'Ice stars' or 'Lake stars' develop under very specific early winter conditions.
First, a cold snap that freezes the pond ice an inch or two thick, followed by warmer days that bump the ice temperature above 32F. Pores form in the ice sheet where there are any imperfections in the water surface (plant matter, logs). Then, some snow falls with a cold front blowing in. Warm water wells up from beneath the thin layer of ice, covered with a coating of snow and slush. Temperature and precipitation have to be perfect for this to happen.
