opinion / advice on what to do??

Sarah

So I was petting my kitty and I noticed there was some kind of hard fur, well at least I thought, so I thought she probably has a mat there (she's got a lot of fur so she gets then sometimes) and then I looked and saw this! I don't even know what happened or even how it happened. It's sore for her (obviously) should I take her to the vet to get it looked at? It looks worse in person.