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News Article | March 1, 2017
Site: spaceref.com

There's a new record holder for brightest pulsar ever found -- and astronomers are still trying to figure out how it can shine so brightly. It's now part of a small group of mysterious bright pulsars that are challenging astronomers to rethink how pulsars accumulate, or accrete, material. A pulsar is a spinning, magnetized neutron star that sweeps regular pulses of radiation in two symmetrical beams across the cosmos. If aligned well enough with Earth, these beams act like a lighthouse beacon -- appearing to flash on and off as the pulsar rotates. Pulsars were previously massive stars that exploded in powerful supernovae, leaving behind these small, dense stellar corpses. The brightest pulsar, as reported in the journal Science, is called NGC 5907 ULX. In one second, it emits the same amount of energy as our sun does in three-and-a-half years. The European Space Agency's XMM-Newton satellite found the pulsar and, independently, NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) mission also detected the signal. This pulsar is 50 million light years away, which means its light dates back to a time before humans roamed Earth. It is also the farthest known neutron star. "This object is really challenging our current understanding of the accretion process for high-luminosity pulsars," said Gian Luca Israel, from INAF-Osservatorio Astronomica di Roma, Italy, lead author of the Science paper. "It is 1,000 times more luminous than the maximum thought possible for an accreting neutron star, so something else is needed in our models in order to account for the enormous amount of energy released by the object." The previous record holder for brightest pulsar was reported in October 2014. NuSTAR had identified M82 X-2, located about 12 million light-years away in the "Cigar Galaxy" galaxy Messier 82 (M82), as a pulsar rather than a black hole. The pulsar reported in Science, NGC 5907 ULX, is 10 times brighter. Another extremely bright pulsar, the third brightest known, is called NGC 7793 P13. Using a combination of XMM-Newton and NuSTAR, one group of scientists reported the discovery in the Astrophysical Journal Letters, while another used XMM-Newton to report it in the Monthly Notices of the Royal Astronomical Society. Both studies were published in October 2016. Scientists call three extremely bright pulsars "ultraluminous X-ray sources" (ULXs). Before the 2014 discovery, many scientists thought that the brightest ULXs were black holes. "They are brighter than what you would expect from an accreting black hole of 10 solar masses," said Felix Fuerst, lead author of the Astrophysical Journal Letters study based at the European Space Astronomy Center in Madrid. Fuerst did this work while at Caltech in Pasadena, California. How these objects are able to shine so brightly is a mystery. The leading theory is that these pulsars have strong, complex magnetic fields closer to their surfaces. A magnetic field would distort the flow of incoming material close to the neutron star. This would allow the neutron star to continue accreting material while still generating high levels of brightness. It could be that many more ULXs are neutron stars, scientists say. "These discoveries of 'light,' compact objects that shine so brightly, is revolutionizing the field," Israel said. Please follow SpaceRef on Twitter and Like us on Facebook.


News Article | March 1, 2017
Site: phys.org

A pulsar is a spinning, magnetized neutron star that sweeps regular pulses of radiation in two symmetrical beams across the cosmos. If aligned well enough with Earth, these beams act like a lighthouse beacon—appearing to flash on and off as the pulsar rotates. Pulsars were previously massive stars that exploded in powerful supernovae, leaving behind these small, dense stellar corpses. The brightest pulsar, as reported in the journal Science, is called NGC 5907 ULX. In one second, it emits the same amount of energy as our sun does in three-and-a-half years. The European Space Agency's XMM-Newton satellite found the pulsar and, independently, NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) mission also detected the signal. This pulsar is 50 million light years away, which means its light dates back to a time before humans roamed Earth. It is also the farthest known neutron star. "This object is really challenging our current understanding of the accretion process for high-luminosity pulsars," said Gian Luca Israel, from INAF-Osservatorio Astronomica di Roma, Italy, lead author of the Science paper. "It is 1,000 times more luminous than the maximum thought possible for an accreting neutron star, so something else is needed in our models in order to account for the enormous amount of energy released by the object." The previous record holder for brightest pulsar was reported in October 2014. NuSTAR had identified M82 X-2, located about 12 million light-years away in the "Cigar Galaxy" galaxy Messier 82 (M82), as a pulsar rather than a black hole. The pulsar reported in Science, NGC 5907 ULX, is 10 times brighter. Another extremely bright pulsar, the third brightest known, is called NGC 7793 P13. Using a combination of XMM-Newton and NuSTAR, one group of scientists reported the discovery in the Astrophysical Journal Letters, while another used XMM-Newton to report it in the Monthly Notices of the Royal Astronomical Society. Both studies were published in October 2016. Scientists call three extremely bright pulsars "ultraluminous X-ray sources" (ULXs). Before the 2014 discovery, many scientists thought that the brightest ULXs were black holes. "They are brighter than what you would expect from an accreting black hole of 10 solar masses," said Felix Fuerst, lead author of the Astrophysical Journal Letters study based at the European Space Astronomy Center in Madrid. Fuerst did this work while at Caltech in Pasadena, California. How these objects are able to shine so brightly is a mystery. The leading theory is that these pulsars have strong, complex magnetic fields closer to their surfaces. A magnetic field would distort the flow of incoming material close to the neutron star. This would allow the neutron star to continue accreting material while still generating high levels of brightness. It could be that many more ULXs are neutron stars, scientists say. "These discoveries of 'light,' compact objects that shine so brightly, is revolutionizing the field," Israel said. Explore further: The brightest, furthest pulsar in the universe More information: For more information on NuSTAR, see http://www.nasa.gov/nustar Gian Luca Israel et al. An accreting pulsar with extreme properties drives an ultraluminous x-ray source in NGC 5907, Science (2017). DOI: 10.1126/science.aai8635


News Article | February 16, 2017
Site: news.yahoo.com

NASA's Dawn spacecraft image of the limb of dwarf planet Ceres shows a section of the northern hemisphere in this image on October 17, 2016. Courtesy NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/Handout via REUTERS CAPE CANAVERAL, Fla. (Reuters) - A NASA spacecraft has detected carbon-based materials, similar to what may have been the building blocks for life on Earth, on the Texas-sized dwarf planet Ceres that orbits between Mars and Jupiter in the main asteroid belt, scientists said on Thursday. The finding puts Ceres, a rock-and-ice world about 590 miles (950 km) in diameter, on a growing list of places in the solar system of interest to scientists looking for life beyond Earth. The list includes Mars and several ocean-bearing moons of Jupiter and Saturn. The discovery, published in the journal Science, was made by a team of researchers using NASA's Dawn spacecraft, which has been orbiting Ceres for nearly two years. "I think these organic molecules are a long way from microbial life," Dawn lead scientist Christopher Russell of the University of California Los Angeles (UCLA) wrote in an email to Reuters. "However, this discovery tells us that we need to explore Ceres further." Ceres is the largest object in the asteroid belt and is located about three times farther from the sun than Earth. The composition of Ceres is thought to reflect the material present in parts of the solar system when it was forming some 4-1/2 billion years ago. "The discovery indicates that the starting material in the solar system contained the essential elements, or the building blocks, for life," Russell said. "Ceres may have been able to take this process only so far. Perhaps to move further along the path took a larger body with more complex structure and dynamics," like Earth, Russell added. The organic material was found near a 31-mile-wide (50-km-wide) crater in Ceres' northern hemisphere. Although the exact molecular compounds in the organics could not be identified, they matched tar-like minerals, such as kerite or asphaltite, the scientists wrote. "Because Ceres is a dwarf planet that may still preserve internal heat from its formation period and may even contain a subsurface ocean, this opens the possibility that primitive life could have developed on Ceres itself," planetary scientist Michael Kuppers of the European Space Astronomy Center in Madrid wrote in an related essay in the journal Science. Based on the location and type of organics found on Ceres, scientists ruled out the possibility they were deposited by a crashing asteroid or comet. Lead researcher Maria Cristina De Sanctis of Italy's National Institute for Astrophysics and colleagues suspect the material formed inside Ceres through hydrothermal activity, though how the organics reached the surface remains a mystery.


van Rossum D.R.,Hamburger Sternwarte | Ness J.-U.,European Space Astronomy Center
Astronomische Nachrichten | Year: 2010

Super Soft Source (SSS) spectra are powered by nuclear burning on the surface of a white dwarf. The released energy causes a radiatively-driven wind that leads to a radially extended atmosphere around the white dwarf. Significant blue shifts in photospheric absorption lines are found in the spectra of novae during their SSS phase, being an evidence of continued mass loss in this phase. We present spherically symmetric PHOENIX models that account for the expansion of the ejecta. A comparison to a plane parallel, hydrostatic atmosphere model demonstrates that the mass loss can have a significant impact on the model spectra. The dynamic model yields less pronounced absorption edges, and harder X-ray spectra are the result. Therefore, lower effective temperatures are needed to explain the observed spectra. Although both types of models are yet to be fine-tuned in order to accurately determine best fit parameters, the implications on the chemical abundances are going in opposite directions. With the expanding models the requirement for strong depletion of the crucial elements that cause these edges is now avoidable. © 2010 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim.


News Article | January 11, 2017
Site: www.sciencenews.org

Water ice lies just beneath the cratered surface of dwarf planet Ceres and in shadowy pockets within those craters, new studies report. Observations from NASA’s Dawn spacecraft add to the growing body of evidence that Ceres, the largest object in the asteroid belt between the orbits of Mars and Jupiter, has held on to a considerable amount of water for billions of years. “We’ve seen ice in different contexts throughout the solar system,” says Thomas Prettyman, a planetary scientist at the Planetary Science Institute in Tucson and coauthor of one of the studies, published online December 15 in Science. “Now we see the same thing on Ceres.” Ice accumulates in craters on Mercury and the moon, an icy layer sits below the surface of Mars, and water ice slathers the landscape of several moons of the outer planets. Each new sighting of H O contributes to the story of how the solar system formed and how water was delivered to a young Earth. A layer of ice mixed with rock sits within about one meter of the surface concentrated near the poles, Prettyman and colleagues report. And images of inside some craters around the polar regions, from spots that never see sunlight, show bright patches, at least one of which is made of water ice, a separate team reports online December 15 in Nature Astronomy. “Ceres was always believed to contain lots of water ice,” says Michael Küppers, a planetary scientist at the European Space Astronomy Center in Madrid, who was not involved with either study. Its overall density is lower than pure rock, implying that some low-density material such as ice is mixed in. The Herschel Space Observatory has seen water vapor escaping from the dwarf planet (SN Online: 1/22/14), and the Dawn probe, in orbit around Ceres since 2015, spied a patch of water ice in Oxo crater, though the amount of direct sunlight there implies the ice has survived for only dozens of years (SN Online: 9/1/16). The spacecraft has also found minerals on the surface that formed in the presence of water. But researchers would like to know where Ceres’ water is. Knowing whether it is blended throughout the interior or segregated from the rock could help piece together the story of where Ceres formed and how the tiny world was put together. That, in turn, could provide insight into how diverse the worlds around other stars might be. To map the subsurface ice, Prettyman and colleagues used a neutron and gamma-ray detector onboard Dawn. As Ceres is bombarded with cosmic rays — highly energetic particles that originate outside the solar system — atoms in the dwarf planet spray out neutrons. The amount and energy of the neutrons can provide a clue to the abundance of hydrogen, presumably locked up in water molecules and hydrated minerals. Finding patches of ice was a bit more straightforward. Planetary scientist Thomas Platz and colleagues pinpointed permanently shadowed spots on Ceres, typically in crater floors near the north and south poles. The team then scoured images of those locations for bright patches. Out of the more than 600 darkened craters they identified, the researchers found 10 with bright deposits that could be surface ice. One had a chunk sticking out into just enough sunlight for Dawn to measure the spectrum of the reflected light and detect signs of water. Water vapor escaping from inside the dwarf planet likely falls back to Ceres, where some of it gets trapped in these cold spots, says Platz, of the Max Planck Institute for Solar System Research in Göttingen, Germany. Just because there is water doesn’t mean Ceres is a good place for life to take hold. Temperatures in the shadows don’t get above  –216° Celsius. “It’s pretty cold, there’s no sunlight. We don’t think that’s a habitable environment,” Platz says. Although, he adds, “one could mine for future missions to get fuel.” Ceres is now the third major heavily cratered body, along with Mercury and the moon, with permanently shadowed regions where ice builds up. “All the ones we’ve got info on to test this show you’ve accumulated something,” says Peter Thomas, a planetary scientist at Cornell University, who is not a part of either research team. Those details improve researchers’ understanding of how water interacts with a variety of planetary environments.


Sanchez Contreras C.,CSIC - National Institute of Aerospace Technology | Sanchez Contreras C.,European Space Astronomy Center | Sahai R.,Jet Propulsion Laboratory
Astrophysical Journal, Supplement Series | Year: 2012

We have performed interferometric observations of the 12CO(J= 1-0) emission in a sample of 27 objects spanning different evolutionary stages from the late asymptotic giant branch (late-AGB), through the post-AGB (pAGB) phase, and to the planetary nebula (PN) stage, but dominated by pAGB objects and young PNs (≥81%). In this paper (the first in a series) we present our maps and main nebular properties derived for the whole sample. Observations were performed with the Caltech Millimeter Array at the Owens Valley Radio Observatory. The angular resolution obtained in our survey ranges between 23 and 107. The 13CO and C 18O (J= 1-0) transitions as well as the 2.6mm continuum emission have also been observed in several objects. The detection statistics in the 12CO, 13CO, C 18O transitions and 2.6mm continuum are 89%, 83%, 0%, and 37%, respectively. We report first detections of 12CO(J= 1-0) emission in 13 targets and confirm emission from several previous marginal detections. The molecular envelope probed by 12CO(J= 1-0) emission is extended for 18 (out of 24) sources; envelope asymmetries and/or velocity gradients are found in most extended objects. Our data have been used to derive accurate target coordinates and systemic velocities and to characterize the envelope size, morphology, and kinematics. We also provide an estimate of the total molecular mass and the fraction of it contained in fast flows, lower limits to the linear momentum and to the isotopic 12C/ 13C ratio, as well as the AGB mass-loss rate and timescale for sources with extended CO emission. © 2012. The American Astronomical Society. All rights reserved..


Dobrotka A.,Slovak University of Technology in Bratislava | Ness J.-U.,European Space Astronomy Center
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present timing analyses of eight X-ray light curves and one optical/UV light curve of the nova V4743 Sgr (2002) taken by Chandra and XMM-Newton on the following days after outburst: 50 (early hard emission phase), 180, 196, 302, 371, 526 [super soft source (SSS) phase], and 742 and 1286 (quiescent emission phase). We have studied the multifrequency nature and time evolution of the dominant peak at ∼0.75 mHz using the standard Lomb-Scargle method and a 2D sine fitting method. We found a double structure of the peak and its overtone for days 180 and 196. The two frequencies were closer together on day 196, suggesting that the difference between the two peaks is gradually decreasing. For the later observations, only a single frequency can be detected, which is likely due to the exposure times being shorter than the beat period between the two peaks, especially if they are moving closer together. The observations on days 742 and 1286 are long enough to detect two frequencies with the difference found for day 196, but we confidently find only a single frequency. We found significant changes in the oscillation frequency and amplitude. We have derived blackbody temperatures from the SSS spectra, and the evolution of changes in frequency and blackbody temperature suggests that the 0.75-mHz peak was modulated by pulsations. Later, after nuclear burning had ceased, the signal stabilized at a single frequency, although the X-ray frequency differs from the optical/UV frequency obtained consistently from the Optical Monitor onboard XMM-Newton and from ground-based observations. We believe that the late frequency is the white dwarf rotation and that the ratio of spin/orbit period strongly supports that the system is an intermediate polar. © 2010 The Authors. Journal compilation © 2010 RAS.


Motta S.E.,European Space Astronomy Center | Belloni T.M.,National institute for astrophysics | Stella L.,National institute for astrophysics | Munoz-Darias T.,University of Southampton | Fender R.,University of Southampton
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present a systematic analysis of the fast time variability properties of the transient black hole binary GRO J1655-40, based on the complete set of Rossi X-ray Timing Explorer observations.We demonstrate that the frequencies of the quasi-periodic oscillations and of the broad-band noise components and their variations match accurately the strong field general relativistic frequencies of particle motion in the close vicinity of the innermost stable circular orbit, as predicted by the relativistic precession model.We obtain high-precision measurements of the black hole mass [M = (5.31 ± 0.07)M⊙, consistent with the value from optical/NIR observations] and spin (a = 0.290 ± 0.003), through the sole use of X-ray timing. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Ingram A.,University of Amsterdam | Motta S.,European Space Astronomy Center
Monthly Notices of the Royal Astronomical Society | Year: 2014

The relativistic precession model (RPM) can be used to obtain a precise measurement of the mass and spin of a black hole when the appropriate set of quasi-periodic oscillations is detected in the power-density spectrum of an accreting black hole. However, in previous studies, the solution of the RPM equations could be obtained only through numerical methods at a price of an intensive computational effort. Here, we demonstrate that the RPM system of equations can be solved analytically, drastically reducing the computational load, now limited to the Monte Carlo simulation necessary to estimate the uncertainties. The analytical method not only provides an easy solution to the RPM system when three oscillations are detected, but in all the cases where the detection of two simultaneous oscillations is coupled with an independent mass measurement. We also present a computationally inexpensive method to place limits on the black hole mass and spin when only two oscillations are observed. © 2014 The Authors.


Ness J.-U.,European Space Astronomy Center
Astronomische Nachrichten | Year: 2010

For several novae, a bright X-ray source with a spectrum resembling the class of Super Soft X-ray Sources (SSS) has been observed a few weeks to months after outburst. Novae are powered by explosive nuclear burning on the surface of a white dwarf, and enough energy is produced to power a radiatively driven wind. Owing to the evolution of the opacity of the ejecta, the observable spectrum gradually shifts from optical to soft X-rays (SSS phase). It has sometimes been assumed that at the beginning of the SSS phase no more mass loss occurs. However, high-resolution X-ray spectra of some novae have shown highly blue-shifted absorption lines, indicating a significant expansion. In this paper, I show that all novae that have been observed with X-ray gratings during their SSS phase show significant blue shifts. I argue that all models that attempt to explain the X-ray bright SSS phase have to accommodate the continued expansion of the ejecta. © 2010 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim.

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