Black holes spew out powerful jets that span millions of light-years – we're trying to understand their whole life cycle
There is a supermassive black hole at the centre of nearly every big galaxy – including ours, the Milky Way (it's called Sagittarius A*). Supermassive black holes are the densest objects in the universe, with masses reaching billions of times that of the Sun.
Sometimes a galaxy's supermassive black hole 'wakes up' due to a sudden influx of gas and dust, most likely supplied from a neighbouring galaxy. It begins eating up lots of nearby gas and dust. This isn't a calm, slow or passive process. As the black hole pulls in material, the material gets superheated on a scale of millions of degrees, far hotter than the surface temperature of our Sun, and is ejected from the galaxy at near-light speeds. This creates powerful jets that look like fountains in the cosmos.
The accelerated high-speed plasma matter prompts these 'fountains' to emit radio signals that can only be detected by very powerful radio telescopes. This gives them their name: radio galaxies. While black holes are common, radio galaxies are not. Only between 10% and 20% of all galaxies exhibit this phenomenon.
Giant radio galaxies are even less common. They account for only 5% of all radio galaxies and take their name from the fact that they reach enormous distances. Some radio galaxies' jets reach nearly 16 million light-years. (That's almost six times the distance between the Milky Way and the Andromeda galaxy.) The largest jet discovered spans nearly 22 million light-years across.
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But how do these structures cover such enormous distances? To find out, I led a study in which we used modern supercomputers to develop models that simulated behaviour of giant cosmic jets within a mock universe, constructed on the basis of fundamental physical laws governing the cosmos.
This allowed us to observe how radio jets propagate over hundreds of millions of years – a process impossible to track directly in the real universe. These sophisticated simulations provide deeper insights into the life cycle of radio galaxies, highlighting the differences between their early, compact stages and their later, expansive forms.
Understanding the evolution of radio galaxies helps us unravel the broader processes that shape the universe.
Cutting-edge technology was key to this study.
Sensitive observations from world-class radio telescopes like South Africa's MeerKAT and LOFAR in the Netherlands have recently led to several discoveries of cosmic fountains.
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However, modelling their origins has been challenging. Tracking events over millions of years is impossible in real-time.
That's where supercomputers come in. These high-performance computing systems are designed to process massive amounts of data. They can perform complex simulations at incredible speeds. In this study, their power was crucial for modelling the evolution of giant radio jets over millions of years.
The necessary supercomputing power was provided by South Africa's Inter-University Institute for Data Astronomy, a network comprising the University of Pretoria, the University of Cape Town and the University of the Western Cape.
Our universe is governed by fundamental forces like gravity, which can be described through mathematical formulas. These formulas, essentially numbers, are fed into supercomputers to create a simulated 'mock universe' that follows the same physical laws as the real cosmos. This allows scientists to experiment with how jets from supermassive black holes evolve over time. With their immense processing power, supercomputers can simulate millions of years of cosmic jet evolution in just a month.
Gravity is the dominant force in the universe, pulling heavier matter and dragging nearby lighter matter. If gravity were the only force at play, the universe might have collapsed by now. Yet we see galaxies, galaxy clusters and even life itself thriving. We suspect that these cosmic fountains play a key role in solving the mystery of how this happens.
By releasing thermal and mechanical energy, they heat up the surrounding collapsing gas, counteracting gravity and maintaining a balance that sustains cosmic structures.
Our models also shed light on why some radio galaxies' jets bend sharply, forming an 'X' shape in radio waves instead of following a straight trajectory, and revealed the conditions under which giant fountains can continue growing even in dense cosmic environments (that is, in a galaxy cluster).
The study also suggests that giant radio galaxies may be statistically more common than previously believed. There are potentially thousands of undiscovered giant cosmic fountains. Thanks to world-class telescopes like MeerKAT and LOFAR – and the power of supercomputers – there's plenty more to explore as we try to understand our universe.
The research on which this article is based required extensive collaboration with an international team, including Jacinta Delhaize from the University of Cape Town, Joydeep Bagchi from Christ University, India, and DJ Saikia from the Inter-University Centre for Astronomy and Astrophysics in India. Essential contributions by Kshitij Thorat and Roger Deane from the University of Pretoria also played a crucial role in shaping the study.
This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Gourab Giri, University of Pretoria
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Gourab Giri does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
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