IUB researcher joins study that sharpens hubble tension debate

An international consortium of astronomers has achieved the most precise direct measurement yet of the universe's current expansion rate, providing new data that fuels one of modern cosmology's most persistent unresolved questions.

The H0 Distance Network (H0DN) Collaboration, leading the international study, directly measured the universe's current expansion rate at 73.50 kilometres per second per megaparsec, with a margin of error of ±0.81.

Dr Syed Ashraf Uddin, Associate Professor of Physical Sciences and core group member of the Centre for Astronomy, Space Science and Astrophysics (CASSA) at Independent University, Bangladesh (IUB), contributed as part of the global H0DN collaboration.

The study, titled 'The Local Distance Network: A community consensus report on the measurement of the Hubble constant at ∼1% precision', appears in Astronomy & Astrophysics.

This finding is significant amid the enduring 'Hubble tension'—the mismatch between measurements of the universe's current expansion rate and estimates derived from early-universe observations, particularly the cosmic microwave background.

Dr Uddin said the new research strengthens the case that the discrepancy is unlikely to be the result of errors in any single measurement method.

For years, scientists have debated whether the gap stems from hidden errors in techniques or deficiencies in existing theories. The new study demonstrates that multiple independent methods converge on the same higher value. This makes it difficult to blame the discrepancy on one flawed approach and suggests the tension may reflect deeper, unresolved physics, he said.

Rather than relying on a single cosmic distance ladder, the team used a broader 'distance network' approach. This method combines various techniques for measuring cosmic distances—including variable stars, supernovae, and galaxy properties—within one unified framework.

The researchers accounted for overlaps and shared uncertainties across these methods. This allowed them to cross-validate results and generate a more robust estimate.

The collaboration brought together nearly 40 researchers from diverse backgrounds. It included scientists who had previously worked in different teams, each employing their own techniques to measure the universe's expansion rate.

Dr Uddin noted that past differences in calibration, data quality, and underlying assumptions had led to slightly different outcomes.

The new study addresses these variations by integrating all major methods within a consistent framework. It shows that, when considered together, the methods yield a stable and mutually consistent result, he said.

He added that the work would provide a stronger foundation for future inquiries into whether new physics may be required to resolve the discrepancy.

Dr Khan Muhammad Bin Asad, Assistant Professor of Physical Sciences and Director of CASSA at IUB, said the university's involvement reflected its expanding engagement with global scientific research.

Through CASSA, we have worked for several years to connect researchers in Bangladesh with the international astronomy and astrophysics community. We also create opportunities for students and young researchers to join cutting-edge research, he said.