Molecular clouds: Molecular clouds are dense regions of gas and dust in space, primarily composed of hydrogen molecules. They serve as the primary sites for star formation, providing the necessary conditions for gravity to collapse and form stars. These clouds are typically cold, with temperatures around 10-20 K, and their high density allows them to shield molecules from dissociation by ultraviolet radiation, making them crucial for the formation of new stars and planetary systems.
Nuclear starbursts: Nuclear starbursts are intense periods of star formation occurring in the central regions of galaxies, often associated with high levels of gas and dust. These starbursts lead to the rapid creation of new stars, which can outshine the entire galaxy for a brief period. The phenomenon is often triggered by interactions with other galaxies or mergers, causing gas to be funneled into the core and igniting a flurry of stellar activity.
Post-starburst galaxies: Post-starburst galaxies are a specific type of galaxy that exhibit characteristics of having recently experienced an intense burst of star formation, followed by a rapid decline in star production. This transition phase indicates that these galaxies have exhausted their gas reserves and are now entering a period of reduced star activity, which can significantly impact their evolutionary path. Understanding post-starburst galaxies helps astronomers grasp the life cycle of galaxies and the effects of starbursts on their long-term development.
Robert Z. Lynds: Robert Z. Lynds was an influential astronomer known for his work on starburst galaxies, particularly his role in discovering the unique properties and dynamics of these galaxies. He contributed significantly to understanding how intense star formation occurs in specific regions of galaxies, leading to bursts of stellar activity. His research helped shape the modern perspective on galaxy evolution and the processes driving stellar nurseries within starburst galaxies.
Starburst galaxies: Starburst galaxies are a class of galaxies that experience an exceptionally high rate of star formation, often several times greater than that of typical galaxies. This intense star formation is usually triggered by interactions such as mergers with other galaxies or gravitational forces, leading to a burst of activity within the galaxy. The properties and phenomena associated with starburst galaxies connect to various aspects like HII regions, star formation rates, and hierarchical merging.
Starburst-agn connection: The starburst-agn connection refers to the relationship between starburst galaxies, which are characterized by an exceptionally high rate of star formation, and active galactic nuclei (AGN), where supermassive black holes at the center of galaxies are actively accreting matter. In starburst galaxies, intense star formation can trigger the fueling of the AGN, while AGN activity can influence the surrounding environment and potentially quench star formation in the host galaxy. This interplay highlights the dynamic processes occurring in galaxies that are undergoing rapid evolution.
Starbursts in the early universe: Starbursts in the early universe refer to intense periods of star formation that occurred shortly after the Big Bang, resulting in a rapid production of new stars in galaxies. These starbursts are characterized by their high rates of star formation, often several times higher than what is typically observed in present-day galaxies. This phenomenon played a crucial role in shaping the structure and evolution of galaxies during the early stages of cosmic history.
Stellar evolution: Stellar evolution refers to the process by which a star changes over the course of time, from its formation in a molecular cloud to its eventual death and transformation into another astronomical object. This dynamic lifecycle involves several stages, including the main sequence phase, red giant stage, and ultimately leads to outcomes like supernovae or the formation of white dwarfs, neutron stars, or black holes. Understanding stellar evolution is crucial for grasping the complexities of galaxy formation and the phenomena observed in different types of galaxies.
Stellar nurseries: Stellar nurseries are regions in space where new stars are born, characterized by dense clouds of gas and dust. These areas often contain young, hot stars that emit strong ultraviolet radiation, which helps to ionize the surrounding hydrogen gas, creating HII regions. The intense activity and rapid star formation in these nurseries can also lead to the development of starburst galaxies, where a significant number of stars are formed in a short period.
Supernova: A supernova is a powerful and luminous explosion that occurs at the end of a star's life cycle, signaling the death of the star. This explosive event can outshine entire galaxies for a brief period and plays a crucial role in cosmic processes by dispersing heavy elements into space, contributing to stellar feedback, enriching the interstellar medium, and influencing star formation in galaxies.
Ultraluminous Infrared Galaxies (ULIRGs): Ultraluminous infrared galaxies (ULIRGs) are a class of galaxies that emit an exceptionally high amount of infrared radiation, typically more than 10^12 solar luminosities. These galaxies are often characterized by intense star formation and significant activity in their central regions, often housing active supermassive black holes. ULIRGs are vital in understanding the processes behind starburst activity and the evolution of galaxies.
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