std::thread started from a function without waiting the thread to complete

I am confuse to see this small program aborts if I comment t.join()

void my_thread()
{
    std::this_thread::sleep_for(std::chrono::seconds(1));
    std::cout << "thread completed\n";
}

void main()
{
    std::cout << "starting thread...\n";
    std::thread t(my_thread);

    t.join();  //<=== my program aborts when I comment this line

    std::cout << "press a key to quit..." << std::endl;
    std::getchar();
}

I want to write a function that does not wait the thread to complete.

How should I fix this working example?

#include <iostream>
#include <thread>
#include <chrono>

void my_thread()
{
    std::this_thread::sleep_for(std::chrono::seconds(1));
    std::cout << "thread completed\n";
}

void send_message()
{
    std::cout << "starting thread...\n";

    std::thread t(my_thread);

    t.join();  //<=== the function aborts when I comment this line
}

void main()
{
    send_message();
    std::cout << "press a key to quit..." << std::endl;
    std::getchar();
}