Final answer:
Supernova SN 1987A was distinct because it was a blue supergiant observed with modern instruments before exploding, and its aftermath provided data supporting the synthesis of heavy elements via radioactive nuclei decay, which kept it unusually bright.
Step-by-step explanation:
Supernova SN 1987A Characteristics
Supernova SN 1987A was exceptional among observed supernovae for several reasons. Firstly, it was the first to be observed with modern instruments, allowing unprecedented study of the death of a nearby star.
Importantly, SN 1987A's progenitor star was a blue supergiant, Sanduleak -69° 202, which had been cataloged in previous surveys of the Large Magellanic Cloud.
This detail differs from typical supernova precursors, which are often red supergiants. Another distinct feature of SN 1987A was the detection of brightening due to radioactive nuclei in the aftermath of the explosion, which confirmed theories about the formation of new elements within supernovae.
Observations showed that as the radioactive nuclei decayed, the emitted gamma-ray heating was primarily responsible for the radiation from SN 1987A after day 40 post-explosion.
What's more, the star did not fade as expected but remained bright due to energy from the decay of newly formed radioactive elements, such as nickel and cobalt, whose gamma rays were detected by Earth-orbiting telescopes, a direct confirmation of heavy element synthesis.