Old Supernova Dust Factory Revealed at the Galactic Center by SOFIA/FORCAST
Abstract
Using FORCAST aboard the Stratospheric Observatory for Infrared Astronomy to image dust emission at 7.7, 19.7, 25.2, 31.5, and 37.1 μm, we reveal the presence of ~0.01 M⊙ of warm (Td ~ 100 K) dust near the center of the ~104 yr-old Sgr A East supernova remnant (SNR) located at the Galactic center. We argue that the dust is associated with the SNR ejecta based on analysis of its thermal structure and possible heating sources such as collisions with energetic (Te ~ 107 K) electrons in the ejecta and/or radiative heating by the luminous central cluster (Lcent ~ 4 × 107 L⊙). Utilizing the DustEM code, we fit dust emission models to spectral energy distributions (SEDs) at six different locations throughout the dusty concentration that require both a very small (VSG; a ~ 0.001 μm) and a larger (LG; a ~ 0.04 μm) distribution of grains. The SED models reveal an enhanced VSG-to-LG mass ratio (~ 14 - 71%) relative to the Milky Way interstellar medium (~13%). In order to explain the location, size distribution, and morphology of the dust within the SNR, we propose a dust evolution scenario in which the SNR expands into an asymmetric, dense surrounding medium that leads to the preferential destruction of ejecta dust southwest of the center of the remnant. Since sputtering timescales in diffuse (ne ~ 10 cm-3) regions of the shocked ejecta are much shorter than the age of the remnant, we require the dust to have formed in dense (ne ~ 150 cm-3) ejecta knots. The speed of the reverse shock in the knots is slowed to a regime where sputtering timescales become longer than the remnant age and shattering via grain-grain collisions is efficient at redistributing mass from large to small grains, which explains the existence of the grains as well as the enhanced VSG-to-LG mass ratio. These results suggest that dust formation in ejecta knots, followed by grain-grain shattering may be a viable mechanism for explaining how dust survives the destructive processes of a supernova to be injected into the interstellar medium.
- Publication:
-
American Astronomical Society Meeting Abstracts #225
- Pub Date:
- January 2015
- Bibcode:
- 2015AAS...22514021L