What determines how long a PHP $_SESSION lasts, after closing browser

I've noticed the PHP $_SESSION is still intact even after closing the browser window and then returning back to website. what governs how long the PHP $_SESSION lasts?,

is there something in the admin that controls this?,

It is determined by the combination of your PHP configuration on your server and your cookie configuration in your browser.
Most PHP configurations are set to 24 minutes after the last click, and most browsers are set to correctly expire session cookies when the browser is closed, which normally trumps the PHP setting.
If you've added extra things to extend session cookies, either with browser plugins or by altering Zen Cart code or adding ZC plugins to extend cart operations, then of course all the normal things Zen Cart does are no longer valid, but are superceded by your own environment.

as always, thanks Dr. Byte

but just to be clear, ZC does not create cookies via PHP?,

when you say PHP config on the server, is that set in the ini.php file?, or can be seen via phpinfo()

thanks

ZC works with PHP to set a session cookie. That's the only cookie that ZC sets, well out-of-the-box anyway.

When I use the phrase "PHP configuration", I mean the server's PHP configuration. That's typically done with php.ini