Information about the Universe’s beginning is hard to glean. But researchers have gained some details of this period by monitoring the redshift of hydrogen’s “21-cm line.” This spectral line is created by a change in the relative spin orientations of the protons and electrons in neutral hydrogen atoms, which became abundant around 370,000 years after the Big Bang. Observing the early Universe via the 21-cm line is tricky, however, as its faint signal is masked by more intense radiation from younger astronomical objects and more recent events. Now Patrick Breysse of New York University, Simon Foreman of the Perimeter Institute, Canada, and colleagues have explored the possibility of using one of the emission lines of hydrogen deuteride to improve these observations . The team says that monitoring two emission lines in different parts of the electromagnetic spectrum could make it easier to remove foregrounds that currently mask early-Universe signals.
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