Cailin Rugema, Ritvik Ravikiran
Astronomy-Space objects
When we think of a nebula, it is typically defined as a vast cloud of gas and dust in space, primarily made up of hydrogen and helium. Though the gas and dust are dispersed over large areas, gravity gradually pulls these particles together. As the clumps grow larger, the gravitational pull strengthens, eventually causing the cloud to collapse under its own weight. This collapse leads to the formation of a hot, dense core at the centre, marking the birth of a new star.
A dark nebulae itself can be considered as a contrast of star-studded night skies, also known as absorption nebulae, these common type of nebulae get their name due to their prominent feature of being able to block visible light wavelengths from objects that emit of reflect behind it, these help it be more recognisable due to the emphasised borders surrounding the cloud. This sensation is caused by the high density of dust and gas, the dust scattering the light in all directions reducing the amount of light that can travel in a straight line through the cloud, as well as absorption of photons from dust and gases, turning their energy into heat or re-emitting it at longer wavelengths, which we cannot see with the naked eye. These factors account for less light being able to penetrate this type of nebula.
One of the most famous examples of this type of nebula is the Horsehead nebula (Barnard 33) which is roughly 1,300 light-years away, this nebula has been known as one of the most well-observed dark nebulae out in space. The nebula formed from a collapsing interstellar cloud of material, and glows because it is illuminated by a nearby hot star; while most regions of interstellar gas is dense enough to remain neutral, it is not entirely dense enough to prevent the penetration of UV light from massive stars (due to their much shorter light wavelength). Other examples of dark nebulae are the Coalsack Nebula which is 600 light-years away from earth, located in the southern hemisphere; and the Great Rift which is about 6000-7000 light years away from earth, and it stretches across a large portion of the Milky Way.
For the most part, larger complexes of these nebulae are known as Giant molecular clouds and small dark nebulae are known as ‘Bok Globules’, these smaller complexes have a mass of around 2 to 50 solar masses, while giant molecular clouds have a mass of 10⁴ to 10⁶solar masses. In a nebula's lifetime, it eventually starts to dissipate, this can be a results of multiple different reasons; if a supernova happens to be in the vicinity of a dark nebulae then the shockwaves from the explosion can significantly compress the nebula or even disperse its material, accelerating its dissipation, another reason being leading to the formation of new stars, As stars form, they generate stellar winds and radiation that begin to erode the nebula, particularly in the surrounding regions, these can results on the dissipation and eventual eradication of the dark nebulae, depending on the type of complex it is it can live for a very long lifetime, small complexes like Barnard 68 have a relatively short lifespan of a few million years, depending on the nearby stellar activity; while larger complexes like the great rift may last for tens of millions of years as they slowly convert their gas and dust into stars.
In the past when astronomists were studying the dark nebula, they found it relatively difficult to observe the activity happening due to the limitations that the early telescope had and its reliance on visible light to observe anything in space. Today, dark nebulae are observed through a number of different methods, the most common method being infrared observations. To use this method Infrared telescopes like the James Webb Space Telescope (JWST) are designed to detect infrared light, they do this by collecting infrared light from a object behind or inside a dark nebulae, the telescope's detectors then convert the infrared light into images or data. These images show what’s inside or behind the dark nebula from stars to planets forming, or any other hidden objects.
To conclude, as technology continues to advance, so do our studies of dark nebulae, yielding deeper insights into the universe. Notably, dark nebulae serve as a stellar nursery where new stars are said to be born, enhancing our understanding of star formation processes. Through the study of dark nebulae, we are continually uncovering new layers of the universe's evolution and better understanding the complex it has.
Image by NASA Hubble Space Telescope via Unsplash
Figure 1.1; The image shows the horsehead nebula, using the hubble webb telescope to view it.
References:
[1]NASA. (2013, April 18). NASA’s Hubble Sees a Horsehead of a Different Color - NASA Science. Nasa.gov. https://science.nasa.gov/missions/hubble/nasas-hubble-sees-a-horsehead-of-a-different-color/
[2]NASA Webb Mission Team. (2024, April 29). Webb Captures Top of Iconic Horsehead Nebula in Unprecedented Detail - NASA Science. Science.nasa.gov. https://science.nasa.gov/missions/webb/webb-captures-top-of-iconic-horsehead-nebula-in-unprecedented-detail/
[3]Erickson, K. (2022, August 29). What Is a Nebula? | NASA Space Place – NASA Science for Kids. Nasa.gov. https://spaceplace.nasa.gov/nebula/en/
[4]Mathewson, S. (2023, June 27). Dark nebula dominates gorgeous new view of Orion constellation (photo). Space.com; Space. https://www.space.com/dark-nebula-orion-constellation-photo
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[6]Japelj , J. (2024, October 10). Webb Telescope Images Planet-Shaping Winds Around Young Stars. Sky & Telescope. https://skyandtelescope.org/astronomy-news/webb-telescope-images-planet-shaping-winds-around-young-stars/
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