An international team of astronomers, including a researcher from 麻豆直播, has answered a long standing question about the enigmatic jets emitted by black holes, in findings published recently in prestigious journal Nature.
Jets are narrow beams of matter spat out at high speed from near a central object, like a black hole.
The team studied the radio waves and X-rays emitted by a small black hole a few times the mass of the Sun. The black hole in question was known to be active, but the team鈥檚 radio observations did not show any jets, and the X-ray spectrum didn鈥檛 reveal anything unusual.
However, a few weeks later, the team took another look and this time saw radio emissions corresponding to the sudden appearance of these jets, and even more interestingly, lines had appeared in the X-ray spectrum 鈥� the tell-tale signature of ordinary atoms 鈥� around the black hole.
鈥淚ntriguingly, we found the lines were not where they should be, but rather were shifted significantly,鈥� Dr James Miller Jones from the 麻豆直播 node of the International Centre for Radio Astronomy Research (ICRAR), who led the radio observations, said.
The same effect occurs when a siren from a vehicle changes pitch as it moves towards or away from us, as the sound wave is shortened or lengthened by the movement.
鈥淚t led us to conclude the particles were being accelerated to fast speeds in the jets, one directed towards Earth, and the other one in the opposite direction,鈥� team member Dr Simone Migliari from the University of Barcelona said.
Dr Miller-Jones said this was the first strong evidence of such particles in jets from a typical small black hole.
鈥淯ntil now, we weren鈥檛 sure what they are made of, or what powers them,鈥� European Southern Observatory astronomer Dr Mar铆a D铆az Trigo, lead author of the study, said.
鈥淲e鈥檝e known for a long time that jets contain electrons, but haven鈥檛 got an overall negative charge, so there must be something positively charged in them too,鈥� Dr Miller Jones said.
鈥淯ntil now it wasn鈥檛 clear whether the positive charge came from positrons, the antimatter 鈥榦pposite鈥� of electrons, or positively charged atoms. Since our results found nickel and iron in these jets, we now know ordinary matter must be providing the positive charge.鈥�
Positively charged atoms are much heavier than the positrons astronomers thought might make up the jets, and therefore the jets can carry away far more energy from the black hole than previously confirmed.
What鈥檚 more, astronomers aren鈥檛 sure whether the jets are powered by the spin of the rotating black hole itself, or whether they are instead launched directly from the disk of matter that surrounds the black hole.
鈥淥ur results suggest it鈥檚 more likely the disk is responsible for channelling the matter into the jets, and we are planning further observations to try and confirm this,鈥� Dr Miller-Jones said.
Using the X-ray data, the team also determined the jets were moving at two-thirds of the speed of light, or 198,000 km/s, the most accurate determination to date of the jet speed from a run-of-the-mill black hole a few times the mass of the Sun.
For their observations, the team used the European Space Agency鈥檚 XMM-Newton satellite to observe X-ray emission from the black hole, as well as CSIRO鈥檚 Australia Telescope Compact Array for the radio observations.
The paper, Baryons in the relativistic jets of the stellar-mass back holes candidate 4U1630-47 can be found at www.nature.com, published 13/11/2013. DOI: 10.1038/nature12672
