Credit: ESO
This beautiful image portrays the galaxies NGC 799 (below) and NGC
800 (above) located in the constellation of Cetus (The Whale). This
pair of galaxies was first observed by the American astronomer Lewis
Swift back in 1885.
Located at a distance of about 300 million light-years, our face-on
view allows us to clearly appreciate their shapes. Like the Milky Way —
our galaxy — these objects are both spiral galaxies, with
characteristic long arms winding towards a bright bulge at the centre.
In the prominent spiral arms, a large number of hot, young, blue stars
are forming in clusters (tiny blue dots seen in the image) whereas in
the central bulge a large group of cooler, redder, old stars are packed
into a compact, almost spherical region.
At first glance, these galaxies look rather similar, but the devil
is in the detail. Apart from the obvious difference in size, only NGC
799 has a bar structure, extending from its central bulge, and the
spiral arms wind out from the ends of the bar. Galactic bars are
thought to act as a mechanism that channels gas from the spiral arms to
the centre, intensifying star formation. A supernova was also observed
in NGC 799 in 2004, and was given the name SN2004dt.
Another interesting differentiating feature is the number of spiral
arms. The small NGC 800 has three bright, knotty spiral arms, whilst
NGC 799 only has two relatively dim, but broad spiral arms. These start
at the end of the bar and wrap nearly completely around the galaxy
forming a structure that looks almost like a ring.
While it might seem that this image depicts two impressive close
spiral galaxies coexisting in an everlasting peace, nothing can be
further than the truth. We could be just witnessing the calm before the
storm. We don’t know exactly what the future will bring, but
typically, when two galaxies are close enough, they interact over
hundreds of millions of years by means of gravitational disturbances.
In some cases, only minor interactions occur, causing shape
distortions, but sometimes galaxies collide, merging to form a single,
new and larger galaxy.
The image was obtained using the FORS1 instrument on the 8.2-metre
ESO Very Large Telescope (VLT) atop Cerro Paranal, Chile. It combines
exposures taken through three filters (B, V, R).
Five asteroids can also be seen — can you find them all? The
asteroids moved between the different exposures leaving colourful
streaks in the image.
Source: ESO
