Stellar Population Mapping
Stellar Population Mapping is a scientific process that categorizes the stars of the Milky Way Galaxy based on their location, composition, and age. This methodology helps astronomers understand the dynamic nature of stars over time and the evolutionary history of the galaxy. By analyzing attributes such as spatial distribution, kinematics, star chemistry, and age, researchers can identify patterns and relationships among stars, including potential "sibling" stars that originated from the same source. Various tools, particularly spectroscopy, play a crucial role in this mapping process, allowing scientists to investigate light frequencies and determine the chemical composition and other characteristics of stars.
Moreover, techniques using infrared technologies enable astronomers to observe dim stars obscured by dust, revealing valuable data about these celestial bodies. Through this comprehensive mapping, stars are organized into different components of the galaxy: the disk, halo, and bulge, each with unique characteristics. Stellar population mapping not only provides insights into the formation and evolution of the Milky Way but also enhances our understanding of the conditions necessary for life to develop, both on Earth and potentially elsewhere in the universe.
Stellar Population Mapping
FIELDS OF STUDY: Astronomy; Astrophysics; Stellar Astronomy
ABSTRACT: Stellar populations are collections of stars with similar chemical content, age, or distribution in space. Scientists have determined that the Milky Way Galaxy has three key stellar populations: disk, halo, and bulge. By studying these groupings, and the ways their stars have changed, astronomers can learn more about the way stars evolved to form the galaxy.
Stellar Mapping
Researchers have determined that the stars of the Milky Way Galaxy can be grouped into categories based on location, composition, and age. This is known as stellar mapping. The characteristics of stars are not necessarily fixed, so the way a star changes over time is also part of the mapping process. Studying, categorizing, and tracking star groupings provides a wealth of information about the origins of the galaxy and how it has evolved over time. For example, European spacecraft Gaia released information about the galaxy showing the movement of nearly a billion stars in 2018. Astronomers discovered ancient stars as well as evidence of collisions shaping the Milky Way’s youth.
Scientists map the stellar population of areas by first determining the attributes of individual stars. The key factors under consideration include spatial distribution (the number of stars in relation to the area occupied), kinematics (the speed or velocity ranges of these stellar objects), star chemistry (the kinds and amounts of chemicals present), and the age of stars in the area. Scientists then look for similarities in these traits among the star population. By first identifying the attributes of individual stars and then comparing them to others nearby, researchers can determine patterns of star distribution. They can identify "sibling" stars that may have come from the same source. They can also develop theories about how these stars, and others like them, formed and how they will act in the future.
Stellar Mapping Methods and Tools
Scientists have a number of methods and tools for studying and categorizing stellar populations. One of the most powerful tools is spectroscopy. Both light and radiation are organized in spectra by color, intensity, or wavelength. Astronomers use spectroscopy to examine the light frequencies emitted by different parts of a celestial body. This allows them to determine the body’s light wavelengths; its velocity, age, and degree of extinction; and the temperature and pressure of the body’s atmosphere.
Spectroscopy can also reveal the composition of a stellar body. An object’s metallicity is its chemical components that are heavier than the helium and hydrogen commonly fused into energy in a star’s core. This includes oxygen and carbon, which are not normally considered metals. Astronomers have determined that the higher the metallicity of a stellar object—that is, the more oxygen, silicon, carbon, or iron it has—the more likely it is to survive. They have also learned that objects with heavier metals are more likely than those with lighter metals to have the materials necessary to develop a planetary system.
When an object is too dim to be seen with a conventional telescope or satellite-mounted camera, astronomers turn to other tools. Sometimes a star is dimmed by a process known as extinction. Stellar extinction refers to the visual obstruction of a star by a cloud of dust. The dust blocks the blue waves that are most easily seen by observers, making the object appear both less bright and redder. In this case, scientists turn to infrared technologies to reveal the red light that is emitted by all celestial bodies. Some examples include NASA's Hubble Space Telescope, the James Webb Space Telescope, and the Stratospheric Observatory for Infrared Astronomy (SOFIA). Infrared allows scientists to see, study, and categorize stars that would otherwise not be visible. In February 2021, NASA received approval for the development of a next-generation space telescope, initially called the Wide Field Infrared Survey Telescope (WFIRST), but renamed the Nancy Grace Roman Space Telescope in honor of NASA’s first Chief of Astronomy. It is designed as an observatory for NASA to analyze dark energy, exoplanets, and infrared astrophysics.
Examples of Stellar Population Mapping
Using these tools and methods, astronomers group the stars in Earth’s galaxy into disk, halo, and bulge components. The isotropic halo component (which has equal properties in all directions) includes the oldest stars and globular clusters (spherical groups of stars with similar origins). It is located at the outer edge of the galaxy. The bulge component rotates in the center of the galaxy and includes some old stars as well as a violently active core. The disk population includes gas and mostly young stars. It makes up the rotating, flat part of the Milky Way Galaxy.
Uses of Stellar Population Mapping
Stellar population mapping enables astronomers to theorize about the origins of the galaxy. The presence of enough heavy elements to enrich Earth and its sun to their current levels indicates that other, earlier stars experienced supernovas (massive explosions) and expelled these elements into the universe.
By studying and mapping the bodies of the Milky Way Galaxy, scientists can explain why stars with a higher metallicity and relatively slow dispersing cloud of dust and gas are able to form planetary systems. Stellar mapping gives scientists an understanding of the processes that led to the formation of the Milky Way and other galaxies. Understanding how and why stars and planets form provides insight not only into how conditions evolved to allow life to develop on Earth, but also how and where conditions might exist for life in other parts of the universe.
PRINCIPAL TERMS
- extinction: the dimming of stellar objects because of the presence of dust between the object and observer.
- infrared: light just beyond that which is visible on the electromagnetic spectrum at the red end.
- metallicity: in astronomy, elements such as iron and silicon that are heavier than the hydrogen and helium that are fused in star cores.
- spectra: plural of "spectrum"; a range or distribution of light or wavelengths.
- spectroscopy: the study of the light frequency emitted by atoms and molecules.
Bibliography
"Extinction." Cosmos: The SAO Encyclopedia of Astronomy. Centre for Astrophysics and Supercomputing, Swinburne U of Technology, n.d. Web. 29 Mar. 2015.
"Infrared Waves." NASA: Mission Science. NASA, 13 Aug. 2014. Web. 28 Mar. 2015.
Klesman, Alison. "NASA's Spitzer Space Telescope Will Soon Retire. What Will Take Its Place?" Discover, Kalmbach Media, 28 Jan. 2020, www.discovermagazine.com/the-sciences/nasas-spitzer-space-telescope-will-soon-retire-what-will-take-its-place. Accessed 28 July 2021.
Majewski, Steven R. "Stellar Populations and the Formation of the Milky Way." Globular Clusters. Ed. C. Martinez Roger, I. Pérez-Fournon, and F. Sanchez. New York: Cambridge UP, 1999. Print.
"NASA Telescope Named for 'Mother of Hubble' Nancy Grace Roman." National Aeronautics and Space Administration, 20 May 2020, www.nasa.gov/press-release/nasa-telescope-named-for-mother-of-hubble-nancy-grace-roman. Accessed 28 July 2021.
Sanders, Ray. "When Stellar Metallicity Sparks Planet Formation." Astrobiology Magazine. Astrobio.net, 9 Apr. 2012. Web. 29 Mar. 2015.
Schultheis, M., et al. "Mapping the Milky Way Bulge at High Resolution: The 3D Dust Extinction, CO, and X Factor Maps." Astronomy & Astrophysics 566 (2014): n. pag. Web. 10 Apr. 2015.
"Spectroscopy." Cosmos: The SAO Encyclopedia of Astronomy. Centre for Astrophysics and Supercomputing, Swinburne U of Technology, n.d. Web. 29 Mar. 2015.
"Stellar Populations." Astrophysics. Amer. Museum of Natural History, n.d. Web. 29 Mar. 2015.
Wood, Charlie. "The New History of the Milky Way." Quanta Magazine, 2020, www.quantamagazine.org/the-new-history-of-the-milky-way-20201215. Accessed 28 Jul. 2021.