Technically SN 1987A* is much older than Cassiopeia A**, which is only about 11,330 years old.
At its distance of about 168,000 light years in the LMC, SN 1987A is more like ca. 168,033 years old, just for the sake of accuracy.
And one might reasonably assume that it would be pretty hot for some time following core collapse. That was not a firecracker going off!
SN 1987A rewrote the book on type II supernovas, which previously were thought to occur only with red giants. The progenitor star for this SN was a blue giant. An excerpt from the below link*:
"Four days after the event was recorded, the progenitor star was tentatively identified as Sanduleak −69 202 (Sk -69 202), a blue supergiant.[7] After the supernova faded, that identification was definitively confirmed by Sk −69 202 having disappeared. This was an unexpected identification, because models of high mass stellar evolution at the time did not predict that blue supergiants are susceptible to a supernova event."
end quote
Noting that : "models of high mass stellar evolution at the time did not predict that blue supergiants are susceptible to a supernova event" makes one wonder what else they are
so very wrong about. Of course they didn't even know they were wrong until nature demonstrated it in no uncertain terms with this SN.
It seems likely that nature will be correcting other "models" before long!!!!!!! ( Time will tell, as it usually does.)
*
https://en.wikipedia.org/wiki/SN_1987A
To see an image of SN 1987A, check out this poster's avatar!
**
https://en.wikipedia.org/wiki/Cassiopeia_A
You can watch short trailers using BING or Google searches. The angular resolution reported for this blob by ALMA is 80 mas. At 51.4E+3 pc distance, the size of this blob is at least 4112 AU across 
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