Which is the biggest star?
Short answer: We're not sure but some of the largest stars we know of are Stephenson 2-18, MY Cephei and WY Velorum.
Long answer: When we talk about the biggest stars in the Universe, we can obviously only compare the stars we know about. Since we know there are many stars too far away to study, and we don't really know how big a star can get, it's likely that there are stars out there somewhere that are bigger than the ones we're aware of. Therefore, all we can currently report are the biggest known stars, not the biggest stars that exist.
In addition, it's very difficult to measure the size of faraway stars, so it's not clear which of them are the biggest. According to our best estimates, here is a list of the ten largest known stars, with the number of times larger than the Sun each one is:
- Stephenson 2-18 (2,150 × the Sun)
- MY Cephei (2,061 × the Sun)
- WY Velorum (2,028 × the Sun)
- RX Telescopii (1,898 × the Sun)
- LGGS J004520.67+414717.3 (1,870 × the Sun)
- MG73 46 (MSX LMC 891) (1,838 × the Sun)
- LGGS J004539.99+415404.1 (1,792 × the Sun)
- HV 888 (WOH S140) (1,765 × the Sun)
- WOH S274 (1,724 × the Sun)
- UY Scuti (1,708 × the Sun)
Remember, these are estimates—some of them rough estimates. This list is subject to change as we learn more about these and other stars.