Download Messing Up a Galaxy

Astronomy and Space articles
by Martin George of the Launceston Planetarium
12 December 2015
Messing Up a Galaxy
Going out in the evenings to gaze at the stars is a wonderfully peaceful pastime. Of
course, we have different views at different times of the night and of the year, with the
cold winter nights offering a superb panorama of the Milky Way and the summer nights
giving us the best view of the Magellanic Clouds — two of the nearest galaxies to us —
high in our southern sky.
Because of this sort of view, you may be forgiven for thinking that the Universe is a
peaceful place. Far from it, at least in some places! We know that entire galaxies can
collide, and a recent image from the European Southern Observatory (ESA) shows an
interesting result of such an event.
Images of colliding galaxies have revealed to us the amazing way in which they distort
each other's shapes, drawing out long lines of stars and other material and even
triggering star formation. However, in the case of the galaxy NGC 5291, we can see
clumps of debris from a collision that took place 360 million years ago.
NGC 5291 and its surroundings, showing material that has
resulted from a major collision. CREDIT: ESO
The ESO image, made using a special instrument called the Focal Reducer and Low
Dispersion Spectrograph on the observatory's Very Large Telescope, clearly reveals
several bluish-white patches in the vicinity of the galaxy, which is the brightest object in
the picture, just above centre.
Astronomy and Space articles
by Martin George of the Launceston Planetarium
12 December 2015
These patches are star-forming regions and dwarf galaxies that have resulted from the
material ejected by the collision, which first formed a ring around NGC 5291 and then
coalesced into these clumps.
You may have heard of dwarf galaxies. Astronomers think that large galaxies were
formed from collections of these dwarfs coalescing, but this is the opposite situation:
dwarf galaxies being born from the collisions between galaxies.
It's interesting to note how astronomers know the difference — but there is a telltale
observation that they can make. The largest of these clumps of material is the dwarf
galaxy that has been named NGC 5291N. If this were a primitive dwarf galaxy from the
early history of the Universe, it would contain very old stars. However, it doesn't:
measurements have failed to show such ancient objects in NGC 5291N, strongly
supporting the view that it is made up of collision-related material.
It does, however, look like the ancient dwarf galaxies that have survived, and is therefore
an important object for study.
In general, the collision has made somewhat of a mess of NGC 5291. But the galaxy's
troubles are continuing: it is currently interacting with yet another galaxy, called the
Seashell Galaxy, which resembles a comma and is clearly visible in the picture.
A rather fascinating aspect of collisions between galaxies is that collisions between the
stars themselves are very rare indeed. This is because the spaces between the stars in
a galaxy are typically very large compared with the stars' sizes. In our region of space,
the distance from the Sun to its nearest stellar neighbour is about 29 million times the
Sun's diameter!
Our Milky Way Galaxy is also interacting with other, very small galaxies, but the big one
is yet to come: in a few billion years, the Milky Way and the Andromeda Galaxy —
another large spiral system — will collide. However, I'm sure that there will be no
humans around to witness that event!
Article by Martin George, Launceston Planetarium, QVMAG.
Reproduced with permission of the Mercury newspaper.