Lost In The Galactic Core? There's a Map For That: Big Pic

Aug. 15, 2011 -- If you were aboard a starship capable of traveling deep into the galactic core, some 27,000 light-years from Earth, you'd be looking into a very alien volume of the Milky Way.

Dense with stars, your sky would be a veritable feast of bright star clusters and thick clouds of gas. You'd better hope your vehicle's shielding is up to the task; the central region of our galaxy will be humming with radiation in the form of ionizing cosmic rays and powerful X-rays from clutches of baby stars bursting to life. Oh, and be careful not to fall into that supermassive black hole.

Welcome to the Galactic Core. Try not to get lost.

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With the help of astronomers from the Harvard-Smithsonian Center for Astrophysics (CfA), your journey just got easier. For the first time, the galactic core has been completely mapped using far-infrared data from the European Hershel Space Telescope. The image shows the location Sagittarius A* (Sgr A*), the intense radio wave emission source known to be the location of the Milky Way's supermassive black hole with a gargantuan mass of 4 million suns.

Around Sgr A* is a donut-shaped structure ("CND") approximately eight light-years across surrounding the inner volume of neutral gas and thousands of stars, all orbiting the black hole like bees around a hive. Extending 700 light-years around that are massive star-forming regions sparkling with luminous stars, giant molecular clouds and regions we don't fully understand.

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So why map this exciting region of the Milky Way in near-infrared light? As the galactic core is choked with gas and dust, most wavelengths of electromagnetic radiation (including visible light) are blocked. However, infrared, radio and X-ray wavelengths can penetrate the murk.

That's not all. From the CfA press release:

"One span of the spectrum of particular interest to astronomers is the four octaves of infrared light from the short infrared band (just adjacent to the visible) to the submillimeter. It is precisely in this span that a large fraction of the universe emits most of its radiation -- the reason being that ubiquitous, cool dust absorbs starlight (and many other kinds of radiation) from sources and re-radiates it here, in this far-infrared band. The Herschel Space Telescope, launched last year, is a facility able to detect this light."

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Therefore, Herschel data shows us structures in the center of the Milky Way that we've never seen before; the emissions from the cool dust can now be mapped. And by "cool," we mean very cool. The vast majority of the dust residing in this region has a temperature of 23 degrees Kelvin -- that's only 23 degrees above absolute zero. The near-infrared radiation generated by this dust has now been mapped, literally shining new light on this mysterious volume of our galaxy.

-- by Ian O'Neill

Image: A false-color composite image of the central 50 light-years of the Milky Way as seen for the first time in the entirely of the far infrared. Many of the previously-known structures in the region are labeled; the location of the black hole is labeled "Sgr A*," and the inner donut as "CND." Colder material is shown in red; warmer (but still relatively cold) in blue. Credit: NASA; ESA and M. Etxaluze.