function invoiceOrder($order){
    $invoice = Mage::getModel('sales/service_order', $order)->prepareInvoice();
    $invoice->setRequestedCaptureCase(Mage_Sales_Model_Order_Invoice::CAPTURE_ONLINE);
    $invoice->register();

    $transaction = Mage::getModel('core/resource_transaction')
        ->addObject($invoice)
        ->addObject($invoice->getOrder());

    $transaction->save();
}