Indian Study Uncovers Black Holes’ Role in Halting Star Formation

Recent research from the Indian Institute of Astrophysics (IIA) has provided significant insights into the influence of supermassive black holes on star formation within their host galaxies. The study reveals how these colossal entities, located at the centers of many galaxies, may be responsible for inhibiting the birth of new stars, thereby shaping the evolutionary paths of galaxies.

Supermassive black holes, with masses ranging from millions to billions of times that of the Sun, are known for their intense gravitational pull. However, their effects extend beyond mere matter consumption. They also emit vast amounts of energy in the form of radiation and powerful jets of particles, which can dramatically reshape their surrounding environments.

Understanding the relationship between black holes and their host galaxies has been a key focus of astronomical research. A lingering question has been whether it is the outflow of gas caused by the black hole’s activity or the radiation emitted that primarily regulates star formation. The recent findings provide clarity on this matter.

Key Findings from the Study

The research, published in The Astrophysical Journal, was led by PhD student Payel Nandi, alongside co-authors C. S. Stalin and Dhruba J. Saikia. The team analyzed data from the Sloan Digital Sky Survey (SDSS) and the Very Large Array (VLA), focusing on over 500 local galaxies with active galactic nuclei (AGN). These areas, located near supermassive black holes, are characterized by intense radiation and the occasional emergence of high-speed jets.

Their examination revealed that both the radiation emitted near black holes and the jets they produce work in tandem to expel gas from the centers of galaxies. This process significantly curtails the potential for new star formation in these regions. Nandi explained, “We found that outflows of warm ionized gas are widespread in AGN. Radiation from the black hole is the main driver, but galaxies with radio jets show significantly faster and more energetic outflows.”

The data indicated that outflows occur in over 56 percent of galaxies emitting radio wavelengths, compared to just 25 percent in those without such emissions. This illustrates that the presence of jets, which can travel at speeds nearing 2,000 kilometers per second, greatly enhances the outflow strength.

The researchers constructed a schematic model to visualize their results, comparing AGN that emit only radiation with those that also produce jets. The findings demonstrated that galaxies exhibiting both features experience much stronger outflows, leading to a more rapid depletion of their gas supply and a significant decrease in star formation within their central regions.

The Implications of Black Hole Activity

The study highlights the importance of integrating multiple wavelengths of observation to attain a comprehensive understanding of galaxy evolution. Co-author C. S. Stalin emphasized the significance of this approach, stating, “This study highlights how crucial it is to bring together optical and radio data to get a complete picture of galaxy evolution.”

The research also uncovered a strong correlation between the energy of the outflows and the total power emitted by the black holes. In galaxies with jets, this relationship was markedly more pronounced. While radiation serves as the primary driver of these outflows, jets enhance the black hole’s ability to eject matter, effectively “starving” the galaxy of the necessary materials for new star formation.

The researchers confirmed their findings by analyzing the optical signatures of stellar populations and infrared colors, which allowed them to differentiate between gas expelled by black hole activity and that associated with young stars. This pointed to a phenomenon known as negative AGN feedback, where black hole activity actively suppresses the formation of new stars, creating a dormant and silent core.

This groundbreaking study sheds light on a fundamental question in astrophysics: why do certain galaxies cease star formation while others continue for billions of years? According to Dhruba J. Saikia, “These findings are an important step toward understanding the complex interrelationships between supermassive black holes, radio jets, star formation, and the evolution of their host galaxies.”

As galaxies progress through distinct life cycles—transitioning from vibrant, star-forming phases to quieter periods—this research indicates that supermassive black holes play a crucial regulatory role in determining the timing of these transitions. By expelling or heating the gas essential for star formation, they influence the evolutionary trajectory of their galaxies.

The implications of this study extend beyond individual galaxies; they may also offer insights into the evolutionary history of our own Milky Way galaxy. The supermassive black hole at its center, known as Sagittarius A*, is currently dormant but may have experienced active phases in the past that impacted nearby star formation rates.

As astronomers continue to explore the universe with advanced telescopes such as the James Webb Space Telescope (JWST) and the Square Kilometre Array (SKA), further discoveries may illuminate the ways in which these immense cosmic forces shape galaxies over vast timescales. The work conducted by the IIA team plays a critical role in this ongoing quest, unveiling the profound influence of supermassive black holes on their galactic surroundings.