Can't use property in Tinker even that the relations exists

I have 4 tables (users,teachers,courses,course_teacher)

so I have a foreign key in teachers table references id on users table, and course_teacher as pivot table (many to many relationship)

users table has (id,firstname,lastname,email,password) teachers table has (id,users_id,about) courses table has (id,name)

and I have these relations in the models:

// User.php
public function teacher() {
        return $this->hasMany(Teacher::class);
 }

// Teacher.php
public function course() {
        return $this->belongsToMany(Course::class);
    }

    public function user() {
        return $this->belongsTo(User::class);
    }

// Course.php
public function teacher() {
        return $this->belongsToMany(Teacher::class);
    }

in my database I have data in each of these three tables and I attached teacher and course together in the pivot table

in tinker I tried this:

$course = App\Course::find(1);
// I got here some data

$teacher = App\Teacher::find(1);

$course->teacher;
// I got (id,users_id,about)

$teacher->user;
// I got his data from users table

but when I tried to get the name and email of the teacher :

$course->teacher->user;

it gives me this error: Exception with message 'Property [user] does not exist on this collection instance.'

how can I get this teacher data as user ?