Institute of Astronomy

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Rosetta: 'Spuds in space'

Astronomy News - 10 July 2014 - 2:14pm
Rosetta's comet quarry shapes up

Rosetta:The three faces of Rosetta's comet

Astronomy News - 10 July 2014 - 2:13pm
What a difference a week can make. Even in the six days since the last image, the shape of comet 67P/Churyumov-Gerasimenko is becoming much more apparent, although still heavily pixelated.

Exoplanet names will be put to public vote

Astronomy News - 10 July 2014 - 12:51pm
The international group that names cosmic bodies is crowd-sourcing names for exoplanets – but will you be able to name a planet Alderaan or Westeros?

VLT Clears Up Dusty Mystery

Astronomy News - 9 July 2014 - 6:00pm
A group of astronomers has been able to follow stardust being made in real time — during the aftermath of a supernova explosion. For the first time they show that these cosmic dust factories make their grains in a two-stage process, starting soon after the explosion, but continuing for years afterwards. The team used ESO's Very Large Telescope (VLT) in northern Chile to analyse the light from the supernova SN2010jl as it slowly faded. The new results are published online in the journal Nature on 9 July 2014.

Astrophysics: Survival of the largest

Astronomy News - 9 July 2014 - 1:00am

Astrophysics: Survival of the largest

Nature 511, 7509 (2014). doi:10.1038/nature13640

Authors: Haley Gomez

Whether supernovae create most of the dust in the cosmos is a controversial question. Observations of a distant supernova have revealed signs of freshly formed dust, but the properties of the dust are unexpected. See Letter p.326

Rapid formation of large dust grains in the luminous supernova 2010jl

Astronomy News - 9 July 2014 - 1:00am

Rapid formation of large dust grains in the luminous supernova 2010jl

Nature 511, 7509 (2014). doi:10.1038/nature13558

Authors: Christa Gall, Jens Hjorth, Darach Watson, Eli Dwek, Justyn R. Maund, Ori Fox, Giorgos Leloudas, Daniele Malesani & Avril C. Day-Jones

The origin of dust in galaxies is still a mystery. The majority of the refractory elements are produced in supernova explosions, but it is unclear how and where dust grains condense and grow, and how they avoid destruction in the harsh environments of star-forming galaxies. The recent detection of 0.1 to 0.5 solar masses of dust in nearby supernova remnants suggests in situ dust formation, while other observations reveal very little dust in supernovae in the first few years after explosion. Observations of the spectral evolution of the bright SN 2010jl have been interpreted as pre-existing dust, dust formation or no dust at all. Here we report the rapid (40 to 240 days) formation of dust in its dense circumstellar medium. The wavelength-dependent extinction of this dust reveals the presence of very large (exceeding one micrometre) grains, which resist destruction. At later times (500 to 900 days), the near-infrared thermal emission shows an accelerated growth in dust mass, marking the transition of the dust source from the circumstellar medium to the ejecta. This provides the link between the early and late dust mass evolution in supernovae with dense circumstellar media.

Planetary Science: Hit-and-run origin for Mercury

Astronomy News - 9 July 2014 - 1:00am

Planetary Science: Hit-and-run origin for Mercury

Nature 511, 7508 (2014). doi:10.1038/511129c

Mercury may have formed as the result of one or more 'hit-and-run' collisions between the many protoplanets in the early Solar System.Mercury, the closest planet to the Sun, is unusual because its large metallic core lacks a massive rocky mantle like the ones that

Testing Completed on NASA's James Webb Space Telescope Backplane

Astronomy News - 8 July 2014 - 5:00pm
NASA's James Webb Space Telescope has reached another development milestone with the completion of static load testing of its primary mirror backplane support structure (PMBSS) moving the telescope one step closer to its 2018 launch.

Jet acceleration of the fast molecular outflows in the Seyfert galaxy IC 5063

Astronomy News - 6 July 2014 - 1:00am

Jet acceleration of the fast molecular outflows in the Seyfert galaxy IC 5063

Nature 511, 7510 (2014). doi:10.1038/nature13520

Authors: C. Tadhunter, R. Morganti, M. Rose, J. B. R. Oonk & T. Oosterloo

Massive outflows driven by active galactic nuclei are widely recognized to have a key role in the evolution of galaxies, by heating the ambient gas, expelling it from the nuclear regions, and thereby affecting the star-formation histories of the galaxy bulges. It has been proposed that the powerful jets of relativistic particles (such as electrons) launched by some active nuclei can both accelerate and heat the molecular gas, which often dominates the mass budgets of the outflows. Clear evidence for this mechanism, in the form of detailed associations between the molecular gas kinematics and features in the radio-emitting jets, has however been lacking. Here we report that the warm molecular hydrogen gas in the western radio lobe of the Seyfert galaxy IC 5063 is moving at high velocities—up to about 600 kilometres per second—relative to the galaxy disk. This suggests that the molecules have been accelerated by fast shocks driven into the interstellar medium by the expanding radio jets. These results demonstrate the general feasibility of accelerating molecular outflows in fast shocks driven by active nuclei.

First life-friendly exoplanet may not exist after all

Astronomy News - 3 July 2014 - 7:00pm
Touted since 2007 as a top contender for hosting life, the rocky world Gliese 581 d may be no more than sunspots, according to a re-analysis of its signal

Cool planet hints at potential for life in double stars

Astronomy News - 3 July 2014 - 7:00pm
It is an unlikely spot for life, but a chilly exoplanet orbiting one star in a binary system suggests possible locations for more habitable worlds

Rosetta:The comet takes shape, one pixel at a time!

Astronomy News - 3 July 2014 - 12:54pm
Rosetta's scientific imaging system OSIRIS is slowly but surely resolving comet 67P/Churyumov-Gerasimenko in its narrow angle camera (NAC), giving the first tantalising hints of its shape.

Biggest void in universe may explain cosmic cold spot

Astronomy News - 3 July 2014 - 11:46am
A cold spot in the big bang's afterglow may be a "shadow" of the biggest known hole in the cosmos – not a sign of a collision with another universe

Rival 'inflation' teams to share data

Astronomy News - 3 July 2014 - 10:23am
Scientists on rival projects looking for evidence that the early Universe underwent a super-expansion are in discussion about working together and publishing a joint paper.

Asteroids at the “photo finish”

Astronomy News - 3 July 2014 - 8:00am

Today's Gaia blog post is contributed by Paolo Tanga, Associate Astronomer at the Observatoire de la Côte d’Azur, Nice (France).

We tend to think that a still picture, shot with an ordinary camera, represents a subject at a given time. But this is not always the case. In some situations, a picture can show the evolution in time of the depicted subject. This is the case, for example, of the well-known “photo finish” technique widely used in athletics to record the competing athletes as they cross the arrival line at the end of the race.

How does it work? Simply, the camera aims only at a vertical strip containing the finish line and repeatedly photographs it at high speed. By putting all the strips together side-by-side, one can obtain the evolution of the image of the finish line as a function of time. As weird as it may sound, the CCD camera onboard Gaia works exactly the same way – by transforming the recorded star positions into times, the finish line being a thin strip of pixels on the edge of the detector.

Let’s imagine that we are looking at a number of athletes all running at the same speed on a straight track, but each of them having started the race at a different time: in this analogy, these are the stars, which drift across the Gaia telescopes all at the same velocity – given by the constant rotation of the satellite. If Gaia observes them several times, they will always appear spaced by the same delays.

Now, let’s add to these well-behaved competitors a different type of athlete, a rebel one who's not playing by the rules, always running either much faster or much slower than the others, and not following the direction of the track lanes but drifting as he/she pleases. Each time this eccentric athlete crosses the finish line, it will be in a different position relative to the competing runners. This is how an asteroid appears to Gaia, as its motion relative to stars makes it appear always in a different position, as a function of the time at which it is observed.

This unorthodox behaviour opens up a specific category of problems when dealing with asteroid observations. The first one is predicting when – and where – Gaia will observe a given object. In practice, it’s like predicting in advance the delays of the eccentric athlete relative to the others, when on the finish line. To perform this computation, we need to have an exact knowledge of its trajectory (the orbit of the asteroid), along with the precise speed of the “ordinary” competitors (the stars). In the case of Gaia, all these pieces of information are known, but the complexity of the scanning law, which displaces the “arrival line” in non-trivial patterns, makes the task extremely delicate. Besides, there are several “finish lines” on the Gaia focal plane (at least one per CCD), so the whole geometry of the system plays a role.

The second type of problem concerns the processing of asteroid observations, especially in the case of newly detected asteroids or of asteroids whose orbit is not yet known to great precision. In fact, each time the asteroid crosses the “finish line” it will be in a different region of the sky. Only observations that are close in time can be easily linked together, as the asteroid displacement relative to its background will be small. If the observations are performed over longer time spans, the presence of several such “rebel runners” can make things extremely complex.

These various aspects are illustrated in the following pictures. The first one (right) is a test image of the asteroid (54) Alexandra, a bright moving target. It was obtained by programming Gaia in a special imaging mode. As described before, this is a “photo finish” image. It was reconstructed by moving along the horizontal axis, which is equivalent to the observer moving in time: each pixel column represents the signal present on the “finish line” (in practice: the edge of the CCD) at a given moment. In the image, the time delay between the arrival at the finish line of the bright star and the asteroid is about 1.26 seconds. A very accurate timing of each source “arrival” is the basis of the extraordinary astrometric capabilities of Gaia.

More important, however, is the fact that in this image the predicted position of the asteroid is very close to the observed one, only a few pixels away. Given the computational difficulties involved in this process, this is an achievement with important consequences, such as the possibility to predict well enough very close “encounters” between a star and an asteroid on the plane of the sky – these are potential sources of confusion while searching for other types of anomalies (when monitoring the brightness of a star, for example). Many astronomers want to be alerted when an interesting change occurs, not when an asteroid is just passing by!

On the other hand, other astronomers (planetary scientists!) are interested in the asteroids themselves. In fact, Gaia will observe 350,000 asteroids, providing the richest sample of precise orbits and physical properties that we could dream of. Those rebel runners, containing clues about the Solar System's formation, are really interesting, and come in large quantities. Our capability to track their position is essential in the identification process.

The case of the asteroid (4997) Ksana (above) is more difficult, and showcases the capabilities of Gaia in detecting and identifying asteroids. Because it is very faint, it may have been confused with several stars – some not even present in current catalogues – making its identification more ambiguous. The presence of a source very close to the position where the asteroid was predicted to be is very encouraging, but only a comparison of data acquired over time can provide a confirmation.

The result is shown in (left), which represents an intermediate product of the processing itself: the preliminary positions of the sources seen by Gaia, as determined by the “Initial Data Treatment”. In these images, each point is a source and the point size is proportional to the source's brightness. Different colours represent the stars observed during five different sweeps of the same sky region, each lasting 6 seconds, by a single CCD.

The asteroid (4997) Ksana is now clearly seen moving from one sweep to the next (as indicated by the arrows). Checking the presence and motion of the object at the corresponding epoch provides a secure confirmation of its nature. A final remark: the observations are not equally spaced in time, and the closer couple of detections correspond to the source passing through the two telescopes (106 minutes apart) while the satellite rotates. A full rotation of the satellite (every 6 hours) separates the two detections in each pair.

Gaia asteroid observations will be processed using the software pipeline designed and implemented by Coordination Unit 4 of the DPAC, running at the CNES processing centre (Toulouse, France).

The data presented here are extracted from the results obtained by the Initial Data Treatment (IDT) pipeline, which was largely developed at the University of Barcelona and runs at the Data Processing Centre at ESAC.

Saturn's moon Titan has a very salty ocean

Astronomy News - 3 July 2014 - 3:06am
Scientists analyzing data from NASA’s Cassini mission have found evidence of an ocean inside Saturn's largest moon, Titan, which might be as salty as the Earth's Dead Sea.

Ocean on Saturn Moon Could be as Salty as the Dead Sea

Astronomy News - 2 July 2014 - 5:00pm
Scientists analyzing data from NASA’s Cassini mission have firm evidence the ocean inside Saturn's largest moon, Titan, might be as salty as the Earth's Dead Sea.

A Stellar Womb Shaped and Destroyed by its Ungrateful Offspring

Astronomy News - 2 July 2014 - 11:00am
The little-known cloud of cosmic gas and dust called Gum 15 is the birthplace and home of hot young stars. Beautiful and deadly, these stars mould the appearance of their mother nebula and, as they progress into adulthood, will eventually also be the death of her.

Astronomy: Tiny asteroid in sights for capture

Astronomy News - 2 July 2014 - 1:00am

Astronomy: Tiny asteroid in sights for capture

Nature 511, 7507 (2014). doi:10.1038/511009c

Astronomers have identified an asteroid small enough to be potentially suitable for NASA's mission to capture such a body.NASA plans to use a robotic spacecraft to either net a small asteroid or grab a rock off a larger one, before dragging the body into

Awards: Longitude Prize now an objective decision

Astronomy News - 2 July 2014 - 1:00am

Awards: Longitude Prize now an objective decision

Nature 511, 7507 (2014). doi:10.1038/511031e

Author: Carl G. Ribbing

Martin Rees writes that John Harrison “came closest to receiving the reward money” offered in the 1714 Longitude Act (Nature509, 401; 10.1038/509401a2014). This description conceals a long and painful battle between astronomers and those who argued that Harrison should