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

ESO VLT Atacama: Largest yellow hypergiant star observed

HR 5171, the brightest star just below the centre of this wide-field image, is a yellow hypergiant, a very rare type of stars with only a dozen known in our galaxy. 

Its size is over 1,300 times that of the Sun -- one of the 10 largest stars found so far. 

Observations with ESO's Very Large Telescope Interferometer have shown that it is actually a double star, with the companion in contact with the main star. 

Credit: ESO/Digitized Sky Survey 2

ESO's Very Large Telescope has revealed the largest yellow star—and one of the 10 largest stars found so far.

This hypergiant has been found to measure more than 1,300 times the diameter of the Sun, and to be part of a double star system, with the second component so close that it is in contact with the main star.

Observations spanning over 60 years also indicate that this remarkable object is changing very rapidly.

Olivier Chesneau

Using ESO's Very Large Telescope Interferometer (VLTI), Olivier Chesneau (Observatoire de la Côte d'Azur, Nice, France) and an international team of collaborators have found that the yellow hypergiant star HR 5171 A is absolutely huge—1300 times the diameter of the Sun and much bigger than was expected.

This makes it the largest yellow star known. It is also in the top ten of the largest stars known, 50% larger than the famous red supergiant Betelgeuse and about one million times brighter than the Sun.

"The new observations also showed that this star has a very close binary partner, which was a real surprise," says Chesneau.

"The two stars are so close that they touch and the whole system resembles a gigantic peanut."

The astronomers made good use of interferometry to combine the light collected from multiple individual telescopes, effectively creating a giant telescope up to 140 metres in size.

The new results prompted the team to thoroughly investigate older observations of the star spanning more than sixty years, to see how it had behaved in the past.

Chesneau concludes "The companion we have found is very significant as it can have an influence on the fate of HR 5171 A, for example, stripping off its outer layers and modifying its evolution."

This new discovery highlights the importance of studying these huge and short-lived yellow hypergiants, and could provide a means of understanding the evolutionary processes of massive stars in general.

More information: This research was presented in a paper "The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in the common envelope phase", by Chesneau et al., to appear in the journal Astronomy & Astrophysics. arxiv.org/pdf/1401.2628v2.pdf

Tiny Galaxies Hide Dark Secret

Credit: P-A Duc/CEA-CNRS/NRAO-NASA

Galaxy NGC5291 (orange, at the center) and its ring of debris (in blue) as seen by the Very Large Array interferometer.

Researchers have found evidence for the presence of dark matter in dense star-forming groups (shown in red), where 'recycled' dwarf galaxies exist.

The birth of a Radio Telescope 30 times larger than Earth

Artist's impression of Spektr-R, the 10-meter space-borne antenna of the RadioAstron project. Credit: Lavochkin Association.

On 15 November 2011, the Effelsberg 100-meter radio telescope, together with three Russian and one Ukrainian telescope, took part in the first interferometric observations with the orbiting 10-meter antenna Spektr-R of the Russian RadioAstron project. 

The observations were made at a wavelength of 18 centimeters, targeting the distant, bright, and very compact quasar 0212+735. 

Interferometric signals have been successfully detected by the RadioAstron team between Spektr-R and the ground antennas, setting a new world record for the size of a radio interferometer and opening a new era in interferometric studies of cosmic radio emission. 

Hawaii Astronomers Find Planet in the Process of Forming

Artist's conception of the area near the planet LkCa 15 b. Click on picture for larger view. Credit: Karen L. Teramura, UH IfA.

The first direct image of a planet in the process of forming around its star has been captured by University of Hawaii astronomer Adam Kraus.

What astronomers are calling LkCa 15 b, looks like a hot "protoplanet" surrounded by a swath of cooler dust and gas, which is falling into the still-forming planet.

Images have revealed that the forming planet sits inside a wide gap between the young parent star and an outer disk of dust.

Kraus (UH Institute for Astronomy) and colleague Michael Ireland (Macquarie University and the Australian Astronomical Observatory) combined the power of the 10-meter Keck Observatory telescopes with a bit of optical sleight of hand.

"LkCa 15 b is the youngest planet ever found, about 5 times younger than the previous record holder," said Kraus.

"This young gas giant is being built out of the dust and gas. In the past, you couldn't measure this kind of phenomenon because it's happening so close to the star. But, for the first time, we've been able to directly measure the planet itself as well as the dusty matter around it."

Kraus will be presenting the discovery at an Oct. 19 meeting at NASA's Goddard Space Flight Center. The meeting follows the acceptance of a research paper on the discovery by Kraus and Ireland by The Astrophysical Journal.

The optical sleight of hand used by the astronomers is to combine the power of Keck's Adaptive Optics with a technique called aperture mask interferometry. The former is the use of a deformable mirror to rapidly correct for atmospheric distortions of starlight.

The latter involves placing a small mask with several holes in the path of the light collected and concentrated by a giant telescope. With that, the scientists can manipulate the light waves.

"It's like we have an array of small mirrors," said Kraus. "We can manipulate the light and cancel out distortions." The technique allows the astronomers to cancel out the bright light of stars. They can then resolve disks of dust around stars and see gaps in the dusty layers where protoplanets may be hiding.

"Interferometry has actually been around since the 1800s, but through the use of adaptive optics has only been able to reach nearby young suns for about the last 7 years." said Dr. Ireland.

"Since then we've been trying to push the technique to its limits using the biggest telescopes in the world, especially Keck."

The discovery of LkCa 15 b began as a survey of 150 young dusty stars in star-forming regions. That led to the more concentrated study of a dozen stars.

"LkCa 15 was only our second target, and we immediately knew we were seeing something new," said Kraus. "We could see a faint point source near the star, so thinking it might be a Jupiter-like planet we went back a year later to get more data."

Russian Radio Astron: New space telescope is biggest yet

A Russian space telescope set to launch on Monday will be the biggest ever, a feat that perhaps makes up for the fact that it has taken more than 30 years to develop.

The RadioAstron, which was first conceived during the Cold War, only has a 10-meter antenna, which is tiny compared to the 100-meter-long antennas on Earth’s largest radio telescopes.

But combining the RadioAstron’s signals with those of earthbound telescopes in a process called interferometry creates images that are as sharp as those produced by a single satellite whose dish was as wide as the distance between the space telescope and its partner on Earth.

The RadioAstron will be launched to a distance almost as far away as the moon, creating a “dish” that, in effect, will be 30 times the Earth’s diameter. The resolution of its images will be 10,000 times that of images by the Hubble Space Telescope.

If that isn’t mind-boggling enough, to put it another way, its images will be exact down to angles of just seven microarcseconds, which is 0.000000001944 of a degree.

Inferometry has been used to make Earth-sized radio telescopes for the last few decades. The first space telescope dedicated to radio interferometry, HALCA, was launched by the Japanese Space Agency in 1997. Images by RadioAstron will have ten times greater resolution because its orbit will be ten times as far from Earth.

RadioAstron’s applications

RadioAstron will aim its sights on objects such as the nearby galaxy M87, which has a gargantuan black hole at its core. The satellite may get images from near the black hole’s event horizon, which is the boundary around which nothing can escape the black hole’s gravity.

The telescope will also look at the microwave radiation given off by water masers, which are clouds of water molecules in the discs of galaxies. Such data could help determine the rotation rate of galaxies and determine their distance from Earth.

Combining that data with data on the speed at which galaxies are moving can help with another calculation: how quickly space is expanding right now.

The telescope will also look at pulsars, which are the remains of exploded stars, and the lighthouse-like radio waves they emit, in order to understand how dust and gas are distributed around them.

Meeting and Greeting the Nearest Aliens Will Take Centuries

Although our telescopes will likely become good enough to detect signs of life on exoplanets within the next 100 years, it would probably take many centuries before we could ever get a good look at the aliens.

"Unfortunately, we are perhaps as far away from seeing aliens with our own eyes as Epicurus was from seeing the first other worlds when, 23 centuries ago, he predicted the existence of these planets," said astrobiologist Jean Schneider at the Paris Observatory at Meudon. He and his colleagues discussed the difficulties of studying distant alien life in the journal Astrobiology.

Schneider and his colleagues say that in the next 15 to 25 years, there will likely be two generations of space missions able to analyze exoplanets in greater detail. The first generation will feature 1.5-to-2.5-meter-wide coronagraphs to block out the direct light from a star to help search for giant planets and nearby super-Earths.

The second generation will feature interferometers, coronagraphs and other equipment to better analyze the light reflected off these exoplanets. These missions could reveal what the planets might look like, and what they might have in their atmospheres or on their surfaces. At the same time, there will likely be coronagraphic cameras on extremely large ground-based telescopes.

After these projects, future missions could search for more potentially habitable planets either by peering at more distant stars more than 50 parsecs away or at rocky moons of giant planets seen in the habitable zones of nearby stars. The follow-up missions also could deeply investigate any exoplanets that display potential signs of life.

Such missions will require much larger arrays in space - for instance, taking a 100-pixel image of a planet twice the width of Earth some 16.3 light years away would require the elements making up a space telescope array to be more than 43 miles apart.

Such pictures of exoplanets could make out details such as rings, clouds, oceans, continents, and perhaps even hints of forests or savannahs. Long-term monitoring could reveal seasonal shifts, volcanic events, and changes in cloud cover. One might even detect the presence of moons by shadows they project on the planets.

More sensitive instruments could hunt for the wavelengths of infrared light associated with carbon dioxide, which could tell a lot about the atmosphere.

Beyond conventional signs of life as we know it, such as oxygen in atmospheres, another type of signal could be "technosignatures," features that cannot be explained simply by complex organic chemistry. Technosignatures could include laser light, chlorofluorocarbon gases, or even artificial constructions.

"Looking for aliens is philosophically important - it would tell us what is essential in the human condition," Schneider said.

However, if scientists actually detect signs of life, it will frustratingly take many centuries before humanity can realize the hope of seeing what these aliens might actually look like, Schneider and his colleagues explained.

"It is very disappointing," Schneider said.