NASA Chandra X-Ray Observatory: Pink Opaque

An extraordinary outburst produced by a black hole in a nearby galaxy has provided direct evidence for a population of old, volatile stellar black holes. 

The discovery, made by astronomers using data from NASA's Chandra X-ray Observatory, provides new insight into the nature of a mysterious class of black holes that can produce as much energy in X-rays as a million suns radiate at all wavelengths.

Researchers used Chandra to discover a new ultraluminous X-ray source, or ULX. 

These objects give off more X-rays than most binary systems, in which a companion star orbits the remains of a collapsed star. These collapsed stars form either a dense core called a neutron star or a black hole. 

The extra X-ray emission suggests ULXs contain black holes that might be much more massive than the ones found elsewhere in our galaxy.

A paper describing these results will appear in the May 10, 2012, issue of The Astrophysical Journal.

Image Credits: X-ray: NASA/CXC/Curtin University/R. Soria et al., Optical: NASA/STScI/ Middlebury College/F. Winkler et al.

NASA Chandra: A Pulsar and Its Mysterious Tail

A spinning neutron star is tied to a mysterious tail -- or so it seems. Astronomers using NASA's Chandra X-ray Observatory have found that this pulsar, known as PSR J0357+3205 (or PSR J0357 for short), apparently has a long, X-ray bright tail streaming away from it.

This composite image shows Chandra data in blue and Digitized Sky Survey data in yellow.

The position of the pulsar at the upper right end of the tail is seen by mousing over the image.

The two bright sources lying near the lower left end of the tail are both thought to be unrelated background objects located outside our galaxy.

PSR J0357 was originally discovered by the Fermi Gamma Ray Space Telescope in 2009. Astronomers calculate that the pulsar lies about 1,600 light years from Earth and is about half a million years old, which makes it roughly middle-aged for this type of object.

If the tail is at the same distance as the pulsar then it stretches for 4.2 light years in length. This would make it one of the the longest X-ray tails ever associated with a so-called "rotation-powered" pulsar, a class of pulsar that get its power from the energy lost as the rotation of the pulsar slows down. (Other types of pulsars include those driven by strong magnetic fields and still others that are powered by material falling onto the neutron star.)

The Chandra data indicate that the X-ray tail may be produced by emission from energetic particles in a pulsar wind, with the particles produced by the pulsar spiraling around magnetic field lines.

Other X-ray tails around pulsars have been interpreted as bow-shocks generated by the supersonic motion of pulsars through space, with the wind trailing behind as its particles are swept back by the pulsar's interaction with the interstellar gas it encounters.

However, this bow-shock interpretation may or may not be correct for PSR J0357, with several issues that need to be explained. For example, the Fermi data show that PSR J0357 is losing a very small amount of energy as its spin slows down with time. This energy loss is important, because it is converted into radiation and powering a particle wind from the pulsar. This places limits on the amount of energy that particles in the wind can attain, and so might not account for the quantity of X-rays seen by Chandra in the tail.

ESA XMM-Newton: Neutron star bites off more than it can chew

This animated sequence of images illustrates the partial ingestion of a clump of matter by the neutron star hosted in the Supergiant Fast X-Ray Transient, IGR J18410-0535.

The ingestion of the clump material produced a dramatic increase in the X-rays released by the neutron star, which was detected with XMM-Newton.

The peak in the X-ray luminosity corresponds to the period when the accretion rate was at its maximum.

Credits: ESA/AOES Medialab

Visit the ESA Portal to see the full sequence

Neutron Stars Are Doomed if Vacuum Energy goes out of control

Artist's illustration of an "isolated neutron star"--a neutron star that does not have an associated supernova remnant, binary companion or radio pulsations. Credit: Casey Reed/Penn State University.

A mind-bogglingly huge buildup of "vacuum energy," which would occur in just milliseconds, could lead the stellar remnants known as neutron stars to instantly collapse or explode, scientists now suggest.

What is often thought of as the empty vacuum of space is actually filled with ghostly energy and virtual particles wavering in and out of existence, a bizarre prediction of quantum theory that numerous experiments have proven true.

This "vacuum energy," as scientists call it, is usually thought of as extremely weak at best. But theoretical physicists in Brazil suggest that the immensely powerful gravitational fields of neutron stars could "awaken the vacuum," causing its energy to build up exponentially very quickly.

NASA Chandra and ESA XMM-Newton Images: Rotating Neutron Star

Observations with NASA's Chandra, Swift, and Rossi X-ray observatories, Fermi Gamma-ray Space Telescope, and ESA's XMM-Newton have revealed that a slowly rotating neutron star with an ordinary surface magnetic field is giving off bursts of X-rays and gamma rays.

This discovery may indicate the presence of an internal magnetic field much more intense than the surface magnetic field, with implications for how the most powerful magnets in the cosmos evolve.

The neutron star, SGR 0418+5729, was discovered on June 5, 2009 when the Fermi Gamma-ray Space Telescope detected bursts of gamma-rays from this object. Follow-up observations four days later with the Rossi X-Ray Timing Explorer (RXTE) showed that, in addition to sporadic X-ray bursts, the neutron star exhibits persistent X-ray emission with regular pulsations that indicate that the star has a rotational period of 9.1 seconds.

RXTE was able to monitor this activity for about 100 days. This behaviour is similar to a class of neutron stars called magnetars, which have strong to extreme magnetic fields 20 to 1000 times above the average of the galactic radio pulsars.

As neutron stars rotate, the radiation of low frequency electromagnetic waves or winds of high-energy particles carry energy away from the star, causing the rotation rate of the star to gradually decrease. Careful monitoring of SGR 0418 was possible because

Chandra and XMM-Newton were able to measure its pulsation period even though it faded by a factor of 10 after the initial detection. What sets SGR 0418 apart from other magnetars is that careful monitoring over a span of 490 days has revealed no detectable decrease in its rotation rate.

The lack of rotational slowing implies that the radiation of low frequency waves must be weak, and hence the surface magnetic field must be much weaker than normal. But this raises another question: where does the energy come from to power bursts and the persistent X-ray emission from the source?

The generally accepted answer for magnetars is that the energy to power the X- and gamma-ray emission comes from an internal magnetic field that has been twisted and amplified in the turbulent interior of the neutron star, as depicted in the illustration above.

Theoretical studies indicate that if the internal field becomes about ten or more times stronger than the surface field, the decay or untwisting of the field can lead to the production of steady and bursting X-ray emission through the heating of the neutron star crust or the acceleration of particles.

The Cosmic Hand; Constellations and Galaxies of Stars

The ultra-dense remains of a massive star light up surrounding gas and dust to create what appears to be a cosmic hand. This pulsar, seen in bright blue at the base of the "palm", is called B1509. The star is so dense that the electrons and protons in its atoms have combined to form neutrons. B1509 spins some 7 times a second and measures just 19 kilometres in diameter. The magnetic field at its surface is 15 trillion times stronger than the Earth's magnetic field. The field drives a wind of electrons and charged atoms that illuminates finger-like structures that extend north.

The pulsar's reach extends to a neighbouring gas cloud called RCW 89, where the wind lights up knots of gas, making them glow brightly in X-rays (visible in orange and red in the upper-right). The temperature in the cloud seems to vary in a circular pattern, which could mean the pulsar is precessing like a spinning top. B1509 sits some 17,000 light years away from Earth, and is estimated to be about 1700 years old. This image was captured by the orbiting Chandra X-ray Observatory. (Image: NASA/CXC/SAO/P Slane et al)

The Cigar Galaxy, or M82, earns its name when viewed in optical and infrared light (left). But X-rays (right) paint a different picture. M82, which sits some 12 million light years away, is one of the most active nearby galaxies, making it a popular subject of study.

Violent starbursts, likely triggered by the gravitational tugs of a neighbouring galaxy, light up the starry disc near its centre. These intense bursts of new star formation blast out plumes of hot gas that glow in the X-ray part of the spectrum (blue). It took 52.5 hours of observing time to create these images, which were taken by the European Space Agency's orbiting XMM-Newton satellite. (Images: ESA)

The chaotic structure of the spiral galaxy NGC 7793 makes it difficult to identify individual spiral arms, though it is possible to discern some rotation. NGC 7793 sits some 12.5 million light years away from Earth. It is one of the brightest members of the Sculptor Group, a cluster of galaxies that is one of the closest neighbours to our Local Group of galaxies. The Very Large Telescope in the Atacama Desert in Chile snapped this image. (Image: ESO)

A nascent bar sits at the centre of NGC 3359, a delicate spiral galaxy that sits some 49 million light years away in the constellation Ursa Major. Bars are elongated, rectangular bodies of stars, gas and dust that are often seen in spiral galaxies, though it is not yet clear how they fit into galaxies' evolution. Although NGC 3359 is several billion years old, this bar seems to be just 500 million years old.

The galaxy's arms are dotted with light-red patches, hydrogen-rich regions that are sites of intense star formation, similar to those seen in the Orion Nebula in the Milky Way. This image was taken by the Gemini North telescope on Mauna Kea in Hawaii. NGC 3359 can be seen with amateur telescopes. (Image: Gemini Observatory Legacy Image)

A stellar nursery is not uniformly bright, a fact highlighted by this image of NGC 3582, a nebula that sits some 10,000 light years away in the constellation Carina. Here, dark dust clouds share space with glowing gas that is energised by the ultraviolet light of young stars. Wispy structures in the clouds are created by radiation from these young stars, as well as by the explosions of short-lived, massive neighbours. This image was taken by the Gemini South telescope on Cerro Pachon in the Chilean Andes. (Image: Gemini Observatory Legacy Image)

This trio of galaxies, which together form a system called Arp 274, seem to be heading toward a cosmic collision. In fact, the two large spirals (middle and right) already seem to be entangled. But their proximity is just an illusion – the galaxies lie at different distances from Earth and are far enough from one another that astronomers do not think they interact. Two foreground stars in the Milky Way can also be seen on the right.

All three galaxies show colourful evidence of new star formation. The energised gas of stellar nurseries (pink) and clusters of young, massive stars (blue) dot the arms of the two spiral galaxies and encircle their compact companion (left). Older stars appear yellow.

Arp 274 sits 400 million light years away in the constellation Virgo. The Hubble Space Telescope snapped the ensemble in early April, after it was chosen by the public from six candidate targets. (Image: NASA/ESA/M. Livio/Hubble Heritage Team/STScI/AURA)

Organic molecules mixed with dust glow green in this infrared image of M33 captured by the Spitzer Space Telescope. M33, also called the Triangulum Galaxy, sits some 2.9 million light years away from Earth. The spiral is a member of the Milky Way's Local Group, a band of dozens of galaxies that travel as an ensemble because they are gravitationally bound. Star-forming regions appear orange-red in this image. Cool material, possibly carried outwards by winds from giant stars or supernovae, glows at infrared wavelengths beyond what optical telescopes detect as the galaxy's edge. (Image: NASA/JPL-Caltech/University of Arizona)

NASA's Galaxy Evolution Explorer captured this ultraviolet image of the nearby planetary nebula NGC 3242, also called "Jupiter's Ghost" (blue and white region at centre). It may sit as little as 1400 light years away in the constellation Hydra. As sun-like stars run out of fuel, they swell into red giants. These bloated stars jettison their outer layers of gas, eventually exposing a dense core of carbon and oxygen called a white dwarf. The ultraviolet light released by the white dwarfs lights up the surrounding gas, creating planetary nebulae. Although sun-like stars live for billions of years, planetary nebulae only last some 10,000 years. Astronomers are not sure whether the wispy white cloud that curves around the blue nebula is a chance passerby or gas that was ejected while the star was still a red giant. (Image: NASA/JPL-Caltech)