Source

File: wp-includes/rest-api.php

function rest_get_avatar_urls( $id_or_email ) {
	$avatar_sizes = rest_get_avatar_sizes();

	$urls = array();
	foreach ( $avatar_sizes as $size ) {
		$urls[ $size ] = get_avatar_url( $id_or_email, array( 'size' => $size ) );
	}

	return $urls;
}