Science Behind the Birth and Death of the Stars

When we look up at the night sky, we are entranced by the millions of bright dots scattered across the airspace. Some of these dots are planets, and others are galaxies. Most, however, are stars. Stars came into existence around 400 million years after the creation of our universe- also known as the “big bang”. Their significant ages provide a plethora of information about the past. By studying different types of stars, how they’re created, and how they die, we are able to see the span of our universe from its birth to its death.

All successful stars are created in molecular clouds. Molecular clouds consist mainly of dust and hydrogen gas. As far as we know, this is the only place stars are able to be created. The birth of a star begins with hydrogen gas being pulled into tight quarters by gravity. This space is called a protostar. This gas spins around the center of said gravity.

This process continues until a temperature of up to 15,000,000 K° is reached, where nuclear fusion can take place. A helium core forms and the nuclear fusion will continue for millions, if not billions, of years. For reference, this is around 90% of a star’s life. The star is now considered to be a main sequence star, similar to our sun. Eventually, the star runs out of hydrogen and becomes unstable. Its core contracts and the temperature rises enough to ignite the hydrogen shell surrounding the star. When this happens, the star becomes far brighter and increases its size.

Once this process is complete, it is classified as a red giant. The core temperature does not stop rising despite this and begins fusing helium into carbon. This process is much faster than the conversion of hydrogen to helium. Just as with the previous fusion, once the helium supply is gone, the star’s core begins to contract again. Instead of a hydrogen shell being ignited, however, a helium shell begins to burn below it. There are now two shells of burning matter surrounding the progressively massing core.

This process continues with more fusion; carbon fuses into neon and continues to produce heavier elements until an iron core is formed. If this core weighs more than 3 M☉, the immense pressure will collapse the core and create a black hole. If the core weighs less than 3 M☉, the neutrons’ pressure will halt the inevitable collapse, creating a neutron star.

Sometimes, stars don’t form correctly and die before their birth. These objects are known as brown dwarf stars. These stars are unable to achieve nuclear fusion as they didn’t take on enough mass when they formed. All energy emitted from brown dwarf stars come from heat stored from the gaseous explosion from which it was born. Even though brown dwarf stars contain energy, their surface temperatures barely reach 1000 K°. Due to their minute temperatures and energy, they don’t give off enough light to see them with a standard telescope. Despite being almost impossible to see, scientists have observed brown dwarf stars. The first confirmed sighting was recorded in 1995.

Neutron stars are very small, with a diameter of only 10-20 kilometers. Even though these stars are small, they weigh over 1017 kg/m3 metric tons. The density is so great, one teaspoon of neutron star has a mass of more than one million white dwarf stars. Neutron stars hold onto the angular momentum of the explosion they were born from, and because of this can rotate over 600 times a second. This creates a powerful magnetic field and intense gravity. Escaping a neutron star is only possible if an object travels over half the speed of light.

Some neutron stars emit electromagnetic radiation, these are called pulsars. The radiation is shot out of both ends of the axis, creating a “beam”. As the star rotates, the radiation beam does too. From earth, we can only see these beams if they are pointed directly at us. (2) If not, we see a supernova remnant- an expanding nebula created from a supernova blast. As a pulsar spews its energy, its rotation gradually slows down. Eventually, it ceases the creation of radiation and the rotation stops.

A more common result of a collapsed star is a black hole. These fascinating objects are formed when a star with a mass greater than 3 M☉ reaches the end of its life and implodes. This specific event creates a Stellar mass black hole, the most common type of black hole. All black holes have infinite gravity which compresses all matter it “eats” into a single point called a singularity, where mass is infinite. All particles and waves that are engulfed add to the black hole’s mass. The area around a singularity is impossible to escape; even travelling at the speed of light won’t permit an exit. The very edge of this inescapable zone is known as the event horizon. The event horizon is the part of a black hole we can see, and it presents itself as space-time being warped around a giant, lightless mass.

Quarks are elementary particles that function as the building blocks of matter. There are six “flavors” of quarks: up, down, top, bottom, charm, and strange. Up and down quarks most commonly create protons and neutrons. It is important to note that neutrons are comprised of two down quarks and one up quark.

It is theorized that sometimes, stars will collapse and skip the point of being a neutron star but won’t be dense enough to become a black hole. They have been dubbed “quark stars”. Quark stars are predicted to be only 11 kilometers across and be comprised of quark matter, an incredibly dense material made up entirely of unpaired quarks. Scientists may have discovered two potential quark stars in 2002, but more evidence is needed to support their theories.

All stars, even neutron stars, eventually burn out and die. Most stars, however, become white dwarves after their red giant stage ends. White dwarf stars are similar to neutron stars in a sense that they are condensed, but instead of neutrons, electrons are the main component. The smaller a white dwarf is, the more mass it has. When a white dwarf becomes too small for its mass, it will implode to either a neutron star or a black hole.

If it doesn’t implode, it decays over quadrillions of years until it becomes a black dwarf star. Black dwarf stars are the theoretical end of a white dwarf star’s life. When a white dwarf fizzles out, it is predicted to cool down but keep its mass. The star doesn’t emit any radiation or energy, and will either fade with the rest of the universe in something called a “heat death” or will be swallowed by a black hole.)

Heat death is one of the three theoretical ends of the universe. Heat death is exactly what the name entails: the death of heat. In this particular theory, the second law of thermodynamics- entropy- plays a significant role. Entropy is best defined as the randomization and disorder of thermal energy. Over time, entropy will cause all of the universe’s energy to evenly distribute itself, ending all energy-consuming processes.

As the universe expands, particles will find themselves floating alone. Without other particles, energy cannot be maintained and they cool down. Eventually, all particles will come to a halt. This is the point of no return; the temperature of the universe has hit absolute zero.