No backup - then you have minimal chances of restoring the photos - you MUST always have good up to date backups to protect against errors - like the one you made - Apple even provides free backup software on every Mac - all you have to purchase an external hard drive formatted Mac OS extended (journaled) and start running TimeMachine all the time and you will always have an hourly backup
You can try file recovery software like FileSalvage - the free trial will tell you what can be recovered - you must purchase to actually recover the files - and you will have to trash your iphoto library an start over with a new one losing all edits and organization and metadata changes you made
And you better start backing up if anything on your computer including your photos has any value to you so you do not lose them again - sooner or later you will lose everything on your computer with no backjup
LN