The prominent feature that allows for the existence of life on Earth is the Sun. Radiation from our closest star provides heat and energy to our planet, driving biological processes and providing the necessary conditions for liquid water to naturally exist.
But our Sun is only but one star in this vast Universe. And as it turns out, most stars are quite different than the one that illuminates our day. For this reason, scientists have, for hundreds of years, attempted to study the other stars in our galaxy and beyond.
Out of these stellar studies arose the field of Stellar Astrophysics. (Also sometimes called Stellar Astronomy, but since the field deals more with physical modeling of stellar systems and relies less on large amounts of observational data – with the exception of the specific subfield of Solar Astronomy – the Astrophysical designation is usually more appropriate.)
Stellar Formation and Evolution
One of the primary questions facing stellar astronomers asks, “How do stars form?” For millennia this was unclear, and even today there are certainly details that are up for debate.
From observations of large gas structures in our galaxy, we see that disruptions in the cloud give rise to clumping. From there, gravity begins to drive the collapse of the gas cloud, ultimately creating a star.
Of course, as we look out into the cosmos we notice that not all stars are the same. Most are a small fraction of the Sun’s mass, while others are tens or hundreds of times as hefty.
Understanding how these different stars form can be challenging, especially since some of the largest stars in our galaxy are so big, they appear to defy the very laws of physics.
To try to get at the heart of the matter, researchers study stars of all sizes and at all different stages of their evolution. The goal is to find clues about their life cycles, and then build numerical models that predict how these stars will behave over time.
For centuries one of the most perplexing properties of the Sun is that it has shined for billions of years – and will shine for billions more. This requires a massive energy reserve; one that only in the last century or so was well understood.
Since the Sun is often described as a raging ball of fire, astronomers once posited that perhaps the Sun was simply a burning ember, similar to how wood burns in a fireplace. But such a model of the Sun could not explain how it could live so long – in fact it would have extinguished billions of years ago.
Similarly, other models failed to explain how the Sun could burn so brightly for so long. It was not until physicists began to understand the nature of nuclear fusion that an answer was at hand.
Even then, there have been bumps along the way. Observations of solar neutrinos cast doubt on our understanding. (Though it was finally determined that it was not our solar model that was flawed, but rather our understanding of neutrinos themselves.)
But, still more plagues us. The science of how the star brings energy to the surface is still studied, but we do have a good general idea of this. Also, questions about stellar life times and equations of state are still active areas of research.
Studying stars is, in general, difficult. Like most areas of astronomy, we lack the ability to travel right up to the object that we are interested in to study it. Instead, we have to rely on light emitted from the object, which has traveled across the cosmos, for us to gather any kind of information at all.
For this reason, we rely heavily on our Sun – by far the closest star to Earth – to shed light on stars and stellar evolution in general. Also, because of its proximity we can study surface features, such as sunspots, solar prominences, and solar flares. These phenomena give us clues about solar magnetic fields, and stellar rotations.
In addition to being the canonical model for other stars in the Universe, we also study our Sun to gain insight into how stars interact with their planets, and to possibly trace back the history of our own solar system.
Image Caption: LH 95 stellar nursery in the Large Magellanic Cloud. Credit: Wikipedia/NASA/ESA