GBT NRAO: Pulsar in stellar triple system makes unique gravitational laboratory

The pulsar (L) is orbited by a hot white dwarf star (C) both of which are orbited by a cooler, distant white dwarf (R)

Credit: NRAO

Astronomers using the National Science Foundation's Green Bank Telescope (GBT) have discovered a unique stellar system of two white dwarf stars and a superdense neutron star, all packed within a space smaller than Earth's orbit around the Sun.

The results appear in Nature journal and will be presented at the 223rd American Astronomical Society meeting.

The closeness of the stars, combined with their nature, has allowed the scientists to make the best measurements yet of the complex gravitational interactions in such a system.

In addition, detailed studies of this system may provide a key clue for resolving one of the principal outstanding problems of fundamental physics—the true nature of gravity.

"This triple system gives us a natural cosmic laboratory far better than anything found before for learning exactly how such three-body systems work and potentially for detecting problems with General Relativity that physicists expect to see under extreme conditions," said Scott Ransom of the National Radio Astronomy Observatory (NRAO).

West Virginia University graduate student Jason Boyles (now at Western Kentucky University) originally uncovered the pulsar as part of a large-scale search for pulsars with the GBT.

Pulsars are neutron stars that emit lighthouse-like beams of radio waves that rapidly sweep through space as the object spins on its axis.

GALEX satellite

One of the search's discoveries was a pulsar some 4200 light-years from Earth, spinning nearly 366 times per second.

Such rapidly-spinning pulsars are called millisecond pulsars, and can be used by astronomers as precision tools for studying a variety of phenomena, including searches for the elusive gravitational waves.

Subsequent observations showed that the pulsar is in a close orbit with a white dwarf star, and that pair is in orbit with another, more-distant white dwarf.

WIYN NRAO Telescope

"This is the first millisecond pulsar found in such a system, and we immediately recognized that it provides us a tremendous opportunity to study the effects and nature of gravity," Ransom said.

The scientists began an intensive observational program using the GBT, the Arecibo radio telescope in Puerto Rico, and the Westerbork Synthesis Radio Telescope in the Netherlands.

They also studied the system using data from the Sloan Digital Sky Survey, the GALEX satellite, the WIYN telescope on Kitt Peak, Arizona, and the Spitzer Space Telescope.

"The gravitational perturbations imposed on each member of this system by the others are incredibly pure and strong," Ransom said.

"The millisecond pulsar serves as an extremely powerful tool for measuring those perturbations incredibly well," he added.

More information: Nature DOI: 10.1038/nature12917

When Galaxies Collide: Early Merger

A very wide 130,000 light-years separates the two galaxies in the object known as 2MASXJ09133888-1019196.

But they are caught in one another’s gravitational spell and have begun a slow dance that will one day result in a merger.

The galaxies are about 700 million light-years away in the constellation Hydra.

Image: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

Earth's Gravitational Pull Threatens Near-Earth Asteroids

Asteroids, such as Itokawa, pictured here, are thought to be more like piles of rubble loosely clung together, than solid chunks of rock. Credit: ISAS/JAXA

steroids may want to think twice before they swing too close to Earth. A new study has found that our planet's gravity can cause seismic tremors, or asteroid-quakes, if the space rocks stray too close.

This process could explain why many space rocks orbiting nearby appear pristine, as if they were covered in a new and clean surface, researchers said.

Normally, asteroids are weather-beaten, their top coats of rock made dirty and reddened by the onslaught of charged particles streaming off the sun during up to 4 billion years or more of wandering the solar system.

"Any part of the surface that's facing into the sun is hit by the solar wind, which damages the mineral grains and turns them red," said the study's lead researcher Richard Binzel of MIT. "An analogy is a sunburn."

Like a sunburn on your skin, the reddening of an asteroid is only skin deep, with fresher material lurking just beneath the sun-drenched surface of the space rock, he added.

But when asteroids approach the Earth, our planet's gravity may induce small quakes that shake up the space rocks, causing the weathered pebbles on their surface to turn over, revealing their cleaner undersides. Asteroids are thought to be more like piles of rubble loosely clung together, than solid chunks of rock, which means even a small tremble could displace surface material.

"All of the particles that got reddened are going to flip over and you're going to have new material that's fresh now out facing the sun," Binzel told SPACE.com. "So it's going to change the color of the asteroid from red to a brighter gray."

The idea has been suggested before, but now Binzel and his colleagues have finally found observational evidence that it's happening.