The birth, life, and death of stars
Space has always been viewed as a very enigmatic place, and scientists are still trying to uncover the origins and future of the universe along with our place in it. One of the most common objects in space that lights up the night sky is stars. On a clear night away from urban cities, thousands of stars from our very own Milky Way galaxy can be observed. Some will appear extremely bright, whereas others are much fainter and difficult to see with the naked eye. The nearest star to Earth is the Sun. This post explores what a star is, how it is born, and the lifespan of this enormous ball of plasma.
The Orion nebula
The Birth of a Star
A star's life begins with the gravitational collapse of a nebula primarily made of hydrogen and some helium. A nebula is an interstellar cloud mostly composed of dust, hydrogen, and helium. Most nebulas are enormous, hundreds of light years in diameter. A light year is equivalent to the distance that light travels in one year, which is nearly 6 trillion (6,000,000,000,000) miles. Nebulas have an extremely low density. If a nebula were the size of Earth, it would have a total mass of just a few kilograms. The star-forming regions in nebulas contain denser regions of gas and dust that then attract other matter. Eventually, this clump will become dense enough to gravitationally collapse and form stars. The remaining material in the nebula is then thought to form planets and other celestial objects like comets and asteroids.
The Life and Death of a Star
When the core of a star is sufficiently dense, hydrogen steadily becomes converted into helium through thermonuclear fusion. This fusion releases energy that travels across the interior of the star through convective heat transfer and then radiates to outer space. All of these processes going on inside a star generates pressure that prevents it from collapsing under its own gravity. A star with a mass greater than 0.4 times the Sun's will expand to become a red giant once the hydrogen fuel at its core is exhausted. Very massive, hot stars can fuse helium into heavier elements up to iron at the core or in shells around the core.
Supernova remnant W49B
As the star expands it throws a part of its mass with those heavier elements into the interstellar environment, which then becomes a part of new stars. Once this happens, the core of the star becomes a stellar remnant: either a white dwarf, neutron star, or black hole depending on how massive the star was. If a star is about the same mass as the Sun, it will turn into a white dwarf. If the star is more massive (between 10 and 29 solar masses), it can undergo a supernova explosion and leave behind an unbelievably dense neutron star. However, if the core of the star is sufficiently massive, nothing can stop the collapse of its core. This ultimately results in an implosion that creates a black hole. Neutron stars and black holes will be individually discussed in future posts since they are both magnificent, surreal objects.
