Galaxies – PostcardsFrom…

Every star in the sky could show us the location of another solar system just like ours. Nearly all the stars you can see at night – if you just use your eyes, not a telescope – are in the Milky Way galaxy.

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Image credit: NASA/Two Micron All-Sky Survey (2MASS)
Image credit: ESO/B. Tafreshi

A galaxy is a collection of hundreds of billions of stars, held near to each other by gravity. Actually, they’re a really long way apart, but the Universe is so big that the distances between stars inside one galaxy could be called ‘near’. The nearest star outside our solar system is 41 000 000 000 000 kilometres away!

The galaxy captured in this image, called UGC 12158, certainly isn’t camera-shy: this spiral stunner is posing face-on to the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys, revealing its structure in fine detail. UGC 12158 is an excellent example of a barred spiral galaxy in the Hubble sequence — a scheme used to categorise galaxies based on their shapes. Barred spirals, as the name suggest, feature spectacular swirling arms of stars that emanate from a bar-shaped centre. Such bar structures are common, being found in about two thirds of spiral galaxies, and are thought to act as funnels, guiding gas to their galactic centres where it accumulates to form newborn stars. These aren’t permanent structures: astronomers think that they slowly disperse over time, so that the galaxies eventually evolve into regular spirals. The appearance of a galaxy changes little over millions of years, but this image also contains a short-lived and brilliant interloper — the bright blue star just to the lower left of the centre of the galaxy is very different from the several foreground stars seen in the image. It is in fact a supernova inside UGC 12158 and much further away than the Milky Way stars in the field — at a distance of about 400 million light-years! This stellar explosion, called SN 2004ef, was first spotted by two British amateur astronomers in September 2004 and the Hubble data shown here form part of the follow-up observations. This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through blue (F475W, coloured blue), yellow (F606W, coloured green) and red (F814W, coloured red) as well as a filter that isolates the light from glowing hydrogen (F658W, also coloured red) have been included. The exposure times were 1160 s, 700 s, 700 s and 1200 s respectively. The field of view is about 2.3 arcminutes across.

Some galaxies have the classic spiral shape.

This one includes a bar of stars across the centre. This is called a ‘Barred Spiral’ galaxy.

Image credit: NASA/JPL-Caltech image of galaxy UGC 12158

Not all galaxies are neatly shaped, as this new NASA/ESA Hubble Space Telescope image of NGC 6240 clearly demonstrates. Hubble previously released an image of this galaxy back in 2008, but the knotted region, shown here in a pinky-red hue at the centre of the galaxies, was only revealed in these observations from Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys. NGC 6240 lies 400 million light-years away in the constellation of Ophiuchus (The Serpent Holder). This galaxy has an elongated shape with branching wisps, loops and tails. This mess of gas, dust and stars bears more than a passing resemblance to a butterfly and, though perhaps less conventionally beautiful, a lobster. This bizarrely-shaped galaxy did not begin its life looking like this; its distorted appearance is a result of a galactic merger that occurred when two galaxies drifted too close to one another. This merger sparked bursts of new star formation and triggered many hot young stars to explode as supernovae. A new supernova was discovered in this galaxy in 2013, named SN 2013dc. It is not visible in this image, but its location is indicated here. At the centre of NGC 6240 an even more interesting phenomenon is taking place. When the two galaxies came together, their central black holes did so too. There are two supermassive black holes within this jumble, spiralling closer and closer to one another. They are currently only some 3000 light-years apart, incredibly close given that the galaxy itself spans 300 000 light-years. This proximity secures their fate as they are now too close to escape each other and will soon form a single immense black hole. Links Images of Hubble

But any collection of many stars together is a galaxy.

This one though is just a mess of dust, gas, and stars in weird arms and curls. It looks a bit like a butterfly, or maybe a lobster. What do you think it looks like?

Image credit: NASA/ESA Hubble Space Telescope image of galaxy NGC 6240

Activity

Name that galaxy! Another name for the Whirlpool Galaxy is NGC5194. There are so many galaxies (and stars) that in most cases scientists just give them numbers instead of names. You can see this with the examples above: NGC6240 and UGC12158. The black hole that Tanno and Iguda visited is in galaxy M87.

Do some research to find out how the galaxies get their names – what do the initials NGC, UGC, M, ESO, mean?

For each letter code, choose an example galaxy and find a picture of it online. Then write an explanation of which of these types of galaxy you think it might be:

Spiral – galaxy with tightly wound spiral arms
Elliptical – slightly elliptical to nearly circular
Barred Spiral – spiral with a bright bar of gas through the center
Peculiar – fits none of the descriptions
Irregular – small, patchy, irregularly shaped galaxy

Extra fun? Check out this activity from NASA!

You can go to the previous DeepSpace secret pages by clicking the places below.