NGC 1187, an impressive spiral galaxy in Eridanus

 
NGC 1187, an impressive spiral galaxy in Eridanus

NGC 1187 is an impressive spiral galaxy that looks to be relatively young. It is located about 60 million light-years away in the constellation of Eridanus (The River), and is receding from us at 1393 kilometers per second.

NGC 1187 is seen almost face-on, which gives us a good view of its spiral structure. About half a dozen prominent spiral arms can be seen, each containing large amounts of gas and dust. The bluish features in the spiral arms indicate the presence of young stars born out of clouds of interstellar gas.

Looking towards the central regions, we see the bulge of the galaxy glowing yellow. This part of the galaxy is mostly made up of old stars, gas and dust. Unlike other spiral galaxies, which feature a round bulge, NGC 1187 boasts a subtle central bar structure. The latter is not large enough to classify the galaxy as a barred spiral. Such bar features are thought to act as mechanisms that channel gas from the spiral arms to the centre, enhancing star formation there.

NGC 1187 looks tranquil and unchanging, but it has hosted two supernovae explosions since 1982. In October 1982, the first supernova, SN 1982R, was discovered and in 2007 the other one, called SN 2007Y which astronomers could study in detail. In this annotated image the Type Ib supernova SN 2007Y can be seen, long after the time of maximum brightness, near the bottom of the image.

A supernova is a violent stellar explosion, resulting from the death of either a massive star or a white dwarf in a binary system. Supernovae are amongst the most energetic events in the Universe and are so bright that they often briefly outshine an entire galaxy before fading from view over several weeks or months. During this short period a supernova can radiate as much energy as the Sun is expected to emit over its entire life span.

Type Ib supernovae are categories of stellar explosions that are caused by the core collapse of massive stars. These stars have shed (or been stripped of) their outer envelope of hydrogen. This type is usually referred to as stripped core-collapse supernova.

Most spirals have supernovae in them about every three centuries, so two supernovae within 30 years was a bit unusual. The rate is statistical though, so you might get two close together, or a long stretch without one. The last one in our Milky Way was about 170 years ago, and the last known before that was 400 years ago.

NGC 1187 is a gas-rich galaxy, and is forming lots of stars. That might lead to a higher-than-normal supernova rate, since that means more high-mass stars are being born, only to explode a few million years later. Both of the recent supernovae in NGC 1187 were caused by the core collapse of a high-mass star – so maybe this does play into it.

Around the outside of the galaxy many much fainter and more distant galaxies can also be seen. Some even shine right through the disc of NGC 1187 itself. Their mostly reddish hues contrast with the pale blue star clusters of the much closer galaxy.

This picture was taken with ESO’s Very Large Telescope at the Paranal Observatory in Chile.
Image Credit: ESO

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