What Are Stars Made Of?

Stars are one of the most beautiful celestial beings. They come in a wide variety of sizes and colors, depending on their mass and temperature. For centuries, they have been used in the most iconic romantic scenes from books and movies, and visual novels. Now, what are they made of?

What Are Stars Made Of?

Stars and the rest of the universe are alike when it comes to composition. These celestial beings are made of hydrogen, helium and other elements. This is because, after the Big Bang, the universe was a hot, dense sphere, like the core of a star. Then, it kept expanding until it cooled down, hence why it’s components are distributed as follows: 73% hydrogen, 25% helium and 2% of other elements.

The first stars created after the Big Bang were humungous. They likely became supernovas in the course of a million years of forming. These stars created heavy elements like oxygen, carbon, gold, and uranium, among other things, during their lifespan. On the other hand, stars have been around from the beginnings of the Universe. Some have heavy elements that came from their metal-rich predecessors, while others come from their metal-poor progenitors.

The Sun is the best example of a metal-rich star. It has a similar ratio to the rest of the Universe, which is 71% hydrogen, 27.1% helium and the remaining percentage has heavier elements, like oxygen, carbon, and nitrogen. Even if the Sun and other stars are constantly exploding in a nuclear reaction, they’re so large that it will take them billions of years to use all of the matter inside them. The continuous release of energy, also known as electromagnetic radiation, makes them visible. Other stars have a composition similar to the Sun, being 3/4 oxygen and 1/4 helium.

What Are Stars Made Of?
Image Source NASA

How Do We Know what Are Stars Made Of?

Despite the high amount of stars in the Universe, scientists have found ways to study them. One of the techniques they’ve used is using instruments to examine the light that they emanate. In the 1800s, the scientist William Hyde Wollaston split the white light that came from the Sun with a prism and noticed dark lines in the rainbow spectrum. Then, Joseph von Fraunhofer built a spectrometer a few years later to disperse the light.

After analyzing the dark lines, scientists determined that they represented colors that were missing from the spectrum. This is due to elements in the Sun’s composition absorbing wavelengths of light. Therefore, the dark lines indicated the presence of hydrogen, sodium, and calcium, to name a few.

Despite being practical, Philipp Podsiadlowski states that this method only tells the astronomer what the composition is on a surface level, without reaching the center.

Another technique that has been used to study stars like the Sun is the Super-Kamiokande (Super-K) detector, which is buried 1,000 meters below the surface of a mountain. This strange device is built to detect special particles in its center and it is said to be able to detect 40 a day. The light they create is faint but it generates a halo that can be picked up by the Super-K’s detectors that cover its walls.

Why Are Some Stars Larger Than Others?

Stars not only come in different colors, but they also have different sizes. This might seem shocking since they pretty much have similar components as other celestial beings since the Big Bang. Now, why are they bigger than others? The rest of this section will explain the reason behind it.

There are indirect measurements that allow astronomers to calculate the size of a star. The amount of radiation that it emits relies on its temperature and physical size because the surface is the only place that produces. Being able to measure the distance to the star, its temperature and apparent brightness allows astronomers to determine its radius, which can be calculated with the same formula for the area of a sphere.

Some stars are a few kilometers in size while others can get as big as the sun. UY Scuti is the largest of the supergiants with a diameter of 2.4 billion kilometers. However, astronomers suggest that this example doesn’t apply to stars that are not in the main sequence category like the sun which is made of hydrogen and it obtains energy from fusing it into helium. In this case, its size is determined by its mass.

When a star is born, the conversion of potential energy into kinetic energy comes as a result of gravitational contraction. Once a star has enough mass, it can heat up until it’s possible to ignite nuclear fusion since hydrogen turns into helium. In smaller stars, only a tiny portion of its mass can reach the 4,000,000 Kelvin and a slow fusion begins. Now, when it comes to bigger stars, they can achieve core temperatures reaching ten million degrees, fusing hydrogen into helium with a larger rate than the sun.

Stars in Our Galaxy

The Milky Way is the galaxy in which the Earth is located. The thick band of stars is visible on a clear night and some of them are easy to spot without using a telescope. The barred spiral is about 100,000 light-years from planet earth and its major constellations are Perseus and Saggitarius. It is estimated that the Milky Way harbors around 100 billion stars.

Milky Way
Milky Way

The Milky Way is mostly comprised of main-sequence stars. This means that they have a stable nuclear fusion by converting hydrogen to helium, which radiates x-rays. During this process, these celestial beings emit a lot of energy, which keeps the star bright and hot. On the other hand, research suggests that the oldest stars live in the Milky Way’s halo and almost reach 10 billion years old.

The primitive side of the Milky Way, which made suns and grabbed gas as it quietly grew, is comprised of old, red stars that were born during the universe’s first billion years. Part of the primordial population, they have gas, dust, and metals in their composition. However, the blue stars that are part of this galaxy have a different structure, leading researchers to believe that they belong to a different side of the space. They tend to move differently as well, something that Amina Helmi from Groningen’s University was quick to point out.

What happens When Stars Die?

Once a star has been around several billion years, it starts to die. The way they decide to leave the universe depends on the type that is reaching the end of its lifespan. For example, stars like the Sun tend to contract under the weight of gravity, which happens when they run out of hydrogen fuel. However, the upper layers will endure a hydrogen fusion.

Then, the core stars contracting and heating up, which causes the upper layers to expand. Once this happens, the radius will increase, thus, turning into a red giant. Right after that, the core will become hot enough to cause the helium to fuse into carbon, which will cause it to expand and cool. Next, it will eject material that will gather around the star in its death bed, forming a planetary nebula. Finally, after turning into a white dwarf, it will transform into a black dwarf. A star like the Sun is expected to last a billion years, so it’s not something that should worry the Earth’s inhabitants for now.

When it comes to stars that are more massive than the sun, the process is quite similar. They fuse helium into carbon, but once the helium is gone, they have enough mass to transform it into oxygen, neon, silicon, magnesium, sulfur, and iron. The core is unable to burn once it has turned into iron, so the star collapses by its gravity, heating it in the process. Then, it shrinks to a neutron core with a radius of approximately 6 miles.

What happens next is equally depressing as seeing a hero fall. Once the outer layers fall inward on the neutron core, it gets crushed and explodes, turning into a supernova. Afterward, the transformation is completed, and a lot of energy and material is released into space. However, not all is lost, since this allows star formation in interstellar clouds. Not only that, this can lead to forming a neutron star or a black hole.


Stars are mostly comprised of hydrogen, oxygen, and helium, as well as other components since they were born at the same time as the Universe. Scientists in the 1800s were able to determine the composition of the sun by dispersing the sun’s white light using a prism. However, this technique only allowed them to study stars at a surface level, so they had to resort to using an underground detector that can easily spot 40 particles a day. They come in different sizes and this is mainly because of their mass. Stars die once they burn all of their oxygen.