Star-Forming Regions
Star-forming regions, often referred to as "stellar nurseries," are areas in space characterized by dense, cold clouds of hydrogen gas and dust known as molecular clouds. These regions are crucial for the birth of new stars, as the gravitational influence from nearby objects can cause parts of these clouds to collapse, leading to the formation of protostars. Protostars are young stars that have not yet reached the necessary mass and temperature for nuclear fusion, making them faint and challenging to detect. Astronomers often utilize infrared observations to study these protostars, as infrared light can penetrate the dense clouds obscuring them.
As protostars gather material, they also expel jets of gas, creating structures known as Herbig-Haro objects, which glow brightly where they interact with surrounding material. Nearby regions, such as Bok globules, often accompany these formations and are thought to be linked to the creation of individual stars. Over time, protostars evolve into T Tauri stars, which are still in the process of forming and may play a role in developing planetary systems. Notably, active star formation has been observed in regions like the Orion constellation, revealing insights into how stars like our Sun came into existence. Overall, star-forming regions represent the dynamic processes that lead to the birth of stars and the development of galaxies.
Star-Forming Regions
FIELDS OF STUDY: Stellar Astronomy; Astrophysics
ABSTRACT: Astronomers have determined that certain circumstances are needed for stars to form. These conditions exist in places where molecular clouds—gatherings of very dense, relatively cold dust and gas—are affected by gravity. Scientists study these star-forming regions to learn how existing stars came into being and to determine where new stars and planetary systems will form in future.
Star Nurseries
Certain areas of space contain very dense, relatively cold clouds of hydrogen gas and dust known as molecular clouds. When gravity from nearby objects affects part of this cloud, the affected region can begin to collapse inward. As gravity continues to act on the region, it begins to form a cloud fragment both denser and hotter than the surrounding gas cloud. This fragment draws more dust and debris toward itself, forming an accretion disk that is surrounded by even more dust and gas. Astronomers call this newly formed star a protostar.
Some parts of the universe feature conditions that are favorable to the creation of protostars. These are known as star-forming regions, sometimes called "stellar nurseries." The protostars in these nurseries have yet to reach a mass and temperature that would allow for fusion and the creation of energy and light. For this reason, they are very dim, making them difficult to detect and observe.
Astronomers have discovered that telescopes and other tools that detect infrared light can be very helpful in finding and watching these young stars as they continue to form. Infrared light is not visible to the human eye. However, it gives off a distinct signature that can be detected by instruments even when the target objects are obscured by dense clouds of dust and gas, as in the case of protostars.
Characteristics of a New Star
Astronomers have discovered that protostars not only collect matter in their core and accretion disk but also eject material from both poles. This outflow is expelled in jets, typically following the protostar’s axis of rotation. It can reach speeds of hundreds of kilometers per second. As it streams out, the flow interacts with the material around it. The resulting hot, ionized gas creates glowing balls of matter known as Herbig-Haro (HH) objects. HH objects are typically brightest at the point of first contact between the emissions and the surrounding cloud.
HH objects are often found near another space formation known as a Bok globule. These small, dark nebulas surround the newborn star. They are named for Dutch American astronomer Bart Bok (1906–83), who first theorized that they were related to protostars. Bok globules may be associated with the formation of individual stars, as opposed to star clusters.
As these new stars age, they begin to change. Lower-mass stars less than ten millions years old have not yet reached a temperature high enough for fusion to take place in their cores. However, they still sometimes release radiation in variable bursts. They also tend to be brighter than main-sequence stars such as Earth’s sun. These stars represent an intermediate stage between a protostar and a main-sequence star. Such stars are called T Tauri stars, after T Tauri, the first such star discovered. Because T Tauri stars retain accretion disks, they are likely candidates to play a role in the formation of planets and even entire planetary systems.
Nearby Star Formation
Astronomers from the National Aeronautics and Space Administration (NASA) have determined that the constellation Orion contains a huge active star-formation region about 1,400 light-years away from Earth. Using the Spitzer Space Telescope, NASA researchers have identified at least three hundred protostars in this region.
In March 2015, NASA scientists announced that they had observed one of these protostars, known as HOPS 383, releasing outbursts of light and heat. They believe that the brightness of these outbursts was caused by a sudden influx of gas from the protostar’s accretion disk. As material from the accretion disk neared the protostar’s core, the temperatures of both rose, causing their brightness to increase. By studying HOPS 383 and other protostars, astronomers get a firsthand look at how Earth’s sun and other stars and planetary systems may have formed.
In 2019, astronomers detected a distant galaxy seemingly obscured by giant clouds of gas and dust. The galaxy, named 3MM-1, is about 12.5 billion light years away, meaning astronomers are looking at the galaxy as it was in the early stages of the formation of the universe. The galaxy is in the process of producing new stars at a rate more than one hundred times that of our own Milky Way galaxy.
PRINCIPAL TERMS
- Bok globule: the smallest detectable dark nebula, associated with the formation of protostars.
- Herbig-Haro (HH) object: a bright object formed when the hot, high-velocity gas ejected from a protostar interacts with and ionizes the cooler material surrounding it. HH objects are often associated with Bok globules.
- infrared: long-wavelength light that is just below visible light on the electromagnetic spectrum.
- protostar: an infant star that forms when a cold, dense molecular cloud of dust and gas collapses, its gravity causing part of it to become hotter and denser until it eventually produces the core of the new star.
- T Tauri star: a low-mass star that formed less than ten million years ago and is not hot enough for nuclear fusion to begin. In terms of stellar evolution, T Tauri stars come between protostars and low-mass main-sequence stars such as Earth’s sun.
Bibliography
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