May 22, 2006
Astrophysicists Discover ‘Compact Jets’ From Neutron Star
By Kim McDonald and Linda Vu
Compact jets that shoot matter into space in a continuous stream at near the speed of light have long been assumed to be a unique feature of black holes. But these odd features of the universe may be more common than once thought.
Astrophysicists using NASA's Spitzer Space Telescope recently spotted one of these jets around a super-dense dead star, confirming for the first time that neutron stars as well as black holes can produce these fire-hose-like jets of matter. A paper detailing their surprising discovery appears in this week’s issue of the Astrophysical Journal Letters.
"For years, scientists suspected that something unique to black holes must be fueling the continuous compact jets because we only saw them coming from black hole systems,” said Simone Migliari, an astrophysicist at the University of California, San Diego’s Center for Astrophysics and Space Sciences and the lead author of the paper. “Now that Spitzer has revealed a steady jet coming from a neutron star in an X-ray binary system, we know that the jets must be fueled by something that both systems share.”
A neutron star X-ray binary system occurs when a normal star orbits a dead star that is so dense all of its atoms have collapsed into neutrons, hence the name “neutron star.” The normal star circles the neutron star the same way Earth orbits the Sun.
Migliari and his colleagues from four institutions in the U.S. and Europe used Spitzer's super sensitive infrared eyes to study a jet in one such system called 4U 0614+091. In this system, the neutron star is more than 14 times the mass of its orbiting stellar companion.
“Our data show that the presence of an accretion disk and an intense gravitational field may be all we need to form and fuel a compact jet,” he said.
Typically, radio telescopes are the tool of choice for observing compact jets around black holes. At radio wavelengths, astronomers can isolate the jet from everything else in the system. However, because the compact jets of a neutron star can be more than 10 times fainter than those of a black hole, using a radio telescope to observe a neutron star's jet would take many hours of observations.
With Spitzer's supersensitive infrared eyes, Migliari's team detected 4U 0614+091's faint jet in minutes. The infrared telescope also helped astronomers infer details about the jet's geometry. System 4U 0614+091 is located approximately 10,000 light years away in the constellation Orion.
Other co-authors of the paper are John Tomsick of UCSD; Thomas Maccarone, Rob Fender and David Russell of the University of Southampton, UK; Elena Gallo of UC Santa Barbara; and Gijs Nelemans of the University of Nijmegen in the Netherlands.
NASA's Jet Propulsion Laboratory manages the Spitzer Space Telescope and science operations for the mission are conducted at the Spitzer Science Center at the California Institute of Technology.
Neutron Stars Join The Black Hole Jet Set
ScienceDaily (Jun. 28, 2007) — NASA's Chandra X-ray Observatory has revealed an X-ray jet blasting away from a neutron star in a binary system. This discovery may help astronomers understand how neutron stars as well as black holes can generate powerful beams of relativistic particles.
The jet was found in Circinus X-1, a system where a neutron star is in orbit around a star several times the mass of the Sun, about 20,000 light years from Earth. A neutron star is an extremely dense remnant of an exploded star consisting of tightly packed neutrons.
Many jets have been found originating near black holes - both the supermassive and stellar-mass variety - but the Circinus X-1 jet is the first extended X-ray jet associated with a neutron star in a binary system. This detection shows that the unusual properties of black holes - such as presence of an event horizon and the lack of an actual surface - may not be required to form powerful jets.
"Gravity appears to be the key to creating these jets, not some trick of the event horizon," said Sebastian Heinz of the University of Wisconsin at Madison, who led the study.
The discovery of this jet with Chandra also reveals how efficient neutron stars can be as cosmic power factories. Heinz and his colleagues estimate that a surprisingly high percentage of the energy available from material falling onto the neutron star is converted into powering the jet.
"In terms of energy efficiency across the Universe, this result shows that neutron stars are near the top of the list," said Norbert Schulz, a coauthor from the Massachusetts Institute of Technology in Cambridge. "This jet is almost as efficient as one from a black hole."
The Chandra results also help to explain the origin of diffuse lobes of radio emission previously detected around Circinus X-1. The team found the X-ray jets of high-energy particles are powerful enough to create and maintain these balloons of radio-emitting gas.
"We've seen enormous radio clouds around supermassive black holes at the centers of galaxies," said Heinz. "What's unusual here is that this pocket-sized version, relatively speaking, is being powered by a neutron star, not a black hole."
The main evidence for the newly found jet comes in two extended features in the Chandra data. These two fingers of X-ray emission are separated by about 30 degrees and may represent the outer walls of a wide jet. When overlapped with radio images, these X-ray features, which are at least five light years from the neutron star, closely trace the outline of the radio jet.
Another interpretation is that these two features represent two separate, highly collimated jets produced at different times by a precessing neutron star. That is, the neutron star wobbles like a top as it spins and the jet fires at different angles at different times.
Jet precession is also consistent with radio observations taken at different times, which show varying orientation angles of the jet. If the precession scenario is correct, Circinus X-1 would possess one of the longest, narrowest jets found in X-ray binary systems to date, representing yet another way in which neutron stars can rival and even outdo their larger black hole relatives.
These results will appear in an upcoming issue of The Astrophysical Journal Letters. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.
If Blanford-Znajek mechanism is the unique and correct mechanism to generate relativistic jets, it should also be able to explain the jets from the neutron stars as well. But it doesn't, which only means that the Blanfod-Znajek mechanism fails by its own weight contrary to what people in the field may believe. On the other hand, the first conspicuous feature of dipole gravity was the unquestionable jets from the rotating compact stellar objects.
In fact any theory that requires a strong magnetic field to explain the relativistic jets faces the same problem. It breaks down when there is no magnetic field involved in the jet phenomenon. Penrose's mechanism and William's extension of it are certainly in this category. Other than the Kerr metric itself, no one seems to be able to explain why the strong magnetic field has to be present around the black holes or around the rotating neutron stars.
Also, the observed jets seem to be symmetric in both poles. If the magnetic field and the plasma are responsible for the jets, one side of the jets has to be very long while the other side must be at least 1836 times shorter because the mass of a proton is 1836 times larger than that of an electron, since in both cases the force that is responsible for the jets must come from the electromagnetic interactions according to their theories. And the oppositely charged particles can not be ejected in the same direction due to the fundamental properties of the Maxwell's equation.
It has also been speculated that the positrons are created in equal numbers of the electrons in the jet emitting process. If this assumption is correct, one side of the jets will be totally made of the electrons and the other side will be of the positrons. They(the positrons and the electrons) can not travel in the same direction. And it will eventually create a gigantic electrostatic dipole along the direction of the jets and the shear amount of the electrostatic energy accumulated in the process will halt such a stream of particles in a matter of a second. Conventionally, the observed X-ray was explained as due to the annihilation of these pairs along their path, which must have been going on for billions of years.
In conclusion, regardless of what kind of numerical simulation is introduced, there is no way of going around these stumbling blocks of the fundamental electromagnetic physical principles. It is simply impossible to explain the observed jets using the magnetic field and plasma.
Wednesday, January 30, 2008
Questions on the Validity of Blanford Znajek Mechanism on the Relativistic Jets
Posted by Eue Jin Jeong at 1:23 PM