In class we discussed the spectral classification system which is how stars are organized and categorized.
Each class of stars has distinctive characteristics from the others. Through these characteristics we can see which classes are most likely to host planets capable of supporting potential life like we have here on earth. First, we need to learn the classification system so we can closely look into which classes can support life better. The spectral classes include: O, B, A, F, G, K, and M type stars. As you move from O to M class stars you can see trends in their characteristics. The O class stars have a blue color, hottest surface temperatures, largest mass, largest radius, and longest life span. The M class stars have a red color, the least hot surface temperature, smallest mass, smallest radius, and shortest life span. These characteristics decrease as you move from O class to M class stars.
Now that we know more about each class, we can look at which class best suits hosting a planet capable of supporting life. In addition, when we look at what class stars would be best for supporting life it would be more practical to look for a reasonably long-lived star, with a spectrum similar to our own. If the evolution of life on Earth is typical, then it takes life about 4 billion years for life to evolve even as far as we have. The central star must be stable for this whole time. The Sun is about half way through the stable phase of its life.
Since a star’s lifetime depends upon its mass, the heavier a star the hotter it burns and the shorter its life, this implies that the star must be no heavier than the Sun. The range of star types that can support Earth-type life on planets may be limited to those lower mass stars that live long enough as stable luminous stars for planets to form and complex life to evolve.Lastly, if we are looking for stars similar to our own, then spectral class G is the first choice, possibly F as well. The hotter classes, like O and B would emit too much hard radiation, and wouldn’t live long enough for life to evolve. A class K or M star would have a very narrow habitable zone. While G and F are most likely the class stars scientists should turn to when trying to find planets with life, we should remember that each spectral class star has its own habitable zone which varies in distance from the star based on stellar output.
Even the largest, possibly suitable stars may only be able to support Earth-type life for around two billion years, and so planets in its orbit may not have sufficient time to develop complex life on land such as trees. In conclusion, spectral classification plays a key role in helping identify stars that are able to host planet capable of supporting life. The classification allows scientists to focus on classes of stars that are most likely to have the suitable conditions of hosting a planet, instead of looking at all of the different classes of stars out there. This allows them to narrow down the amount of looking, and hopefully speed up the process of making scientific discoveries.