Active Galatic Nuclei (AGN), often called quasars, are the bright centers of galaxies. They can shine brighter than all the stars in their galaxy combined, thanks to supermassive black holes (SMBHs) at their cores. These black holes pull in gas and dust, causing intense radiation across the electromagnetic spectrum—from visible light to X-rays.
For a long time, it was thought that SMBHs were common in all types of galaxies, including dwarf galaxies. However, recent findings show that many dwarf galaxies don’t have these black holes. This raised questions about how we study these smaller galaxies.
At a recent meeting of the American Astronomical Society, scientists from the Harvard & Smithsonian Center for Astrophysics and the University of North Carolina presented a groundbreaking census of AGNs. They assessed more than 8,000 nearby galaxies for signs of black hole activity.
Typically, earlier surveys found about 10 AGNs in every 1,000 dwarf galaxies, equating to around 1%. But this new study revealed 20 to 50 AGNs per 1,000 dwarf galaxies, or 2% to 5%. While this is still lower than the rates seen in larger galaxies, it highlights that AGNs occur more frequently in dwarf galaxies than previously thought.
Mugdha Polimera, a CfA astronomer and lead author, stated, “The rise in AGN activity between dwarf and mid-sized galaxies suggests something significant is changing.” She mentioned two possibilities: either the dwarf galaxies are evolving, or our detection methods need improvement.
An important part of their work was minimizing the interference from star formation, which often hides emissions from black holes. However, they acknowledge some uncertainty due to the fainter black holes that might still be missed. Sheila J. Kannappan, a co-author, pointed out, “By reducing the glare from star formation, we’re uncovering black holes that have previously gone unnoticed in dwarf galaxies.”
Understanding AGNs in dwarf galaxies can help us learn more about black hole origins and their role in shaping galaxies. Knowing how likely different galaxies are to host active black holes provides astronomers with a clearer starting point for future studies.
Interestingly, this research coincides with theory suggesting the Milky Way formed from many smaller galaxies. If that’s true, we should find more SMBHs in dwarf galaxies, as they likely merged to form the Milky Way’s black hole.
To sum up, this new census is a significant step forward in understanding the connection between black holes and galaxies. As future studies enhance our detection methods, we could gain even deeper insights into the mysteries of our universe.
For more details, check the study’s findings from the CfA.
