John Blakeslee
Science Highlights
This 2018 year-in-review recaps some of the most significant
and innovative science conducted by the Gemini user
community.
JANUARY 2019
Nearby Supernova Illuminates Early Origins of Distant Dust
Interstellar dust constitutes about 1% of the mass of interstellar matter in the Milky Way.
Most of this dust is thought to originate in intermediate-mass evolved stars that ejected
their outer layers as red giants or thermally pulsating asymptotic giant branch stars. Once
the ejecta cool to temperatures lower than about 2,000 K, dust particles inevitably start
to form from carbon and other elements. However, this process cannot explain the large
amounts of dust observed in some galaxies in the early Universe, since such stars would
not have had time to evolve to the dust-producing stage. The only viable explanation for
the dust observed in such galaxies is production in the ejecta of core-collapse supernovae
(ccSNe), and this can be tested through careful observations of ccSNe in the local Universe.
Until now, detailed evolution of dust production in such supernovae, which can take place
over several years, has only been followed in one object, SN 1987A in the Large Magellanic
Cloud.
However, the recent explosion of SN 2017eaw in the nearby galaxy NGC 6946 has provided
another excellent opportunity to follow that evolution in detail over an extended period.
NGC 6946 is only about 7 megaparsecs away and is popularly known as the Fireworks Gal-
axy because it is a prodigious producer of supernovae, all of the core-collapse variety. SN
2017eaw was discovered in May 2017, just as its host galaxy became observable in the east-
ern sky before dawn. This fortuitous circumstance provided an opportunity to follow SN
2017eaw continuously from May until December, before it became too low in the western
sky to observe from Maunakea.
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GeminiFocus
January 2019 / 2018 Year in Review