Death of a Star, Birth of a Black Hole March 24th, 2014, by colwiz Team
Following the announcement by scientists from the BICEP2 collaboration of new, compelling evidence supporting the Big Bang theory, specifically the concept of cosmic inflation, it seems fitting to provide readers with a colwiz Insight also looking to the stars. This Insight calls to attention a fascinating article in this month’s National Geographic, written by Michael Finkel, entitled ‘Star Eater‘. By contrast to the findings of BICEP2, which reinforces Einstein’s general theory of relativity through proven existence of gravitational waves, Finkel’s article discusses an astronomical idea according to which ‘Albert Einstein, one of the most imaginative thinkers in the history of physics, never believed … [was] real’ – the black hole. Einstein’s general theory permitted the existence of black holes, but as Finkel notes he was always sceptical of the concept.
What are black holes?
Space is warped by the gravitational forces exerted by matter. For massive objects, such as planets and stars, the gravitational effect is enormous. This effect increases with increasing mass (gravity is proportional to mass). Depending on the mass of a star, the outcome of its destruction will vary. A star such as our own sun will eventually collapse to form a compact star known as a White Dwarf. Larger stars form stellar remnants of even greater density, called neutron stars. The largest stars implode with such ferocity that to ‘detonate a Hiroshima-Like bomb every millisecond for the entire life of the universe … would still fall short of the energy released in the final moments of a giant-star collapse.’ These stars collapse to form black holes, areas of space so dense that the gravitational forces they invoke prevent anything escaping their grasp, including light. The interface between the exterior and interior of a black hole is known as the event horizon. Once this is crossed, there is no coming back!
Given black holes are invisible, how do we know they exist?
The presence of a black hole is surmised from its interaction with surrounding matter and radiation. For example, it is postulated that at the centre of each galaxy (of which there are billions within the universe) there lies a supermassive black hole, inferred from the formation of an accretion disc at the event horizon boundary. An accretion disc comprises the leftovers of the matter devoured by the black hole. The friction generated by the gravitational pull raises the temperature of the material in the accretion disc such that it emits electromagnetic radiation, which can be observed with sophisticated telescopes.
While the existence of black holes has become axiomatic in modern physics, their exact nature remains a mystery. For example, Stephen Hawking has recently questioned the reality of an event horizon, suggesting this idea be replaced with that of an ‘apparent horizon’, redefining the boundary and accounting for his earlier observation that radiation can in fact be emitted from black holes, so called ‘Hawking radiation’.
For more information on this alluring topic, why not check out the following references, and add them to your colwiz Library today:
(Hawking, S. W. 2014, arXiv:1401.5761)
(In Hawking, S. W.; Israel, W. 300 Years of Gravitation. Cambridge University Press. ISBN 978-0-521-37976-2)