When a married man dies childless, his wife has a Mitzva to do "Yibbum" i.e marrying his living brother, alternatively Chalitza which is like a divorce is performed to enable her to remarry someone else.
When a married man dies childless, his wife has a Mitzva to do "Yibbum" i.e marrying his living brother, alternatively Chalitza which is like a divorce is performed to enable her to remarry someone else.