Is there any option for continuous authentication on Android ? Suppose you unlock your smartphone and put it aside and someone takes it before it gets locked, is there any mechanism currently to authenticate the new user and lock him out of the phone ?   

I see that there are many articles speaking about continuous authentication like this one and this but is there actually an implementation on current versions of Android ?  

I have a Samsung Galaxy S7 with Android 7.0
I've looked at those papers and the problem always is getting enough data from the attacker's actions to know the user is no longer the owner.

Which means that some other signal has to be provided to indicate that the owner is absent. The Bluetooth signal from a separate device provides such a signal.

Its called Smart Lock.

How to Use Smart Lock on Galaxy S7


  
  Launch the settings app from your Home screen or the app drawer.
  Tap on the Lock screen and security button. 
  Tap on Secure lock settings.
  Tap on Smart Lock. 
  Enter your password, pin, or pattern. 
  Tap on Trusted devices. 
  Tap on Add trusted device. 
  Tap on Bluetooth.
  Tap on the device you want to be trusted.
  Tap on Yes, Add.
  


The article also mentions 'On-Body' detection but notes only so-so accuracy.