A distant object that appears as a point of light shows a large decrease in brightness every three days, and a smaller decrease in brightness exactly among the large decreases. Both decreases last just a few hours. What kind of object is it?
1- It is pulsating star that is swelling and shrinking in size
2- It is a star going through the planetary nebula stage of its life
3- It is a binary star system seen edge-on, so that the two stars eclipse each other from out point of view
4- It is a red supergiant star that has moved off the main sequence and is about to blow up as a supernova