A stellar nursery refers to a region in interstellar space where new stars are born. These regions are characterized by dense concentrations of gas and dust, which provide the necessary materials for the formation of stars. Stellar nurseries are important cosmic environments where the process of star formation occurs, leading to the creation of individual stars, stellar clusters, and even entire galaxies.
A “stellar nursery” is a romantic way of referring to a molecular cloud in the process of forming new stars. A molecular cloud is a region of space dense enough with hydrogen atoms that molecules, most commonly H2, or diatomic hydrogen, can form. Molecular clouds may be giant, with 1000 to 100,000 times the mass of the Sun, or smaller, less than a few hundred times the mass of the Sun. These are called giant molecular clouds and small molecular clouds respectively. – Michael Anissimov
Within a stellar nursery, also known as a star-forming region or stellar birthplace, several key processes take place. The initial trigger for star formation often comes from the compression or disturbance of the interstellar medium, which can be caused by various factors such as supernova explosions, shockwaves from nearby stars, or gravitational interactions between gas clouds.
Astronomers at the Physics at High Angular Resolution in Nearby Galaxies (PHANGS)[1] project have systematically charted more than 100,000 nurseries across 90 galaxies and found that each one is far more unique than first thought. Stars can take tens of millions of years to form — growing from billowing clouds of turbulent dust and gas into gently glowing protostars before finally materializing into gigantic orbs of fusion-powered plasma like our sun. But how quickly this process depletes a nursery’s store of gas and dust, and how many stars are subsequently able to form in a given place, depends on a stellar nursery’s location in a galaxy.
As a result, the gas and dust in the region become denser and gravitationally collapse under their weight. The collapse of the gas cloud leads to the formation of a protostar, a dense core that will eventually develop into a newborn star. As the protostar accumulates more mass, it heats up and begins to emit infrared radiation. At this stage, the protostar is often surrounded by a rotating disk of gas and dust known as a protoplanetary disk, from which planets and other celestial objects may eventually form.
We used to think that all stellar nurseries across every galaxy must look more or less the same, but this survey has revealed that this is not the case, and stellar nurseries change from place to place. These nurseries are responsible for building galaxies and making planets, and they’re just an essential part in the story of how we got here.
Adam Leroy – associate professor of astronomy at The Ohio State University
Over time, the protostar continues to accrete mass and undergoes further gravitational collapse. Eventually, the central core reaches a critical temperature and pressure, initiating nuclear fusion reactions in its core. At this point, the protostar becomes a main-sequence star and enters a stable phase of its life. Stellar nurseries are typically found within large molecular clouds, which are vast regions of interstellar gas and dust.
The five-year survey, conducted across a section of the cosmos known as the nearby universe because of its proximity to our own galaxy, used the Atacama Large Millimeter/Submillimeter Array (ALMA) radio telescope[2] located in Chile’s Atacama Desert. By conducting their survey in the radio part of the electromagnetic spectrum, rather than the optical part, the astronomers could focus on the faint glow from the dust and gas of the dark and dense molecular clouds, as opposed to the visible light from the young stars birthed by them. This allowed the researchers to study how a star’s home cloud shapes its formation.
These clouds are primarily composed of hydrogen, along with traces of helium and other elements. They are also associated with regions of active star formation, such as H II regions, where newborn stars ionize the surrounding gas, causing it to emit characteristic wavelengths of light. Observations of stellar nurseries are conducted using a variety of telescopes and instruments, including radio telescopes, infrared telescopes, and space-based observatories.
This is the first time we have gotten a clear view of the population of stellar nurseries across the whole nearby universe. In that sense, it’s a big step towards understanding where we come from. While we now know that stellar nurseries vary from place to place, we still do not know why or how these variations affect the stars and planets formed. These are questions that we hope to answer in the near future.
Adam Leroy
These observations allow astronomers to study the physical processes involved in star formation, track the evolution of protostars, and understand the properties of newborn stars and their surrounding environments.
NASA’s Spitzer Space Telescope[3] captured a glowing stellar nursery within a dark globule that reveals the birth of new protostars, or embryonic stars, and young stars never before seen. The Elephant’s Trunk Nebula is an elongated dark globule within the emission nebula IC 1396 in the constellation of Cepheus. Within the globule, a half dozen newly discovered protostars are easily discernible as the bright red-tinted objects, mostly along the southern rim of the globule. These were previously undetected at visible wavelengths due to obscuration by the thick cloud (‘globule body’) and by the dust surrounding the newly forming stars. The newborn stars form in the dense gas because of compression by the wind and radiation from a nearby massive star (located outside the field of view to the left). The winds from this unseen star are also responsible for producing the spectacular filamentary appearance of the globule itself, which resembles that of a flying dragon. Image credit: NASA/JPL-Caltech/W. Reach (SSC/Caltech)
Footnotes
- The Physics at High Angular Resolution in Nearby Galaxies (PHANGS) project is a comprehensive observational effort aimed at studying the physical processes occurring in nearby galaxies at high spatial resolution. By combining observations from various telescopes and instruments, PHANGS focuses on understanding the mechanisms responsible for star formation, the structure and dynamics of interstellar gas, and the formation and evolution of molecular clouds in galaxies. The project utilizes a range of wavelengths, including radio, infrared, and optical, to investigate these processes in a sample of galaxies within 20 megaparsecs of the Milky Way. The ultimate goal of PHANGS is to provide a detailed understanding of the physical processes driving the lifecycle of galaxies and the formation of stars within them, shedding light on the fundamental mechanisms shaping our own cosmic neighborhood. [Back]
- The Atacama Large Millimeter/Submillimeter Array (ALMA) is a state-of-the-art radio telescope located in the Atacama Desert of northern Chile. It is a collaborative effort between international partners, including North America, Europe, and East Asia, and is operated by the European Southern Observatory (ESO), the National Radio Astronomy Observatory (NRAO), and other organizations. ALMA consists of an array of 66 high-precision antennas that work together to capture radio waves in the millimeter and submillimeter wavelengths. By observing these wavelengths, ALMA enables astronomers to study a wide range of astronomical phenomena, including the formation of stars, the structure of galaxies, the chemistry of interstellar space, and the search for life’s building blocks in protoplanetary disks. Its location in the high and dry Atacama Desert provides excellent atmospheric conditions for these observations, making ALMA one of the most powerful instruments for radio astronomy in the world. [Back]
- NASA’s Spitzer Space Telescope, launched in 2003 and retired in 2020, was an infrared observatory designed to study the universe across a wide range of infrared wavelengths. Equipped with a highly sensitive camera and three spectrographs, Spitzer provided valuable insights into various astronomical phenomena, including the formation of stars and planetary systems, the structure and composition of galaxies, and the detection of distant and faint objects. By observing in the infrared part of the electromagnetic spectrum, Spitzer was able to penetrate dusty regions of space and capture the faint heat signatures emitted by celestial objects, unveiling hidden structures and uncovering crucial information about the universe’s evolution. [Back]
Further Reading
Sources
- “100,000-star nurseries mapped in the first-of-its-kind survey” (June 13, 2021) https://www.livescience.com/star-nurseries-mapped.html
- Lada, C. J., & Lada, E. A. (2003). Embedded clusters in molecular clouds. Annual Review of Astronomy and Astrophysics, 41, 57-115.
- “Stellar Nursery” (Mar 23, 2008) https://www.nasa.gov/multimedia/imagegallery/image_feature_643.html
- Evans, N. J., II. (1999). Interstellar disks and the search for other planetary systems. Annual Review of Astronomy and Astrophysics, 37, 311-362.
- Ward-Thompson, D., André, P., Crutcher, R., Johnstone, D., Onishi, T., & Wilson, C. (2007). Star formation in the interstellar medium: Infrared and submillimeter observations. In Protostars and Planets V (pp. 33-46). University of Arizona Press.
- “What is a Stellar Nursery?” (June 19, 2023) https://www.allthescience.org/what-is-a-stellar-nursery.htm
- Stahler, S. W., Palla, F., & Ho, P. T. P. (2000). The Formation of Stars (Vol. 34). Wiley-VCH.
- Elmegreen, B. G. (2000). Triggered star formation in molecular clouds. The Astrophysical Journal, 530(1), 277-287.
- ALMA Observatory. (n.d.). About ALMA. Retrieved from https://www.almaobservatory.org/en/about-alma/ National Radio Astronomy Observatory. (n.d.). ALMA – Atacama Large Millimeter/submillimeter Array. Retrieved from https://public.nrao.edu/telescopes/alma/
- NASA. (2020). Spitzer Space Telescope. Retrieved from https://www.nasa.gov/mission_pages/spitzer/main/index.html
