Do sentences in English always have object?

No, sentences in English do not always have an object. Many sentences are perfectly grammatical without one. These are often intransitive sentences, meaning the verb doesn't take a direct object.

Examples:

* She sleeps. (Sleeps is an intransitive verb)

* The dog barks. (Barks is an intransitive verb)

* He runs. (Runs is an intransitive verb)

* It rained. (Rained is an intransitive verb)

These sentences have a subject (she, the dog, he, it) and a verb, but no object receiving the action of the verb.