This image shows a densely packed field of stars,
laid on top of a background of dust, gas, and light from more distant
celestial objects. The stars take up so much of the field of view in
this image that it is a little tricky to discern that you are in fact
looking at most of a galaxy,
known as ESO 245-5. This galaxy is a relatively close neighbour of the
Milky Way, lying at the fairly modest distance of 15 million light-years
from Earth in the constellation Phoenix.
Another reason that it is perhaps a little tricky to spot that ESO
245-5 is a galaxy is its apparent lack of structure. We frequently enjoy
Hubble’s spectacular images of spiral galaxies,
which are so interesting to look at in part because of their seemingly
extraordinarily ordered arms of stars, gas and dust. ESO 245-5, in
contrast, is classified as an IB(s)m type galaxy under the system of
galaxy classification known as the De Vaucouleurs system. The IB(s)m
designation specifically means that the galaxy is irregular (I), barred
(B), has a slight spiral structure ((s)), and is of the Magellanic type
(m).
Irregular in this context is quite intuitive: the galaxy does not
appear to have a regular, ordered structure. In fact, essentially the
entire view here is covered by the stars of this galaxy. The second term
means that the galaxy has a barred shape at its centre: this is the
dense stretch of stars that crosses through the centre of this image.
The third term says that there are hints of a spiral structure, but
nothing clear or definitive (hence the ‘s’ is bracketed). Finally, the
last term indicates ESO 245-5’s similarity to the Magellanic clouds, the
two dwarf galaxies that are close neighbours of the Milky Way.
