Briefs · Frontier Science
A New Map of ‘Empty’ Space Challenges a Tranquil Picture of the Galaxy
Empty space is not empty. It is busy, and lots of textbooks are going to be burned (sorry, trees).
Firstly, the old model. Space between stars was supposed to be tidy: cold gas at 100 kelvins, warm gas at 8,000 kelvins, hot plasma at half a million — nothing in between. Officially, the middle did not exist; unofficially, it was 41% of the neighbourhood.
Secondly, the map. Gaia measured nearly 2 billion stars by parallax, like closing one eye, then the other. That gave astronomers a 3D dust map 4,000 light-years wide. Then an undergraduate (Jonathan Shelest at the Technion) added a map of ultraviolet radiation: dust plus heat equals temperature. Simple, except the answer was not simple.
27% cold. 32% warm. 41% unstable, sitting squarely in the forbidden zone. Shelest thought he was wrong, but he was not wrong, or not wrong enough! The unstable gas wraps the cold clouds like a blanket that refuses to settle.
Why does it matter? Galaxies are terrible at making stars. This churn may be why. Gas is constantly heated, cooled, stirred, and pushed around, so it cannot collapse quietly into stars. The universe is not a set-piece dinner; it is a kitchen in the middle of cooking.
Caveat: the paper is under peer review, and smoothing could inflate the number. The authors tested another map. The figure moved by only 5%.
Conclusion: space is not mostly empty. It is full of stuff and it is moving around, fast and furious.
Read the original at Quanta Magazine
Summary in our own words. The original belongs to its publisher.