Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

NASA Astronomers Find Bizarre Planet-Mass Object Orbiting Neutron Star

14.09.2007
Using NASA’s Swift and Rossi X-ray Timing Explorer (RXTE) satellites, astronomers have discovered one of the most bizarre planet-mass objects ever found.

The object’s minimum mass is only about 7 times the mass of Jupiter. But instead of orbiting a normal star, this low-mass body orbits a rapidly spinning pulsar. It orbits the pulsar every 54.7 minutes at an average distance of only about 230,000 miles (slightly less than the Earth-Moon distance).


In this artist depiction of the SWIFT J1756.9-2508 system, the foreground object is the planet-mass object. The pulsar, located at the upper right, is tidally distorting the companion into a teardrop-shaped object, and ripping gas from it. This material flows in a stream toward the pulsar and forms a disk around it. Eventually, enough gas builds up in the disk to produce an outburst bright enough to make the system visible from Earth. Click on image to enlarge. Credit: Aurore Simonnet/Sonoma State University

"This object is merely the skeleton of a star," says co-discoverer Craig Markwardt of NASA’s Goddard Space Flight Center in Greenbelt, Md. "The pulsar has eaten away the star’s outer envelope, and all the remains is its helium-rich core."

Hans Krimm of NASA Goddard discovered the system on June 7, when Swift’s Burst Alert Telescope picked up an outburst of X rays and gamma rays in the direction of the galactic center. The source was named SWIFT J1756.9-2508 for its sky coordinates in the constellation Sagittarius.

RXTE began observing SWIFT J1756.9 on June 13 with its Proportional Counter Array (PCA). After analyzing the PCA data, Markwardt realized that the object was pulsing in X rays 182.07 times per second, which told him that it was a rapidly spinning pulsar. These so-called millisecond pulsars are neutron stars that spin hundreds of times per second, faster than a kitchen blender. Normally, the spin rate of neutron stars slows down as they age, but much like we can pull a string to “spin up” a top, gas spiraling onto a neutron star from its companion can maintain or even increase its fast spin.

In the case of SWIFT J1756.9-2508, Markwardt detected subtle modulations in the X-ray timing data that revealed a low-mass companion tugging the pulsar toward and away from Earth. His calculations show that the companion has a minimum mass about 7 times that of Jupiter. Because we don’t know the orbital inclination of the system, the companion’s actual mass is unknown, but it is extremely unlikely to exceed 30 Jupiters.

MIT astronomers led by Deepto Chakrabarty also observed the system with RXTE, before it faded to invisibility on June 21. Chakrabarty’s group reached identical conclusions, and the two teams have coauthored a paper that has been accepted for publication in the Astrophysical Journal Letters.

The system is only the eighth millisecond pulsar that is observed to be accreting mass from a companion. Only one other such system has a pulsar companion with such a low mass. The companion in this system, XTE J1807-294, also has a minimum mass of about 7 Jupiters. "Given that we don’t know the exact mass of either companion, ours could be the smallest," says Krimm.

The system probably formed several billion years ago, when it consisted of a very massive star and a smaller star with perhaps 1 to 3 solar masses. The more massive star evolved quickly and exploded as a supernova, leaving behind the neutron star. The smaller star eventually started to puff up en route to becoming a red giant, and the two objects became embedded in the extended stellar envelope. This drained orbital energy, causing the two stars to draw ever nearer, while simultaneously ejecting the envelope.

Today, the two objects are so close to each other than the neutron star’s powerful gravity produces a tidal bulge on its companion, siphoning off gas that flows into a disk that surrounds the neutron star. The flow eventually becomes unstable and dumps large quantities of gas onto the neutron star, causing an outburst like the one observed in June.

Evolution models by Christopher Deloye of Northwestern University suggest that the low-mass companion is helium dominated. "Despite its extremely low mass, the companion isn’t considered a planet because of its formation," says Deloye. "It’s essentially a white dwarf that has been whittled down to a planetary mass."

After billions of years, little remains of the companion star, and it remains unclear whether it will survive. "It’s been taking a beating, but that’s part of nature," adds Krimm.

With an estimated distance of roughly 25,000 light-years, the system is normally too faint to be detected at any wavelength, and is only visible during an outburst. SWIFT J1756.9 has never been seen to erupt until this June, so as Markwardt points out, "We don't know how long it will slumber before it wakes up again."

Robert Naeye | EurekAlert!
Further information:
http://www.nasa.gov
http://www.nasa.gov/centers/goddard/news/topstory/2007/millisecond_pulsar.html

More articles from Physics and Astronomy:

nachricht Mars 2020 mission to use smart methods to seek signs of past life
17.08.2017 | Goldschmidt Conference

nachricht Gold shines through properties of nano biosensors
17.08.2017 | American Institute of Physics

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Gold shines through properties of nano biosensors

17.08.2017 | Physics and Astronomy

Greenland ice flow likely to speed up: New data assert glaciers move over sediment, which gets more slippery as it gets wetter

17.08.2017 | Earth Sciences

Mars 2020 mission to use smart methods to seek signs of past life

17.08.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>