Did you think that the light from explosions decreases with time? That makes sense, right? Think again. Recent optical (Hubble), radio, and X-ray images of SN1987a have found that is getting brighter with time. The reason why is that, as the material ejected in this explosion expands, it sweeps up more and more of the surrounding material, heating them up such that they emit light in these wavelengths. In fact, very recently the ejecta collided with dense gas released by the star about 20-30 years before it exploded, causing it to light up. Go here to read more. Enjoy!