The Oldest and Youngest Stars in Our Galaxy

For as long as humans have existed, they've gazed up into the night sky and marveled at the beauty of the twinkling lights above. They created legends to explain the origin and creation of the celestial world and passed them down from generation to generation. Even today, despite the impressive advancements of science and technology, there is still a vast amount of mystery and intrigue surrounding the heavens above. Astronomers have, however, learned a great deal about the birth and death of stars and identified the oldest and youngest stars in our galaxy.

Our solar system is in the Milky Way galaxy. This name was inspired by the cloudy appearance when the Milky Way is visible in the night sky. This barred spiral-shaped galaxy spans about 120,000 light-years and is primarily located in the Sagittarius constellation. The Milky Way is home to between 100 – 400 billion stars.  

Before we get into the oldest and youngest stars, we must first understand that many different stars exist. To help distinguish between the various types, astronomers began classifying them by the stage of development they are currently in. Here are a few of the major categories of stars. 

A Protostar is a collection of gas that has collapsed down from a molecular cloud. It is the phase before a star as we know it forms. 

The next stage is a T Tauri Star. This phase occurs when the gravitational pressure holds the star together, but there isn't enough pressure or temperature to induce the nuclear fusion process. 

Most of the stars in our galaxy are in the Main Sequence Star phase. Our sun is a main-sequence star that is fueled by nuclear fusion. Several other stars also fall into this category of stars. 

A Red Giant Star has consumed its hydrogen supply, so the fusion stops, and the star no longer generates an outward pressure. A hydrogen shell around the star's core ignites and causes the star to increase in size. 

A White Dwarf Star no longer generates nuclear fusion and slowly cools down.

The Red Dwarf Star is the most common in the universe. While they are still considered main sequence stars, they have much lower masses and are much cooler than our sun. 

Neutron Stars form after a star dies in a supernova explosion. This star is composed entirely of neutrons and could potentially form into black holes if the mass is great enough. 

Lastly, there are Supergiant Stars. These are the largest stars in the universe. 

Stars are formed when the denser parts of a cloud of gas and dust collapse under their weight or gravity. This process usually takes millions of years to complete. Once completed, a new star is born. 

Once a star is born, it remains alive by the nuclear fusion of hydrogen into helium. Nuclear fusion is a process where two lighter nuclei, in this case, hydrogen, merge to form a single, heavier nucleus, usually helium. During this process, energy is released, which fuels the star's existence. It is this reaction that causes the twinkling effect that humans enjoy while stargazing. A star will live as long as it has a source of fuel. 

The gravitational pull of the star's mass tries to squeeze it down into a point while the energy released in the nuclear fusion pushes outward. This balance is what fuels and sustains a star's life span. The lifespan of a star varies greatly depending on its mass. Usually, the heavier the star is, the faster it burns up. So, heavier stars have shorter life spans. A star as large as our sun may live ten billion years, while a star three times its size, may only live ten million years. 

Once a star has burned away its fuel source, it dies by collapsing its inner core while the outer layer explodes. If the star is not entirely consumed in the process, a neutron star has the potential to form. The neutron star is the remaining collapsed core of a massive supergiant star after the supernova explosion. This densely clumped matter then develops its gravitational collapse. In some instances, if there is a great enough mass, a black hole will form.  

Scientists have recently discovered the youngest neutron star in our galaxy. This star, a pulsar named Swift J1818.0-1607, is located in the Sagittarius constellation. Swift J1818.0-1607 is believed only to be about 240 years old. Discovered just last year, March 12, 2021, this star released a large burst of X-rays. Since this behavior is not typical of older stars, all eyes turn on Swift J1818.0-1607. Follow-up studies revealed more properties that solidified its status as the youngest neutron star in the galaxy. One of these properties was the rate at which this star rotates. It is the fastest spinning star, completing a rotation every 1.4 seconds! 

Another unique feature about this star is that it is a magnetar. This means that it has a particularly powerful magnetic field. It is believed that there are currently only about thirty other magnetars in our galaxy, and only five of them are also radio pulsars. This incredibly rare star provides scientists an extraordinary opportunity to study the early stages of stars, as well as their unique magnetic properties. 

The oldest star in our galaxy and the universe is HD 140283, also known as the Methuselah star. There is some debate about this star's actual age, as it is believed to be older than our universe itself. While the universe is believed to be 13.8 billion years old, astronomers believe this star is more than 14 billion years old! The most significant debate is whether a star can be older than the universe itself. 

Found in the Libra constellation, the Methuselah star is a yellow subgiant located about 200 light-years away from Earth. The moniker, Methuselah, comes from the Bible. The oldest known star was named after the oldest known person in Biblical times, Methuselah, who supposedly died at the age of 969 years old. 

So, why do scientists believe that this star is older than the universe itself? It is due to the physical composition of Methuselah. Since Methuselah contains very little iron in its design, it is believed this star was born before iron became more accessible. This quality is known as metal-poor. The Methuselah is one of the most metal-poor (and therefore oldest) stars in the galaxy. 

The Methuselah is part of the second generation, or Population II, of stars. Most Population II and Population III stars are no longer observable. It has a radius of 605,460 miles and a surface temperature of 5,787 K.

In a galaxy with about 200 billion stars, astronomers have identified both the oldest and youngest stars. As we continue learning more about our galaxy and universe and make new discoveries about our stars, remember to look up and enjoy the sheer energy those little twinkling lights represent.

Check out other articles from our blog for more astronomy and star facts.