Nancy A. Levenson
Science Highlights
From standard candles to the serendipitous use of one of the most distant
known supernovae to study the interstellar medium in very distant galaxies,
learn about four of Gemini’s most recent contributions to the understanding of
our universe.
The Best Standard Candle for Cosmology
Exploding stars offer some of the most precise measurements of cosmic distances. Astronomers have long used observations of these supernovae at visible wavelengths for this purpose, and they provide the basis for the 2011 Nobel Prize in Physics. Supernovae do have
some intrinsic differences in visible light, however, so the observations must be corrected;
that is, to standardize the candles (to the same absolute luminosity). Visible light also suffers from the complication of attenuation
by dust anywhere along the line-of-sight,
from the supernova’s host galaxy to our
vantage point in the Milky Way.
In contrast, at near-infrared wavelengths,
Type Ia supernovae serve as the best
“standard candle” for these determinations. As Rob Barone-Nugent (University
of Melbourne, Australia) and colleagues
show in the Monthly Notices of the Royal
Astronomical Society, Type Ia supernovae
are intrinsically more consistent in their
peak luminosity when viewed in the nearinfrared (NIR), so they do not require these corrections. Because of this characteristic, the
team can measure cosmological distances to an accuracy of 5 percent (Barone-Nugent et
al., Monthly Notices of the Royal Astronomical Society, 425: 1007, 2012). Such precise mea-
December2012
GeminiFocus
Figure 1.
The residual Hubble
diagram for supernovae
observed in the H band
(green), compared with
previous NIR samples
(blue). The deviation
of each measurement
from the overall mean is
plotted against redshift,
z, which indicates
distance.
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