Free Astronomy Magazine May-June 2020

38 MAY-JUNE 2020 SMALL BODIES light-years of Earth. Although no other event has left clear traces, this frequency, extrapolated to the entire Milky Way, makes acceptable the hypothesis that interstellar space is crossed by a non-negligible quan- tity of very small agglomerations of matter endowed with sub-relativistic speeds. The value of the speed depends, of course, on the mass of matter accelerated by a given supernova. Currently, we do not know if, in the ejecta rain that supernovae pour into in- terstellar space, there are also solid particles more massive than the dust grains. In their study, Siraj and Loeb are optimistic in this re- gard, relying on the fact that concentrations of low-density ejecta have been observed in the remnants of several supernovae, which could at least in part be made up of the tiny solid bodies considered in the study. The two researchers estimate that if just 0.01% of the dust ejected from a supernova were contained in particles measurable in millimeters, we could expect to observe, on average, one sub-relativistic meteor per month. This estimate takes into account the average supernovae rate estimated for the Milky Way (~1 every 50 years), the average mass of dust released by a supernova (~0.1 solar masses), and our distance from the galactic center (~26,000 light-years).

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