A close-in view of a spiral galaxy. It is seen face-on, showing its circular shape and tightly winding spiral
arms. The galaxy glows brightly in the centre and dims to cool colours
towards the edge. Dark, faint filaments of dust and brightly glowing,
pink and orange bubbles of star formation mark the face of the galaxy.Credit: ESA/Hubble & NASA, R. Chandar, J. Lee and the PHANGS-HST team
This glittering image shows the spiral galaxy
IC 5332, which lies about 30 million light-years away in the
constellation Sculptor, and has an almost face-on orientation to Earth.
To explain what is meant by ‘face-on’, it is helpful to visualise a
spiral galaxy as an (extremely) large disc. If the galaxy is oriented so
that it appears circular and disc-shaped from our perspective here on
Earth, then we can say that it is ‘face-on’. In contrast, if it is
oriented so that it appears squashed and oval-shaped, then we would say
that it is ‘edge-on’. The key thing is that the same galaxy would look
extremely different from our perspective depending on whether it was
face-on or edge-on as seen from Earth. Check out these previous Hubble Pictures of the Week for examples of another face-on spiral galaxy and an almost edge-on spiral galaxy.
IC 5332 is designated as an SABc-type galaxy in the De Vaucouleurs
system of galaxy classification. The ‘S’ is straightforward, identifying
it as a spiral galaxy, which it clearly is, given the well-defined arms
of bright stars and darker dust that curl outwards from the galaxy’s
dense and bright core. The ‘AB’ is a little more complex. It means that
the galaxy is weakly barred, which refers to the shape of the galaxy’s
centre. The majority of spiral galaxies do not spiral out from a single
point, but rather from an elongated bar-type structure.
SAB galaxies — which are also known as intermediate spiral galaxies —
do not have a clear bar-shape at their core, but also do not spiral out from a single point,
instead falling somewhere in between. The lowercase ‘c’ describes how
tightly wound the spiral arms are: ‘a’ would indicate very tightly
wound, and ‘d’ very loosely wound. Thus, IC 5332 is quite an
intermediate spiral galaxy on many fronts: weakly barred, with quite
loosely wound arms, and almost completely face-on!
Source: ESA/Hubble/potw
