A massive balloon, designed to measure the background radiation left over from the 'Big Bang' and help scientists better understand the infancy and evolution of our Universe, has just moved to the next stage of development
Thirty years after the Cosmic Microwave Background (CMB) spectrum was first precisely characterised by NASA's Cosmic Background Explorer (COBE) mission, a new experiment - known as BISOU (for Balloon Interferometer for Spectral Observations of the Universe) - is expected to significantly advance these measurements, gaining a factor of ~25 in sensitivity.
If successful, the results could provide unprecedented insights into the Universe's thermal history, validate predictions of the standard Big Bang Theory and potentially reveal new physics beyond our current understanding, marking a transformational step towards an ambitious future space-based CMB spectrometer to form part of the European Space Agency's Voyage 2050 programme.
The CMB is leftover radiation from the time when the Universe began. Although the CMB is everywhere in the Universe, humans can't see it with the naked eye. But, using specialist equipment, it can be made visible even through the atmosphere's curtain, offering novel insights into the Universe's earliest moments.
While the CMB's near-perfect blackbody spectrum was first accurately measured three decades ago, and space missions such as WMAP and Planck have since revolutionised our understanding of the Universe by mapping the spatial variations in CMB temperature and linear polarisation across the sky, tiny deviations in the CMB known as spectral distortions remain largely unexplored. These distortions, predicted by theory, carry vital information about various cosmic processes in regimes that have not previously been explored.
With BISOU, scientists are intensively working on a new balloon-borne differential spectrometer to measure the distortions. The Phase 0 study, which concluded earlier this year, has already demonstrated the feasibility. Now, moving into Phase A, over the next two years, the consortium of researchers from France, Italy, Ireland, Spain, the UK, the USA and Japan, will finalise the detailed concept of the BISOU stratospheric balloon project before hopefully taking it to the skies in 2028/29.
The specialist equipment - a so-called Fourier Transform Spectrometer - builds on the long heritage of the COBE/FIRAS instrument and leverages insights from earlier studies like NASA's PIXIE and the European Space Agency's FOSSIL mission proposals.
The project is coordinated by Professor Bruno Maffei and the Institute of Space Astrophysics (IAS - Institut d'Astrophysique Spatiale) Cosmology team and is funded by the French National Centre for Space Studies (CNES), which recently announced the transition of BISOU to Phase A.
