7.4 Infrared and submillimeter astronomy
7 min read•august 14, 2024
Infrared and submillimeter astronomy lets us peek into dusty cosmic regions invisible to regular telescopes. These wavelengths reveal hidden star nurseries, , and even the heart of our galaxy.
By studying light from cool dust and molecules, we can learn about the chemistry of space. This helps us understand how stars and planets form, and maybe even how life began in the universe.
Principles of Infrared and Submillimeter Astronomy
Wavelength Ranges and Penetration of Interstellar Dust
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- Infrared astronomy studies electromagnetic radiation with wavelengths longer than visible light but shorter than radio waves, typically in the range of 1 to 100 microns
- Submillimeter astronomy focuses on wavelengths between and microwave regions, usually 0.3 to 1 millimeter
- Infrared and submillimeter radiation can penetrate clouds, allowing the observation of regions obscured at visible wavelengths
- Enables the study of star-forming regions, molecular clouds, and the galactic center
Sources of Infrared and Submillimeter Emission
- Infrared and submillimeter emission arises from various sources
- from dust grains
- Molecular rotational and vibrational transitions
- Fine-structure lines of atoms and ions
- The Earth's atmosphere is largely opaque to infrared and submillimeter radiation due to absorption by and other molecules
- Observations are conducted using high-altitude telescopes, airborne observatories (SOFIA), or space-based telescopes (Herschel, JWST) to minimize atmospheric interference
Resolution and Techniques in Infrared and Submillimeter Astronomy
- The resolution of infrared and submillimeter telescopes is typically lower than that of visible-light telescopes due to the longer wavelengths
- Larger apertures and interferometric techniques are employed to improve angular resolution
- Interferometry combines signals from multiple telescopes to achieve higher resolution (ALMA)
- is widely used to study molecular transitions and chemical compositions
- Provides information about abundances, temperatures, and densities of interstellar gas
Key Molecules in Infrared and Submillimeter Astronomy
Molecular Transitions and Chemical Composition
- Infrared and submillimeter astronomy is particularly sensitive to the rotational and vibrational transitions of molecules
- Provides valuable information about the chemical composition, temperature, and density of interstellar gas
- (CO) is one of the most abundant and easily observable molecules in the interstellar medium
- Its rotational transitions, especially the J=1-0 transition at 2.6 mm, are used to trace molecular gas and study the structure and kinematics of molecular clouds
- Water (H2O) is another important molecule observed in the infrared and submillimeter
- Its rotational transitions serve as a tracer of shock-heated gas and a probe of the physical conditions in star-forming regions and circumstellar envelopes
Complex Organic Molecules and Prebiotic Chemistry
- Complex organic molecules, such as methanol (CH3OH), formaldehyde (H2CO), and methyl cyanide (CH3CN), are detected through their rotational and vibrational transitions in the infrared and submillimeter
- Provides insights into the chemistry of star-forming regions and potential pathways for the formation of prebiotic molecules
- Polycyclic aromatic hydrocarbons (PAHs) exhibit characteristic emission features in the mid-infrared, typically between 3 and 20 microns, arising from their vibrational modes
- These features are ubiquitous in the interstellar medium and are used to study the properties and evolution of PAHs
Dust Emission and Grain Properties
- Infrared and submillimeter observations also probe the thermal emission from interstellar dust grains, which peaks in the far-infrared and submillimeter regions
- The spectral energy distribution of dust emission provides information about the temperature, composition, and size distribution of dust grains
- Helps understand the role of dust in interstellar chemistry and processes
- Dust grains can act as catalysts for chemical reactions and provide surfaces for molecule formation
- Studying dust properties is crucial for understanding the chemical evolution of the interstellar medium
Telescopes for Infrared and Submillimeter Astronomy
Ground-Based Telescopes and Interferometers
- The Atacama Large Millimeter/submillimeter Array (ALMA) is a groundbreaking interferometric telescope located in the Atacama Desert in Chile
- Consists of 66 high-precision antennas operating at wavelengths from 0.32 to 3.6 mm
- Provides unprecedented sensitivity and angular resolution for studying the chemistry of molecular clouds, protoplanetary disks, and distant galaxies
- Ground-based submillimeter telescopes, such as the Submillimeter Array (SMA) in Hawaii and the NOrthern Extended Millimeter Array (NOEMA) in the French Alps, provide high-resolution observations of molecular lines and dust continuum emission
- Complements the capabilities of ALMA and space-based observatories
Space-Based Observatories
- The (JWST) is an infrared-optimized space observatory launched in 2021
- Has a 6.5-meter primary mirror and advanced instruments covering wavelengths from 0.6 to 28.5 microns
- Poised to revolutionize our understanding of the chemical evolution of the Universe, from the formation of the first galaxies to the birth of stars and planets
- The , which operated from 2009 to 2013, was a space-based telescope that observed the Universe in the far-infrared and submillimeter wavelengths (55 to 672 microns)
- Its instruments, such as the Heterodyne Instrument for the Far-Infrared (HIFI) and the Photodetector Array Camera and Spectrometer (PACS), provided detailed observations of the chemistry in various astrophysical environments
Airborne Observatories
- The Stratospheric Observatory for Infrared Astronomy (SOFIA) is an airborne observatory consisting of a 2.7-meter telescope mounted on a modified Boeing 747 aircraft
- Flies at altitudes up to 45,000 feet, observing the infrared universe (0.3 to 1,600 microns) above 99% of the Earth's atmospheric water vapor
- Enables high-resolution spectroscopy and of astrochemical targets
- Airborne observatories provide a unique platform for infrared and submillimeter observations, combining the advantages of reduced atmospheric absorption with the flexibility of a mobile telescope
Importance of Infrared and Submillimeter Observations
Studying Star and Planet Formation
- Infrared and submillimeter observations are essential for studying the chemical composition and physical conditions of the cold, dense regions where stars and planets form
- These wavelengths probe the rotational and vibrational transitions of molecules, which are sensitive to the gas temperature and density
- Observations of molecular lines in the infrared and submillimeter provide crucial information about the abundances, excitation, and kinematics of interstellar molecules
- This data is used to constrain astrochemical models, test theories of molecular formation and destruction, and understand the chemical evolution of the Universe
- Infrared and submillimeter observations can penetrate the dusty envelopes surrounding young stellar objects and protoplanetary disks
- Allows the study of the chemical processes that lead to the formation of complex organic molecules and the building blocks of life
High-Resolution Mapping and Chemical Substructures
- The high angular resolution achieved by interferometric observatories like ALMA enables the detailed mapping of molecular emission on scales comparable to protoplanetary disks
- Allows the identification of chemical substructures within these disks, providing insights into the chemical environment in which planets form
- Resolving chemical substructures helps understand the distribution and evolution of molecules during the planet formation process
- Provides constraints on the initial chemical conditions for planetary systems and the potential for the emergence of life
Galactic and Extragalactic Astrochemistry
- Infrared and submillimeter observations of external galaxies allow the investigation of the chemical properties and evolution of galaxies across cosmic time
- These studies shed light on the interplay between chemistry and galaxy evolution, star formation, and the build-up of heavy elements in the Universe
- Studying the astrochemistry of different galactic environments (e.g., spiral arms, central regions, halos) helps understand the role of chemistry in regulating star formation and galactic structure
- Observations of high-redshift galaxies in the infrared and submillimeter provide insights into the chemical evolution of the early Universe
- Allows the study of the first generations of stars and the formation of heavy elements
Infrared and Submillimeter Astronomy vs Other Wavelength Ranges
Comparison with Visible-Light Astronomy
- Compared to visible-light astronomy, infrared and submillimeter observations can penetrate interstellar dust clouds, revealing the hidden regions of star formation and the galactic center
- However, the angular resolution of infrared and submillimeter telescopes is typically lower than that of visible-light telescopes due to the longer wavelengths
- Requires larger apertures or interferometric techniques to achieve high resolution
Comparison with Radio Astronomy
- Radio astronomy, which focuses on wavelengths longer than 1 mm, is also sensitive to molecular transitions and can probe the cold, dense regions of the interstellar medium
- However, radio observations generally have lower angular resolution than submillimeter observations
- The number of observable molecular transitions decreases at longer wavelengths
Comparison with High-Energy Astronomy
- X-ray and gamma-ray astronomy probe the hot, energetic processes in the Universe, such as stellar coronae, supernova remnants, and active galactic nuclei
- While these wavelengths are not directly sensitive to molecular transitions, they can provide information about the high-energy processes that drive chemical reactions and ionization in astrophysical environments
- Ultraviolet astronomy is sensitive to the electronic transitions of atoms and molecules, and it is particularly useful for studying the chemistry of diffuse interstellar clouds and the ionized regions around hot stars
- However, ultraviolet observations are strongly affected by interstellar extinction and require space-based observatories
Unique Niche of Infrared and Submillimeter Astronomy
- Infrared and submillimeter astronomy occupy a unique niche in the electromagnetic spectrum, bridging the gap between the cold, dense regions probed by radio observations and the hot, ionized regions studied by ultraviolet, X-ray, and gamma-ray astronomy
- The combination of observations across multiple wavelength ranges provides a comprehensive view of the chemical processes and physical conditions in astrophysical environments
- Allows the study of the full range of chemical phenomena, from the formation of simple molecules to the synthesis of complex organic compounds
- Infrared and submillimeter observations are crucial for understanding the chemical evolution of the Universe and the origins of life
- Provides a unique window into the hidden regions of star and planet formation, where the building blocks of life are assembled
Key Terms to Review (24)
Absorption features: Absorption features are specific wavelengths in the spectrum of light where certain elements or molecules absorb radiation, leading to a decrease in intensity at those wavelengths. These features are crucial for identifying the chemical composition and physical conditions of astronomical objects since they provide insights into the presence of various elements and compounds in space.
Ammonia: Ammonia (NH₃) is a simple nitrogen-containing molecule crucial in astrochemistry, serving as a fundamental building block for more complex organic compounds. Its presence in various astronomical environments, such as interstellar clouds and planetary atmospheres, provides key insights into chemical processes that shape celestial bodies and the evolution of the universe.
Blackbody radiation: Blackbody radiation refers to the electromagnetic radiation emitted by an idealized perfect absorber and emitter of energy at thermal equilibrium. This concept is crucial for understanding the emission spectra of astronomical objects, as it describes how objects radiate energy depending on their temperature. The blackbody radiation curve illustrates how intensity varies with wavelength and temperature, playing a significant role in infrared and submillimeter astronomy.
Carbon monoxide: Carbon monoxide (CO) is a colorless, odorless gas that plays a crucial role in astrochemistry as a key molecular species in the interstellar medium and various astrophysical environments. It is significant for understanding chemical processes and interactions among molecules, particularly in regions where star formation occurs and around evolved stars.
Chemical Kinetics: Chemical kinetics is the branch of physical chemistry that studies the rates of chemical reactions and the factors that influence these rates. It plays a critical role in understanding how quickly reactions occur in various environments, which is essential for analyzing processes in space, like gas-phase reactions in the interstellar medium and chemical transformations in protoplanetary disks.
Doppler Shift: Doppler shift refers to the change in frequency or wavelength of waves from a source that is moving relative to an observer. This phenomenon is significant in understanding how celestial objects are moving towards or away from us, which is especially important in the study of infrared and submillimeter astronomy, where light emitted from distant galaxies and star-forming regions can be redshifted or blueshifted.
Far-infrared: Far-infrared refers to the portion of the electromagnetic spectrum that lies between the wavelengths of 15 micrometers and 1 millimeter. This range is crucial for understanding various astronomical phenomena, particularly in the study of cool celestial objects such as star-forming regions, comets, and interstellar dust. Far-infrared observations help astronomers investigate the thermal emission from these objects, providing insight into their physical conditions and chemical compositions.
Herschel Space Observatory: The Herschel Space Observatory was a space telescope launched by the European Space Agency (ESA) in 2009 to observe the universe in the far-infrared and submillimeter wavelengths. It played a crucial role in studying the formation of stars, the chemical composition of protostellar objects, and the cold regions of space where new stars are born.
Imaging: Imaging refers to the process of capturing and visualizing astronomical objects and phenomena using various wavelengths of electromagnetic radiation. In infrared and submillimeter astronomy, imaging is crucial because it allows scientists to observe cooler celestial bodies, like star-forming regions and distant galaxies, that emit radiation primarily in these wavelengths, providing valuable insights into their structure and composition.
Infrared telescopes: Infrared telescopes are specialized instruments designed to observe astronomical objects by detecting infrared radiation, which is a type of electromagnetic radiation with wavelengths longer than visible light. These telescopes allow astronomers to study cool and dim objects such as dust clouds, star-forming regions, and distant galaxies that are not easily visible through traditional optical telescopes. By capturing infrared light, these instruments reveal information about the temperature, composition, and dynamics of celestial bodies.
Interstellar dust: Interstellar dust refers to tiny solid particles found in the space between stars, primarily composed of elements like carbon, silicon, and oxygen. These grains play a crucial role in various cosmic processes, such as star formation, chemical reactions, and the thermal balance of the interstellar medium.
James Webb Space Telescope: The James Webb Space Telescope (JWST) is a large, space-based observatory designed to observe the universe in infrared light. Its advanced technology enables astronomers to study the formation of stars and galaxies, investigate the chemical composition of celestial objects, and explore the potential for life on other planets.
Molecular Clouds: Molecular clouds are dense regions in the interstellar medium where gas and dust are concentrated, leading to conditions that allow for the formation of molecules, particularly hydrogen molecules (H₂). These clouds play a crucial role in the lifecycle of stars and the chemical evolution of the universe, serving as the primary sites for star formation and the birthplace of various celestial objects.
Near-infrared: Near-infrared refers to a region of the electromagnetic spectrum with wavelengths ranging from about 0.75 to 1.5 micrometers, situated just beyond the visible light spectrum. This range is significant for astronomical observations as it allows scientists to study celestial objects that may be obscured by dust or gas, providing insights into their temperature, composition, and dynamics.
Photometry: Photometry is the science of measuring visible light and its intensity as perceived by the human eye. This technique plays a crucial role in various fields, including astronomy, where it helps in determining the brightness of celestial objects and their distance from Earth. Understanding photometry is essential for analyzing the spectra of light emitted or absorbed by atoms and molecules, which can reveal critical information about atomic structure and chemical compositions across the universe.
Radiative transfer models: Radiative transfer models are mathematical frameworks used to describe the transfer of radiation through a medium, which is crucial for understanding how light interacts with matter in various astrophysical environments. These models help analyze how energy from stars and other celestial objects propagates through dust and gas, particularly in the infrared and submillimeter wavelengths, allowing astronomers to interpret observations and derive physical properties of astronomical objects.
Spectral lines: Spectral lines are specific wavelengths of light that are absorbed or emitted by atoms and molecules during electronic transitions. These lines appear as distinct features in a spectrum and provide crucial information about the composition, temperature, density, and motion of astronomical objects. The presence of spectral lines is a key tool for astronomers to analyze celestial bodies, especially in infrared and submillimeter wavelengths, where many important molecular transitions occur.
Spectrometers: Spectrometers are scientific instruments used to measure and analyze the spectrum of light or electromagnetic radiation. They separate light into its component wavelengths, allowing scientists to study the properties of different substances based on how they interact with various wavelengths of light, which is particularly important in understanding celestial bodies and phenomena in infrared and submillimeter astronomy.
Spectroscopy: Spectroscopy is a scientific technique used to analyze the interaction between matter and electromagnetic radiation. This method allows scientists to determine the composition, structure, and physical properties of substances by studying the light they emit, absorb, or scatter.
Star formation: Star formation is the process by which dense regions within molecular clouds in the interstellar medium collapse under their own gravity to form stars. This phenomenon is crucial for understanding the lifecycle of matter in the universe and how stars contribute to the evolution of galaxies and the cosmos.
Submillimeter interferometers: Submillimeter interferometers are advanced astronomical instruments that combine signals from multiple telescopes to achieve high-resolution imaging of celestial objects in the submillimeter wavelength range. These instruments are crucial for studying cold and dense regions of space, such as star-forming regions and molecular clouds, which emit radiation primarily in the submillimeter spectrum, revealing important information about their composition and dynamics.
Submillimeter waves: Submillimeter waves are a type of electromagnetic radiation with wavelengths ranging from 0.1 to 1 millimeter, which places them between infrared radiation and microwaves on the electromagnetic spectrum. These waves are significant in astronomy because they can penetrate dense interstellar dust, allowing scientists to study celestial objects and phenomena that are otherwise obscured in other wavelengths.
Thermal emission: Thermal emission refers to the process by which an object emits electromagnetic radiation due to its temperature. This radiation can be in the form of infrared or submillimeter waves, which are particularly important for understanding the thermal characteristics of celestial objects. Objects at different temperatures emit radiation at varying wavelengths, allowing astronomers to study their composition, temperature, and energy processes through the analysis of this emitted radiation.
Water vapor: Water vapor is the gaseous state of water that exists in the atmosphere and plays a crucial role in various atmospheric and astronomical processes. As a key component of clouds, it influences weather patterns, climate, and the chemical composition of planetary atmospheres, while also being an important molecule in star formation and interstellar chemistry.