Circumgalactic medium (CGM)

Why in News?

Astronomers from the Raman Research Institute (RRI) and Arizona State University have found evidence for a possible mechanism through which supermassive black holes (SMBHs) can influence gas in the circumgalactic medium (CGM). The findings provide insights into how black-hole activity may regulate gas cooling and, consequently, star formation and galaxy evolution.

About Circumgalactic Medium (CGM)

The circumgalactic medium is a vast, diffuse envelope of gas surrounding a galaxy beyond its visible disk. It can extend up to 10–20 times the size of the galaxy and acts as a major reservoir of material available for future star formation.

Although the CGM contains gas that can eventually fuel star formation, not all of it collapses into stars. Astronomers have proposed that energy released by actively feeding supermassive black holes may prevent excessive cooling and collapse of this gas.

Role of Black-Hole Jets

When a supermassive black hole actively accretes matter, it can launch powerful jets of extremely hot plasma consisting of charged particles. Researchers found that when these jets interact with the CGM, they can deposit energy into the surrounding gas and excite it.

This interaction heats and ionises the gas, thereby inhibiting its cooling and clumping. As a result, the gas becomes less likely to collapse under gravity and form stars. This provides a possible explanation for how black-hole feedback regulates star formation and influences the long-term evolution of galaxies.

Source: PIB

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