Difference between list

I am learning the Observer pattern and I don't understand the extra * in code provided. The Subject.h has this code

//Subject.h
#pragma once
#include<list>
#include "Observable.h"

using namespace std;

class Subject : public Observable {

public:
    Subject();
    ~Subject();

    void attach(Observer *);
    void detach(Observer *);
    void notify();
private:
    list<Observer*>* _observers; // ----------Here there is two *
};

And the Obervable.h has this code (implementing the Observer.h...)

//Observable.h
#pragma once
#include <list>
using namespace std;

class Observer;

class Observable
{
public:
    virtual ~Observable() {};
    virtual void attach(Observer *) = 0;
    virtual void detach(Observer *) = 0;
    virtual void notify() = 0;
protected:
    Observable() {};
private:
    list<Observer*> _observers; // ----------Here there is only one *
};