New technique improves estimates of pulsar ages

Jun 09, 2009
Isolated pulsars gradually slow their spins, but the opposite happens if the pulsar is joined by a companion star as part of a binary system. Gas accreted from the star can force the pulsar to spin faster, resulting in rotation periods of just a few milliseconds. Credit: NASA/Dana Berry.

Astronomers at the University of California, Santa Cruz, have developed a new technique to determine the ages of millisecond pulsars, the fastest-spinning stars in the universe.

The standard method for estimating ages is known to yield unreliable results, especially for the fast-spinning millisecond pulsars, said Bülent Kiziltan, a graduate student in astronomy and astrophysics at UCSC.

"An accurate determination of pulsar ages is of fundamental importance, because it has ramifications for understanding the formation and evolution of pulsars, the physics of , and other areas," he said.

Kiziltan has been working with Stephen Thorsett, professor of astronomy and astrophysics at UCSC, to study the evolution of millisecond pulsars. He will present their new findings at the American Astronomical Society meeting in Pasadena on Monday, June 8.

A pulsar is a rapidly rotating neutron star, the collapsed core that remains after a massive star explodes as a supernova. The pulsar emits beams of (as well as x-rays and ) from the magnetic poles of the neutron star. Because the magnetic poles are not aligned with the star's spin axis, the beams sweep around like a lighthouse beacon, sending pulses of radio waves toward observers on Earth. The period between each pulse of radio waves corresponds to the rotation rate of the neutron star.

"In most cases, the only information we have is the radio pulse we receive from these compact stars. From these pulses we are trying to determine the ages, masses, and orbital parameters--a very challenging task indeed," Kiziltan said.

Ordinary pulsars tend to rotate a few times per second, and they gradually slow down with age, eventually becoming too faint to detect. Millisecond pulsars, however, rotate hundreds of time per second. They achieve these extraordinary spin rates by pulling in material from a binary companion star, a process that transfers angular momentum from the companion to the pulsar.

"This spin-up process is essentially like giving CPR to a dead or dying pulsar, giving it a second lease on life," Kiziltan said.

The standard approach to determine the "characteristic" or "spin-down" age of a pulsar is based on two parameters: the period between pulses and the rate at which they slow down. Kiziltan and Thorsett showed that this method may over- or under-estimate the age of a pulsar by a factor of 10 when applied to millisecond pulsars.

To improve the accuracy of the standard technique, they incorporated additional constraints that arise from the spin-up process and physical limits on the maximum spin period. "We modified the age calculations to be consistent with these constraints and showed that this approach can achieve estimates closer to the true age of the pulsar," Kiziltan said.

They show that, in some cases, millisecond pulsars that appear to be young can, in fact, be several billion years older. In other cases, young millisecond pulsars may mimic the characteristics of pulsars that are as old as the galaxy itself.

Source: University of California, Santa Cruz


Explore further: The origins of local planetary orbits

add to favorites email to friend print save as pdf

Related Stories

Fermi telescope unveils a dozen new pulsars

Jan 06, 2009

(PhysOrg.com) -- NASA's Fermi Gamma-ray Space Telescope has discovered 12 new gamma-ray-only pulsars and has detected gamma-ray pulses from 18 others. The finds are transforming our understanding of how these ...

Astronomers discover fastest-spinning pulsar

Jan 12, 2006

A team of astronomers led by McGill University graduate student Jason Hessels has discovered the fastest-spinning neutron star, or pulsar, ever found. The 20-mile-diameter superdense pulsar, which at 716 revolutions ...

Strange star stumps astronomers

May 16, 2008

An obese oddball of a star has left astronomers wondering how it could have formed. Dr David Champion and his colleagues at CSIRO’s Australia Telescope National Facility publish their findings about the ...

Astronomers weigh 'recycled' millisecond pulsar

Jan 12, 2006

A team of U.S. and Australian astronomers is announcing today that they have, for the first time, precisely measured the mass of a millisecond pulsar -- a tiny, dead star spinning hundreds of times every second. ...

Recommended for you

The origins of local planetary orbits

1 hour ago

A plutino is an asteroid-sized body that orbits the Sun in a 2:3 resonance with Neptune. They are named after Pluto, which also orbits the Sun twice for every three orbits of Neptune. It is thought that Pluto ...

Wild ducks take flight in open cluster

2 hours ago

The Wide Field Imager on the MPG/ESO 2.2-meter telescope at ESO's La Silla Observatory in Chile has taken this beautiful image, dappled with blue stars, of one of the most star-rich open clusters currently ...

Image: The Pillars of Creation

3 hours ago

The Pillars of Creation (seen above) is an image of a portion of the Eagle nebula (M16) taken by Hubble Space Telescope in 1995. It soon became one of the most iconic space images of all time. The Eagle nebula ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

omatumr
1 / 5 (1) Jun 15, 2009
AGE OF A PULSAR?

"A pulsar is a rapidly rotating neutron star . . . that remains after a massive star explodes as a supernova."

Might be rephrased as, "A pulsar is a rapidly rotating neutron star . . . that is visible after a massive star explodes as a supernova."

The question is whether the neutron star was present in the core of the star before it exploded?

With kind regards,
Oliver K. Manuel
http://myprofile....anuelo09