American charges for checked bags; Southwest lets you check two bags for free as long as they don't weigh over 50 pounds; JetBlue gives you the first checked bag free; and only Spirit also charges for carry on bags unless they're small enough to fit under the seat in front of you.
Remnant definition, a remaining, usually small part, quantity, number, or the like. See more.
A supernova remnant is simply what is left over (i.e. the remnant) of a supernova. That probably isn't a very helpful definition, so I'll try to explain what I mean. A supernova is simply the explosion of a star.