Fermi Catches a ‘Transformer’ Pulsar

Zoom into an artist’s concept of AY Sextantis, a binary star system whose pulsar switched from radio emissions to high-energy gamma rays in 2013. This transition likely means the pulsar’s spin-up process is nearing its end.

In late June 2013, an exceptional binary containing a rapidly spinning neutron star underwent a dramatic change in behavior never before observed. The pulsar’s radio beacon vanished, while at the same time the system brightened fivefold in gamma rays, the most powerful form of light, according to measurements by NASA’s Fermi Gamma-ray Space Telescope.

It’s almost as if someone flipped a switch, morphing the system from a lower-energy state to a higher-energy one,” said Benjamin Stappers, an astrophysicist at the University of Manchester, England, who led an international effort to understand this striking transformation. “The change appears to reflect an erratic interaction between the pulsar and its companion, one that allows us an opportunity to explore a rare transitional phase in the life of this binary.” Continue reading Fermi Catches a ‘Transformer’ Pulsar

Einstein’s gravity theory passes toughest test yet

Record-breaking pulsar takes tests of general relativity into new territory

Astronomers have used ESO’s Very Large Telescope, along with radio telescopes around the world, to find and study a bizarre stellar pair consisting of the most massive neutron star confirmed so far, orbited by a white dwarf star. This strange new binary allows tests of Einstein’s theory of gravity — general relativity — in ways that were not possible up to now. So far the new observations exactly agree with the predictions from general relativity and are inconsistent with some alternative theories. The results will appear in the journal Science on 26 April 2013….
… Read more at http://www.eso.org/public/news/eso1319/

Read also: A Massive Pulsar in a Compact Relativistic Binary

Celestial Bauble Intrigues Astronomers

 With the holiday season in full swing, a new image from an assembly of telescopes has revealed an unusual cosmic ornament. Data from NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton have been combined to discover a young pulsar in the remains of a supernova located in the Small Magellanic Cloud, or SMC. This would be the first definite time a pulsar, a spinning, ultra-dense star, has been found in a supernova remnant in the SMC, a small satellite galaxy to the Milky Way.

In this composite image, X-rays from Chandra and XMM-Newton have been colored blue and optical data from the Cerro Tololo Inter-American Observatory in Chile are colored red and green. The pulsar, known as SXP 1062, is the bright white source located on the right-hand side of the image in the middle of the diffuse blue emission inside a red shell. The diffuse X-rays and optical shell are both evidence for a supernova remnant surrounding the pulsar. The optical data also displays spectacular formations of gas and dust in a star-forming region on the left side of the image. A comparison of the Chandra image with optical images shows that the pulsar has a hot, massive companion.

Astronomers are interested in SXP 1062 because the Chandra and XMM-Newton data show that it is rotating unusually slowly — about once every 18 minutes. (In contrast, some pulsars are found to revolve multiple times per second, including most newly born pulsars.) This relatively leisurely pace of SXP 1062 makes it one of the slowest rotating X-ray pulsars in the SMC.

Two different teams of scientists have estimated that the supernova remnant around SXP 1062 is between 10,000 and 40,000 years old, as it appears in the image. This means that the pulsar is very young, from an astronomical perspective, since it was presumably formed in the same explosion that produced the supernova remnant. Therefore, assuming that it was born with rapid spin, it is a mystery why SXP 1062 has been able to slow down by so much, so quickly. Work has already begun on theoretical models to understand the evolution of this unusual object.

Credits: NASA/CXC/Univ. of Potsdam/L. Oskinova et al.
Read more: www.nasa.gov

The Fastest Spinning Normal Star

How fast can a star spin? Our sun rotates at a leisurely 2 kilometers per second, but now astronomers have discovered that a star in another galaxy spins 300 times faster—with a record-breaking speed of 600 kilometers per second. At that velocity, an airplane could circle Earth in little more than a minute. The star, named VFTS 102, is hot, blue, and young, residing in the Tarantula Nebula, a huge star-forming cloud of gas and dust 160,000 light-years away in the Large Magellanic Cloud, the brightest galaxy that orbits our own. As the astronomers will report in a future issue of The Astrophysical Journal LettersVFTS 102 spins faster than any other normal star ever measured; the only stars known to spin faster are dead ones called pulsars. In fact, a pulsar seems to be fleeing from the fast-spinning star, suggesting the two were once a pair that split up when a companion star exploded and became the pulsar we see today. Before the explosion, the companion star may have dumped gas onto VFTS 102, spinning it up to extreme speed the way falling water makes a water wheel turn. If the star spun just 20% faster, the centrifugal force would fling it apart.


Neutron star blows away models for thermonuclear explosions

Amsterdam astronomers have discovered a neutron star that confounds existing models for thermonuclear explosions in such extreme objects. In the case of the accreting pulsar IGR J17480-2446, it seems to be a strong magnetic field that causes some parts of the star to burn more brightly than the rest. The results of the study, by Yuri Cavecchi et al. (2011), are to be published in the journal Astrophysical Journal Letters.
The neutron star concerned is part of the X-ray binary IGR J17480-2446 (hereafter J17480). X-ray binaries consist of a neutron star and a companion star in orbit around each other. Neutron stars, which are about 1.5 times as massive as the Sun, with a diameter of about 25 km, have a strong gravitational field that can pull gas from the companion star. This gas can build up on the neutron star surface and explode in a fast, high-energy thermonuclear reaction. Normally, the entire surface of the star explodes uniformly. However, in about 10 percent of cases, some parts of the star become much brighter than the rest. Why this occurs is not understood……. Continue reading Neutron star blows away models for thermonuclear explosions

‘Odd Couple’ Binary Star System Makes Dual Gamma-Ray Flares

This diagram, which illustrates the view from Earth, shows the binary's anatomy as well as key events in the pulsar's recent close approach.

In December 2010, a pair of mismatched stars in the southern constellation Crux whisked past each other at a distance closer than Venus orbits the sun. The system possesses a so-far unique blend of a hot and massive star with a compact fast-spinning pulsar. The pair’s closest encounters occur every 3.4 years and each is marked by a sharp increase in gamma rays, the most extreme form of light.

The unique combination of stars, the long wait between close approaches, and periods of intense gamma-ray emission make this system irresistible to astrophysicists. Now, a team using NASA’s Fermi Gamma-ray Space Telescope to observe the 2010 encounter reports that the system displayed fascinating and unanticipated activity…… Continue reading ‘Odd Couple’ Binary Star System Makes Dual Gamma-Ray Flares