Violent Milky Way's Halo HI (image 7)


This is a false-color image showing the structure of the HI (neutral hydrogen) halo of the Milky Way near the Scutum spiral arm approximately 2 kpc above the Galactic disk. Brighter yellow corresponds to more and darker red to less hydrogen density. This region lays about 7 kpc from the Sun and 4 kpc from the Galactic center. Image shows that the halo in this region is abundant with outflows breaking into numerous clouds and filaments of gas. Each of the separate "little" hydrogen clouds has a size of tens of parsecs and a mass of tens to hundreds solar masses. The mass of the whole system of outflows shown is probably little less than a million solar masses. The exact nature and the mechanism of this phenomenon is yet unknown. This picture of "violent" Galactic halo has not been seen before and was discovered only thanks to the unique capabilities of the new NRAO instrument -- the 100 m Green Bank Telescope (GBT).
The resolution of the image is 9 arcmin, corresponding to about 20 pc. Spectra were taken "on-the-fly" with the angular separation of 3 arcmin and exposures ranging from 2 to 7 sec. This image has been produced by integrating over the range of 60 to 160 km/s. The cubic interpolation has been applied. Some of the noise has been clipped out by using larger than zero lower imaging threshold. The values of the pixels has been multiplied by sine of the Galactic latitude to smooth out the steep vertical contrast so the image should be understood as a schematic of the HI distribution rather than the map of actual HI column densities. The distance has been estimated assuming the structure's location near the tangent point.


Legacy Astronomical Images


NRAO/AUI/NSF does not hold full copyright for this image. Contact the archivist for details.


Legacy Astronomical Image

Object Name

MW Neutral Halo-7

Photo Credit

Yurii Pidopryhora, NRAO & Ohio University


Y. Pidopryhora (NRAO & Ohio U), F.J. Lockman (NRAO), J. Shields (Ohio U)


Green Bank Telescope (GBT)

Observation Date


Type of Observation

spectral line

Center of Image

RA 18:21:11.000, Dec: 0:35:43.000 (J2000)

Field of View

20.000000 x 13.000000 degrees


Contact the archivist for a high resolution tif of this image.


Galactic Sources Series


Galactic Halo Unit


Legacy Astronomical Images, “Violent Milky Way's Halo HI (image 7),” NRAO Archives, accessed December 3, 2021,