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The Edge of Space

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A Blue Whirlpool in The River

August 8th 2012

NGC 1187 in Eridanus via VLT
Spiral galaxy NCG 1187 in Eridanus (credit: ESO)

The galaxy NGC 1187, discovered 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. In the case of NGC 1187, rather than a round bulge, there is a subtle central bar structure. Such bar features are thought to act as mechanisms that channel gas from the spiral arms to the centre, enhancing star formation there.

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 object.

NGC 1187 may look tranquil and unchanging, but it has hosted two supernova explosions since 1982. 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. One class of supernova explosions occur at the end of a massive—more than eight times the mass of our Sun—star’s lietime, when its nuclear fuel is exhausted and the star is no longer able to counteract gravitational collapse, producing a violent explosion. Alternatively, a supernova explosion can occur in a binary star system, in which a carbon-oxygen white dwarf is pulling matter from a higher-mass companion star. If enough matter is transferred, the star will begin to collapse, producing the supernova.

In October 1982, the first supernova seen in NGC 1187—SN 1982R was discovered at ESO’s La Silla Observatory and more recently, in 2007, the amateur astronomer Berto Monard in South Africa spotted another supernova in this galaxy—SN 2007Y. A team of astronomers subsequently performed a detailed study and monitored SN 2007Y for about a year using many different telescopes. This new image of NGC 1187 was created from observations taken as part of this study and the supernova can be seen, long after the time of maximum brightness, near the bottom of the image.

This article is adapted from EurekAlert.


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