Old Stars Never Die, They Slowly Fade Away

Las Campanas Observatory, Chile (January 9, 2006)

Like old soldiers in the WWII army ballad, most stars never die, they slowly fade away.

The fate of stars is assigned at birth. A few stars are born very massive, and they live a fast and furious life, burning bright like candles lit on both ends. After just a few million years, they run out of nuclear fuel and collapse under their own weight. This collapse rebounds in a final stupendous explosion, so bright that can be seen across the Universe. These are the events that we call supernovae. Massive stars are however very rare, and most stars are instead born with a low mass, like the Sun or even lighter. These stars burn quietly for a very long time, many billions of years, ending their life in a much less dramatic way. When they feel that the end is night, they become giants: swollen balloons of warm gas, deep red jewels in the night sky. They pulsate, like a tired throbbing heart, one single beat per year. They also smoke: a sooty fog blown out by a slow inexorable wind. A smog so thick that ends up engulfing the star and its planets in a dark cocoon, hiding them from sight. That's when these old stars disappear, fading away from the visible universe behind their curtain of death. Even for stars, however, nothing is forever. The veil finally dissipates, revealing the hot cinder remnant of the star, surrounded by a glowing nebula like a butterfly emerged from it cocoon. We call these fleeting beauties planetary nebulae.

Magellan telescope

I am telling you this story because the primary scientific reason for my 2002 trip to Chile was to spy on these cocoons where old stars hide in their final moments. For this project we used the newly built Magellan telescope (photo on the left), equipped with a new camera we shipped all the way from Arizona: an infrared camera, because with light of this invisible color we can lift the veil surrounding these stars, revealing their secrets. There are many reasons why we want to understand the how and why these stars end their like in such a mysterious way. For starters, the Sun is one of them, although it will take several more billion years before all this will happen. The more pressing reason, however, rests in the nature of the holy smoke that these old stars spew around in their final disappearing act. Talking about smoke was not a poetic license on my part, but rather a quite literal description. For many of these stars the composition of these cocoons is rich in carbon and many complex organic molecules: the building blocks of life. Studying the death of these stars will lead to understand how life arose in the Universe. We literally are stardust, and these stars are the fairies that seeds an otherwise sterile Galaxy with the ingredients of life.

Las Campanas Observatory, Chile (January 8, 2006)