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The Infrared Sky (and more) in VR

(Nicer QuickTime version click here.)

[1] 408 MHz Radio Emission	[2] 1.4 GHz = 21 cm H I Line Emission (neutral hydrogen)	[3] 23, 41, 94 GHz Microwave Emission

[4] 115 GHz CO Line Emission (molecular gas)	[5] 100, 60, 12 μm Infrared Emission	[6] 3.5, 2.2, 1.25 μm Infrared Emission

[7] 6563 Å Hα Line Emission (ionized hydrogen)	[9] 0.1-0.4, 0.5-0.9, 0.9-2.0 keV X-Ray Emission	[10] 30-100, 100-1000, 1000-10000 MeV γ-Ray Emission

[2] H I: This VR movie shows emission from cool neutral hydrogen as revealed by 21 cm radio emission measured by the Leiden/Dwingeloo H I Survey. (The lower resolution coverage at southern declinations is provided by data presented by Dickey & Lockman.) The Galaxy is optically thin at these wavelengths, so we see the entire disk of the Galaxy, as we do at the far-IR wavelengths. However, comparison with the far-IR DIRBE data shows that the H I emission is not as strongly peaked as the IR emission at sites of star formation in the Galactic plane. At high latitudes, you can see a very strong correlation between the emission from the neutral hydrogen and the far-infrared emission. Several nearby external galaxies, such as M31 and M33, can also be identified as compact sources of H I emission.

[3] Microwave: The microwave sky seen in this movie was observed by the WMAP (Wilkinson Microwave Anisotropy Probe). In this portion of the spectrum, the relatively faint emission of the Milky Way is generated by synchrotron emission from relativistic electrons (cf. radio emission), free-free emission from ionized gas (cf. Hα emission), and thermal emission from dust (c.f. far-infrared emission). However the truly interesting part of the sky at these wavelengths is the faint background structure that appears all across the sky. Observation of this mottled pattern, which reveals the beginning of the formation of structure (galaxies and clusters of galaxies) in the Universe, was the primary objective of the WMAP mission. To make the cosmic microwave background (CMB) anisotropies visible in this depiction, the mean intensity of the CMB is removed, as well as a large-scale dipole variation that is caused by our local motion with respect to the CMB. WMAP data and additional depictions of the data can be obtained at the LAMBDA website.

[4] CO: This movie of line emission from the CO (carbon monoxide) molecule is a bit different from the others in several respects. CO emission is used a a tracer of molecular gas in the interstellar medium. Molecular hydrogen is far more abundant, but because it is a symmetric molecule, it produces little observable emission in the typical cold conditions that prevail in molecular clouds. The asymmetric CO molecule, on the other hand, is easily observed even at relatively low densities. Molecular gas is only found in the most dense and cold parts of the interstellar medium. Thus molecular clouds are always found close to the Galactic plane. The Survey of CO emission does not actually cover the full sky, simply because there is little or no molecular gas to be seen at high galactic latitudes. (Regions not covered by the survey are entirely black.) So while there is a diffuse Galactic component to the emission at other wavelengths, there is no such background for molecular emission. Molecular gas can also be traced indirectly by the far-infrared emission of cold dust in the gas, and by the absorption of some radiation as it passes through the dense gas (e.g. X-rays).
(This movie and the Hα movie allow you to zoom in until the field of view is only 30 degrees, instead of the 45 degree limit of the other movies.)

[5] Far-Infrared: This VR movie shows a DIRBE view of the sky at far-infrared wavelengths. The brightenesses are scaled logarithmically, with red = 100 micron emission, green = 60 micron emission, and blue = an average of 25 and 12 micron emission. At these wavelengths most of the emission seen is thermal radiation from warm and cold dust. Some stars are visible as "blue" dots at 12 microns, but in these cases you're usually seeing thick shells of warm dust around the stars rather than the stars themselves. The wispy clouds all over the sky are referred to as infrared "cirrus" for the apparent resemblance to the familiar ice clouds in the Earth's atmosphere. The IR cirrus seen here is from cold dust in the interstellar medium, i.e. the gas and dust that is spread out between the stars. In some places the gas and dust become more tightly clumped and stars begin to form. These star-forming regions appear as brighter and slightly warmer spots. Because they're relatively distant compared to the cirrus, the star-forming regions tend to lie along the Galactic plane.

[6] Near-Infrared: This VR movie allows you to view the sky as observed by DIRBE at near-IR wavelengths. The image shows a false-color view of the Milky Way in which red = 3.5 micron emission, green = 2.2 micron emission, and blue = 1.25 micron emission. The images are scaled logarithmically because that allows a wider range of brightness to be shown, and because it's qualitatively how your eyes respond to light. A linear scaling of intensities would emphasize similarities between these DIRBE images and optical images of nearby edge-on galaxies. Even though these wavelengths are too long for the human eye to see, the Milky Way is still dominated by starlight, and looks fairly familiar. However, one significant difference is that light at these wavelengths penetrates the clouds of dust throughout the Galaxy. Therefore at infrared wavelengths we can see clear to the Galactic bulge and get a better idea of the overall shape of the Milky Way.

[7] Hα: This VR movie shows the sky as mapped in the Hα emission line at 6563 Å. This emission comes from hot clouds of gas, where strong ultraviolet light from nearby young stars ionizes the gas. The data are from the recent Wisconsin H-Alpha Mapper (WHAM) survey, and the Southern Hα Sky Survey Atlas (SHASSA), which are supported by the National Science Foundation (details). The WHAM Survey is more sensitive, and includes detailed velocity information, but is at a lower spatial resolution (1 degree). The color in the image only represents the brightness of the emission, though the Hα line does appear in the red part of the visible spectrum. Many bright nearby star forming regions (H II regions) can be identified in this survey, even though the resolution is lower than that of the DIRBE data. At these wavelengths, dust in the Galactic plane causes significant extinction of emission from distant H II regions. Therefore, this image does not reveal emission from the Galactic center or other distant star forming regions that appear as bright sources in the long wavelength DIRBE data.
(This movie and the CO movie allow you to zoom in until the field of view is only 30 degrees, instead of the 45 degree limit of the other movies.)

[8] Optical: I don't have an optical VR movie of the sky here because a beautiful version has been photographed and presented by Axel Mellinger at his Virtual Reality All-Sky Milky Way Panorama page. In his panorama, you will see a stellar component that resembles that near-IR data here, but which is more strongly affected by interstellar extinction. You'll also see many H II or star-forming regions, which correspond to the brighter sources in the WHAM data shown here. Mellinger's optical panorama is at higher resolution than any of the data shown here.

[9] X-ray: This VR movie shows the sky at X-ray wavelengths as seen by ROSAT. The movie was constructed from 12' resolution maps generated by the ROSAT All-Sky Survey. Intensities are scaled logarithmically, with the lowest energies (0.1 - 0.4 keV) shown as red, middle energies (0.5 - 0.9 keV) in green, and the highest energies (0.9 - 2.0 keV) in blue. Some of the strongest X-ray source in the Galaxy are supernova remnants (like the Cygnus Loop), which are much harder to see at other wavelengths. Many point-like X-ray sources are interacting binary star systems. The cold diffuse clouds that produce IR emission absorb X-rays, especially at the lower energies. Some of the densest and nearest clouds are clearly seen in silhouette against more distant X-ray emission from the inner Galaxy.

[10] γ-ray: This VR movie shows the sky at γ-ray wavelengths as seen by the EGRET instrument on the Compton Gamma Ray Observatory. Gamma rays with energies 30 - 100, 100 - 1000, and 1000 - 10000 MeV are color coded as red, green and blue. The diffuse γ-ray emission along the Galactic plane is produced when cosmic rays interact with the interstellar medium. Nearby neutron stars appear as point sources in the Galactic plane. [In this VR movie, three of these pulsars can be heard spinning at rates of 4 to 30 Hz (cycles per second), with γ-ray waveforms taken from Fierro et al. (1998).] Galaxies with active black holes at their cores are visible as high energy γ-ray sources at high Galactic latitudes.

Go Home!

The Shape of the Milky Way

An Astronomical Alphabet

The Multiwavelength Milky Way

The Sounds of Pulsars

Axel Mellinger's Milky Way VR Panorama

Apple's Gallery of other cubic VR movies