We present a new analysis of the infrared ( IR ) emission from the ejecta of SN1987A covering days 615 , 775 , 1144 , 8515 , and 9090 after the explosion .
We show that the observations are consistent with the rapid formation of about 0.4 M _ { \odot } of dust , consisting of mostly silicates ( MgSiO _ { 3 } ) , near day 615 , and evolving to about 0.45 M _ { \odot } of composite dust grains consisting of \sim 0.4 M _ { \odot } of silicates and \sim 0.05 M _ { \odot } of amorphous carbon after day \sim 8500 .
The proposed scenario challenges previous claims that dust in SN ejecta is predominantly carbon , and that it grew from an initial mass of \sim 10 ^ { -3 } M _ { \odot } , to over 0.5 M _ { \odot } by cold accretion .
It alleviates several problems with previous interpretations of the data : ( 1 ) it reconciles the abundances of silicon , magnesium , and carbon with the upper limits imposed by nucleosynthesis calculations ; ( 2 ) it eliminates the requirement that most of the dust observed around day 9000 grew by cold accretion onto the \sim 10 ^ { -3 } M _ { \odot } of dust previously inferred for days 615 and 775 after the explosion ; and ( 3 ) establishes the dominance of silicate over carbon dust in the SN ejecta .
At early epochs , the IR luminosity of the dust is powered by the radioactive decay of ^ { 56 } Co , and at late times by at least ( 1.3 - 1.6 ) \times 10 ^ { -4 } M _ { \odot } of ^ { 44 } Ti .
Even if only a fraction \gtrsim 10 % of the silicate dust survives the injection into the ISM , the observations firmly establish the role of core collapse SNe as the major source of thermally condensed silicate dust in the universe .