The Blue by Stephanie Void

What would you do with a mysterious starship and a giant housecat?

Alan Michael Wolf is an ordinary 19-year-old boy from a backwater colony world whose only dream was to go to military school. However, when he is sent home to recover from an injury, he finds himself stranded when he recieves unthinkable news: his home planet is gone. Destroyed. He is left with nothing until a chance encounter with an old man at a spaceport leaves him with three things: a mysterious starship, a giant housecat, and the news that his younger sister Katelyn may still be alive.

Alan takes off across the galaxy in search of her but discovers the old man's ship may have led him to a big secret, one that will lead him to an even bigger truth about why his home planet was destroyed. But there are forces out there who will hunt him down to make sure he is silenced before he can reveal the truth...