By Bibiana Bonmatí, University of Barcelona Press
If you have a look at the Norma constellation, in the southern hemisphere, you could find 4U 1630-47, a binary system formed by a massive star and a black hole candidate that share matter. It is known that black holes launch relativistic jets both in stellar-mass binary systems and at the centres of galaxies, in what are known as quasars.
Although jets have been studied for decades, their composition remains uncertain. Now, research published in the journal Nature describes the detection of atomic nuclei in the relativistic jets from the black hole binary system 4U 1630-47.
“We have found the composition of relativistic jets launched from around black holes; however, more studies are needed to understand if results can be extrapolated to other relativistic jet sources”, explains Simone Migliari, from the Institute of Sciences of the Cosmos of the University of Barcelona (ICCUB). The expert affirms that “the study proves that relativistic jets might be ‘heavy jets’ containing atomic nuclei, rather than ‘light jets’ consisting of electrons and positrons only”. “The finding”, he adds, “implies that ‘heavy jets’ carry away significantly more energy from the black hole than ‘lighter’ ones”.
“Observations revealed signs of highly ionized nuclei of two heavy elements, iron and nickel. The discovery came as a surprise — and a good one — since it shows beyond doubt that the composition of black hole jets is much richer than just electrons”, explains María Díaz Trigo from the European Southern Observatory in Munich, Germany, lead author of the paper.
Black holes in binary systems catch companions’ matter in order to create a disc that rotates around the black hole at high speed, called the accretion disc. Consequently, matter is compressed and gets hot enough to emit X-rays. The research also provides an accurate estimate of the speed of jets, which was found to be 2/3 of the speed of light.
Baryonic jets, composed of heavy matter, are more likely to be powered by the accretion disc rather than the spin of the black hole. “If baryons can be accelerated to relativistic speeds, these systems should be strong sources of gamma rays and neutrino emission”, concludes Migliari.
In 2012, observations were done nearly simultaneously by means of two types of facilities: first, the telescopes XMM-Newton of the European Space Agency (ESA), which enable researchers to perform X-ray observations in order to observe the disc that surrounds the black hole; and second, the Australia Telescope Compact Array (ATCA), used to carry out radio observations to see the relativist jet.
Concerning the research’s relevance, it is important to highlight that 4U 1630-47 is a common binary system in accreting black holes; therefore, these results can be extrapolated to other similar systems. New observations of 4U1630–47 will help astronomers to learn more about the physical mechanism that launches jets from a black hole’s accretion disc.
Image: Artist’s impression of a black hole with disc and jets (Copyright: Riccardo Lanfranchi).
Further information:
http://www.ub.edu/web/ub/en/menu_eines/noticies/2013/11/022.html
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