* Stars are not solid objects: Stars are giant balls of plasma, not solid objects with a fixed boundary.
* Gravity: If you tried to force a star into another, their immense gravitational forces would create immense pressure and heat, likely leading to a catastrophic explosion.
However, we can compare the volumes of the Sun and Sirius A to get a sense of how much bigger Sirius A is:
* Sirius A's radius: About 1.71 times the Sun's radius.
* Volume is proportional to radius cubed: This means Sirius A has about 1.71 cubed, or roughly 5 times the volume of the Sun.
Therefore, you could fit about 5 Suns worth of volume into Sirius A, but not in a literal, physical sense.
