A small object is placed at the center of a large evacuated hollow spherical container. Assume that the container is maintained at 0 K . At time $\mathrm{t}=0$, the temperature of the object is 200 K . The temperature of the object becomes 100 K at $\mathrm{t}=\mathrm{t}_1$ and 50 K at $\mathrm{t}=\mathrm{t}_2$. Assume the object and the container to be ideal black bodies. The heat capacity of the object does not depend on temperature. The ratio ( $\mathrm{t}_2 / \mathrm{t}_1$ ) is $\_\_\_\_$ .