Very Large Telescope Interferometer detects exozodiacal light

This artist's view from an imagined planet around a nearby star shows the brilliant glow of exozodiacal light extending up into the sky and swamping the Milky Way. 

This light is starlight reflected from hot dust created as the result of collisions between asteroids, and the evaporation of comets. 

The presence of such thick dust clouds in the inner regions around some stars may pose an obstacle to the direct imaging of Earth-like planets in the future. 

Credit: ESO/L. Calçada

By using the full power of the Very Large Telescope Interferometer an international team of astronomers has discovered exozodiacal light close to the habitable zones around nine nearby stars.

This light is starlight reflected from dust created as the result of collisions between asteroids, and the evaporation of comets.

The presence of such large amounts of dust in the inner regions around some stars may pose an obstacle to the direct imaging of Earth-like planets.

Using the Very Large Telescope Interferometer (VLTI) in near-infrared light, the team of astronomers observed 92 nearby stars to probe exozodiacal light from hot dust close to their habitable zones and combined the new data with earlier observations.

Bright exozodiacal light, created by the glowing grains of hot exozodiacal dust, or the reflection of starlight off these grains, was observed around nine of the targeted stars.

From dark clear sites on Earth, zodiacal light looks like a faint diffuse white glow seen in the night sky after the end of twilight, or before dawn.

It is created by sunlight reflected off tiny particles and appears to extend up from the vicinity of the Sun.

This reflected light is not just observed from Earth but can be observed from everywhere in the Solar System.

The glow being observed in this new study is a much more extreme version of the same phenomenon.

While this exozodiacal light, zodiacal light around other star systems, had been previously detected, this is the first large systematic study of this phenomenon around nearby stars.

In contrast to earlier observations the team did not observe dust that will later form into planets, but dust created in collisions between small planets of a few kilometres in size, objects called planetesimals that are similar to the asteroids and comets of the Solar System. Dust of this kind is also the origin of the zodiacal light in the Solar System.

"If we want to study the evolution of Earth-like planets close to the habitable zone, we need to observe the zodiacal dust in this region around other stars," said Steve Ertel, lead author of the paper, from ESO and the University of Grenoble in France.

"Detecting and characterising this kind of dust around other stars is a way to study the architecture and evolution of planetary systems."

Detecting faint dust close to the dazzling central star requires high resolution observations with high contrast.

Interferometry, combining light collected at the exact same time at several different telescopes, performed in infrared light is, so far, the only technique that allows this kind of system to be discovered and studied.

By using the power of the VLTI and pushing the instrument to its limits in terms of accuracy and efficiency, the team was able to reach a performance level about ten times better than other available instruments in the world.

Research paper on exozodiacal light: www.eso.org/public/archives/re… eso1435/eso1435a.pdf 

Complementary research paper on stellar companions: arxiv.org/abs/1409.6105

Three Telescopes track laws of Nature 10 billion years ago

Astronomers have focused the three most powerful optical telescopes in the world on a single point in the sky to test one of Nature's fundamental laws.

An international team, led by researchers from Swinburne University of Technology, observed a quasar, the extremely bright surroundings of a supermassive black hole, using the ESO's Very Large Telescope (VLT) in Chile and the W M Keck Observatory and Subaru Telescope, both in Hawaii.

The quasar light passed through three different galaxies, some 10, 9 and 8 billion years ago, on its way to Earth.

These galaxies absorbed a characteristic pattern of colours out of the quasar light, revealing the strength of electromagnetism, one of Nature's four fundamental forces, in the early and distant Universe.

"We spread the light very finely into its component colours, producing a rainbow with a `barcode' pattern of missing colours."

"We can then measure electromagnetism by `reading' this barcode," said Tyler Evans, Swinburne PhD student and lead author of the new study.

"We need to compare the barcode patterns from three telescopes to be sure they're right."

Previous studies, using a large number of quasars, had found hints that electromagnetism might be different in the distant reaches of the Universe, slightly weaker or slightly stronger than on Earth.

"If that's true, we'd need a completely new understanding of fundamental physics," Mr Evans said.

"So it's crucial to triple check whether and how the telescopes are distorting the barcodes."

By comparing the barcodes, the researchers found small differences between the telescopes.

"The beauty of our method is that we can also use the barcodes themselves to correct each telescope accurately," said Swinburne Associate Professor Michael Murphy, who co-authored the work.

"Once corrected, all three telescopes gave the same answer: electromagnetism hasn't changed, within a few parts per million, over 10 billion years. I think this is the most reliable measurement of its kind so far".

The team is now making similarly careful measurements in many other galaxies.

"With our new techniques and new quasar observations recently complete, we can make the most accurate check to see whether electromagnetism's strength really is changing or not," Associate Professor Murphy said.

More information: "The UVES Large Program for testing fundamental physics - III. Constraints on the fine-structure constant from 3 telescopes." T. M. Evans, M. T. Murphy, J. B. Whitmore, T. Misawa, M. Centurion, S. D'Odorico, S. Lopez, C. J. A. P. Martins, P. Molaro, P. Petitjean, H. Rahmani, R. Srianand, M. Wendt arXiv:1409.1923 [astro-ph.CO] arxiv.org/abs/1409.1923

Gamma-ray bursts (GRB): Afterglow discovery surprises scientists

Measurements of polarized light in the afterglow of GRB 120308A by the Liverpool Telescope and its RINGO2 instrument indicate the presence of a large-scale stable magnetic field linked with a young black hole, as shown in this illustration. 

Credit: NASA's Goddard Space Flight Center /S. Wiessinger

Research from an international team of scientists led by the University of Leicester has discovered for the first time that one of the most powerful events in our universe, Gamma-Ray Bursts (GRB), behave differently than previously thought.

The study, published in the prestigious scientific journal Nature, uses evidence from observation of a GRB to rule out most of the existing theoretical predictions concerning the afterglow of the explosions.

Klaas Wiersema

For Dr Klaas Wiersema, of the University of Leicester's Department of Physics and Astronomy, it was handy that he was up in the middle of the night tending to his three-year-old son which is when he got the alert that a GRB had occurred.

He said: "When a suitable GRB is detected by a satellite, I get a text message on my phone, and then I have to very quickly tell the observatory in Chile exactly which observations I want them to take, and how.

"This is usually a rather stressed and frantic few hours of working, as fast as possible, on my laptop throughout our night-time, and I remember very well that my son, who was three at the time, was up a lot that night too, so I kept on running back and forth between my laptop, my phone to call the observatory in Chile, and my son's cot!"

The effort was worth it- and has led to scientific findings that will change theoretical understandings of the afterglows of GRBs.

Dr Wiersema explains: "About once per day, a short, very bright flash of gamma-rays (the most energetic form of light) is detected by satellites. These flashes are called gamma-ray bursts (GRBs), and take place in galaxies far away, when a massive star collapses at the end of its life.

"These GRBs are followed by a so-called "afterglow", slowly fading emission that can be seen at all wavelengths (including visible light), for a few days to weeks."

"We know that the afterglow emission is formed by a shockwave, moving at very high velocities, in which electrons are being accelerated to tremendous energies."

"These fast moving electrons then produce the afterglow light that we detect.

When a massive star dies it explodes as a supernova. 

The core of the star collapses into a black hole, and in care cases a jet is formed along the rotation axis of the newly formed black hole. 

Processes in this jet emits gamma radiation, which we observe as a so-called gamma-ray burst. 

Typically gamma-ray bursts last a few minutes. 

When the jet hits material surrounding the dying star an afterglow is formed. 

New observations of the degree of polarisation of the afterglow light has shown that the afterglow behaves differently than expected 

Credit: NASA

"However, how this acceleration process actually works is very hard to study on Earth in laboratories, or using computer simulations."

"What we do, is study the polarised light of the afterglow using large optical telescopes, and special filters, that work much like the filters in Polaroid sunglasses."

Gamma-ray burst 121024A, as seen on the day of burst by ESO's Very Large Telescope (VLT) in Chile. Only a week later the source had faded completely. 

Credit: Dr Klaas Wiersema, University of Leicester, UK and Dr Peter Curran, ICRAR.

Dr Wiersema says it is important to remember that light is a wave, when light is linearly polarised, it means that the wave vibrations lie in a plane; and when light is circularly polarised, it means that that this plane rotates on the sky.

He added: "Different theories for electron acceleration and light emission within the afterglow all predict different levels of linear polarisation, but theories all agreed that there should be no circular polarisation in visible light."

Peter Curran, ICRAR

"This is where we come in: we decided to test this by carefully measuring both the linear and circular polarisation of one afterglow, of GRB 121024A, detected by the Swift satellite."

"Using the ESO Very Large Telescope (VLT) in Chile, we measured both the linear and circular polarisation of an afterglow with high accuracy."

"Much to our surprise we clearly detected circular polarisation, while theories predicted we should not see any at all."

"We believe that the most likely explanation is that the exact way in which electrons are accelerated within the afterglow shockwave is different from what we always thought."

"It is a very nice example of observations ruling out most of the existing theoretical predictions – exactly why observers like me are in this game!

More information: Paper: Circular polarisation in the optical afterglow of GRB 121024A, Nature, DOI: 10.1038/nature13237

ESO VLT: Chance meeting creates celestial diamond ring

Astronomers using ESO's Very Large Telescope in Chile have captured this eye-catching image of planetary nebula Abell 33. 

Created when an aging star blew off its outer layers, this beautiful blue bubble is, by chance, aligned with a foreground star, and bears an uncanny resemblance to a diamond engagement ring. 

This cosmic gem is unusually symmetric, appearing to be almost perfectly circular on the sky. 

Credit: ESO

Most stars with masses similar to that of our Sun will end their lives as white dwarfs—small, very dense, and hot bodies that slowly cool down over billions of years.

On the way to this final phase of their lives the stars throw their atmospheres out into the space and create planetary nebulae, colourful glowing clouds of gas surrounding the small, bright stellar relics.

This image, captured by ESO's Very Large Telescope (VLT), shows the remarkably round planetary nebula Abell 33, located some 1500 light-years from Earth.

Being perfectly round is uncommon for these objects—usually something disturbs the symmetry and causes the planetary nebula to display irregular shapes.

The strikingly bright star located along the rim of the nebula creates a beautiful illusion in this VLT image.


This is just a chance alignment, the star, named HD 83535, lies in the foreground of the nebula about halfway between Earth and Abell 33, in just the right place to make this view even more beautiful.

Together, HD 83535 and Abell 33 create a sparkling diamond ring.

Spectrograph (FORS) instrument

The remnant of Abell 33's progenitor star, on its way to becoming a white dwarf, can be seen just slightly off-centre inside the nebula, visible as a tiny white pearl.

It is still bright, more luminous than our own Sun and emits enough ultraviolet radiation to make the bubble of expelled atmosphere glow.

Abell 33 is just one of the 86 objects included in astronomer George Abell's 1966 Abell Catalogue of Planetary Nebulae.

Abell also scoured the skies for galaxy clusters, compiling the Abell Catalogue of over 4000 of these clusters in both the northern and southern hemispheres of the sky.

This image uses data from the FOcal Reducer and low dispersion Spectrograph (FORS) instrument attached to the VLT, which were acquired as part of the ESO Cosmic Gems programme.

ESA: Yepun, one of the Unit Telescopes of ESO’s Very Large Telescope (VLT)

Yepun (UT4), one of the Unit Telescopes of ESO’s Very Large Telescope (VLT) stands beneath bright star trails appearing to circle the south celestial pole, lying in the southern constellation of Octans (The Octant). 

Many exposures were taken over time and combined to give the final appearance of circular tracks.

Four Unit Telescopes (UTs) make up the VLT at Paranal, Chile.

Each UT possesses a name in the language of the native Mapuche tribe.

The names of the UTs — Antu, Kueyen, Melipal, and Yepun — represent celestial objects: the sun, moon, the Southern Cross constellation and Venus, respectively.

The UT in this photograph is Yepun, also known as UT4. Image released Jan. 7, 2013.One of the Unit Telescopes of ESO’s Very Large Telescope (VLT) stands beneath bright star trails appearing to circle the south celestial pole, lying in the southern constellation of Octans (The Octant).

Many exposures were taken over time and combined to give the final appearance of circular tracks. Four Unit Telescopes (UTs) make up the VLT at Paranal, Chile. Each UT possesses a name in the language of the native Mapuche tribe.

The names of the UTs — Antu, Kueyen, Melipal, and Yepun — represent celestial objects: the sun, moon, the Southern Cross constellation and Venus, respectively.