A "massive" press release

this is a photo release I wrote a couple of months ago while I was still an intern @ESO, but it just got published today... well, I wrote many more while I was there, but they were mostly about (arguably!) boring clouds of dust and gas where stars are born... this time instead I managed to write about real stuff for a change! finally something MASSIVE i.e. a galaxy cluster and weak lensing! and since the image was not that new, I made it pretty pedagogical, so here it is... enjoy :-)

A Cluster and a Sea of Galaxies

A new wide-field image released today by ESO displays many thousands of distant galaxies, and more particularly a large group belonging to the massive galaxy cluster known as Abell 315. As crowded as it may appear, this assembly of galaxies is only the proverbial “tip of the iceberg”, as Abell 315 — like most galaxy clusters — is dominated by dark matter. The huge mass of this cluster deflects light from background galaxies, distorting their observed shapes slightly.


When looking at the sky with the unaided eye, we mostly only see stars within our Milky Way galaxy and some of its closest neighbours. More distant galaxies are just too faint to be perceived by the human eye, but if we could see them, they would literally cover the sky. This new image released by ESO is both a wide-field and long-exposure one, and reveals thousands of galaxies crowding an area on the sky roughly as large as the full Moon.

These galaxies span a vast range of distances from us. Some are relatively close, as it is possible to distinguish their spiral arms or elliptical halos, especially in the upper part of the image. The more distant appear just like the faintest of blobs — their light has travelled through the Universe for eight billion years or more before reaching Earth.

Beginning in the centre of the image and extending below and to the left, a concentration of about a hundred yellowish galaxies identifies a massive galaxy cluster, designated with the number 315 in the catalogue compiled by the American astronomer George Abell in 1958 [1]. The cluster is located between the faint, red and blue galaxies and the Earth, about two billion light-years away from us. It lies in the constellation of Cetus (the Whale).

Galaxy clusters are some of the largest structures in the Universe held together by gravity. But there is more in these structures than the many galaxies we can see. Galaxies in these giants contribute to only ten percent of the mass, with hot gas in between galaxies accounting for another ten percent [2]. The remaining 80 percent is made of an invisible and unknown ingredient called dark matter that lies in between the galaxies.

The presence of dark matter is revealed through its gravitational effect: the enormous mass of a galaxy cluster acts on the light from galaxies behind the cluster like a cosmic magnifying glass, bending the trajectory of the light and thus making the galaxies appear slightly distorted [3]. By observing and analysing the twisted shapes of these background galaxies, astronomers can infer the total mass of the cluster responsible for the distortion, even when this mass is mostly invisible. However, this effect is usually tiny, and it is necessary to measure it over a huge number of galaxies to obtain significant results: in the case of Abell 315, the shapes of almost 10 000 faint galaxies in this image were studied in order to estimate the total mass of the cluster, which amounts to over a hundred thousand billion times the mass of our Sun [4].

To complement the enormous range of cosmic distances and sizes surveyed by this image, a handful of objects much smaller than galaxies and galaxy clusters and much closer to Earth are scattered throughout the field: besides several stars belonging to our galaxy, many asteroids are also visible as blue, green or red trails [5]. These objects belong to the main asteroid belt, located between the orbits of Mars and Jupiter, and their dimensions vary from some tens of kilometres, for the brightest ones, to just a few kilometres in the case of the faintest ones.

This image has been taken with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. It is a composite of several exposures acquired using three different broadband filters, for a total of almost one hour in the B filter and about one and a half hours in the V and R filters. The field of view is 34 x 33 arcminutes.

Notes:

[1] The Abell catalogue from 1958 comprised 2712 clusters of galaxies, and was integrated with an additional 1361 clusters in 1989. Abell put together this impressive collection by visual inspection of photographic plates of the sky, seeking those areas where more galaxies than average were found at approximately the same distance from us.

[2] Ten percent of a galaxy cluster’s mass consists of a very hot mixture of protons and electrons (a plasma), with temperatures as high as ten million degrees or more, which makes it visible to X-ray telescopes.

[3] Astronomers refer to these slight distortions as weak gravitational lensing, as opposed to strong gravitational lensing, characterised by more spectacular phenomena such as giant arcs, rings and multiple images.

[4] A weak lensing study of the galaxy cluster Abell 315 has been published in a paper that appeared in Astronomy & Astrophysics in 2009 (“Weak lensing observations of potentially X-ray underluminous galaxy clusters”, by J. Dietrich et al.).

[5] The blue, green or red tracks indicate that each asteroid has been detected through one of the three filters, respectively. Each track is composed of several, smaller sub-tracks, reflecting the sequence of several exposures performed in each of the filters; from the length of these sub-tracks, the distance to the asteroid can be calculated.

Image credit: ESO/J. Dietrich

Hubble's birthday and a contest

Hubble (the Space Telescope!) celebrates 20 years in orbit today... yep, it was 1990 when they kicked this bus-sized observatory out in space, although it was not until late 1993 that it started delivering "pretty pictures", due to a sperical aberration in the mirror which had to be fixed via a manned servicing mission.

But then, it was like a bullet set free: the nineties of last century were literally flooded with Hubble images, which went all the way from science magazines to all sort of products, ranging from desktop screensavers to super-cool animations in sci-fi movies, and so on... I was a teenager in those years (and kind of a "star-struck" one must I add) so I remember that pretty well, and I have no hesitation (although I did not study art nor communication) to state that Hubble images have largely affected the field of graphic design and, at the same time, the very perception of the Universe to the general public's eye.

That's why I'm promoting this contest, launched in honour of Hubble's 20th: search for Hubble images in popular culture and how they contributed shaping it. I find it pretty cool. Well, I must add I had quite a say in the whole thing... ;-) but I really think it will be nice, in the end, to look at all the funny pics collected by people all around the world.

If you're interested in the inter-connection between astronomy, science and popular culture, have a look at these two articles on related issues from The Guardian:
Art: the final frontier - 1st February, 2010
How science became cool - 13th April, 2010

In the image, likely Hubble's most iconic shot, are the so-called "pillars of creation", huge structures of gas and dust, in the Eagle Nebula, where newborn stars come to life. I must shyly admit this was my first desktop background in the late 1990s...
Credits: Jeff Hester and Paul Scowen (Arizona State University), and NASA/ESA.

Venus Express Celebrates Four Years of Orbit and Discoveries

ESA’s Venus Express spacecraft celebrates today its fourth anniversary orbiting our planetary neighbour. During these four years of operations, the mission has thoroughly surveyed the atmosphere of Venus, unveiling several mysteries about the climate on this planet and highlighting some similarities with the one on Earth.


Launched on November 9, 2005 from the Baykonur cosmodrome in Kazakhstan, Venus Express was successfully inserted in orbit around the planet on April 11, 2006. Its elliptical orbit is highly eccentric, with a pericentre height of only 250 km and an apocentre distance of about 66,000 km. The choice of such an orbit makes both observations from a global point of view and zooming on certain regions possible. The so-called nominal mission took place between June 2006 and October 2007, a total of about 500 Earth days, which correspond to only two days on Venus, due to this planet’s extremely slow rotation; the mission kept collecting data in the following years as well, and most likely will continue until 2013.

Venus Express has enormously increased our knowledge about this planet. Thanks to these extraordinary data, it is now possible to characterise the distribution and composition of clouds on Venus in unprecedented detail.

Amongst the seven instruments on board Venus Express, the Venus Monitoring Camera (VMC) and the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) have investigated the thick layer of clouds covering Venus between 50 and 70 km above surface. The stunning images delivered by the two instruments, thanks to their exceptional spatial resolution ranging between 50 km to a few hundred metres, highlighted different patterns in the structure of the clouds. Patchy and fragmented clouds at low latitudes show the importance of tumultuous convective phenomena in the equatorial region, where the solar heating is more intense; this mottled scenario smoothly changes into a more streaky structure at mid latitudes, and into circular and spiral features in the polar regions.


The global vortex-like structure of Venus clouds is confirmed by a particularly striking feature, revealed in the infrared wavelengths by VIRTIS: a huge eddy rotating around the southern pole, its appearance varying from oval to S-shaped. Although the eye of this hurricane, about 1500 km across, is much larger than the typical size of hurricanes on Earth, this structure highlights a morphological similarity with the distribution of clouds on our own planet.


Another instrument aboard Venus Express, the Ultraviolet and Infrared Atmospheric Spectrometer (SPICAV/SOIR), studied the planet’s atmosphere indirectly, through a method called stellar occultation. As the spacecraft moves around Venus, its line of sight to a given star moves through the atmospheric layers, and the absorption of such light due to material in the atmosphere changes accordingly. By monitoring these variations over a sample of 30 stars, it was possible to probe the vertical structure of the atmosphere of Venus, revealing an upper haze that surprisingly extends up to an altitude of 90 km.

Besides these exciting discoveries regarding the morphology of the planet’s clouds, during the past four years Venus Express also conducted extensive studies of the atmospheric composition and even peered through it, exploring the surface of the Earth’s sister planet.

--------

This story was also an exercise (and a pretty successful one I must say!) and is based on "Venus express: Highlights of the nominal mission" by D.V. Titov et al, published in 2009 on Solar System Research, Volume 43, Issue 3, pp.185-209.

In the images:
* An artist's impression of Venus Express
(Credits: ESA; Image by AOES Medialab)
* A map of the venusian clouds, with infrared (lower left) data derived from the Visible and Infrared Thermal Imaging Spectrometer, VIRTIS, on the planet’s night-side and ultraviolet (upper right) data captured by the Venus Monitoring Camera, VMC, of the day side
(Credits: ESA/MPS/DLR/IDA and ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA)
* The ‘eye of the hurricane’ close to Venus's south pole (indicated by a yellow dot) as imaged by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board Venus Express
(Credits: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA/Univ. of Oxford)

Job Hunting in the Galaxy Zoo

Massive help from citizen scientists opens new paths for full time astronomers

We are all under the same sky. Sooner or later, we all raise our eyes to gaze at the stars in the celestial vault and wonder about the mysteries of the Universe. As humankind is tied to the skies, it is natural to expect a large participation in citizen science projects inspired by astronomy. However, the massive success of “Galaxy Zoo” exceeded expectations and lead the venture to the next phase, even opening up brand-new academic positions.

Citizen scientists are members of the public that contribute to genuine scientific research. They might count birds, fish or stars, play with proteins on their computers or look for oddities in images of the cosmos, and then send their results back to professional scientists. A long-established tradition for researchers, resorting to the so-called power of the crowds yields myriad benefits to both groups.

The “Galaxy Zoo” project has been running for almost three years. The organisers, a group of astronomers based in the UK and US, had the ambitious goal of asking the public to classify the shapes of a million galaxies. The zoo analogy is striking, as galaxies in the Universe have a plethora of different morphological features; when it comes to their overall shape, however, astronomers have basically two choices: spiral or elliptical.


Understanding the shape of a galaxy goes well beyond a simple catalogue compilation, as it identifies its formation and dynamical history: stars in a spiral galaxy rotate around the centre in an ordered fashion, whereas in an elliptical galaxy they move in a much more chaotic way. Beautiful images of nearby galaxies are usually straightforward to interpret, their stunning spiral arms or roundish appearance leaving astronomers with little doubt. Far away galaxies, instead, look more like small, undefined blobs and sorting them into these two classes is an extremely delicate task.

In the past decades, countless graduate students have devoted years to the classification of galaxy shapes, which is mostly performed via visual inspection. Even though modern astronomy is a highly computer-dominated discipline, it is not trivial to teach a machine how to recognise shapes, and the human brain is still the most powerful tool in this context. Given these premises, the potential of a scheme to involve citizen scientists in galaxy classification was huge, and the “Galaxy Zoo” team has fully exploited it.

Only a few days after the launch of the project’s website, 35 000 enthusiasts had completed the same amount of work that a graduate student could have performed devoting months to this sole task. Employing the public in these operations does not demote professional astronomers; instead, it enables them to perform research with plenty of new, fresh data, without having to perform the “dirty” job themselves. Using the “Galaxy Zoo” samples, astronomers have learned new, exciting details regarding the evolution and the distribution of different galaxies, and even discovered some unexpected and never-before-seen features. More than a dozen papers have already been published in international journals, and many others are in progress, thanks to the devotion of this immense community that self-styled themselves as “Zooites”.

After the first successful results, the project has already moved to the next level: a new online sample of galaxies is ready to be characterised in much greater detail than the previous one; members of the public can also look for additional features, such as mergers between neighbouring galaxies. And there’s more, as the project’s next step involves citizen and professional scientists alike.

In order to turn the massive amount of data analysed by the community into proper results, one or more astronomers have to devote their entire energies to the “Galaxy Zoo” cause. On March 1st, a postdoctoral researcher will start working full time on this project at the University of Oxford, where it all began; soon another post-doc position will be filled at the University of Nottingham, and the Adler Planetarium, an astronomy museum with an active research group in Chicago, is recruiting scientists and software developers to join the “Galaxy Zoo” team.

This and other projects have provided innumerable members of the public with a chance to share the excitement of scientific discovery and to get a glimpse of how research works. In turn, the citizen scientists have contributed, over the years, to close the circle, dutifully delivering data and occasionally leading to scientific breakthroughs. Now, with citizen scientists literally employing professional astronomers, new research perspectives open: the circle has evolved into a spiral.

----------

This story is also an exercise i wrote just over a month ago...
For more info about the project: www.galaxyzoo.org

Image credits: Galaxy Zoo and the Sloan Digital Sky Survey

On exercises and fires

this is an exercise i wrote a couple of months ago... it's not about astronomy or physics, for a change. this time it's about earth system science, and i didn't really know much about it before reading the paper. but still, it's an example of how i write, and pretty interesting too. so, here it is:

Not All Fires Warm the World

Planting trees over vast areas of the planet may help to slow climate change, but what if then forest fires heat the world again? Now researchers say there is no need to worry, as northern forest fires may actually contribute to cooling the climate, at least on decade-long time scales.

Speculations about the role of boreal forests, the mainly evergreen woods found at high northern latitudes, in mitigating the effects of man-made global warming have raised the question of forest fires and their possible intensification due to climate changes. Previous studies focussed mostly on the conspicuous quantities of carbon dioxide and other greenhouse gases emitted during fires, highlighting a possible degeneration into a self-feeding loop. However, there is more than greenhouse gases involved in the complex interactions of forest fires with their landscape and the atmosphere.

A new study led by Earth system scientist James Randerson of the University of California, Irvine, sheds new light on the subject through an in-depth analysis of the 1999 Donnelly Flats fire, which destroyed about 7600 hectares of black spruce in interior Alaska.

Besides monitoring greenhouse gases and aerosol emissions, the team investigated the different amount of sunlight reflected by forests and burned landscapes — the so-called albedo. The bare terrain left behind by a fire reflects much more light than the dark forest’s canopy, especially when snow is lying on the ground. A higher reflecting power results in cooling and, when summed together with all other contributions, it alleviates the warming effect caused by other agents. And there is more: over the 80 years following the fire event, it even reverts the score.

Soot produced in the fire and deposited on surrounding snow and sea ice is also a player in the ‘albedo game’, this time reducing the reflecting power of otherwise almost white surfaces. Its contribution increases warming, but becomes negligible after the first year. The loss of canopy, instead, is a long-term phenomenon, as vegetation needs several decades to recover to pre-fire conditions.

Randerson and his team observed the burn perimeter over five years, and complemented these measurements with satellite data surveying the light-reflecting properties of various areas in interior Alaska where fires occurred at several different epochs in the past century.

This extensive study of the overall impact of boreal forest fires on the temperature of both northern regions and the whole planet bears the reassuring finding that fires do not contribute to the Earth’s warming if we consider long enough time scales. It will be interesting to compare these results with studies of Siberian larch forests, and, even further, to apply a similar approach to temperate and tropical ecosystems.

-----------

This story is based on "The Impact of Boreal Forest Fire on Climate Warming", by J.T. Randerson et al., published on Science on 17 November 2006 (Vol. 314. no. 5802, pp. 1130 - 1132).

The photo of the Donnelly Flats Fire, near Delta Junction, Alaska (June 13-20th 1999) is courtesy of Tom Lucas, Delta News Web.

my first proper freelance story!

last week i managed to write a freelance story for Science NOW, the online news portal of the Science magazine! you can find it here, but i thought i'd share it on my science writing blog :-)

Using Dark Matter to Sense Dark Energy

It's a weird, weird, weird universe we live in. Cosmologists and astronomers know that only 5% of it consists of ordinary matter of the sort found in stars and planets. Another 23% consists of mysterious dark matter that (so far) manifests itself only through its gravity. And a whopping 72% of the universe consists of bizarre, space-stretching dark energy which is speeding up the expansion of the universe. Scientists don't know exactly what dark matter and dark energy are. But now they've pulled off a bit of black magic and used the subtle effects of one to study the other.

Dark matter gives structure to the cosmos. Space is filled with a vast "cosmic web" of strands and clumps of dark matter, which have grown from microscopic variations in the original, nearly smooth distribution of dark matter after the big bang. Through their gravity, the clumps draw in ordinary matter, so the galaxies form and reside within these clumps. Responding to their own gravity, the clumps and strands also grow denser and more compact. At the same time, dark energy stretches the very fabric of space. So if scientists can study the evolution of the cosmic web, they ought to be able to see the effects of dark energy setting in and slightly slowing the growth and coalescence of the clumps.

And that's what astrophysicist Tim Schrabback of the Leiden Observatory in the Netherlands, and colleagues have done. Their study uses data from the Cosmic Evolution Survey, or COSMOS, the largest galaxy survey ever conducted with NASA's orbiting Hubble Space Telescope. Thanks to an improved algorithm to analyze the images, Schrabback's team could study in great detail the shapes of over 446,000 galaxies in a 1.64 square degree patch of sky. During its journey to Earth, the light from these faint galaxies must pass through the lumps and filaments of dark matter in the cosmic web. The gravity exerted by the clumps bends the paths of light rays and distorts the images of the galaxies, so rather than appearing as randomly oriented ellipses on the sky, neighboring galaxies align a bit like fish in a school. The distortions are tiny, but starting in 2000, astronomers managed to detect the effect, which is known as cosmological weak lensing, in surveys of thousands of galaxies. In recent years, they've even begun to trace, at least crudely, the three-dimensional structure of the cosmic web.

Now, Shrabback and colleagues have gone a key step further and have actually detected the effects of dark energy on the evolution of the cosmic web. This was possible thanks to additional ground-based data which allowed them to estimate distances to almost half of the observed galaxies. Together with the shape measurements, the distances helped the researchers produce a 3D "picture" of the distribution of the dark matter in the cosmic web. This tomographic approach is the cosmic analogous of the "reconstruction of the skeleton from a CT scan," adds team member F. William High from Harvard University.

This 3D view on the "cosmic web" shows how many clumps are to be found at different distances from us, and how massive they are. Comparing the results obtained on the different distance slices, the team recorded a slowing of the growth of cosmic structures, a sign that the dark energy is driving the universe to expand faster and faster. The excellent agreement between these and many other measurements indicates that "cosmologists seem to be on the right track on their quest to understand the properties and evolution of the Universe," notes Schrabback.

"This important result shows the power of weak lensing studies from space to track down dark energy," says Yun Wang, a cosmologist at the University of Oklahoma, Norman. She also points out that, in order to fully exploit this method and attempt to understand what dark energy actually is, "a much wider survey is necessary," such as those planned for the future space-telescope missions such as the United States proposed Joint Dark Energy Mission and Europe's proposed Euclid satellite. "This study demonstrates that the method can work, and anticipates the success of these future experiments," she says.

---------

This story is based on "Evidence for the accelerated expansion of the Universe from weak lensing tomography with COSMOS" by Schrabback et al. to appear soon in the journal Astronomy & Astrophysics.

The image shows the reconstruction of the total (mostly dark) matter distribution in the COSMOS field, where the colour coding indicates the distance of the foreground mass concentrations as gathered from the weak lensing effect. Structures shown in white, cyan, and green are typically closer to us than those indicated in orange and red. Credits: NASA, ESA, P. Simon (University of Bonn) and T. Schrabback (Leiden Observatory)

Exoplanet live show - next week

On Saturday, February 13, 2009 the exoplanet XO-3b will transit its parent star. Although the phenomenon itself is not spectacular, as this planet orbits its star in less than four days, it will be accompanied by an extraordinary event on Earth: for the first time ever, a professional telescope will observe the transit and the light curve will be webcast live.

The project is called "Worlds of the Sky", quoting the title of a famous book by Camille Flammarion, and is organised by the Brera and Palermo Observatories of the Italian National Institute of Astrophysics, in cooperation with several associations of amateur astronomers.

The unprecedented event will be broadcast live on the website www.crabnebula.it on February 13, from 7 p.m. on. The webcast will allow users around the world to watch the evolution of the light curve of the star XO-3 as the planet passes in front of it, monitored by the 1.34-metre Ruths Telescope of the Brera Observatory in Merate, Italy. The real-time data will be accompanied by comments of astronomers in English, Italian and Chinese.


The organisers intend to involve as many enthusiasts, students and teachers as possible in this novel outreach project, and wish that amateurs around the globe will monitor the event with their own instrumentation, joining efforts in this planetary "guided" observation of an otherworldly event.

The transit of an exoplanet is one of the main techniques used by astronomers to detect planets orbiting stars other than our Sun, monitoring the variations of a star's brightness. The planet "featured" in this event, XO-3b, was discovered in 2007. It is an extremely massive one, about 13 times as massive as Jupiter, and orbits very closely the star XO-3, also known as GSC 03727-01064, in the constellation Camelopardis. The transit will last about 170 minutes.

A promotional trailer of the event, in English, Italian and Chinese, can be found on YouTube.

Image: the Ruths Telescope of the Brera Observatory in Merate.