I was in a car accident 2 days ago, they did x-rays and ct. no cracked rib, is it possible to have fractured ribs ? do they show up on xray

2 different question: CXR can miss rib fractures. CT is more specific and usually detects fractures 90+% cracked = fracture

An acute : Non displaced rib fracture may be difficult or impossible to detect on X-ray or even CT in the first couple of days, so the answer to your question is yes. They almost always are seen by 7-10 days due to the early healing response making them more conspicuous.