Learn Spanish (Latin America): Mi abuelo se quedó viudo el año pasado. - My grandfather became a widower last year.

We use quedarse for changes of state that are the result of an event or process, often implying a loss or a physical aftermath. Becoming a widower (viudo), blind (ciego), or bald (calvo) all use quedarse because they describe the state someone is left in. Hacerse is for voluntary changes, like a profession, and volverse is for involuntary, deep personality changes.

Why isn't there an article before viudo? In English we say "became a widower".

Just like with professions, Spanish omits the indefinite article (un or una) after verbs of state when referring to unmodified categories like marital status. Saying se quedó un viudo sounds unnatural unless you add a descriptive adjective, like se quedó un viudo muy solitario meaning he became a very lonely widower.

Could I use ser or estar to describe him as a widower instead of focusing on the change?

Yes! If you want to state his marital status rather than the event of becoming one, you can use either. Es viudo treats it as a permanent defining characteristic. Está viudo treats it as his current civil state, contrasting it with when he was married. To focus on the transition itself, though, you must use quedarse.

Does always imply a negative change or a loss?