Why did the glass window in my home suddenly shatter (crack) on its own?

I have a 5ft by 4 ft window on top of my entrance door and this rmoning there was loud and sharp noise and when i saw the window, it was all cracked and shattered.

It has not fallen dow as it is a tempered glass, I believe. My house is about 1.5 years old and I dont understand why this happened?

I dont see any visible signs of stone, ball or bullet i.e., there no holes in the glass (just cracks) and by looking at the pattern it seems to flow from top center outwards towards the bottom.

Thanks