March 23, 2023

Looking into the Dusty Shroud of a Dying Star

The death of a star is one of the most beautiful things in the universe. As they collapse, stars often create nebulae that are so large and complex scientists have yet to fully understand them. The nebula’s composition can vary, but it typically consists of dust particles, plasma, ionized gas and other interstellar material. This dusty shroud is what remains after a star has died for more than 50 years – its final gasp before being extinguished forever into darkness.

Before we talk about the death of a star, it’s important to understand what they are and how they form. Stars begin as large clouds of dust and gas known as nebulae. These cosmic colonies start out cold and dark, but gravity can cause them to collapse under their own weight. As the nebula shrinks in size it begins to spin, flattening out into a spinning disk. Eventually this nebula will become so dense it begins to heat up in the center and a protostar is born. Nuclear fusion then becomes possible, and a star is born.

Stars spend the majority of their lives fusing hydrogen atoms in their core, releasing energy that allows them to grow to enormous sizes. Stars aren’t perfect spheres, though. Their gravity pulls them in different directions, causing them to bulge at the middle in the shape of an oblate spheroid. They also tend to spin rapidly. This causes their poles to flatten out into a disk parallel with their solar system.

It’s at this point a star enters the most stable part of its evolution – adulthood. This is when it begins to shine, fusing atoms together in their core and releasing all kinds of radiation into space. In fact, most stars gradually increase in brightness as they age. Eventually these stars will run out of hydrogen to burn. At this point in their life, they have become red giants. These are the largest stars in existence – so large that they often expand to encompass their closest planets or even smash them to bits. Eventually these red giants will spit out their outer layers, creating planetary nebulae.

The hourglass shape you see in many planetary nebulae is created by the jets expelled from the dying star. As it expels its outer shell of gases, a new one forms inside and shoots out through the gaps in the first. Also – some red giants will eject their innards directly into space as they die, leaving behind a white dwarf at their core.

The death of a massive star is quite different. They begin their lives much the same way as an adult star – fusing hydrogen into helium in its core. As they get older, however, their gravity becomes so strong it begins to compress the star’s core. At this point, fusion changes from converting hydrogen to helium to fusing helium atoms together into elements like carbon and oxygen. When these stars begin to die, they get hot enough inside that they start fusing elements together into iron.

When these stars run out of helium and oxygen, fusion stops entirely and the star collapses under its own weight. Radiation can no longer escape from this dying star’s core, so it quickly heats up and explodes in a spectacular supernova. The remaining core of the star is what’s left – a neutron star.