Black holes that emit different light signatures are actually at different life cycle stages, according to a new study.
The research, published last month in The Astrophysical Journalchallenges a model of supermassive black holes that characterizes them as all having the same properties.
Until now, it was assumed that such black holes are the same type of cosmic objects viewed from different angles.
Scientists, including those from Dartmouth College in the US, said the results could allow researchers to create more accurate models of how the universe evolved and shed more light on black hole evolution.
Previous studies suggest that supermassive black holes are at the center of almost all large galaxies, including the Milky Way, consuming galactic gases, dust and stars — sometimes growing heavier than small galaxies.
When dusty material falls into these black holes at incredible speeds, they light up and emit radiation in infrared or X-ray wavelengths that outshines the entire host galaxy.
Astronomers refer to active supermassive black holes at the center of their host galaxy, growing through the accretion of matter, as active galactic nuclei (AGNs).
“These objects have puzzled researchers for over half a century,” said the study’s lead author Tonima Tasnim Ananna, a postdoctoral researcher at Dartmouth College.
“Over time we have made many assumptions about the physics of these objects. Now we know that the properties of eclipsed black holes differ significantly from the properties of AGNs, which are not as well occluded,” said Dr. pineapple
Scientists have been studying AGNs for decades by assessing their light signatures.
Since the 1980s, when analyzing their light signatures at X-ray wavelengths, they assumed that AGNs typically have an annular ring—or “torus”—of gas and dust around them.
The researchers believed that the objects’ differing brightness and color was due to the angle from which the AGNs were observed and how much torus was obscuring the view.
Based on this belief, the unified theory of AGNs became the dominant understanding, scientists said.
In the new study, the researchers evaluated how fast black holes feed on space matter, or how fast they grow.
They found that the rate of accretion does not depend on the mass of a black hole, but depends heavily on how occluded it is by the ring of gas and dust.
“This supports the idea that the torus structures around black holes are not all the same. There is a connection between the structure and its growth,” explained Ryan Hickox, professor of physics and astronomy and co-author of the study.
The new research suggests that the amount of dust surrounding an AGN is directly related to how much it eats, indicating there are differences between different AGN populations that go beyond orientation.
An actively accreting black hole blows away dust and gas and appears rather brighter, while a less active AGN is surrounded by a denser torus and appears fainter, scientists said.
“Historically, it has been uncertain how the eclipsed AGN population differs from their more easily observable non-eclipsed counterparts. This new research definitely shows a fundamental difference between the two populations that goes beyond perspective,” said Dr. pineapple
By knowing a black hole’s mass and how actively it feeds, the scientists said they can determine when the majority of supermassive black holes have completed most of their growth.
Researchers believe the latest findings solve an important piece of the puzzle of “Where do supermassive black holes come from” and provide valuable information about the evolution of such cosmic entities and the Universe.