spawing new PHP process

I'm interested in spawing a new PHP process -- if that's the correct terminology. The situation is that I've got a very slow loading page, where, for example, I'm using PHP to send, say, 1000 emails. The user clicks submit, and, although PHP is firing out the emails, it appears to the user that page is hanging. I'd like to somehow send that process to the background and let the page load straight-away. In another scripting language I've used, this function was called "spawn." Do we have something like this in PHP (I know we do!! Just can't find it.) I've looked through the docs but don't see what I'm looking for. Thanks in advance. -Bob