Institute of Astronomy

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Cohesive forces prevent the rotational breakup of rubble-pile asteroid (29075) 1950 DA

Astronomy News - 13 August 2014 - 1:00am

Cohesive forces prevent the rotational breakup of rubble-pile asteroid (29075) 1950 DA

Nature 512, 7513 (2014). doi:10.1038/nature13632

Authors: Ben Rozitis, Eric MacLennan & Joshua P. Emery

Space missions and ground-based observations have shown that some asteroids are loose collections of rubble rather than solid bodies. The physical behaviour of such ‘rubble-pile’ asteroids has been traditionally described using only gravitational and frictional forces within a granular material. Cohesive forces in the form of small van der Waals forces between constituent grains have recently been predicted to be important for small rubble piles (ten kilometres across or less), and could potentially explain fast rotation rates in the small-asteroid population. The strongest evidence so far has come from an analysis of the rotational breakup of the main-belt comet P/2013 R3 (ref. 7), although that was indirect and poorly constrained by observations. Here we report that the kilometre-sized asteroid (29075) 1950 DA (ref. 8) is a rubble pile that is rotating faster than is allowed by gravity and friction. We find that cohesive forces are required to prevent surface mass shedding and structural failure, and that the strengths of the forces are comparable to, though somewhat less than, the forces found between the grains of lunar regolith.

Astronomical instrumentation: Atmospheric blurring has a new enemy

Astronomy News - 13 August 2014 - 1:00am

Astronomical instrumentation: Atmospheric blurring has a new enemy

Nature 512, 7513 (2014). doi:10.1038/512144a

Authors: Brent Ellerbroek

A fully automated optics system that corrects atmospheric blurring of celestial objects has imaged 715 star systems thought to harbour planets, completing each observation in less time than it takes to read this article.

NASA's NuSTAR Sees Rare Blurring of Black Hole Light

Astronomy News - 12 August 2014 - 5:00pm
NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) has captured an extreme and rare event in the regions immediately surrounding a supermassive black hole. A compact source of X-rays that sits near the black hole, called the corona, has moved closer to the black hole over a period of just days.

VIDEO: 'Supermoon' lights up world skies

Astronomy News - 11 August 2014 - 10:09pm
Stargazers have been taking images of the spectacular ''supermoon'' overnight, where the moon appears bigger and brighter than usual because of its proximity to the earth.

Supermoon: Your pictures

Astronomy News - 11 August 2014 - 12:40am
Your photos of the August supermoon

Interacting supernovae from photoionization-confined shells around red supergiant stars

Astronomy News - 10 August 2014 - 1:00am

Interacting supernovae from photoionization-confined shells around red supergiant stars

Nature 512, 7514 (2014). doi:10.1038/nature13522

Authors: Jonathan Mackey, Shazrene Mohamed, Vasilii V. Gvaramadze, Rubina Kotak, Norbert Langer, Dominique M.-A. Meyer, Takashi J. Moriya & Hilding R. Neilson

Betelgeuse, a nearby red supergiant, is a fast-moving star with a powerful stellar wind that drives a bow shock into its surroundings. This picture has been challenged by the discovery of a dense and almost static shell that is three times closer to the star than the bow shock and has been decelerated by some external force. The two physically distinct structures cannot both be formed by the hydrodynamic interaction of the wind with the interstellar medium. Here we report that a model in which Betelgeuse’s wind is photoionized by radiation from external sources can explain the static shell without requiring a new understanding of the bow shock. Pressure from the photoionized wind generates a standing shock in the neutral part of the wind and forms an almost static, photoionization-confined shell. Other red supergiants should have much more massive shells than Betelgeuse, because the photoionization-confined shell traps up to 35 per cent of all mass lost during the red supergiant phase, confining this gas close to the star until it explodes. After the supernova explosion, massive shells dramatically affect the supernova light curve, providing a natural explanation for the many supernovae that have signatures of circumstellar interaction.

Rosetta Arrives at Target Comet

Astronomy News - 6 August 2014 - 9:12pm
Today, after a decade-long journey chasing its target, the European Space Agency's Rosetta probe, carrying three NASA instruments, became the first spacecraft to rendezvous with a comet, 67P/Churyumov-Gerasimenko.

NASA's Hubble Finds Supernova Star System Linked to Potential 'Zombie Star'

Astronomy News - 6 August 2014 - 5:45pm

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Supernovae are the most powerful stellar explosions in the universe. Some of them are produced by the detonation of a white dwarf, the stripped-down core of an ordinary star at the end of its life. But 12 years ago, astronomers began noticing weak stellar blasts, a kind of mini-supernova. When one such explosion occurred in the galaxy NGC 1309, astronomers looking through Hubble archival images found for the first time the star system that produced the supernova blast of a white dwarf.

Rosetta captures a comet in close-up

Astronomy News - 6 August 2014 - 5:24pm
New images are released of the mysterious comet called 67P

NASA’s Hubble Finds Supernova Star System Linked to Potential “Zombie Star”

Astronomy News - 6 August 2014 - 5:00pm
Using NASA’s Hubble Space Telescope, a team of astronomers has spotted a star system that could have left behind a “zombie star” after an unusually weak supernova explosion.

Saturn moon may host its own Dead Sea

Astronomy News - 6 August 2014 - 3:27pm
A lab model of hydrocarbon lakes on Titan shows the liquids may be saturated with benzene, with underground cave networks carved out of its deposits






Rosetta:Rosetta arrives at comet destination

Astronomy News - 6 August 2014 - 2:34pm
After a decade-long journey chasing its target, ESA’s Rosetta has today become the first spacecraft to rendezvous with a comet, opening a new chapter in Solar System exploration.

Rosetta arrives – and sends images of 'superstar comet'

Astronomy News - 6 August 2014 - 2:02pm
After a 10-year journey, the European Space Agency's Rosetta probe has reached comet 67P/Churyumov-Gerasimenko and sent back tantalising photos






Triangulum Galaxy Snapped by VST

Astronomy News - 6 August 2014 - 11:00am
The VLT Survey Telescope (VST) at ESO’s Paranal Observatory in Chile has captured a beautifully detailed image of the galaxy Messier 33. This nearby spiral, the second closest large galaxy to our own galaxy, the Milky Way, is packed with bright star clusters, and clouds of gas and dust. The new picture is amongst the most detailed wide-field views of this object ever taken and shows the many glowing red gas clouds in the spiral arms with particular clarity.

Can we overcome our dread of comets?

Astronomy News - 6 August 2014 - 1:41am
Will the Rosetta mission finally end our fear of comets?

Astronomy: Fresh look at Galactic rim

Astronomy News - 6 August 2014 - 1:00am

Astronomy: Fresh look at Galactic rim

Nature 512, 7512 (2014). doi:10.1038/512008b

A survey has provided the most detailed look yet at a mysterious ring of stars at the fringes of the Milky Way.Using data from the Pan-STARRS1 telescope in Hawaii, Colin Slater and Eric Bell at the University of Michigan in Ann Arbor and their

Astrophysics: Best gauge of exoplanet size

Astronomy News - 6 August 2014 - 1:00am

Astrophysics: Best gauge of exoplanet size

Nature 512, 7512 (2014). doi:10.1038/512009b

Astronomers have made the most precise measurement so far of an exoplanet's size — for Kepler-93b, which orbits a star around 100 parsecs away.Sarah Ballard at the University of Washington in Seattle and her colleagues estimated the planet's diameter at about 18,800 kilometres (1.48

Astrophysics: Novae join the γ-ray generators

Astronomy News - 6 August 2014 - 1:00am

Astrophysics: Novae join the γ-ray generators

Nature 512, 7512 (2014). doi:10.1038/512009c

Astronomers have identified a previously unknown source of cosmic γ-radiation.High-energy γ-rays are released in extremely energetic events such as pulsars and supernovae. But they were thought to be unlikely products of classical novae: explosions that occur on the surfaces of compact, burnt-out stars called

Astrophysics: Portrait of a doomed star

Astronomy News - 6 August 2014 - 1:00am

Astrophysics: Portrait of a doomed star

Nature 512, 7512 (2014). doi:10.1038/512034a

Authors: Stephen Justham

Some stars explode in thermonuclear supernovae, but understanding of why this occurs comes mainly from indirect clues. Now, the progenitor of a member of a strange class of such explosions may have been detected directly. See Letterp.54

A luminous, blue progenitor system for the type Iax supernova 2012Z

Astronomy News - 6 August 2014 - 1:00am

A luminous, blue progenitor system for the type Iax supernova 2012Z

Nature 512, 7512 (2014). doi:10.1038/nature13615

Authors: Curtis McCully, Saurabh W. Jha, Ryan J. Foley, Lars Bildsten, Wen-fai Fong, Robert P. Kirshner, G. H. Marion, Adam G. Riess & Maximilian D. Stritzinger

Type Iax supernovae are stellar explosions that are spectroscopically similar to some type Ia supernovae at the time of maximum light emission, except with lower ejecta velocities. They are also distinguished by lower luminosities. At late times, their spectroscopic properties diverge from those of other supernovae, but their composition (dominated by iron-group and intermediate-mass elements) suggests a physical connection to normal type Ia supernovae. Supernovae of type Iax are not rare; they occur at a rate between 5 and 30 per cent of the normal type Ia rate. The leading models for type Iax supernovae are thermonuclear explosions of accreting carbon–oxygen white dwarfs that do not completely unbind the star, implying that they are ‘less successful’ versions of normal type Ia supernovae, where complete stellar disruption is observed. Here we report the detection of the luminous, blue progenitor system of the type Iax SN 2012Z in deep pre-explosion imaging. The progenitor system's luminosity, colours, environment and similarity to the progenitor of the Galactic helium nova V445 Puppis suggest that SN 2012Z was the explosion of a white dwarf accreting material from a helium-star companion. Observations over the next few years, after SN 2012Z has faded, will either confirm this hypothesis or perhaps show that this supernova was actually the explosive death of a massive star.