An international group of astronomers has used two of the world’s largest telescopes to create the most detailed map yet of the distribution of hydrogen in our galaxy.
The project, called HI4PI, required more than 1 million individual observations of the sky and about 10 billion data points. Although hydrogen is the most abundant element in the universe and the main component of stars, it is detectable only via radio waves, where there’s plenty of interference from devices like mobile phones and broadcast stations.
“Besides a careful calibration of the data, we also had to remove man-made noise from the data,” explains Benjamin Winkel of the Max Planck Institute for Radio Astronomy in Germany, and part of the HI4PI project, in a statement. “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. The computational effort for the data processing was huge, adding to the thousands of hours of observations [and] thousands of hours of computing time.”
The map shows the filaments and regions of neutral hydrogen, with the colors reflecting the movement of the gas: that moving towards us is purple/blue, while that moving away from us is orange/green. The brightness traces its amount, and in the lower corner it is possible to see the Large and Small Magellanic Clouds – two of the Milky Way's neighboring galaxies.
The data is going to be publicly available and freely accessible, with their findings to be published in the journal Astronomy & Astrophysics. Among those findings, there’s the discovery of fine structures between the stars of the Milky Way.
“Pilot studies of the HI4PI data show a wealth of filamentary structures never seen before,” said co-author Professor Lister Staveley-Smith, from the International Centre for Radio Astronomy Research, in a separate statement. “Tiny clouds become visible that appear to have fuelled star formation in the Milky Way for billions of years. These objects are too dim and too small to be detected even in the other galaxies closest to us.”
The project will also help with extragalactic observations.
“Like the clouds at the sky, all observations we receive from the distant universe have to pass through hydrogen in our own Milky Way,” said Winkel. “The HI4PI data allows us to correct accurately for all these hydrogen clouds and clean the window we are watching through.”