Neutron Star Fires Powerful Jets
by Barb Sanford | Development Specialist, UW-Madison
Posted Jul 21, 2011
Artists's Impression of Circinus X-1
X-ray image by the Chandra X-ray observatory (smoothed to remove noise and bring out the overall appearance)
Comparison between the X-ray emission (image) and the radio emission (green contours) of the shock around Circinus X-1
Neutron stars can make jets just about as efficiently as black holes.
This groundbreaking discovery was made by Professor Sebastian Heinz, graduate student Paul Sell and an international team of astronomers who observed the influence that powerful jets from a neutron star have on nearby gas.In a 27-hour X-ray observation with NASA’s Chandra Space Telescope, Heinz and Sell imaged X-ray shockwaves at the end of jets originating from a neutron star, which is anextremely dense, collapsed core of an exploded star. Its mass is comparable to the sun compressed to about the size of a city. One teaspoonful would weigh about as much as Mount Everest.
The neutron star is part of a binary system of two stars called Circinus X-1, orbiting each other about 20,000 light years away from Earth, or about halfway across our Milky Way Galaxy. One light year is the distance that light travels in one year, or about 6 trillion miles.
In the process of consuming material from a normal companion star, the neutron star blasts super-heated matter into space along two narrow channels called jets. As the jets race away from the neutron star at close to the speed of light, they eventually collide with denser gas.
“A collision at this speed is bound to create some real havoc,” Heinz explains. “The jets and the interstellar gas are heat- ed by blast waves from the jets and radi- ate brightly, from radio wavelengths all the way to X-rays.” In the case of Circinus X-1, this collision happens several light years away from the neutron star itself (almost a million times farther than the distance between the Earth and the Sun).
What’s spectacular about Heinz’s and Sell’s discovery is that scientists can now study these interstellar shocks in great detail. No other neutron star or black hole within our own galaxy shows anything like this. A careful analysis shows that the shockwaves are only about 1,600 years old, a relatively recent phenomenon in astronomical terms, and that this neutron star is incredibly powerful.
“The jets of Circinus X-1 are thousands of times more powerful than the entire Sun,” Sell explains. “Somehow, the neutron star can tap into the gravitational energy of the infalling material and accelerate the jet with incredible efficiency. If your car’s engine was able to accelerate your car at the same fuel efficiency that Circinus X-1 accelerates material along its jets, your car would get gas mileage of about 2 billion miles per gallon.”
“Jets have long been known to exist in a wide variety of black holes, but what makes them is still a mystery,” says Heinz. “Some theories suggest that they are made by tapping into the rotation energy of a black hole, similar to a giant flywheel that stores energy. In the case of the black hole, this energy is stored in a giant vortex of space-time that is constantly dragged around the black hole. Neutron stars have powerful jets similar to black holes, but there is no vortex effect, so something else must be powering the jet.”
Discovering that a neutron star has the same tricks up its sleeve as a black hole does, when it comes to making jets, chal- lenges scientists to explain this in their models. Knowing that these structures can exist around neutron stars also encourages them to make more obser- vations and explore new avenues with other neutron stars. “The possibility of making exciting, important discoveries to better understand how the world and the universe works at a fundamental level is what motivates me every day at work and is what science is all about,” says Sell.
A more detailed and technical accounting of this observation can be found in the Astrophysical Journal Letters, 2010, p. L194.