Are questions about history behind a scientist or mathematicians life on topic? For example personal life, death etc.
This is motivated by my recent question Why was Évariste Galois killed?
Questions on the personal lives of scientists should certainly be allowed, with the important caveat that the question has to be clearly relevant to the academic work of these people.
Clearly, a question about the eating habits of Albert Einstein should be off-topic, while I think the example question about the death of Galois is on-topic, since the story makes an important claim about the work of Galois (namely, that it was written down in a hasty, last-minute fashion, suggesting perhaps more could have been...).
Update: In case this post becomes a go-to reference for people wondering about this matter, I think it is important to note that we have established the biographical-details tag to mark this type of questions. If you see any questions pertaining to the specifics of the life (or death) of a scientist, please apply the tag.
I feel that it's very important to allow a lot of leeway for questions about lives of scientists/mathematicians. The history of science and mathematics is not just a dry collection of little connected facts about scientific or mathematical results, etc. Part of what's interesting and important about history of ideas in any domain consists of relationships between ideas, individual lives, and broader phenomena such as cultural changes. It's difficult to know in advance what non-scientific or non-mathematical factors might be relevant to understanding the history of scientific and mathematical research.
I understand that this is not a site for free discussion of anything vaguely related to history of science/math. But I don't think that it's profitable to restrict its scope in the way that, say, StackOverflow is restricted (and on SO, I feel that narrow restrictions on what's allowed are profitable.) The problem is that there's more to history than a set of established answers about particular facts. The nature of of the subject matter of hsm.SE requires that it have a more liberal approach to what's on-topic than some other SE sites.
(What if someone notices surprising parallels between the way that Einstein wrote about special relativity, and the way that a late 19th Century chef wrote about how the time needed for certain recipes changes in different cooking contexts? Could what Einstein ate be a clue to what he had heard about cooking, and thereby perhaps provide insight into the germination of special relativity? Obviously he was thinking a lot about physics and math, but so were a lot of other people during the same period. What led Einstein to develop his novel proposals? Do we want to say that this site cannot help with such investigations?)
I would say that questions about the personal lives of mathematicians and scientists are on topic if they relate to math and science.
"Eating habits" might not be on topic, unless they relate to vitamins or nutrition, or something that contributed to someone's "acumen."
The circumstances of Galois death certainly cut short his life span and contributions, and probably contributed to the "fits and starts" of his work. As Samuel Johnson wrote, "If a man knows that he will be hanged in a fortnight, it concentrates his mind wonderfully." Who knows, maybe he wouldn't have risen to intellectual peaks without the imminent threat of death.