Do not use the objectmanager. Using Dependency Injections improves the quality of your module by decreasing coupling and thus increasing extendability. This makes better modules and saves time in the future. The last thing we need is teaching people to use dirty solutions because of inadequacy. If we all make high quality modules for Magento 2 it will improve the platform and everyone profits.
Inject the RedirectFactory in your Block constructor:
public function __construct(
$this->productRepository = $productRepository;
$this->redirectFactory = $redirectFactory
Call the redirect from somewhere in the Block: