Arecibo Finds a Binary Pulsar that is only 112 Thousand Year Old
Pulsars are rapidly spinning, highly magnetized neutron stars that emit beamed emission along their magnetic axes with clock-like stability. The first binary pulsar system, a pair of neutron stars, was discovered with the world's largest radio telescope -- the 305 meter Arecibo Radio Telescope in Puerto Rico -- by astrophysicists Russell Hulse and Joe Taylor in 1974. In the compact 7.75 hour orbit, the two neutron stars are accelerated to speeds of up to 0.1% of the speed of light. Careful measurements over 30 years of one of the neutron stars (which is visible as a pulsar) show that the orbit shrinks at the rate of about 1 mm per day. The orbital decay means that the pair will collide in about 400 million years. Hulse and Taylor received the 1993 Nobel Prize in Physics for their discovery.
An international team of astronomers using a new state-of-the-art receiver system on the Arecibo radio telescope has discovered a new binary pulsar system which promises to be an important test bed for Einstein's theory of general relativity. The new binary system consists of a 144 ms pulsar in a 4 hour orbit around an as yet unseen companion that is very likely another neutron star or a white dwarf. What makes it different from other binary pulsars is the relative youthfulness of the pulsar -- only about 112 thousand years old.
The latest discovery was made using a set of 7 high-sensitivity receivers installed at the focus of the Arecibo Radio Telescope to simultaneously observe 7 adjacent regions of the sky. This greatly increases the amount of sky that the 305 meter telescope can cover in a given time interval. "It is equivalent to having seven Arecibo telescopes working together in parallel", says Prof. Jim Cordes, of Cornell University.
From the orbital parameters measured so far, the team has shown that the pulsar's orbit precesses at a rate of 7.6 degrees per year. This relativistic effect was first identified as part of the precession of the orbit of Mercury around the Sun and its explanation was one of the initial triumphs of Einstein's theory. However, the size of this effect in the new binary system is 60,000 times larger than for Mercury. "Using Einstein's theory, the precession allows us to deduce the total mass of the binary system to be 2.6 solar masses," remarked Ingrid Stairs of the University of British Columbia. Using other constraints from their observations, the team concludes that the companion to this young Pulsar is either another neutron star or a white dwarf star. However, despite intensive searches for a neutron star companion, the nature of this companion remains unclear.
What is most intriguing about the team's measurements of new system is that the pulsar appears to be only about 112 thousand years old. "This is 1000 times younger than the double pulsar system," comments Dr. Paulo Freire, an astronomer at the Arecibo Observatory, "and if the companion is another neutron star, it might well be a baby (or extremely young) version of the double pulsar". Regardless of the nature of the companion star, the young age of the system implies a potentially large rate of formation of similar binaries in our Galaxy. "Given that typical lifetimes for pulsars are tens of millions of years, it would be extremely fortuitous for us to see one in a binary system so young unless such systems are very common," says David Nice of Bryn Mawr College.
The new discovery highlights the fact that there are many uncertainties concerning the binary pulsar population. "From observations over the next few years, we expect to be able to measure the orbital decay and other relativistic effects that will provide an important complement to the existing binary pulsar tests of Einstein's theories" says Stairs. As observed in the other relativistic binary systems, there appears to be evidence for a wobble of the pulsar's spin axis due to another general relativistic effect.
Meanwhile, the search goes on at Arecibo for more pulsars. The new binary system was found in the early stages of the survey, so more are expected. In addition, it is expected that hyperfast pulsars -- those spinning up to about 1000 times per second -- will be found, which will provide further oppportunities to probe gravitational waves and magnetized matter at densities completely inaccessible to terrestrial laboratories.
For More Information:
http://www.jb.man.ac.uk/news/youngestbinarypulsar/
An international team of astronomers using a new state-of-the-art receiver system on the Arecibo radio telescope has discovered a new binary pulsar system which promises to be an important test bed for Einstein's theory of general relativity. The new binary system consists of a 144 ms pulsar in a 4 hour orbit around an as yet unseen companion that is very likely another neutron star or a white dwarf. What makes it different from other binary pulsars is the relative youthfulness of the pulsar -- only about 112 thousand years old.
The latest discovery was made using a set of 7 high-sensitivity receivers installed at the focus of the Arecibo Radio Telescope to simultaneously observe 7 adjacent regions of the sky. This greatly increases the amount of sky that the 305 meter telescope can cover in a given time interval. "It is equivalent to having seven Arecibo telescopes working together in parallel", says Prof. Jim Cordes, of Cornell University.
From the orbital parameters measured so far, the team has shown that the pulsar's orbit precesses at a rate of 7.6 degrees per year. This relativistic effect was first identified as part of the precession of the orbit of Mercury around the Sun and its explanation was one of the initial triumphs of Einstein's theory. However, the size of this effect in the new binary system is 60,000 times larger than for Mercury. "Using Einstein's theory, the precession allows us to deduce the total mass of the binary system to be 2.6 solar masses," remarked Ingrid Stairs of the University of British Columbia. Using other constraints from their observations, the team concludes that the companion to this young Pulsar is either another neutron star or a white dwarf star. However, despite intensive searches for a neutron star companion, the nature of this companion remains unclear.
What is most intriguing about the team's measurements of new system is that the pulsar appears to be only about 112 thousand years old. "This is 1000 times younger than the double pulsar system," comments Dr. Paulo Freire, an astronomer at the Arecibo Observatory, "and if the companion is another neutron star, it might well be a baby (or extremely young) version of the double pulsar". Regardless of the nature of the companion star, the young age of the system implies a potentially large rate of formation of similar binaries in our Galaxy. "Given that typical lifetimes for pulsars are tens of millions of years, it would be extremely fortuitous for us to see one in a binary system so young unless such systems are very common," says David Nice of Bryn Mawr College.
The new discovery highlights the fact that there are many uncertainties concerning the binary pulsar population. "From observations over the next few years, we expect to be able to measure the orbital decay and other relativistic effects that will provide an important complement to the existing binary pulsar tests of Einstein's theories" says Stairs. As observed in the other relativistic binary systems, there appears to be evidence for a wobble of the pulsar's spin axis due to another general relativistic effect.
Meanwhile, the search goes on at Arecibo for more pulsars. The new binary system was found in the early stages of the survey, so more are expected. In addition, it is expected that hyperfast pulsars -- those spinning up to about 1000 times per second -- will be found, which will provide further oppportunities to probe gravitational waves and magnetized matter at densities completely inaccessible to terrestrial laboratories.
For More Information:
http://www.jb.man.ac.uk/news/youngestbinarypulsar/
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