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The Evolution of Dust Mass in the Ejecta of SN1987A

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 Msun of dust, consisting of mostly silicates, near day 615, and evolving to about 0.45 Msun of composite dust grains consisting of ~0.4 Msun of silicates and ~ 0.05 Msun of amorphous carbon after day ~8500. The proposed scenario challenges previous claims that dust in SN ejecta is predominantly carbon, and that it grew from an initial mass of ~1e-3 Msun, to over 0.5 Msun 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 the1e-3 Msun 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 56Co, and at late times by at least (1.3-1.6)e-4 Msun 44Ti. Even if only a fraction greater than ~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.