The center of the galaxy is mostly obscure in visible light. But thanks to the world’s most powerful infrared telescope, we can see inside.
Throughout history, the sight of the Milky Way has fascinated and mystified skywatchers worldwide.
This image is a single projection of Gaia’s all-sky view of our Milky Way Galaxy and neighboring galaxies, based on measurements of nearly 1.7 billion stars. The map shows the total brightness and color of stars observed by the ESA satellite in each portion of the sky between July 2014 and May 2016. However, even with Gaia, the galactic center remains largely obscured, as it cannot penetrate the dust lanes of our galaxy in optical wavelengths. (ESA/GAIA/DPAC)
In visible light, the dark dust lanes
redden and obscure billions of stars lurking behind them. The all-sky infrared map of the sky from NASA’s WISE spacecraft. As spectacular as this image is, it cannot achieve the resolutions or exposure times or cover as many independent wavelengths as the ground-based VISTA observatory can. (NASA / JPL-CALTECH / UCLA, FOR THE WISE COLLABORATION)
Space-based observatories, like NASA’s Wise and Spitzer, have seen through the dust, revealing hidden stars and gas.
This infrared view of the plane of the Milky Way, taken from space by NASA’s Spitzer as part of the GLIMPSE galactic survey, is one of the most ambitious observing projects ever undertaken, taking a decade to complete. At longer wavelengths than are visible from the ground, the gas of different temperatures from our galaxy is highlighted as never before. (NASA/JPL-CALTECH/UNIVERSITY OF WISCONSIN)
NASA’s Spitzer, in particular,
constructed the most comprehensive map of the galactic plane ever seen. This four-panel view shows the Milky Way’s central region in four different wavelengths of light, with the longer (submillimeter) wavelengths at top, going through the far-and-near infrared (2nd and 3rd) and ending in a visible-light view of the Milky Way. Note that the dust lanes and foreground stars obscure the center in visible light, but not so much in the infrared. (ESO/ATLASGAL CONSORTIUM/NASA/GLIMPSE CONSORTIUM/VVV SURVEY/ESA/PLANCK/D. MINNITI/S. GUISARD ACKNOWLEDGEMENT: IGNACIO TOLEDO, MARTIN KORNMESSER)
the most spectacular mosaic of the galactic center itself comes courtesy of the ground-based VISTA telescope. This wide-field image of the VISTA telescope, just one year prior to its ‘first light’ on the night sky, shows the infrared camera equipped and ready for action. The VISTA telescope, the most powerful infrared telescope in history, was built entirely by a variety of UK entities as part of the ESO, which has assured the world that the UK’s membership will not be affected by Brexit. (ESO)
the ESO’s Visible and Infrared Survey Telescope for Astronomy, assembled a whopping 9-gigapixel image of our galaxy’s innermost few degrees. This infrared view of the central part of the Milky Way from the VVV VISTA survey has been labelled to show a selection of the many nebulae and clusters in this part of the sky. Messier 8 (the Lagoon Nebula), Messier 20 (the Trifid Nebula), NGC 6357 (the War and Peace Nebula) and NGC 6334 (the Cat’s Paw Nebula) are all easily seen at low-resolution, while the others can be found by zooming in to the full 9-gigapixel mosaic. (ESO/VVV SURVEY/D. MINNITI; ACKNOWLEDGEMENT: IGNACIO TOLEDO, MARTIN KORNMESSER)
Dusty star-forming regions, like the
Lagoon Nebula, are only faintly identifiable in the infrared. The Lagoon Nebula, part of a larger molecular cloud complex that extends across the frame of the image (but is concentrated in the upper-right), is a large star-forming region in the galactic plane of the Milky Way. In the infrared, it looks enormously different from its bright red visible light appearance. (ESO/VVV SURVEY/D. MINNITI; ACKNOWLEDGEMENT: IGNACIO TOLEDO, MARTIN KORNMESSER)
The great dark cloud known as
Barnard 78 appears as barely a wisp. Sometimes known as the ‘Bowl of the Pipe’ portion of an even larger structure known as the Pipe Nebula, the dark nebula Barnard 78 is a molecular cloud that reduces the brightness of stars behind it by approximately 5 astronomical magnitudes. In the infrared, however, it barely appears as a series of wisps. (ESO/VVV SURVEY/D. MINNITI; ACKNOWLEDGEMENT: IGNACIO TOLEDO, MARTIN KORNMESSER)
Trifid Nebula, famously two-toned in visible light, shows a dusty, blue tinge on the actively star-forming side only. The Trifid Nebula, which normally appears with a blue tone on the left (a reflection nebula) and a red tone on the right (an emission nebula), shows only bright stars on the left side (typically due to red giants or supergiants in the infrared) and a bluish tone on the right, perhaps indicative of either younger stars or large amounts of infrared (heat) radiation coming from the gas in that region. (ESO/VVV SURVEY/D. MINNITI; ACKNOWLEDGEMENT: IGNACIO TOLEDO, MARTIN KORNMESSER)
Molecular clouds and ionized, shocked regions look wildly unfamiliar in the infrared.
Shown here, the ‘War and Peace’ Nebula (left, NGC 6357) and the ‘Heart and Soul’ Nebula (right, NGC 6334), two regions of active star formation near the galactic center, take on wildly different appearances from how they look in the optical. (ESO/VVV SURVEY/D. MINNITI; ACKNOWLEDGEMENT: IGNACIO TOLEDO, MARTIN KORNMESSER)
The exact center itself, meanwhile, reveals millions of stars that are completely invisible in the optical.
The inner galactic center, as viewed in infrared light, shows what appears to be an interwoven web of dust surrounding a yellowish core. In the galactic center, the stars are not necessarily intrinsically yellow, but rather are reddened preferentially by the foreground matter that scatters away the bluer light, similar to how sunsets appear red as our atmosphere scatters the blue light away. (ESO/VVV SURVEY/D. MINNITI; ACKNOWLEDGEMENT: IGNACIO TOLEDO, MARTIN KORNMESSER)
Where the dust is thickest and densest, even infrared light cannot penetrate.
A zoom into the innermost region of the galactic center reveals an enormously dense plethora of stars, just a few of the nearly 100 million contained in the entire mosaic, but also rich lanes of dust that even the long-wavelength infrared light cannot fully penetrate. (ESO/VVV SURVEY/D. MINNITI; ACKNOWLEDGEMENT: IGNACIO TOLEDO, MARTIN KORNMESSER)
full-resolution, zoomable mosaic is available here. VIDEO Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more. Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.