Why Nebulae Defy the Vacuum of Space
- Brooklin Morgan
- Apr 5
- 4 min read
Updated: Apr 25
What makes studying space so captivating is how it challenges everything we think we understand about life on Earth. Naturally, some phenomena require extra insight for us to grasp the why and how. Such questions arise from the wonder of nebulae and their lack of dissipation in space. In order to break down this concept, let us first review what a nebula is and how this question comes about.
Nebulae are immense clouds made up of dust and gases, primarily hydrogen and helium. They foster an environment that allows for new stars or planets to form in their cold, dark, low-density regions. The clouds grow larger as they continue to pick up more gas and dust, intensifying the gravitational pull, eventually collapsing in on itself. The material within the center of the nebula heats up, launching the process of star formation. Nebulae can also show evidence of a late dying star, likely a supernova, which has exploded, leaving its remnants to carry on and serve as a nursery for the next star.
The confusion surrounding the existence of these clouds of gas and dust in space comes from our observations of diffusion on Earth. After blowing out a candle, a visible stream of smoke rises. As the stream trails further away from the wick, diffusion takes over, spreading the particles in every direction. Eventually, you no longer see the smoke. However, you may still smell it because the particles are still there; they have just become less concentrated and invisible to the naked eye.
Why, then, do nebulae exist rather than diffusing into the almost perfect atmospheric vacuum of space? Gravity is the force behind it all. Renowned astrophysicists Dr. Charles Liu and Dr. Neil deGrasse Tyson discuss this very question in an episode of StarTalk. As explained, the more gas and dust accumulates, the stronger its gravitational pull becomes, keeping the particles gathered. Lui explains, “the conditions out in space make it so that these gas particles tend to disperse unless they have a reason to collect.” He continues to bring attention to the many unique conditions we have on earth that affect dissipation and diffusion such as buoyancy. Temperature, another considerable factor, is 2.7 Kelvin in space, or negative 454.81 degrees Fahrenheit. In these conditions, Liu explains, "gravity can overcome much of the motional dispersion." He continues, “when it’s cold, the random motions of the gases are actually overcome by the mutual gravity that they exert on each other.”
Tyson presents another scenario where a gas cloud will create a family of stars that “eats up” a large portion of the mass, leaving remnants that haven't participated in the star or planet formations. Without the required energy it takes to collect the particles and create a new star, the gas is left to dissipate. The portion of gas clouds further away from the pull of gravity has a weak chance of participating in the process. Additionally, with an ever rotating galaxy, these straying gases are prone to being separated from the mass and dispersed throughout the galaxy.
Lui clarifies that factors such as rotational shear, environmental temperature, and the amount of gas gathered at any given moment could allow them to eventually merge with others, forming the next star nursery. These gas and dust particles occupy the space between all celestial bodies in our universe. Yet, these particles are so sparse that the chances of them accumulating in a dense enough volume to form visible nebulae are slim. As Lui contrasts, “Here on Earth, we have trillions upon trillions particles of gas even in the tiniest beaker or vial. In space, just even a couple hundred miles above Earth's surface, we’re lucky if we even get one gas particle.”
The dispersion acting upon these gas clouds is far from evenly applied. Lui notes, this turbulent dispersion is what creates the many different, beautiful combinations of nebulae. “You have gravity holding these clouds together long enough for them to do things like form stars and planets.” Still, the forces and energies acting upon them, actively trying to disperse them, are present.
Learning about nebulae helps us uncover a star's life cycle, something we have yet to see in our lifetime in full. There are millions upon millions of stars at different stages of life. By studying them collectively, we can piece together the story of how stars are born, live, and ultimately fade. It can give us a better understanding of how our solar system formed, and what it may look like when our sun reaches the end of its life. Our sun began in a stellar nursery more than 4.5 billion years ago, prompting the beginning of the life we know today. The formation of a baby star can take over a million years, a true testament to how elaborately our universe as a whole is made.
Investigating how physical laws apply on Earth compared to space conditions is insightful and prepares us for the mysteries of the universe. Every question we ask, regardless of how trivial it may appear, could bridge the gap between our questions and the answers we seek. Understanding the physics behind celestial phenomena gives us a newfound admiration of them. In this case, nebulae hardly need an explanation for us to appreciate the riveting imagery they paint in the cosmos.
Works Cited
Houston, S. C. (2020, March 19). What is a nebula? Space Center Houston. http://spacecenter.org/what-is-a-nebula/
NASA Universe Web Team. (2021, August 23). Decoding Nebulae. Science.nasa.gov. https://science.nasa.gov/universe/decoding-nebulae/
StarTalk, deGrasse Tyson, N., & Lui, C. (2025, February 11). Answering Questions About Why the Big Bang Happened, The Shape of the Universe & More. YouTube.
https://www.youtube.com/watch?v=QEoL0PNaIK4
What Is a Nebula? | NASA Space Place – NASA Science for Kids. (2022, August 29). Spaceplace.nasa.gov. http://spaceplace.nasa.gov/nebula/en/
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