filter Get-ProcessOwner
{
  $id = $_.ID
  $info = (Get-WmiObject -Class Win32_Process -Filter "Handle=$id").GetOwner()
  if ($info.ReturnValue -eq 2)
  {
    $owner = '[Access Denied]'
  }
  else
  {
    $owner = '{0}/{1}' -f $info.Domain, $info.User
  }
  $_ | Add-Member -MemberType NoteProperty -Name Owner -Value $owner -PassThru
}

PS> Get-Process -Id $pid | Get-ProcessOwner | Select-Object -Property Name, ID, Owner

Name                    Id Owner
----                    -- -----
powershell_ise       10080 TOBI2/Tobias

PS> Get-Process | Where-Object MainWindowTitle | Get-ProcessOwner | Select-Object -Property Name, ID, Owner

Name                    Id Owner                   
----                    -- -----                   
chrome               13028 TOBI2/Tobias            
devenv               13724 TOBI2/Tobias            
Energy Manager        6120 TOBI2/Tobias            
ILSpy                14928 TOBI2/Tobias            
(...)