Institute of Astronomy

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Undersea Jacuzzi may give life to Saturn's icy moon

Astronomy News - 12 March 2015 - 10:13am
Dust from Saturn's rings shows Enceladus could have hydrothermal vents similar to those on Earth at the bottom of its ice-covered sea

Spacecraft Data Suggest Saturn Moon's Ocean May Harbor Hydrothermal Activity

Astronomy News - 12 March 2015 - 10:11am

NASA's Cassini spacecraft has provided scientists the first clear evidence that Saturn’s moon Enceladus exhibits signs of present-day hydrothermal activity which may resemble that seen in the deep oceans on Earth. The implications of such activity on a world other than our planet open up unprecedented scientific possibilities.

Ongoing hydrothermal activities within Enceladus

Astronomy News - 12 March 2015 - 10:11am

Ongoing hydrothermal activities within Enceladus

Nature 519, 7542 (2015). doi:10.1038/nature14262

Authors: Hsiang-Wen Hsu, Frank Postberg, Yasuhito Sekine, Takazo Shibuya, Sascha Kempf, Mihály Horányi, Antal Juhász, Nicolas Altobelli, Katsuhiko Suzuki, Yuka Masaki, Tatsu Kuwatani, Shogo Tachibana, Sin-iti Sirono, Georg Moragas-Klostermeyer & Ralf Srama

Detection of sodium-salt-rich ice grains emitted from the plume of the Saturnian moon Enceladus suggests that the grains formed as frozen droplets from a liquid water reservoir that is, or has been, in contact with rock. Gravitational field measurements suggest a regional south polar subsurface ocean of about 10 kilometres thickness located beneath an ice crust 30 to 40 kilometres thick. These findings imply rock–water interactions in regions surrounding the core of Enceladus. The resulting chemical ‘footprints’ are expected to be preserved in the liquid and subsequently transported upwards to the near-surface plume sources, where they eventually would be ejected and could be measured by a spacecraft. Here we report an analysis of silicon-rich, nanometre-sized dust particles (so-called stream particles) that stand out from the water-ice-dominated objects characteristic of Saturn. We interpret these grains as nanometre-sized SiO2 (silica) particles, initially embedded in icy grains emitted from Enceladus’ subsurface waters and released by sputter erosion in Saturn’s E ring. The composition and the limited size range (2 to 8 nanometres in radius) of stream particles indicate ongoing high-temperature (>90 °C) hydrothermal reactions associated with global-scale geothermal activity that quickly transports hydrothermal products from the ocean floor at a depth of at least 40 kilometres up to the plume of Enceladus.

Regulation of star formation in giant galaxies by precipitation, feedback and conduction

Astronomy News - 12 March 2015 - 10:10am

Regulation of star formation in giant galaxies by precipitation, feedback and conduction

Nature 519, 7542 (2015). doi:10.1038/nature14167

Authors: G. M. Voit, M. Donahue, G. L. Bryan & M. McDonald

The Universe’s largest galaxies reside at the centres of galaxy clusters and are embedded in hot gas that, if left undisturbed, would cool quickly and create many more new stars than are actually observed. Cooling can be regulated by feedback from accretion of cooling gas onto the central black hole, but requires an accretion rate finely tuned to the thermodynamic state of the hot gas. Theoretical models in which cold clouds precipitate out of the hot gas via thermal instability and accrete onto the black hole exhibit the necessary tuning. Recent observational evidence shows that the abundance of cold gas in the centres of clusters increases rapidly near the predicted threshold for instability. Here we report observations showing that this precipitation threshold extends over a large range in cluster radius, cluster mass and cosmic time. We incorporate the precipitation threshold into a framework of theoretical models for the thermodynamic state of hot gas in galaxy clusters. According to that framework, precipitation regulates star formation in some giant galaxies, while thermal conduction prevents star formation in others if it can compensate for radiative cooling and shut off precipitation.

Planetary science: Enceladus' hot springs

Astronomy News - 12 March 2015 - 10:10am

Planetary science: Enceladus' hot springs

Nature 519, 7542 (2015). doi:10.1038/519162a

Authors: Gabriel Tobie

The detection of silicon-rich particles originating from Saturn's moon Enceladus suggests that water–rock interactions are currently occurring inside it — the first evidence of ongoing hydrothermal activity beyond Earth. See Letter p.207

Astronomy: Quadruple images of supernova

Astronomy News - 12 March 2015 - 10:01am

Astronomy: Quadruple images of supernova

Nature 519, 7542 (2015). doi:10.1038/519132d

A rare configuration of cosmic objects has produced multiple images of an exploding star in the same frame. If more images of the supernova appear, the system could provide a new way to measure the Universe's growth rate.Patrick Kelly at the University of California,

An array of problems

Astronomy News - 12 March 2015 - 10:00am

An array of problems

Nature 519, 7542 (2015). doi:10.1038/519129a

Political interference in the selection process for the headquarters of the Square Kilometre Array should not go unchallenged.

On Friday 20 March, the UK will have its best solar eclipse since 1999. In this...

Astronomy News - 11 March 2015 - 10:03am
On Friday 20 March, the UK will have its best solar eclipse since 1999.

In this talk, Ian Ridpath explains what you can see during the eclipse, and why they happen.

'Light into dark: Eclipses of the Sun and Moon'

Light into dark: Eclipses of the Sun and Moon

Royal Astronomical Society public lecture, 13 January 2015 by Ian Ridpath Eclipses of the Sun and Moon are among the most awe-inspiring natural phenomena. Mo...

RAS meetings this Friday 13 March: - Ordinary Meeting has talks on the Dragonfl...

Astronomy News - 11 March 2015 - 10:03am
RAS meetings this Friday 13 March:

- Ordinary Meeting has talks on the Dragonfly Telescope, searching for extraterrestrial intelligence, and galaxy bars

- 'Tectonics from Above: Recent Advances in the Use of High-resolution Topography and Imagery'

- 'Building an Open UK SKA-Science Consortium?'

NASA to Investigate Magnetic Explosions

Astronomy News - 11 March 2015 - 10:02am
NASA is about to launch a fleet of spacecraft to investigate the mystery of "magnetic reconnection," which is making things explode across the cosmos.

Curiosity's arm short circuit leaves Mars rover stranded

Astronomy News - 11 March 2015 - 10:02am

NASA's Curiosity rover has been stuck in place on Mars since February 27 after a short circuit triggered on-board safety alerts

Welcome to the neighbourhood: new dwarf galaxies discovered in orbit around the Milky Way

Astronomy News - 11 March 2015 - 9:54am

A team of astronomers from the University of Cambridge have identified nine new dwarf satellites orbiting the Milky Way, the largest number ever discovered at once. The findings, from newly-released imaging data taken from the Dark Energy Survey, may help unravel the mysteries behind dark matter, the invisible substance holding galaxies together.

The new results also mark the first discovery of dwarf galaxies – small celestial objects that orbit larger galaxies – in a decade, after dozens were found in 2005 and 2006 in the skies above the northern hemisphere. The new satellites were found in the southern hemisphere near the Large and Small Magellanic Cloud, the largest and most well-known dwarf galaxies in the Milky Way’s orbit.

The Cambridge findings are being jointly released today with the results of a separate survey by astronomers with the Dark Energy Survey, headquartered at the US Department of Energy’s Fermi National Accelerator Laboratory. Both teams used the publicly available data taken during the first year of the Dark Energy Survey to carry out their analysis.

The newly discovered objects are a billion times dimmer than the Milky Way, and a million times less massive. The closest is about 95,000 light years away, while the most distant is more than a million light years away.

According to the Cambridge team, three of the discovered objects are definite dwarf galaxies, while others could be either dwarf galaxies or globular clusters – objects with similar visible properties to dwarf galaxies, but not held together with dark matter.

“The discovery of so many satellites in such a small area of the sky was completely unexpected,” said Dr Sergey Koposov of Cambridge’s Institute of Astronomy, the study’s lead author. “I could not believe my eyes.”

Dwarf galaxies are the smallest galaxy structures observed, the faintest of which contain just 5000 stars – the Milky Way, in contrast, contains hundreds of billions of stars. Standard cosmological models of the universe predict the existence of hundreds of dwarf galaxies in orbit around the Milky Way, but their dimness and small size makes them incredibly difficult to find, even in our own ‘backyard’.

“The large dark matter content of Milky Way satellite galaxies makes this a significant result for both astronomy and physics,” said Alex Drlica-Wagner of Fermilab, one of the leaders of the Dark Energy Survey analysis. 

Since they contain up to 99 percent dark matter and just one percent observable matter, dwarf galaxies are ideal for testing whether existing dark matter models are correct. Dark matter – which makes up 25 percent of all matter and energy in our universe – is invisible, and only makes its presence known through its gravitational pull.

“Dwarf satellites are the final frontier for testing our theories of dark matter,” said Dr Vasily Belokurov of the Institute of Astronomy, one of the study’s co-authors. “We need to find them to determine whether our cosmological picture makes sense. Finding such a large group of satellites near the Magellanic Clouds was surprising, though, as earlier surveys of the southern sky found very little, so we were not expecting to stumble on such treasure.”

The closest of these pieces of ‘treasure’ is 97,000 light years away, about halfway to the Magellanic Clouds, and is located in the constellation of Reticulum, or the Reticle. Due to the massive tidal forces of the Milky Way, it is in the process of being torn apart.

The most distant and most luminous of these objects is 1.2 million light years away in the constellation of Eridanus, or the River. It is right on the fringes of the Milky Way, and is about to get pulled in. According to the Cambridge team, it looks to have a small globular cluster of stars, which would make it the faintest galaxy to possess one.

“These results are very puzzling,” said co-author Wyn Evans, also of the Institute of Astronomy. “Perhaps they were once satellites that orbited the Magellanic Clouds and have been thrown out by the interaction of the Small and Large Magellanic Cloud. Perhaps they were once part of a gigantic group of galaxies that – along with the Magellanic Clouds – are falling into our Milky Way galaxy.”

The Dark Energy Survey is a five-year effort to photograph a large portion of the southern sky in unprecedented detail. Its primary tool is the Dark Energy Camera, which – at 570 megapixels – is the most powerful digital camera in the world, able to see galaxies up to eight billion light years from Earth. Built and tested at Fermilab, the camera is now mounted on the four-metre Victor M Blanco telescope at the Cerro Tololo Inter-American Observatory in the Andes Mountains in Chile. The camera includes five precisely shaped lenses, the largest nearly a yard across, designed and fabricated at University College London (UCL) and funded by the UK Science and Technology Facilities Council (STFC).

The Dark Energy Survey is supported by funding from the STFC, the US Department of Energy Office of Science; the National Science Foundation; funding agencies in Spain, Brazil, Germany and Switzerland; and the participating institutions.

The Cambridge research, funded by the European Research Council, will be published in The Astrophysical Journal.

Inset image: The Magellanic Clouds and the Auxiliary Telescopes at the Paranal Observatory in the Atacama Desert in Chile. Only 6 of the 9 newly discovered satellites are present in this image. The other three are just outside the field of view. The insets show images of the three most visible objects (Eridanus 1, Horologium 1 and Pictoris 1) and are 13x13 arcminutes on the sky (or 3000x3000 DECam pixels). Credit: V. Belokurov, S. Koposov (IoA, Cambridge). Photo: Y. Beletsky (Carnegie Observatories)

Astronomers have discovered a ‘treasure trove’ of rare dwarf satellite galaxies orbiting our own Milky Way. The discoveries could hold the key to understanding dark matter, the mysterious substance which holds our galaxy together.

Earlier surveys of the southern sky found very little, so we were not expecting to stumble on such treasureVasily BelokurovEuropean Southern ObservatoryThe dwarf galaxies are located near the Large and Small Magellanic Clouds, at the centre of the image.

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Registration is now open for the National Astronomy Meeting 2015. http://nam201...

Astronomy News - 10 March 2015 - 10:35am
Registration is now open for the National Astronomy Meeting 2015.

The UK's biggest gathering of professional astronomers will be held from 5-9 July in Llandudno, north Wales. Topics covered include cosmology, galaxies, interstellar medium, stars, planets, solar physics and more. Register now to book your place!

If you're interested in presenting your own research in a talk or poster, abstract submissions are due by 1 April.

Beasts of the Southern Wild. Discovery of a large number of Ultra Faint satellites in the vicinity of the Magellanic Clouds. (arXiv:1503.02079v1 [astro-ph.GA])

Astronomy News - 10 March 2015 - 10:22am

We have used the publicly released Dark Energy Survey data to hunt for new satellites of the Milky Way in the Southern hemisphere. Our search yielded a large number of promising candidates. In this paper, we announce the discovery of 9 new unambiguous ultra-faint objects, whose authenticity can be established with the DES data alone. Based on the morphological properties, three of the new satellites are dwarf galaxies, one of which is located at the very outskirts of the Milky Way, at a distance of 380 kpc. The remaining 6 objects have sizes and luminosities comparable to the Segue 1 satellite and can not be classified straightforwardly without follow-up spectroscopic observations. The satellites we have discovered cluster around the LMC and the SMC. We show that such spatial distribution is unlikely under the assumption of isotropy, and, therefore, conclude that at least some of the new satellites must have been associated with the Magellanic Clouds in the past.

Key to quantum gravity may lurk in cosmic haze

Astronomy News - 7 March 2015 - 9:18am
Any blurry observations of distant objects could suggest the universe itself is blurry at a minute scale, and hint at how to build a theory of quantum gravity

Introducing the NAVCAM image browser

Astronomy News - 7 March 2015 - 9:17am

The first set of images from Rosetta's NAVCAM has been made available to all users via ESA’s Planetary Science Archive (PSA). This first batch of image data covers the period leading up to 2 July 2014, prior to Rosetta's arrival at comet 67P/C-G. Further releases of image data will be made in blocks on a monthly basis henceforth, with the near-term aim to catch-up so that NAVCAM data will be publicly released six months after they are taken.

NASA Spacecraft Becomes First to Orbit a Dwarf Planet

Astronomy News - 7 March 2015 - 9:15am

NASA's Dawn spacecraft has become the first mission to achieve orbit around a dwarf planet. The spacecraft was approximately 38,000 miles (61,000) kilometers from Ceres when it was captured by the dwarf planet’s gravity at about 4:39 a.m. PST (7:39 a.m. EST) Friday.

VIDEO: The Ceres space probe - in 60 secs

Astronomy News - 7 March 2015 - 9:13am

The US space agency's Dawn probe is set to go into orbit around Ceres. What will it find there?

Mars: The Planet that Lost an Ocean’s Worth of Water

Astronomy News - 6 March 2015 - 10:09am
A primitive ocean on Mars held more water than Earth’s Arctic Ocean, and covered a greater portion of the planet’s surface than the Atlantic Ocean does on Earth, according to new results published today. An international team of scientists used ESO’s Very Large Telescope, along with instruments at the W. M. Keck Observatory and the NASA Infrared Telescope Facility, to monitor the atmosphere of the planet and map out the properties of the water in different parts of Mars’s atmosphere over a six-year period. These new maps are the first of their kind. The results appear online in the journal Science today.

SOHO's 3000th comet - contest

Astronomy News - 6 March 2015 - 10:08am

It may have been designed to probe and monitor the Sun, but the ESA/NASA Solar and Heliospheric Observatory (SOHO) has also found fame as a comet finder. A record-breaking 2890 comets have been discovered with SOHO since its launch in 1995, more than any other comet hunter in history!