Black holes are the subject of scientists’ study
A team led by researchers at the University of North Carolina, USA, has discovered a previously overlooked treasure trove of massive black holes in dwarf galaxies, and these newly discovered black holes provide a glimpse into the life story of the supermassive black hole at the center of our Milky Way.
As a giant spiral galaxy, the Milky Way is believed to have formed from the mergers of many smaller dwarf galaxies, for example, the Magellanic Clouds seen in the southern sky, are dwarf galaxies that will merge into the Milky Way. Each dwarf may bring a central supermassive black hole, amounting to Tens or hundreds of thousands of times the mass of our sun, the Milky Way’s central supermassive black hole would probably swallow it up.
But the number of black holes in dwarf galaxies is unknown, leaving a major gap in our understanding of how black holes and galaxies grow together.
New research published in The Astrophysical Journal helps fill this gap by revealing that supermassive black holes are many times more common in dwarf galaxies than previously thought.
“This result really astounded me because these black holes were previously hidden in plain sight,” Mujda Polymera, lead author of the study, said in a report published on the official University of North Carolina website.
Black holes are usually discovered when they are actively growing by eating gas and swirling stardust around them, causing them to glow intensely.
The problem is that while growing black holes glow with distinct, high-energy radiation, newborn stars can do so, too.
Traditionally, astronomers have distinguished growing black holes from new star formation using diagnostic tests that rely on detailed features of each galaxy’s visible light as it spreads out in a rainbow-like spectrum.
The discovery path began when researchers tried to apply these traditional tests to galaxy-scanning data, and the team realized that some galaxies were sending mixed messages, with two tests indicating the presence of growing black holes, and the third test indicating only star formation.
The research team found that the third, sometimes contradictory, test was more sensitive than the other two tests for typical properties of dwarf galaxies in terms of their simple elemental composition (mainly hydrogen and primordial helium from the Big Bang) and their high rate of new star formation. There are many developing black holes that scientists did not know about.