Space

Understanding the feeding habits of supermassive black holes is a matter of perspective

Understanding the feeding habi...
Artist's impression of a supermassive black hole surrounded by an accretion disk formed from a dead star
Artist's impression of a supermassive black hole surrounded by an accretion disk formed from a dead star
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Artist's impression of a supermassive black hole surrounded by an accretion disk formed from a dead star
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Artist's impression of a supermassive black hole surrounded by an accretion disk formed from a dead star
Cross section of a supermassive black hole displaying an accretion disk formed by a newly destroyed star, and where the different types of radiation are emitted
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Cross section of a supermassive black hole displaying an accretion disk formed by a newly destroyed star, and where the different types of radiation are emitted

A new computer model could help astronomers to interpret the radiation emitted by supermassive black holes as they rip apart and devour unfortunate stars. These extreme "feeding" episodes are known as Tidal Disruption Events (TDEs), and are thought to be incredibly rare, occurring in some galaxies only once every 10,000 years.

Lurking at the heart of most large galaxies, there resides a supermassive black hole – a point in space with such a powerful gravitational pull that not even light can escape its influence. Sagittarius A*, the Milky Way's very own supermassive black hole lurks a mere 26,000 light-years from Earth in the galactic center, and is estimated to have a mass the equivalent of roughly four million Suns.

Astronomers are unable to observe a supermassive black hole directly, as they emit no light of their own. However, a scientist can gain a better understanding of these cosmic monsters by observing how they interact with their environments, and, more specifically, how they feed off them.

These cosmic meals come in all shapes and sizes, but every now and again, a supermassive black hole will over-eat, and feast upon an entire star.

Despite their all-consuming reputations, even a supermassive black hole is unable to devour an entire star all at once. The stellar material which is not immediately consumed falls inward and forms what is known as an accretion disk.

As the accretion disk accelerates and compresses, it becomes super-heated, causing it to shine brightly with visible light and other forms of radiation. Astronomers believe that the processes that occur during a TDE should be essentially universal, yet some events have been observed emitting mostly optical and UV radiation, while others appear to throw out massive amounts of X-rays.

A new computer model developed by an international team of scientists has presented a framework for unifying these disparate events, revealing that the TDEs only appear different due to the angle at which we observe them.

Cross section of a supermassive black hole displaying an accretion disk formed by a newly destroyed star, and where the different types of radiation are emitted
Cross section of a supermassive black hole displaying an accretion disk formed by a newly destroyed star, and where the different types of radiation are emitted

Sadly, astronomers are unable to zip around the universe and observe the subject of their curiosity from any angle that their hearts desire. Instead, scientists are limited to a single view of the cosmos – that which they can see from Earth. This can sometimes lead to confusion, and problems in identifying and understanding an object.

Take for example a classic spiral galaxy. When imaged from the side it appears as a relatively flat band of material, revealing nothing of the structure of its majestic sweeping arms. In order to create a more complete image of a complex object or phenomenon, such as a tidal disruption event, astronomers look to recreate these objects and events in a digital setting, allowing them to gain various insights, including how they would look from a different perspective.

The cutting-edge computer model used in the new study was constructed taking into account what astronomers understand and theorize regarding the characteristics of a supermassive black hole, including for example the nature of its magnet fields and how it emits radiation. Results from the 3D simulations revealed that the apparent discrepancies observed in the radiation emissions of TDEs are likely the result of observing them from different angles.

Simply put, the research supports the idea that the same basic physical processes occur each time a supermassive black hole feeds on a star, and that subsequently, similar types and levels of radiation are emitted during this cataclysmic process. However, TDE events can appear disparate in nature to us depending on the angle of the supermassive black hole lies relative to the perspective of Earth.

The team discovered that the greater the inclination of the supermassive black hole, the more X-ray radiation would be detected by our telescopes during a TDE event, while more neutrally positioned black holes would appear to shine with a greater intensity of optical light.

The new research provides a framework by which signals from these events can be interpreted, allowing scientists to gain a greater understanding of these galaxy-shaping heavyweights. Over the coming years the team behind the new model hope to collect data on thousands more tidal disruption events in order to put their model to the test.

A paper detailing the research as been published in The Astrophysical Journal Letters.

Source: Niels Bohr Institute

1 comment
Nik
Once in 10,000 years in the life of a galaxy, might be rare to humans, but not to the galaxy. Right alongside this comment panel, is the heading, ''Fastest-growing super-massive black hole eats a sun every two days!'' so perhaps not so rare. There have been several articles relating to Black Holes recently. One I read was, that recent observations with new equipment had found that black holes had formed well within the first billion years after the 'big bang'. These black holes would now all be of the super massive variety, and must now exist in hundreds of billions in the periphery of our universe. They would, have swallowed all of the matter of their respective galaxies in their vicinity, long ago, and would be completely undetectable. Another was that scientists had discovered a whole load more black holes than they had expected, and that they would now need to review their mathematical models to account for this. It was at this point that I had a vision of our universe, but, from the outside. What I saw was was a hazy, incandescent blue white globe, (blue in the core as this would be moving towards my point of view), with hundreds of black shapes between it and my point of view. Most shapes were circular, a few were elliptical, and several overlapped each other. These were black holes. Many must be formed from multiple super-massive black holes that had combined. Given that they have been forming throughout the life of our universe, there must be many more than those we can detect in the present visible universe. So our universe would be surrounded by a 'shell' of multi-billions of super-massive, or even 'super humongous' black holes if many of them had combined. To me, this would explain two things, first where all the undetectable ''Dark Matter'' of our universe could be, and second, why the expansion of the universe is accelerating. Its being drawn towards the black holes surrounding our universe, at an ever accelerating rate. The conclusion is, that eventually the universe will consist entirely of black holes, of varying sizes, and these will gradually be attracted to each other until they all collide, in the theorised ''Big Crunch.'' This will be such violent event, that it may well result in another 'Big Bang!' and 'so on ad infinitum'!