PHP has released its new version 5.6 couple of days before. In the new version a new exponent operator has been introduced for the exponentiation operation. Till now exponentiation was carried out using a built-in function pow in PHP. From PHP 5.6 this can be carried using double airstrike (**) to execute exponentiation. The new exponent operator in php is a very handy way to write code than calling a function as required now.
// These two will be equivalent as of PHP 5.6.0
$x = $y ** 2;
$x = pow($y, 2);
Before using Exponent Operator (**) in PHP
If the new exponent operator (**) is used in PHP versions below 5.6, it will throw a parse error Parse error: syntax error, unexpected ‘*’. So make sure your PHP version is 5.6 before you start using the new operator for exponentiation in PHP.