Friday, April 18, 2014
Los Angeles Times
LOS ANGELES — Has a black hole mystery just been solved?
A NASA artist’s illustration shows a supermassive black hole with millions to billions times the mass of our sun at the center, surrounded by matter flowing onto the black hole in what is termed an accretion disk.
Writing in the journal Nature, a team of scientists said it found traces of nickel and iron in the powerful jets shooting out of black hole candidate 4U 1630-47, a small black hole just a few times the mass of our sun. It may help solve a scientific puzzle that has lingered for decades.
Astronomers have known for years that hyper-dense black holes shoot matter into the universe in high-speed streams known as relativistic jets. However, nobody knew exactly what type of material the jets were spewing.
“It was one of the unsolved questions about relativistic jets produced in the vicinity of black holes,” said Avi Loeb, chair of the department of astronomy at Harvard University, who was not involved with the study. “What is their composition?”
Everyone was in agreement that the jets would contain electrons, which have a negative charge. But the jets did not have a negative charge overall. That suggested there was something else in there with a positive charge that canceled it out.
In addition, some models of the jets suggested they were shooting lightweight electrons and positrons away from the black hole and into the universe. Others thought the jets were made of much heavier normal matter.
“Until now, it wasn’t clear whether the positive charge came from positrons, the antimatter ‘opposite’ of electrons, or positively charged atoms,” study coauthor James Miller-Jones of the International Center for Radio Astronomy Research said in a statement. “Since our results found nickel and iron in these jets, we now know that ordinary matter must be providing the positive charge.”
Because it takes a lot more energy to move normal matter than it would to move the lightweight electrons and positrons, the authors suggest that the high-speed jets are carrying more energy away from the black hole than was previously known.
The study also sheds light on another scientific debate – exactly where the jets emerge from. It has been unclear whether the jets are caused by the spin of the rotating black hole, or if they originate from the disk of matter that surrounds the black hole.
“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,” Miller-Jones said in the statement.
To come to these conclusions, the researchers looked at radio waves and X-rays that were emitted by black hole 4U 1630-47.
The X-ray spectrum picked up the characteristic signature of iron and nickel that was off just a bit.