Acknowledgement: D. Calzetti (University of Massachusetts) and the LEGUS Team
This new image from the NASA/ESA Hubble Space Telescope shows NGC
7793, a spiral galaxy in the constellation of Sculptor some 13 million
light-years away from Earth. NGC 7793 is one of the brightest galaxies
in the Sculptor Group, and one of the closest groups of galaxies to the Local Group — the group of galaxies containing our galaxy, the Milky Way and the Magellanic Clouds.
The image shows NGC 7793’s spiral arms and small central bulge.
Unlike some other spirals, NGC 7793 doesn’t have a very pronounced
spiral structure, and its shape is further muddled by the mottled
pattern of dark dust that stretches across the frame. The occasional
burst of bright pink can be seen in the galaxy, highlighting stellar
nurseries containing newly-forming baby stars.
Although it may look serene and beautiful from our perspective, this
galaxy is actually a very dramatic and violent place. Astronomers have
discovered a powerful microquasar within NGC 7793 — a system containing a
black hole actively feeding on material from a companion star. While
many full-sized quasars are known at the cores of other galaxies, it is
unusual to find a quasar in a galaxy’s disc rather than at its centre.
Micro-quasars are almost like scale models — they allow astronomers
to study quasars in detail. As material falls inwards towards this black
hole, it creates a swirling disc around it. Some of the infalling gas
is propelled violently outwards at extremely high speeds, creating jets
streaking out into space in opposite directions. In the case of NGC
7793, these jets are incredibly powerful, and are in the process of
creating an expanding bubble of hot gas some 1000 light-years across.
