A team of astronomers from China and Europe has made used extremely sharp images taken with the radio telescopes of the European VLBI Network to make a surprising discovery. The results are presented in the journal Monthly Notices of the Royal Astronomical Society.
It is believed that every galaxy hosts a supermassive black hole, which is at least million times massive than the sun, in its nucleus. Since there are many galaxy clusters and interacting galaxies in the universe, galaxies with two or more supermassive black holes should be ubiquitous as well. However, it is difficult to find pairs of supermassive black holes that actively accrete mass and have a separation of less than the size of their host galaxies (about the distance between the sun and the centre of the Milky Way). Pairs of active galactic nuclei are interesting because they may provide clues on the formation and the growth of giant galaxies and monster black holes.
NGC 5252 is about 320 million light years from the Milky Way. At the centre, it has an active galactic nucleus with a supermassive black hole, recognized by its optical, radio and X-ray properties. A second very luminous X-ray source, catalogued as CXO J133815.6+043255, was found in the outskirts of NGC 5252 last year. This powerful X-ray source appears quite compact in the optical and radio images, similar to the supermassive black hole in the nucleus. To uncover its mysterious nature, an international team led by Jun Yang, Onsala Space Observatory, Chalmers, has made the highest resolution image of its radio counterpart with the observational technique of very long baseline interferometry (VLBI) provided by the European VLBI Network.
"Thanks to the very high resolution of the image, there's no doubt that we're seeing a compact jet", says Xiaolong Yang, a PhD student supervised by Xiang Liu at Xinjiang Astronomical Observatory, China.
“Most likely, the jet is associated with a supermassive black hole.” adds Xiang Liu.
“This is one of the few unique dual radio-emitting supermassive black holes as far as their small separation is concerned”, comments Tao An, radio astronomer at Shanghai Astronomical Observatory, China.
It is not clear whether the two black holes in NGC 5252 will finally merge or not. However, finding more supermassive black hole pairs will definitely enable astronomers to run statistical studies of their final fate.
1 (top) – Radio emission from the mysterious source CXO J133815.6+043255 in NGC 5252 shows evidence for jets from a supermassive black hole. In this extremely sharp image from the European VLBI Network, the brightest areas are shown in white, and fainter signals in red, green and blue.
Credit: EVN/JIVE/X.-L. Yang et al.
2 – The pair of supermassive black holes in NGC 5252 as observed by the radio telescopes of the European VLBI Network (left) and in X-rays by Chandra (right). In these images, the brightest areas are shown in white, and fainter signals in red, green and blue.
Credit: Radio: EVN/X.-L. Yang et al.; X-ray: NASA/CXC/M. Kim et al.
More about the research
The results have been published in a paper in the journal Monthly Notices of the Royal Astronomical Society
, “NGC 5252: a pair of radio-emitting active galactic nuclei?
”, by X.-L. Yang, J. Yang, Z. Paragi, X. Liu, T. An, S. Bianchi, L.C. Ho, L. Cui, W. Zhao, X.-C. Wu, MNRAS Letters, doi: 10.1093/mnrasl/slw160 (http://mnrasl.oxfordjournals.org/lookup/doi/10.1093/mnrasl/slw160
). The article is also available at https://arxiv.org/abs/1608.02200
More about VLBI, the European VLBI Network and JIVE
VLBI is an astronomical method by which multiple radio telescopes distributed across great distances observe the same region of sky simultaneously. Data from each telescope is sent to a central "correlator" to produce images with higher resolution than the most powerful optical telescopes.
The European VLBI Network (EVN; www.evlbi.org
) is an interferometric array of radio telescopes spread throughout Europe, Asia, South Africa and the Americas that conducts unique, high-resolution, radio astronomical observations of cosmic radio sources. Established in 1980, the EVN has grown into the most sensitive VLBI array in the world, including over 20 individual telescopes, among them some of the world's largest and most sensitive radio telescopes. The EVN is administered by the European Consortium for VLBI, which includes a total of 15 institutes, including the Joint Institute for VLBI ERIC (JIVE).
The Joint Institute for VLBI ERIC (JIVE; www.jive.eu
) has as its primary mission to operate and develop the EVN data processor, a powerful supercomputer that combines the signals from radio telescopes located across the planet. Founded in 1993, JIVE is since 2015 a European Research Infrastructure Consortium (ERIC) with five member countries: Netherlands, United Kingdom, Sweden, France and Spain.
Robert Cumming, communicator, Onsala Space Observatory, Chalmers University of Technology, email@example.com, +46 (0)31 772 5500
Jun Yang, Onsala Space Observatory, Chalmers University of Technology, Sweden, email: firstname.lastname@example.org, tel: +46 (0)31 772 5531