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Black hole flickers for Faulkes
GEMMA LAVENDER
ASTRONOMY NOW
Posted: 16 June 2011


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Astronomers from the University of Glamorgan, including first year undergraduate student Chris O’Morain, are attempting to uncover the mysterious behaviour of a black hole using the Faulkes Telescope South, a remote-controlled telescope located at Siding Spring in Australia.

The black hole system, designated GX 339-4, is located several thousand light years away and appears to rapidly flicker in brightness, loitering between magnitudes of +18 and +20 and recently reaching around magnitude +15. This variability is caused by the disc of matter that surrounds it.


An artist's impression of an X-ray binary system containing a black hole. Image: NASA, ESA, Martin Kornmesser (ESA/Hubble).

“The black hole is dragging material from a normal-ish star, which is probably an F or G-type,” says Fraser Lewis of Glamorgan University, a postgraduate student who is working in collaboration with groups in Amsterdam and at the Massachusetts Institute of Technology (MIT) in the US to study the odd behaviour. “This means that its mass is probably approximately the same as our Sun. We would expect this material to be transferred at a rate of one-hundred millionths (10-8) to a millionth (10-6) of the Sun's mass per year, but in the case of these outbursts it’s clear that these are periods of increased mass transfer or accretion.”

Typically these binary systems are observed in X-rays but in a bid to combine research with education, the set of optical observations yielded by Faulkes Telescope users in New York, Portugal and Kent, were designed to examine the variability of the black hole based on images taken on 19-20 May 2011. These revealed that the system was continuing to flicker dramatically in brightness. Is there any explanation for this peculiar behaviour?

“We know it's to do with the process of accretion, which transports material – and energy – towards the black hole in GX 339-4,” says Lewis. “However, linked to that are processes that appear to send the material away from the centre of this system in the form of jets that travel at extremely high speeds at right angles to the orbital plane of the system.” The system that Lewis speaks of is so complex that observers and theorists from Glamorgan, Amsterdam and MIT are striving to understand how these phenomena interact with each other.

“There are a number of theories that succeed in explaining why outbursts occur, such as the disc instability theory,” explains Lewis. “The exact brightness variations are hard to predict, mainly because the accretion discs are somewhat chaotic. GX 339-4 is an odd system because it has fairly regular outbursts [approximately yearly], which is unlike most other transient X-ray binaries of this type.”

You can read more about Fraser Lewis's work studying X-ray binary systems with the Faulkes Telescope, and watch a video interview with him, at http://www.astronomynow.com/news/n1104/20xray/.