Gravitational Lens Zooms In On Why Some Quasars Have The Radio Turned Down

Mini-jets of material ejected from a central supermassive black hole appear to be the culprits behind faint radio wave emissions in ‘radio-quiet’ quasars. A study of gravitationally-lensed images of four radio-quiet quasars has revealed the structure of these distant galaxies in unprecedented detail. This has enabled astronomers to trace the radio emissions to a very small region at the heart of the quasars, and helped to solve a 50-year-old puzzle about their source. The results will be presented by Dr Neal Jackson at the National Astronomy Meeting in Nottingham on Friday, 1st July. 

“In radio-loud quasars, the intense radio emission clearly comes from vast jets of material blasted out from the region around a central black hole. By contrast, the radio emission from radio-quiet quasars is extremely feeble and difficult to see, so it has been hard to identify its source,” explained Jackson of the Jodrell Bank Centre for Astrophysics in Manchester. “To study most radio-quiet quasars, we will have to wait until future extremely large telescopes, like the Square Kilometre Array, come online. However, if we find radio-quiet quasars which are lensed by galaxies in front of them, we can use the increased brightness to be able to study them with today's radio telescopes.”

Gravitational lensing is a phenomenon where light from distant objects is warped by the gravitational field of massive objects in the foreground, a bit like light travelling through a glass lens. The mass distribution in a galaxy acts rather like a lens shaped like the bottom of a wineglass, and produces multiple images of background objects, with images stretched out into arcs and rings.

Jackson and colleagues used the Karl G. Jansky Very Large Array, in New Mexico, US, to study four examples of gravitational lens systems where the background quasar appears in a ring of four, distorted images. Two of the systems were also observed by the UK’s e-MERLIN array. After correcting for the distorting effects of the lens, the team were able to accurately measure the sizes of the radio-emitting regions in the sample of quasars.

“The cause of radio emissions in radio-quiet quasars has been the subject of debate. One theory suggested that they were caused by multiple explosions of individual supernovae in the galaxy surrounding the quasar,” said Jackson. “These new observations have allowed us to narrow down the emissions to a very small region, typical of an active nucleus – i.e. jets emanating from a supermassive black hole. We are currently working on some further data that we hope will confirm our preliminary findings. If so, we can rule out the supernova explanation, which would show radio emissions from a much larger area, and confirm that the processes driving radio-quiet quasars are the same as their loud counterpart, just on a smaller scale.”

About NAM 2016
The RAS National Astronomy Meeting 2016 (NAM 2016) takes place this year at the University of Nottingham from 27 June to 1 July. NAM 2016 brings together more than 550 space scientists and astronomers to discuss the latest research in their respective fields. The conference is principally sponsored by the Royal Astronomical Society and the Science and Technology Facilities Council. For more information, visit http://nam2016.org.

About The University of Nottingham
The University of Nottingham has 43,000 students and is ‘the nearest Britain has to a truly global university, with a “distinct” approach to internationalisation, which rests on those full-scale campuses in China and Malaysia, as well as a large presence in its home city.’ (Times Good University Guide 2016). It is also one of the most popular universities in the UK among graduate employers and the winner of ‘Outstanding Support for Early Career Researchers’ at the Times Higher Education Awards 2015. It is ranked in the world’s top 75 by the QS World University Rankings 2015/16, and 8th in the UK by research power according to the Research Excellence Framework 2014. It has been voted the world’s greenest campus for four years running, according to Greenmetrics Ranking of World Universities. For more information, visit http://nottingham.ac.uk/.

Impact: The Nottingham Campaign, its biggest-ever fundraising campaign, is delivering the University’s vision to change lives, tackle global issues and shape the future.

About The Science and Technology Facilities Council
The Science and Technology Facilities Council (STFC) is keeping the UK at the forefront of international science and has a broad science portfolio and works with the academic and industrial communities to share its expertise in materials science, space and ground-based astronomy technologies, laser science, microelectronics, wafer scale manufacturing, particle and nuclear physics, alternative energy production, radio communications and radar. STFC's Astronomy and Space Science programme provides support for a wide range of facilities, research groups and individuals in order to investigate some of the highest priority questions in astrophysics, cosmology and solar system science. STFC's astronomy and space science programme is delivered through grant funding for research activities, and also through support of technical activities at STFC's UK Astronomy Technology Centre and RAL Space at the Rutherford Appleton Laboratory. STFC also supports UK astronomy through the international European Southern Observatory. For more information, visit http://www.stfc.ac.uk.

About The Royal Astronomical Society
The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. For more information, visit http://www.ras.org.uk.

The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.