How Often Do Stars Die?

The deaths of stars are among the most spectacular events in the cosmos. How a star dies is dependent upon its mass. Low to medium mass stars, such as our sun, will eventually evolve into red giant stars, expanding many times beyond their original size, eventually blowing off their outer layers and becoming a planetary nebula. High mass stars go out in a far more spectacular manner, eventually exploding in mighty supernovae. When a supernova occurs, it can release more energy than every star in a galaxy combined, and so they are among the brightest known events in the cosmos. How often do stars die in the Milky Way, and if a supernova does occur in our galaxy, could we see it from Earth?

The Rate Of Star Formation And Death

Star cluster
                  Hubble image of a star cluster. NASA

Stars are continuously forming in our galaxy. Deep within stellar nurseries, hydrogen gas is clumping together and stars are forming. In our galaxy alone, the equivalent of three sun-like stars form every year. In other words, the amount of material used in forming new stars is equal to three suns. That could mean one star with three times the mass of the sun, or it could mean a multitude of low mass stars that equal three solar masses. From the moment they are born, every star is powered by the fusion of hydrogen nuclei in their core. Eventually, that hydrogen will run out and the star will enter the final stages of its life. In our galaxy, there are a multitude of stars that are currently in their final stages of life, yet how often do these stars actually cease to exist? Unfortunately, not every star in the Milky Way is visible to us, and so astronomers rely on estimates. Every year, at least one low to medium mass star becomes a planetary nebula in our galaxy. Supernovae are far rarer, and astronomers estimate that one supernova occurs in our galaxy every 100 years. Depending on where the supernova occurs, it could be visible to us on Earth. In fact, supernovae have occurred in the past that outshone every other object in the night sky, the most notable of which occurred over 1,000 years ago. In the year 1054 CE, astronomers in China and Japan recorded observations detailing an extraordinarily bright object in the sky. It was so bright that it outshined a full moon and was even visible in broad daylight. Based on recorded observations, astronomers believe that the bright object was a supernova, and have even linked it to a supernova remnant called the Crab Nebula. 

Will We See A Supernova Anytime Soon?

Crab Nebula
Hubble image of the Crab Nebula. Astronomers believe that the supernova that formed the Crab Nebula was the same supernova observed by astronomers in 1054 CE. NASA

Witnessing a supernova from Earth, as astronomers did in 1054 CE, would be a sight to behold. Back then, humanity had little to no understanding of what was actually occurring, yet today we would be aware that we are currently witnessing the death throes of a massive star. Although a number of supernovae have been visible to the naked eye since 1054 CE, none have been quite as spectacular, or as close to our solar system. There are a number of stars in our Milky Way that are currently in the final stages of their life, and whose masses are high enough that they will become a supernova. The most notable is Betelgeuse. Betelgeuse is one of the most well-known stars in the night sky. Located in the constellation Orion roughly 600 light years away, Betelgeuse is one of the largest stars in the Milky Way and will likely go supernova within the next 100,000 years. When Betelgeuse does go supernova, it will be one of the brightest objects to ever grace the night sky.