Exploring the Inside of a Star: What Are They Made Of?

Introduction

Have you ever looked at the sky in the night full of stars and wondered what they are like up close? What are they made of, and why do they behave the way they do? It turns out there's a whole lot more than meets the eye!

Our Sun is the star we know best. It is only 150 million kilometers away, which might seem far, but compared to other stars that are 4.3 light-years away, that's relatively close.

Most of the Sun's energy comes from its core, the hot center. This energy moves outward until it reaches the convection zone, where it circulates before finally leaving the Sun's surface. But is this the case for all stars?

In this article, we dive deep into the heart of stars to uncover the extraordinary processes happening within them. Get ready to unveil the secrets that make stars shine, understand the fascinating science behind it, learn about their layers, and discover how our Sun differs from other stars.

Inside of a Star

Layers of a Star

Core: The core is like the star's bustling engine room, where the real action happens. It's incredibly hot and dense, packed with hydrogen atoms. Deep inside this core, atoms slam together to form helium through a process called nuclear fusion. This fusion releases an immense amount of energy, which is the star's main power source, keeping it shining brightly.

Radiative Zone: Think of this zone as a snug blanket wrapped around the core, holding all that energy in. Light and heat from the core play a game of tag, bouncing from atom to atom in this layer. Each photon gradually moves outward until it reaches the star's outer layers.

Convective Zone: Imagine a pot of boiling water on the stove, with bubbles rising and sinking. The convective zone of a star is something like that. Here, hot gas blobs rise from the core, carrying heat, while cooler gas sinks down to reheat. This motion helps move energy around the star, and that way, it stays hot and active.

Photosphere: The photosphere is the star's outer shell that we can see from Earth. This is where sunlight comes from, and the energy created in the star's core finally escapes into space, making the star glow.

Chromosphere and Corona: Next come the chromosphere and the corona, the star's outer layers. The chromosphere is like the star's atmospheric boundary, where things become even hotter. After that is the corona, which is like the star's halo, extending far out into space, and is incredibly hot but not very dense, creating phenomena like solar flares and the solar wind.

Laboratory simulation of how solar winds are faster at the stars poles.

What Are Stars Made Of?

Stars are mostly made of hydrogen and helium, the universe's two lightest and most abundant elements. These elements are like the basic building blocks of the universe, created when the universe began in the Big Bang.

Besides hydrogen and helium, stars also contain some heavier elements, known as "metals" in astronomical terms.

As stars evolve and go through different fusion stages, they create heavier and heavier elements, like carbon, oxygen, nitrogen, iron, and others. The exact composition of a star can vary depending on its mass, age, and stage of life. Massive stars, for example, can make heavier elements and contain more metals than smaller stars like the Sun.

So, in short, stars are mostly made of hydrogen and helium, but they can also have some other elements that they have created over time.

What is the Sun Made Of?

Understanding what the Sun is made of is crucial to comprehend the inner workings of stars. As the nearest star to Earth, the Sun is easier to study than more distant stars, providing us with a wealth of information about stellar processes.

Are All Stars the Same?

Small Stars: Small stars, like red dwarfs, have less mass than larger stars like our Sun. Because of that, the pressure and temperature in their cores are not as high. As a result, energy production happens much slower, and they live a lot longer as they don't run out of their fuel so quickly.

These stars mostly fuse hydrogen into helium in their cores. Small stars may not have well-defined convective zones and no radiative zones, and their outer layers are usually less turbulent than larger stars.

Medium-sized Stars: Stars like our Sun fall into this category. In medium-sized stars, the pressure and temperature in the core are higher than in smaller stars, so nuclear fusions happen much faster in them. They also mostly combine hydrogen into helium in their cores but do so faster than small stars. Medium stars have both convective and radiative zones inside, which help move energy around efficiently.

Large Stars: Large stars, like blue giants or red supergiants, have much higher mass than smaller stars. They have extremely high pressure and temperature in the core, so they burn fuel fast. Large stars can combine elements other than helium, including heavier elements like carbon, oxygen, and even iron. Large stars have convective cores, where energy moves around vigorously, creating complex structures inside.

How Can We See Inside a Star?

Now, we know everything there is to know about the insides of stars and the processes that happen there, but one unanswered question remains. How can we observe the internal processes of stars? Since we cannot physically dissect a star, how do we gain this knowledge?

Scientists explore the insides of planets and stars using several different methods:

Helioseismology: Imagine the surface of a star is like the skin of a drum, and the star's insides are like the drum's hollow center. When something happens inside the star, like a burst of energy or a change in pressure, it creates vibrations that reach the surface. The ripples cause the surface of the star to move in subtle ways. Scientists use special spectrographs to measure these tiny movements or study the star's light to learn what is inside.

Waves inside the Sun, called p modes, creating vibrations on its surface. This helps scientists learn about the Sun's inner structure and energy movement.

Neutrino Detection: Stars, including our Sun, give off tiny particles called neutrinos as they burn fuel in their cores. Scientists have underground detectors that catch them, helping them learn about the nuclear reactions happening deep inside stars.

Computer Simulations: Using super-powerful computers, scientists create virtual models of stars. These simulations show how stars work and what happens inside them under different temperatures and pressures.

Stellar Evolution Models: Scientists also use theories and models to understand how stars change over time by comparing them with observations of real stars.

Curious Facts

Here are a few interesting and fun facts about the stars and their inside processes that you might not have known about. They can expand your knowledge about stars and remind you why learning about the universe is so fascinating.

1. Neutrino Ghosts

Neutrinos, particles thrown out from stars' cores, are so tiny and difficult to track down that billions pass through our bodies every second without us even noticing. But don't worry; they can pass through most materials, including our bodies, without causing any harm or noticeable effects.

2. Stellar Recycling

Stellar recycling is a concept in astrophysics that describes the process where matter is cycled between stars and the space between them. This cycle involves the birth, life, and death of stars and how they contribute to the formation of new stars and planetary systems.

When stars reach the end of their lives, they throw out their outer layers into space, which become the building blocks for future generations of stars and planets.

3. Mystery of the Missing Lithium

Lithium is rare in the universe despite being one of the lightest elements. Scientists believe most lithium formed during the Big Bang, but stars have destroyed much of it. They are still studying the exact reasons for this "lithium problem." There are various theories from an astrophysics perspective about why there is so little lithium. Some suggest that nuclear reactions in stars consume lithium faster than it can be replenished. Others suggest lithium gets used up in the space between stars (interstellar medium). This shortage makes it hard for astronomers to understand how stars develop and the chemical history of the universe.

4. Stellar Cannibalism

In binary star systems, where two stars orbit each other, one star can shave off material from its companion. This process, called mass transfer, can dramatically change both of their evolutions. The star that is losing material may become smaller and dimmer, while the star that is gaining material can grow larger and hotter, potentially leading to phenomena like novas or even supernovas in some cases.

This interaction significantly alters their life cycles and final stages, sometimes even resulting in the formation of exotic objects like X-ray binaries or millisecond pulsars.

Conclusion

1. Stars have several layers, including a core where nuclear fusion occurs, producing immense heat and light. Surrounding the core are the radiative and convective zones, where energy moves through radiation and hot gas movement. The outermost layer, the photosphere, emits light. The chromosphere and corona extend into space, affecting the star's activity and interactions.
2. Stars mostly consist of hydrogen and helium, with a few heavier elements like carbon, oxygen, and iron.
3. Stars can be different in their inside structure and processes depending on their size and mass. Smaller stars like red dwarfs are somewhat stable and don't even have convective zones. Meanwhile, blue giants do have them and are much more complex.
4. Scientists learn about the inside layers of stars through helioseismology, neutrino detection, and computer simulations.

References

1. Kippenhahn, R.; Weigert, A. (1990), Stellar Structure and Evolution, Springer-Verlag.
2. Hansen, Carl J.; Kawaler, Steven D.; Trimble, Virginia (2004), Stellar Interiors (2nd ed.), Springer.
3. Wikipedia - "Stellar Structure"
4. Wikipedia  - "Stellar Evolution"
5. Australian Academy of Science - "How can we see inside a star?"