Supermassive black holes are engines of galactic evolution, but new observations of our galaxy and its central hole don’t quite match expectations.
from the surrounding intergalactic medium makes it all the way down and into the hole. “That’s revealing a huge problem,” Natarajan said. “Where is this gas going? What is happening to the flow? It’s very clear that our understanding of black hole growth is suspect.”
Over the past quarter century, astrophysicists have come to recognize what a tight-knit, dynamic relationship exists between many galaxies and the black holes at their centers. “There’s been a really huge transition in the field,” says, a theoretical astrophysicist at Harvard University. “The surprise was that black holes are important as shapers and controllers of how galaxies evolve.”
These giant holes—concentrations of matter so dense that gravity prevents even light from escaping—are like the engines of galaxies, but researchers are only beginning to understand how they operate. Gravity draws dust and gas inward to the galactic center, where it forms a swirling accretion disk around the supermassive black hole, heating up and turning into white-hot plasma. Then, when the black hole engulfs this matter , energy is spat back out into the galaxy in a feedback process.
But researchers have only vague ideas about supermassive black holes’ “active” episodes, which turn them into so-called active galactic nuclei . “What is the triggering mechanism? What is the off switch? These are the fundamental questions that we’re still trying to get at,” saidStellar feedback, which occurs when a star explodes as a supernova, is known to have similar effects as AGN feedback on a smaller scale.
Size-wise, the Milky Way, a typical spiral galaxy, sits in the middle. With few obvious signs of activity at its center, our galaxy was long thought to be dominated by stellar feedback. But several recent observations suggest that AGN feedback shapes it as well.
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