S8 tension.

Why in News ?  The Cosmologists has recently  studied how matter clumps together in the universe post-Big Bang, forming galaxies, clusters, and cosmic structures.

The concept of “clumpiness” is quantified using a parameter called Sigma 8 (S8), which measures the amplitude of matter fluctuations on scales of 26 million light-years.

Relevance :

Prelims : Sigma 8 (S8)/ S8 tension/ /Lambda Cold Dark Matter (CDM

Key points of news:

Cosmic Microwave Background (CMB) Insights:

• The CMB, relic radiation from the Big Bang, shows the early universe was remarkably uniform with tiny density variations (~1 in 100,000).
• These fluctuations evolved into the lumpy structures seen today due to gravitational forces acting on dark matter and baryonic matter.

S8 Tension in Measurements:

• Discrepancy exists between S8 values measured using:

Gravitational lensing and cosmic shear surveys (lower S8 values, around 0.747 as per the Subaru Hyper Suprime-Cam survey).

• CMB data (predicting higher S8 values).
• This disagreement is referred to as the “S8 tension.”

Role of Dark Matter and Dark Energy:

• Dark matter and dark energy, which make up 95% of the universe, influence the distribution of matter and the clumpiness observed.
• Recent studies suggest that ordinary matter cannot fully explain the lower clumpiness values.

Cosmic Shear Surveys and Gravitational Lensing:

• Surveys like the Subaru HSC use gravitational lensing (distortions in starlight caused by massive structures) to map matter distribution.
• Challenges include accurately measuring redshifts of faint galaxies, contributing to uncertainties.

Updates and Potential Model Changes:

• Findings suggest the standard Lambda Cold Dark Matter (CDM) model may require updates or modifications to account for S8 tension.
• Upcoming data from instruments like the Rubin Legacy Survey of Space and Time (LSST) may provide deeper insights.

Future of the Universe:

• New data hints that dark energy’s push may be weakening, possibly leading to a deceleration in the universe’s expansion and a potential “Big Crunch.”

Technological Advances:

• Tools like the Vera C. Rubin Observatory’s LSST aim to provide unprecedented insights into cosmic mysteries by observing deeper and wider than ever before.