Tech by VICE

Behold, the Most Detailed Map of Neutral Hydrogen in the Milky Way

Southern and Northern hemispheres come together for gaseous gala.

by Ben Sullivan
Oct 20 2016, 1:30pm

Image: Luis Calçada

Sometimes you just need to forget about all the small things and focus on the big picture, just like our fatty bear brother Otis. He knows what's up. So, if life's got you down today, Motherboard has the antidote: the most detailed map of the Milky Way galaxy, ever.

The image, which is technically a map of the detailed structure of neutral hydrogen visible in the night sky, has been stitched together by a tag-team of German and Australian scientists. The map is the culmination of a decade-long project called HI4PI, which used two of the world's largest fully steerable radio telescopes—the 100m dish at Effelsberg in Germany and the 64m Parkes/Australia telescope—to assemble a picture space's most abundant element from both hemispheres.

"The entire sky in the light of neutral atomic hydrogen (HI) as seen by the Parkes and Effelsberg radio telescope. Our host galaxy, the Milky Way, appears as a luminous band across the sky with the Galactic Center in the middle." Image: HI4PI Collaboration

Atomic hydrogen is the prime constituent in almost all astronomical entities such as stars and galaxies. Consisting of a single proton, when combined with an electron, it becomes neutral atomic hydrogen, abbreviated as HI.

While detecting HI with modern radio telescopes is pretty straightforward, say the scientists, mapping the entirety of the sky is time consuming and costly. The HI4PI map needed more than a million individual observations using the two telescopes, and in total, dozens of terabytes of raw data have been recorded since the start of 2005. Astronomers in Bonn processed these raw data sets.

Jürgen Kerp from Bonn University, the project coordinator and principal investigator of the Effelsberg survey, tells Motherboard that HI4PI is the most comprehensive map of the Milky Way's hydrogen gas possible to be made from Earth.

"Essentially, hydrogen is the element of the Universe," he says. "Formed within the first three minutes after the Big Bang [it's] the material that eventually forms stars. Thus, HI4PI allows us to study the evolution of the Milky Way galaxy from pure hydrogen gas to stars. The basic evolutionary steps of the star formation are well established today, but the links between them we just start to explore [sic]."

Germany's Effelsberg radio telescope on the left, and the Parkes radio telescope in Australia on the right. Image: Norbert Junkes (left image), Shaun Amy (right image)

The scientists also faced challenges eradicating human noise from the findings. "Besides a careful calibration of the data, we also had to remove man-made noise from the data. This so-called radio frequency interference (RFI) is, for example, produced by telecommunication and broadcast stations, or military RADAR and pollutes the faint emission of the astronomical sources", says Benjamin Winkel from MPIfR, responsible for the data acquisition and processing in the HI4PI collaboration. "The computational effort for the data processing was huge, adding to the thousands of hours of observations thousands of hours of computing time."

The HI4PI collaboration, led by a German team from Bonn University and Max Planck Institute for Radio Astronomy (MPIfR), has published the results in the current issue of Astronomy & Astrophysics.

Read more: Europe Has Added 1.1 Billion Stars to Its Milky Way Map

The teams say the new observations were only possible because radio telescope equipment has improved vastly over the last decade, when capable spectrometers based on state-of-the-art digital processors became available.

The scientists say that the HI4PI map will be a "valuable new resource" for astrophysicists studying Milky Way gas distribution, thanks to the increased sensitivity and better resolution. "Many studies that use pre-release data of the HI4PI survey have already been published in the last years, providing a wealth of new insights and amazing scientific results", says Peter Kalberla from Bonn University, the leading senior scientist in the project. The HI4PI data is freely accessible on request from MPIfR to anyone who wants it.

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