Large Galaxies Can Be Suffocated by Their Black Holes

Tuesday, 02 January 2018 - 6:30PM
Space
Astronomy
Black Holes
Tuesday, 02 January 2018 - 6:30PM
Large Galaxies Can Be Suffocated by Their Black Holes
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ESA/Hubble, L. Calçada (ESO)

Deep at the heart of many galaxies, a black hole serves as an anchor for all the stars and other materials to swirl around. The biggest of these black holes, known as supermassives, are particularly potent, sucking in anything within their reach over time.

Galaxies can live long, fruitful lives while still seeing much of their light being drained away - these supermassive black holes take millennia to gobble up an entire galaxy, and in the meantime, stars can be born, grow old, and die in a natural cycle that's in no way negatively affected by the black holes around which they orbit.

That said, according to a new study, these giant gravity pits might be even more potent than previously thought. They may even be responsible for draining the life from previously healthy galaxies by "quenching" the energy that allows them to develop new stars over time.

A study from a team of astronomers at the University of California Santa Cruz, published in Nature, suggests a reason for this odd phenomenon in which large, otherwise healthy galaxies slowly stop producing new stars, something that scientists have observed many times. This is such a common occurrence that it's considered perfectly normal, but until now, there haven't been many solid explanations for why it happens.



The study gives credence to a popular theory that supermassive black holes might be taking large galaxies' fuel supplies, and expelling them outside the galaxy. New stars are formed from cold gas that swirls around in space, and it's thought that particularly large black holes may attract this fuel source in large clouds that grow volatile, shooting out in huge plumes of energy that then dissipate beyond the galaxy.

As the black holes grow larger, they dissipate too much of this fuel source. And with the galaxy's energy source depleted, the entire celestial community stops producing stars, and the galaxy dies, long before the supermassive black hole has a chance to absorb the entire thing.

While up until now, there hasn't been much evidence to prove this long-held theory, the study managed to compare the relative rates at which galaxies are dying. They've noted that the speed that a large galaxy will stop producing stars matches up with the mass of the black hole at its center, rather than the size or shape of the gravity well. This suggests that the biggest factor in the death of these galaxies is the gravitational pull coming from the massive object at their centers.

According to the study:

Opening quote
"The subsequent quenching of star formation takes place earlier and more efficiently in galaxies that host higher-mass central black holes. The observed relation between black-hole mass and star formation efficiency applies to all generations of stars formed throughout the life of a galaxy, revealing a continuous interplay between black-hole activity and... cooling."
Closing quote


This is still, at present, merely a possible explanation, and one which will be hard to verify given our current limited ability to monitor distant galaxies. That said, it is a first step to understanding what's going on in the farthest reaches of the universe, and how galaxies around us are formed, grow, and then die.

It's also worth noting that our own galaxy, the Milky Way, might well have a large black hole or two at its center, which could combine over time to form something even bigger and stronger.

The kind of destruction we're talking about with the expulsion of cold gas is on such an enormous cosmic scale that there's no way it would affect humanity for millennia to come, but it is interesting to think about what might be going on, in some small way, so close to home.

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