Institute of Astronomy

Astronomy News

NASA’s NuSTAR Telescope Discovers Shockingly Bright Dead Star

8 October 2014 - 5:00pm
Astronomers have found a pulsating, dead star beaming with the energy of about 10 million suns. This is the brightest pulsar – a dense stellar remnant left over from a supernova explosion – ever recorded. The discovery was made with NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR.

Inside exotic dead stars are piles of waffles

8 October 2014 - 4:00pm
Neutron stars are made of some of the densest and strongest material in the universe – and they may look like waffles on the inside

Lutetia's dark side hosts hidden crater

8 October 2014 - 10:38am
Grooves found on Lutetia, an asteroid encountered by ESA's Rosetta spacecraft, point to the existence of a large impact crater on the unseen side of the rocky world.

UK to open 'solar storm' centre

8 October 2014 - 6:08am
The UK Met Office formally opens its Space Weather Operations Centre on Wednesday, to lead the forecasting of the Sun’s disruptive effects on Earth.

Binary orbits as the driver of γ-ray emission and mass ejection in classical novae

8 October 2014 - 1:00am

Binary orbits as the driver of γ-ray emission and mass ejection in classical novae

Nature 514, 7522 (2014). doi:10.1038/nature13773

Authors: Laura Chomiuk, Justin D. Linford, Jun Yang, T. J. O’Brien, Zsolt Paragi, Amy J. Mioduszewski, R. J. Beswick, C. C. Cheung, Koji Mukai, Thomas Nelson, Valério A. R. M. Ribeiro, Michael P. Rupen, J. L. Sokoloski, Jennifer Weston, Yong Zheng, Michael F. Bode, Stewart Eyres, Nirupam Roy & Gregory B. Taylor

Classical novae are the most common astrophysical thermonuclear explosions, occurring on the surfaces of white dwarf stars accreting gas from companions in binary star systems. Novae typically expel about 10−4 solar masses of material at velocities exceeding 1,000 kilometres per second. However, the mechanism of mass ejection in novae is poorly understood, and could be dominated by the impulsive flash of thermonuclear energy, prolonged optically thick winds or binary interaction with the nova envelope. Classical novae are now routinely detected at gigaelectronvolt γ-ray wavelengths, suggesting that relativistic particles are accelerated by strong shocks in the ejecta. Here we report high-resolution radio imaging of the γ-ray-emitting nova V959 Mon. We find that its ejecta were shaped by the motion of the binary system: some gas was expelled rapidly along the poles as a wind from the white dwarf, while denser material drifted out along the equatorial plane, propelled by orbital motion. At the interface between the equatorial and polar regions, we observe synchrotron emission indicative of shocks and relativistic particle acceleration, thereby pinpointing the location of γ-ray production. Binary shaping of the nova ejecta and associated internal shocks are expected to be widespread among novae, explaining why many novae are γ-ray emitters.

A mass of less than 15 solar masses for the black hole in an ultraluminous X-ray source

8 October 2014 - 1:00am

A mass of less than 15 solar masses for the black hole in an ultraluminous X-ray source

Nature 514, 7521 (2014). doi:10.1038/nature13730

Authors: C. Motch, M. W. Pakull, R. Soria, F. Grisé & G. Pietrzyński

Most ultraluminous X-ray sources have a typical set of properties not seen in Galactic stellar-mass black holes. They have luminosities of more than 3 × 1039 ergs per second, unusually soft X-ray components (with a typical temperature of less than about 0.3 kiloelectronvolts) and a characteristic downturn in their spectra above about 5 kiloelectronvolts. Such puzzling properties have been interpreted either as evidence of intermediate-mass black holes or as emission from stellar-mass black holes accreting above their Eddington limit, analogous to some Galactic black holes at peak luminosity. Recently, a very soft X-ray spectrum was observed in a rare and transient stellar-mass black hole. Here we report that the X-ray source P13 in the galaxy NGC 7793 is in a binary system with a period of about 64 days and exhibits all three canonical properties of ultraluminous sources. By modelling the strong optical and ultraviolet modulations arising from X-ray heating of the B9Ia donor star, we constrain the black hole mass to be less than 15 solar masses. Our results demonstrate that in P13, soft thermal emission and spectral curvature are indeed signatures of supercritical accretion. By analogy, ultraluminous X-ray sources with similar X-ray spectra and luminosities of up to a few times 1040 ergs per second can be explained by supercritical accretion onto massive stellar-mass black holes.

Ultraluminous X-ray sources: Small field with a large impact

8 October 2014 - 1:00am

Ultraluminous X-ray sources: Small field with a large impact

Nature 514, 7521 (2014). doi:10.1038/514171a

Authors: Jeanette C. Gladstone

The nature of ultraluminous X-ray astronomical sources has long been unclear. The latest observations of these rare systems provide some crucial clues, but still leave theorists scratching their heads. See Letters p.198 & p.202

An ultraluminous X-ray source powered by an accreting neutron star

8 October 2014 - 1:00am

An ultraluminous X-ray source powered by an accreting neutron star

Nature 514, 7521 (2014). doi:10.1038/nature13791

Authors: M. Bachetti, F. A. Harrison, D. J. Walton, B. W. Grefenstette, D. Chakrabarty, F. Fürst, D. Barret, A. Beloborodov, S. E. Boggs, F. E. Christensen, W. W. Craig, A. C. Fabian, C. J. Hailey, A. Hornschemeier, V. Kaspi, S. R. Kulkarni, T. Maccarone, J. M. Miller, V. Rana, D. Stern, S. P. Tendulkar, J. Tomsick, N. A. Webb & W. W. Zhang

The majority of ultraluminous X-ray sources are point sources that are spatially offset from the nuclei of nearby galaxies and whose X-ray luminosities exceed the theoretical maximum for spherical infall (the Eddington limit) onto stellar-mass black holes. Their X-ray luminosities in the 0.5–10 kiloelectronvolt energy band range from 1039 to 1041 ergs per second. Because higher masses imply less extreme ratios of the luminosity to the isotropic Eddington limit, theoretical models have focused on black hole rather than neutron star systems. The most challenging sources to explain are those at the luminous end of the range (more than 1040 ergs per second), which require black hole masses of 50–100 times the solar value or significant departures from the standard thin disk accretion that powers bright Galactic X-ray binaries, or both. Here we report broadband X-ray observations of the nuclear region of the galaxy M82 that reveal pulsations with an average period of 1.37 seconds and a 2.5-day sinusoidal modulation. The pulsations result from the rotation of a magnetized neutron star, and the modulation arises from its binary orbit. The pulsed flux alone corresponds to an X-ray luminosity in the 3–30 kiloelectronvolt range of 4.9 × 1039 ergs per second. The pulsating source is spatially coincident with a variable source that can reach an X-ray luminosity in the 0.3–10 kiloelectronvolt range of 1.8 × 1040 ergs per second. This association implies a luminosity of about 100 times the Eddington limit for a 1.4-solar-mass object, or more than ten times brighter than any known accreting pulsar. This implies that neutron stars may not be rare in the ultraluminous X-ray population, and it challenges physical models for the accretion of matter onto magnetized compact objects.

Moon water blew in on solar wind

7 October 2014 - 6:22pm
A fresh analysis of Apollo moon samples suggests that most of the moon's surface water came from interactions with the solar wind, not from comets and meteorites as was once believed

Super-close supernova used to map the Cigar Galaxy

7 October 2014 - 3:46pm
Astronomers are using echoes of light from the second-closest supernova ever recorded to build a 3D map of its host galaxy

NASA Holds Teleconference on NuSTAR Discovery

6 October 2014 - 5:00pm
NASA will host a news teleconference at 1 p.m. EDT Wednesday, Oct. 8, to announce new findings from its Nuclear Spectroscopic Telescope Array (NuSTAR) mission. The results describe an unusual source of X-rays that will leave theorists scratching their heads, but also will help astronomers learn more about how black holes and galaxies are formed.

Vast glaciers carved out Martian Grand Canyon

3 October 2014 - 4:20pm
Mineral discoveries high up on the walls of Valles Marineris, the largest, deepest canyon in the solar system, suggest it once hosted glaciers

Moon's hidden valley system revealed

1 October 2014 - 7:44pm
Scientists identify a huge rectangular feature on the Moon that is probably the buried remains of an ancient rift valley system.

Astronomy: To catch a cosmic ray

1 October 2014 - 7:40pm

Astronomy: To catch a cosmic ray

Nature 514, 7520 (2014).

Author: Katia Moskvitch

The Pierre Auger Observatory in Argentina has spent almost ten years looking for the source of ultra-high-energy cosmic rays — but to no avail. Now the observatory faces an uncertain future.

Monster neutrino solves cosmic-ray mystery

1 October 2014 - 7:30pm
A cosmic coincidence hints that high-energy neutrinos and superfast cosmic rays both come from the supermassive black hole at the centre of the galaxy

Look inside a giant supernova that seeded the universe

1 October 2014 - 6:30pm
Some of the very massive stars that populated the early universe exploded completely, sowing the seeds of future stars, solar systems and galaxies

Titan's swirling polar cloud is cold and toxic

1 October 2014 - 6:00pm
The international Cassini mission has revealed that a giant, toxic cloud is hovering over the south pole of Saturn's largest moon, Titan, after the atmosphere has cooled in a dramatic fashion.

NASA Mission Points to Origin of “Ocean of Storms” on Earth’s Moon

1 October 2014 - 5:00pm
Using data from NASA’s Gravity Recovery and Interior Laboratory (GRAIL), mission scientists have solved a lunar mystery almost as old as the moon itself.

Wild Ducks Take Flight in Open Cluster

1 October 2014 - 11:00am
The Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile has taken this beautiful image, dappled with blue stars, of one of the most star-rich open clusters currently known — Messier 11, also known as NGC 6705 or the Wild Duck Cluster.

Astrophysics: Space ripples could pump up stars

1 October 2014 - 1:00am

Astrophysics: Space ripples could pump up stars

Nature 514, 7520 (2014). doi:10.1038/514009c

Gravitational waves could energize and brighten stars — possibly providing indirect evidence for the weak ripples in space time that are thought to be emitted by high-energy events such as exploding stars.Barry McKernan at the City University of New York and his colleagues calculated