* By mass: The most massive stars known are hypergiants like R136a1, which is over 265 times more massive than our Sun. It's hard to find definitive rankings for the second most massive, as there's much uncertainty in measuring star masses.
* By radius: Stars like VY Canis Majoris and UY Scuti are colossal in size, dwarfing our Sun. However, their masses are relatively low, making it difficult to definitively rank them.
* By luminosity: The brightest stars are often very massive and hot, like Eta Carinae. But again, ranking them precisely is challenging.
So, there's no single "second biggest" star in space. It depends on which criterion you use to define "biggest".
