I was trying to find information about what happens to Orpah, Ruth's sister, once she turns her back to them. A few websites I found said according to Jewish history that she married a Philistine and had four sons. One of those sons was Goliath. Is that true?

When the scriptures were silent about various matters, this left room for all sorts of legends and embellishments.

For example, the New Testament tells us almost nothing about the childhood of Jesus. So, not surprisingly, in the second and third centuries many legends grew up describing his juvenile exploits, naughty miracles, and relationships with others. These are all the sorts of things people are interested in -- and rightly so. There is, however, probably a reason for the silences of Scripture. Either we don't need to know, or we wouldn't understand it anyway, or -- armed with the "missing" information -- we might misuse what we learned.

Stick with the scriptures; weigh each extra-biblical tradition carefully. Some may be true, of course, but fortunately our salvation never depends on such things.