November 14, 2013
Black Hole Observations Reveal Contents Of Mysterious Jets
redOrbit Staff & Wire Reports - Your Universe Online
Astronomers have long wondered exactly what the enigmatic jets given off by black holes are made of. Now, an international team of scientists, writing in the journal Nature, has apparently solved the mystery and discovered the composition of those high-speed beams of matter.
Using the European Space Agency’s (ESA) XMM-Newton observatory, lead author Dr. María Díaz Trigo and colleagues studied a black hole binary system located in our own galaxy. This system, called4U1630–47, has been known to show X-ray outbursts over the period of several months or even years, the agency explained in a statement.
“In our observations, we found signs of highly ionized nuclei of two heavy elements, iron and nickel,” said Trigo, who works at the European Southern Observatory in Munich, Germany. “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.”
In September, Trigo’s team analyzed radio waves and X-rays emitted by the black hole which was a few times the mass of the Sun. While 4U1630–47 was known to be active, their radio observations did not reveal any jets, nor did the X-ray spectrum indicate any unusual activity.
A few weeks later, however, they took a second look and found radio emissions that corresponded to the sudden appearance of the jets, as well as the appearance of lines in the X-ray spectrum around the black hole. That latter observation indicated the presence of ordinary atoms, the researchers explained.
“Intriguingly, we found the lines were not where they should be, but rather were shifted significantly,” said Dr. James Miller-Jones, who led the radio observations and is a member of the International Centre for Radio Astronomy Research (ICRAR).
That shift was similar to that of the pitch change of a vehicle’s siren as it moves towards or away from the hearer, and signified that the length of the sound wave is becoming shorter or longer due to the movement. The phenomenon led the study authors to believe that the particles were being accelerated to high speeds while in the jets – one towards the Earth, and the other in the opposite direction.
According to Dr. Miller-Jones, this is the first strong evidence of the presence of such particles in typical black hole jets. “We've known for a long time that jets contain electrons, but haven't got an overall negative charge, so there must be something positively charged in them too,” he explained.
“Until now it wasn't clear whether the positive charge came from positrons, the antimatter 'opposite' of electrons, or positively charged atoms,” the Dr. Miller-Jones added. “Since our results found nickel and iron in these jets, we now know ordinary matter must be providing the positive charge.”
Positively-charged atoms are far heavier than the positrons astronomers had thought might have comprised the jets, and that means that they are capable of carrying a far greater amount of energy from the black hole than scientists had previously believed. Furthermore, the experts are uncertain whether the jets are powered by the spin from the rotating black hole, or if they are launched directly from the surrounding disk of matter.
“Our results suggest it's more likely the disk is responsible for channeling the matter into the jets, and we are planning further observations to try and confirm this,” Dr Miller-Jones said. Based on the X-ray data they collected, he and his colleagues also determined that those jets traveled at two-thirds the speed of light (198,000 km/s) – the most accurate calculation of jet speed from a typical black hole of this size, the researchers said.