Thursday, August 2, 2012

Swirling Along With NGC 1187

Discovered by Sir William Herschel in 1784, galaxy NGC 1187 floats along 60 million light-years away in the river Eridanus. It looks as peaceful as a cool, blue whirlpool... but, is all really quiet? Not hardly. This nearly face-on spiral galaxy is home to some very violent action - like two major supernova events in the last thirty years. Now, thanks to ESO’s Very Large Telescope, we're able to examine all of its facets in one of the most detailed photographs ever taken.

At its heart beats a bulging yellow glow. Here is the home of ancient stars, caught in cobwebs of old gas and dust. Look closely, the nucleus is round, but slightly elongated - the tell-tale sign of a central bar structure. This formation is considered to be a sort of funnel that pushes gas from the spiral arms towards the core and enriches star formation. The arms themselves have blue and pink inclusions - areas rich in star clusters counterpointed by regions forming new stars. However, sometimes stars die, don't they? Yes, they do.

And they don't die quietly.

Since 1982, this calm little galaxy has experienced two supernova events - a violent explosion of either a massive star or a white dwarf in a binary system. During this time they can briefly outshine their host galaxy and linger on for months before fading away. Going down in a blaze of glory? You betcha'. A supernova event is so powerful that the energy expended in that brief moment equals the amount of energy expended by most stars during their entire lifetime!

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In October 1982, the first supernova seen in NGC 1187 - SN 1982R - was discovered at La Silla Observatory. It wasn't just an ordinary supernova - it was surmised to be a core collapse in a disturbed galaxy. "When the galaxies are split into `disturbed' and `undisturbed' categories, a striking difference emerges. The disturbed galaxies have a central excess of core-collapse supernovae, and this excess is almost completely dominated by supernovae of types Ib, Ic and Ib/c, whereas type II supernovae dominate in all other environments." says S.M. Habergham (et al). "The difference cannot easily be explained by metallicity or extinction effects, and thus we propose that this is direct evidence for a stellar initial mass function that is strongly weighted towards high mass stars, specifically in the central regions of disturbed galaxies."

Are their findings correct? Quite possibly. In 2007, the amateur astronomer Berto Monard in South Africa spotted another supernova in this galaxy - SN 2007Y - and it wasn't ordinary either. It was thought to be a core collapse of a helium-rich star. "The oxygen abundance suggests that the progenitor was most likely a ≈3.3 M sun He core star that evolved from a zero-age-main-sequence mass of 10-13 M sun." says M. Stritzinger (et al). "SN 2007Y is among the least energetic normal Type Ib SNe ever studied."

Better to burn out than to fade away? Look again, because there's more to the picture than meets the eye. SN 2007Y may have been the least energetic ever studied, but it ain't gone yet. The supernova can still be seen - long after the time of maximum brightness - near the bottom of the image.

Hey, hey... my, my. Rock and roll will never die.

Written by Tammy Plotner. Original Story Source: ESO News Release. Image Credit: ESO’s Very Large Telescope at the Paranal Observatory in Chile. Video Credit: ESO/A. Fujii/Digitized Sky Survey 2. Acknowledgment: Davide De Martin. Music: Disasterpeace

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