Neutron Stars, White Dwarfs, Brown Dwarfs And More Aren’t Actually Stars
“There is a lesson here that all scientists should be aware of: it doesn’t matter how you name or classify something that you’re studying. Rather, it matters that you understand the properties that it does and doesn’t have. Whether you classify Pluto as a planet or not isn’t what’s important; understanding its physical and orbital properties are. Whether you classify a virus as life or non-life isn’t nearly as important as understanding its structures, functions, and impacts on the environment and the organisms within it. Not every object with “star” in its name fuses hydrogen into helium, helium into carbon, or heavier elements into still heavier ones, but white dwarfs, neutron stars, brown dwarfs, and protostars are no less spectacular for it. Not everything is a star, and that’s a good thing. Every object plays its own unique role in the cosmic story that’s created us.”
It’s right there in the name: neutron star, white dwarf star, brown dwarf star, T Tauri star, etc. So why, then, do we say they aren’t actually stars? Meanwhile, other dwarf stars, like red dwarfs, are stars, and all the giant and supergiants, whether red or blue or anywhere in between, are stars, too?
It seems arbitrary to an outsider, but astronomers have good reasons for classifying the objects we do as stars, while leaving the others out. It isn’t about mass, temperature, or brightness, either. Those might be useful for distinguishing stars from non-stars and one another, but that’s not why the line is drawn.