Science, Maths & Technology

Black holes

Updated Thursday 7th February 2013

Black holes seem to occur in the Universe in two distinct types. Read more about those two types here 

Hercules A Copyrighted image Icon Copyright: NASA, ESA, S. Baum and C. O'Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA) A composite image of the radio galaxy, Hercules A. In this false colour image, radio emission is shown in pink, superimposed on an optical image of the galaxy and other more distant objects. The galaxy is two billion light years away, and the radio jets extend for one and a half million light years, away from the invisible supermassive black hole in the galaxy's centre. Watch this animated video to see if it's possible to make a black hole

Black holes seem to occur in the Universe in two distinct types. First, there are those formed when some massive stars collapse at the end of their lives in supernova explosions. The resulting black holes that are produced have a mass of typically ten times that of the Sun, and are referred to as 'stellar mass black holes'.

Although we can’t see them directly, astronomers have good evidence that they exist in certain binary star systems where an unseen massive object appears to be pulling material off its companion star. Several dozen such systems are currently known within our Galaxy.

The second type are referred to as 'supermassive black holes' and they lie at the centres of many (if not all) large galaxies, including our own Milky Way Galaxy. The supermassive black hole in the centre of our Galaxy is calculated to have a mass of more than four million times that of the Sun.

Astronomers see stars in the centre of the Galaxy rapidly orbiting around this invisible object, and although it’s not ‘feeding’ at the moment, any stars that come too close to the black hole will be torn apart before being swallowed.

The supermassive black holes in the centres of other galaxies have masses up to many billions of times that of the Sun, and not all of them are as dormant as the one in our Galaxy. When astronomers look at very distant galaxies, they are looking back in time, because the light from them has taken millions, or even billions, of years to reach us.

Some of these distant galaxies, seen at a time when the Universe was much younger than now, are intense sources of X-rays, radio waves, and other radiation. These are so-called 'Active Galaxies' and are believed to be galaxies in which the central supermassive black hole is feeding on material that strays too close to it. 

As the material falls towards the black hole and is torn apart, it will end up in a flattened structure surrounding the black hole, known as an accretion disc. Then, as this disc material circles the black hole prior to being swallowed, frictional forces in the disc cause it to heat up to millions of degrees, such that it emits X-rays.

For reasons that are not fully understood, some active galaxies also produce enormous jets of material, which are presumed to be emitted perpendicular to the accretion disc, and which can extend for millions of light years into space. Radio waves emitted from these jets can be detected, allowing the jets to be mapped in great detail.

Because more active galaxies are seen in the distant (early) Universe that in the nearby (present day) Universe, it is possible that the active galaxy behaviour is simply an adolescent phase that most large galaxies go through at some point in their lives. By the time galaxies reach middle age, like our own Milky Way, their supermassive black holes have quietened down somewhat! 

Question:  How might an Active Galaxy appear if the radio jets were pointed directly towards us?

Find out more:
 

For a more in-depth discussion, read this extended piece of learning material about Active Galaxies 

 

For further information, take a look at our frequently asked questions which may give you the support you need.

Have a question?

Other content you may like

An overview of active galaxies Copyrighted image Icon Copyright: Used with permission free course icon Level 3 icon

Science, Maths & Technology 

An overview of active galaxies

Active galaxies provide a prime example of high energy processes operating in the Universe. This free course gives an overview of active galaxies, including the supermassive black holes that power the engines at their centres, and the emission processes by which we detect and study them. It also gives practice in mathematical techniques for analysing data and theoretical models.

Free course
15 hrs
Introduction to active galaxies Copyrighted image Icon Copyright: Used with permission free course icon Level 2 icon

Science, Maths & Technology 

Introduction to active galaxies

The field of active galaxies is recognised as one of increasing importance. But how do we know there are different kinds of galaxy? What are active galaxies? How are they powered? This free course, Introduction to active galaxies, examines the different types of active galaxies and looks at the crucial role of the active galactic nucleus and the energy source at its heart.

Free course
20 hrs
60 Second Adventures in Astronomy: Black holes video icon

Science, Maths & Technology 

60 Second Adventures in Astronomy: Black holes

Is it possible to make your own black hole? DIY experts take note with this animation 

Video
Get your free Matrix of Modern Life poster Copyrighted image Icon Copyright: The Open University article icon

Science, Maths & Technology 

Get your free Matrix of Modern Life poster

A free poster from The Open University that explores the colourful connections between different parts of science, engineering and technology—presented in the inimitable Bang style

Article
Infographic: 12 things to know about Einstein's Theory of Relativity Copyrighted image Icon Copyright: Karl Tate, Space.com article icon

Science, Maths & Technology 

Infographic: 12 things to know about Einstein's Theory of Relativity

What you need to know about Einstein's theories of relativity and how they revolutionized how the world thinks about space, time, mass, energy and gravity.

Article
What is a scientific model? Copyrighted image Icon Copyright: Production team audio icon

Science, Maths & Technology 

What is a scientific model?

BBC Inside Science answers a listener question by discussing scientific models and how they are used.

Audio
The Sun Copyrighted image Icon Copyright: Used with permission free course icon Level 1 icon

Science, Maths & Technology 

The Sun

The Sun dominates our lives by defining our day, but how much do you know and understand about it? This free course will help you to explore the workings of the brightest star in our universe looking at its structure and the main processes taking place within it. You will also examine the phenomenon of sun spots.

Free course
8 hrs
Sleeping spacecraft Rosetta ready to wake up for comet landing Copyright free image Icon Copyright free: IanShazell article icon

Science, Maths & Technology 

Sleeping spacecraft Rosetta ready to wake up for comet landing

As the Rosetta spacecraft awakes, Dr Natalie Starkey takes us through this extraordinary comet-landing mission.

Article

Science, Maths & Technology 

Analytical science: Secrets of the Mary Rose

This free course, Analytical science: Secrets of the Mary Rose, teaches you about the analytical techniques that are used in the research and investigation of historical objects using the case study of the Mary Rose. It covers the use of sonar to locate shipwrecks, and the analysis of the artefacts found on the ship, and the crew and their remains.

Free course
12 hrs