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The Milky Way's
not-so-distant cousin

DR EMILY BALDWIN
ASTRONOMY NOW

Posted: September 3, 2009


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A new image from the European Southern Observatory (ESO) reveals an edge-on galaxy much like our own Milky Way.

Seen edge-on, NGC 4945 appears much like our own Milky Way Galaxy. Sites of active star formation – HII regions – appear pink in this image. The field of view is 30 x 30 arcminutes; north is up and east is left. Image: ESO.

Taken with the Wide Field Imager (WFI) instrument on the 2.2 metre MPG/ESO telescope at the La Silla Observatory in Chile, the image of NGC 4945 reveals a spiral galaxy with swirling arms and a bar shaped central region resembling our home galaxy the Milky Way. But NGC 4945 has a brighter centre that likely hosts a supermassive black hole which is gorging on stellar matter and burping energy out into space.

Astronomers classify NGC 4945 as a Seyfert galaxy, after Ameriacn astronomer Carl Seyfert, who first identified this family of galaxies – a subclass of active galactic nuclei – to have curious light signatures emanating from their central engines. These emissions come from gas and dust falling into a disc around the black hole, which accelerates and heats it up until it emits high energy radiation such as X-rays and ultraviolet light. Most large spiral galaxies, including the Milky Way, host a black hole in their cores, though many of these monsters are at a stage of their lives where they no longer actively feed.

NGC 4945 resides 13 million light years from Earth in the constellation of Centaurus, and can be seen in modest amateur telescopes. It appears cigar-shaped from our perspective but it is actually many times wider than it is thick, with bands of stars and glowing gas marching around its centre. With the use of special optical filters to isolate the colour of light emitted by heated gases such as hydrogen, the new image from ESO displays sharp contrasts in NGC 4945 that indicate active areas of star formation.

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