Dwarf Stars. What Exactly Are They?

 by Sam Haworth

Stars. The nuclear engines of the universe. These incredible balls of energy are produced from fusion reactions. This is the process in which the star fuses hydrogen into helium in its core, which in turn creates a delicate balance between the energy pushing out (from the fusion reactions) and the gravitational pull toward the core. But, how many people have heard of dwarf stars? Despite their significance, dwarf stars often remain a lesser-known topic in popular science discussions. In the shadow of their more glamorous 

counterparts, these stars quietly dot our galaxy, influencing its dynamics. In this article, I aim to shed light on these stellar underdogs, exploring their unique characteristics and the role they play in the universe.

White Dwarf Stars

What happens when a star dies? Well for 97% of stars, they will end their life as a white dwarf. These stars are like cosmic zombies. The corpses of once great stars. So how are they made?

As a star ages, it eventually exhausts its hydrogen fuel. When this happens, it undergoes a stunning transformation, shedding its outer layers and forming a breathtaking and beautiful display known as a planetary nebula.

What remains after this spectacle is the core of the star, now a white dwarf. These remnants are roughly the size of Earth, yet immensely dense, with a mass comparable to that of the Sun. White dwarfs can reach temperatures of up to 100,000 kelvin (approx. 99726 Celsius), and their gravity is so intense that a teaspoon of white dwarf material would weigh tons on Earth.

White dwarfs have a fascinating fate. Over extremely long time scales, they will eventually cool down and fade away, theoretically becoming what scientists call 'black dwarfs.' However, due to the long time it takes for them to cool, it is believed that no black dwarfs currently exist in the universe. It takes so long because white dwarf stars can only lose heat through their outer layer, and they can only do this via radiation (which is an incredibly inefficient form of energy transfer).

Black Dwarf Stars

What happens when even white dwarfs meet their end? Well, as mentioned before, they become black dwarfs, celestial entities so elusive that none are believed to currently exist in the universe.

The transition from white dwarf to black dwarf is a long process, occurring over timescales that defy human comprehension. Black dwarfs, the theoretical end point of stellar evolution, are cloaked in mystery. These dormant remnants, once ablaze, are characterised by their near-zero temperatures - a contrast to their white-hot progenitors. Theoretically, a black dwarf is a cold ember, a time capsule, forever removed from the stellar life cycles.

Yet, there is irony at play. While black dwarfs are presumed to exist, the universe's age, 13.8 billion years, pales in comparison to the huge timescales required for a white dwarf to cool into this theoretical state. As such, it is believed that no black dwarfs currently exist in the universe - a testament to the infancy of our galactic existence.

Red Dwarf Stars

While red dwarf stars may dwell in the shadows of cosmic giants, their significance in the universe cannot be overstated. These stars hold the promise of extraordinary longevity. Their compact size and cooler temperatures allow them to stretch their existence to unbelievable timescales, with lifespans that can extend up to one trillion years. This remarkable endurance stems from their efficient use of convection in the fusion process, a slow-burning approach that makes their hydrogen fuel reserves last far longer than their more massive counterparts.

In the vast expanse of the universe, red dwarfs dominate, constituting the majority of stars in our galaxy. Accounting for approximately 70 to 80% of all stellar entities, they form the silent majority, their influence shaping the cosmic landscape (although you cannot see them with the naked eye as they emit electromagnetic waves in the infrared part of the electromagnetic spectrum). Their surface temperatures, ranging from 2,500 to 3,500 degrees Celsius, contrast to the heat of stars like our own Sun, which have a surface temperature of around 5,600 degrees Celsius. This relative coolness is not a limitation, but rather a testament to their unique ability to endure through eons.

In the quest for habitable environments beyond our solar system, red dwarf systems emerge as strong and interesting candidates. Their extended lifespans provide ample time for the development and evolution of potential life forms. Planets orbiting within a red dwarf's habitable zone - where conditions are right for liquid water to exist - might enjoy stable environments for durations that surpass human comprehension. 

As we gaze into the abyss of space, red dwarf stars beckon us to reevaluate our understanding of dwarf stars and their potential to have life on distant worlds. These stars hold the key to unlocking mysteries of the universe.

Brown Dwarf Stars

Brown dwarfs emerge as intriguing enigmas, challenging our conventional understanding of stellar existence. They are neither star nor planet, these misfits occupy a unique niche in the cosmos. Their distinctness offers a fascinating glimpse into the array of objects that populate the universe.

Brown dwarfs occupy a grey area in space. Too massive to be considered true planets, yet not large enough to sustain the fusion reactions characteristic of stars, they sit in the boundary between these categories. Essentially, brown dwarfs are "failed stars," born from the same stellar nurseries as their luminous cousins. 

Brown dwarfs play a pivotal role in shaping the dynamics of populations and planetary systems. Their existence challenges common classifications, expanding our understanding of celestial objects beyond the distinction of stars and planets. By studying brown dwarfs, astronomers get insights into the intricacies of stellar formation, evolution, and the diversity of planetary environments. 

The life story of a brown dwarf unfolds in stark contrast to the fiery, hydrogen-fueled cores of stars. Lacking the critical mass necessary for sustained nuclear fusion, brown dwarfs find themselves in a constant state of cool, dim twilight. Over eons, they radiate away the residual heat from their formation, gradually fading into cosmic obscurity. While their existence challenges standard notions of stellar evolution, brown dwarfs play an essential role in shaping the dynamics of their cosmic neighbourhoods.

As time goes on, brown dwarfs embark on an extraterrestrial journey that differs dramatically from their dazzling peers. Without the energy-producing mechanisms of stars, they lack the fiery deaths and explosive supernova finales that characterise stellar endpoints. Instead, brown dwarfs quietly transition into relics, gradually cooling and fading over long periods of time. Their ultimate fate lies in the deep cold of space.

Conclusion

In the vast expanse of the universe, dwarf stars emerge as subtle yet significant entities, each with its own unique narrative. From the mesmerising display of planetary nebulae marking the birth of white dwarfs to the intriguing concept of black dwarfs, these stars assume pivotal roles in the research of celestial bodies. Red dwarfs, though understated in appearance, hold the potential for enduring existence, potentially fostering life on distant worlds. Brown dwarfs, straddling the line between stars and planets, challenge our understanding of stellar existence, offering a glimpse into the rich diversity of celestial objects.

As we peer into the depths of space, dwarf stars invite us to contemplate the staggering broadness of the universe and our place within it. Their stories remind us that the universe is not a static phenomenon, but a dynamic and ever-changing vacuum. These are the stellar underdogs. Dwarf Stars.