This bright spiral galaxy is known as NGC 2441, located in the
northern constellation of Camelopardalis (The Giraffe). However, NGC
2441 is not the only subject of this new Hubble image; the galaxy
contains an intriguing supernova named SN1995E, visible as a small dot
at the approximate centre of this image. For a labelled view, see potw1425b.
Supernova SN1995E, discovered in 1995 as its name suggests is a type
Ia supernova. This kind of supernova is found in binary systems, where
one star — a white dwarf — drags matter from its orbiting companion
until it becomes unstable and explodes violently. White dwarf stars all
become unbalanced once they reach the same mass, meaning that they all
form supernovae with the same intrinsic brightness. Because of this,
they are used as standard candles to measure distances in the Universe.
But SN1995E may be useful in another way. More recent observations of
this supernova have suggested that it may display a phenomenon known as
a light echo, where light is scattered and deflected by dust along our
line of sight, making it appear to “echo” outwards from the source. In
2006, Hubble observed SN1995E to be fading in a way that suggested its
light was being scattered by a surrounding spherical shell of dust.
These echoes can be used to probe both the environments around cosmic
objects like supernovae, and the characteristics of their progenitor
stars. If SN1995E does indeed have a light echo, it would belong to a
very elite club; only two other type Ia supernovae have been found to
display light echoes (SN1991T and SN1998bu).
NGC 2441 was first seen by Wilhelm Tempel in 1882, a German
astronomer with a keen eye for comets. In total, Tempel observed and
documented some 21 comets, several of which were named after him.
A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Nick Rose.
