Monthly Archives: March 2013

Sun Block for the “Big Dog”

Sun block for the “Big Dog”

Astronomers detect titanium oxide and titanium dioxide around the giant star VY Canis Majoris

March 27, 2013

An international team of astronomers, including researchers from the Max Planck Institute for Radio Astronomy and from the University of Cologne, successfully identified two titanium oxides in the extended atmosphere around a giant star. The object VY Canis Major is one of the largest stars in the known universe and close to the end of its life. The detection was made using telescope arrays in the USA and in France.

Gone with the stellar wind: an extended dusty nebula surrounds VY CMa in the constellation Big Dog, one of the largest known stars in the universe. In the atmosphere of this huge sun, astronomers discovered the molecules TiO and TiO<sub>2</sub>. Zoom Image

Gone with the stellar wind: an extended dusty nebula surrounds VY CMa in the constellation Big Dog, one of the largest … [more]
© Molecule symbols: CDMS/T. Kamiński. Background image: NASA/ESA and R. Humphreys (University of Minnesota)

 

The discovery was made in the course of a study of a spectacular star, VY Canis Majoris or VY CMa for short, which is a variable star located in the constellation Canis Major (Greater Dog). “VY CMa is not an ordinary star, it is one of the largest stars known, and it is close the end of its life,” says Tomasz Kamiński from the Max Planck Institute for Radio Astronomy (MPIfR). In fact, with a size of about one to two thousand times that of the Sun, it could extend out to the orbit of Saturn if it were placed in the centre of our Solar System.

The star ejects large quantities of material which forms a dusty nebula. It becomes visible because of the small dust particles that form around it which reflect light from the central star. The complexity of this nebula has been puzzling astronomers for decades. It has been formed as a result of stellar wind, but it is not understood well why it is so far from having a spherical shape.

Neither is known what physical process blows the wind, i.e. what lifts the material up from the stellar surface and makes it expand. “The fate of VY CMa is to explode as a supernova, but it is not known exactly when it will happen”, adds Karl Menten, head of the “Millimetre and Submillimetre Astronomy” Department at MPIfR.

Observations at different wavelengths provide different pieces of information which is characteristic for atomic and molecular gas and from which physical properties of an astronomical object can be derived. Each molecule has a characteristic set of lines, something like a ’bar code’, that allows to identify what molecules exist in the nebula.

“Emission at short radio wavelengths, in so-called submillimetre waves, is particularly useful for such studies of molecules”, says Sandra Brünken from the University of Cologne. “The identification of molecules is easier and usually a larger abundance of molecules can be observed than at other parts of the electromagnetic spectrum.”

Observatory at the volcano: the SMA interferometer where the discovery of the new molecules in VY CMa was made. Zoom Image

Observatory at the volcano: the SMA interferometer where the discovery of the new molecules in VY CMa was made.
© N. Patel/SMA

 

The research team observed TiO and TiO2 for the first time at radio wavelengths. In fact, titanium dioxide has been seen in space unambiguously for the first time. It is known from every-day life as the main component of the commercially most important white pigment (known by painters as “titanium white”) or as an ingredient in sunscreens. It is also quite possible that the reader consumed some amounts of it as it is used to colour food (coded as E171 in the labels).

However, stars, especially the coolest of them, are expected to eject large quantities of titanium oxides, which, according to theory, form at relatively high temperatures close to the star. “They tend to cluster together to form dust particles visible in the optical or in the infrared,” says Nimesh Patel from the Harvard-Smithsonian Center for Astrophysics. “And the catalytic properties of TiO2 may influence the chemical processes taking place on these dust particles, which are very important for forming larger molecules in space”, adds Holger Müller from the University of Cologne.

Absorption features of TiO have been known from spectra in the visible region for more than a hundred years. In fact, these features are used in part to classify some types of stars with low surface temperatures (M- and S-type stars). The pulsation of Mira stars, one specific class of variable stars, is thought to be caused by titanium oxide. Mira stars, supergiant variable stars in a late stage of their evolution, are named after their prototype star “Mira” (the wonderful) in the constellation of Cetus (the ‘sea monster’ or the ‘whale’).

The observations of TiO and TiO2 show that the two molecules are easily formed around VY CMa at a location that is more or less as predicted by theory. It seems, however, that some portion of those molecules avoid forming dust and are observable as gas phase species. Another possibility is that the dust is destroyed in the nebula and releases fresh TiO molecules back to the gas. The latter scenario is quite likely as parts of the wind in VY CMa seem to collide with each other.

The new detections at submillimetre wavelengths are particularly important because they allow studying the process of dust formation. Also, at optical wavelengths, the radiation emitted by the molecules is scattered by dust present in the extended nebula which blurs the picture, while this effect is negligible at radio wavelengths allowing for more precise measurements.

The discoveries of TiO and TiO2 in the spectrum of VY CMa have been made with the Submillimetre Array (SMA), a radio interferometer located at Hawaii, USA. Because the instrument combines eight antennas which worked together as one big telescope 226-meters in size, astronomers were able to make observations at unprecedented sensitivity and angular resolution. A confirmation of the new detections was successively made later with the IRAM Plateau de Bure Interferometer (PdBI) located in the French Alps.

Gazing into the frozen Stillness of the Universe

Gazing into the frozen stillness of the universe

The ALMA telescope installation begins delivering images of fresh planets, young stars, and distant galaxies.

March 19, 2013

Astronomers have a new window on the universe: The ALMA telescope installation has now officially gone into operation. This array, known as the Atacama Large Millimeter/submillimeter Array, is located atop the Chilean Chajnantor Plateau and will comprise 66 antennas in its final construction configuration at the end of the year. Astronomers from the Max Planck Institute for Radio Astronomy are already working with this powerful instrument. And they had a large part in the development and construction of a prototype.

Astronomy in the desert: An aerial photograph of the Chajnantor Plateau with the antennas of the ALMA Observatory situated more than 5,000 m above sea level in the Chilean Andes. The peaks of Juriques, Cerro Toco, and Cerro Chajnantor (from left) are visible on the horizon. The photograph was taken in December 2012, three months before the official opening of ALMA. Zoom Image

Astronomy in the desert: An aerial photograph of the Chajnantor Plateau with the antennas of the ALMA Observatory … [more]
© Clem & Adri Bacri-Normier / ESO

 

Up here at 5,100 m above sea level, the air is clear, cold, and dry. This last characteristic in particular makes the highlands of the Chilean Atacama Desert one of the best observational locations in the world. After all, terrestrial water vapour cannot be allowed to interfere with visibility in the quest to peer into the dusty, cool regions of the universe. Oxygen above all weakens the radio waves at the edge of infrared light and obscures the images of the cosmic worlds. The unspoiled view rewards the astronomers for the difficult life on the Chajnantor Plateau.

ALMA Director Thijs de Graauw spoke before an audience of more than 500 invited guests at the official opening of the observatory about “the untold hours of hard work by our scientists and engineers”, and not without reason. The installation cannot be compared with any other; it is the most advanced millimetre and submillimetre telescope of our day.

In its final configuration, ALMA will comprise 54 antennas each with a diameter of 12 metres, and 12 antennas each with a diameter of seven metres. Every individual dish collects the radiation from space and focuses it on a receiver. The signals from all the telescopes are subsequently superposed and prepared for further processing in a supercomputer known as the ALMA Correlator. The array can change its geometry, i.e. the 66 antennas can be arranged in different configurations on the plateau. The engineers can tow the arrays into position for separations between one another of 150 metres to 16 kilometres.

ALMA observes space by means of light that is invisible to the human eye. From an astronomical point of view, this submillimetre-light region is a comparatively little-researched area of the electromagnetic spectrum. However, this region is very important for astronomers: the cold universe reveals itself here. Cold, expanded clouds of molecules whose temperatures lie only a few tenths of a degree above absolute zero (- 273.15 degrees Celsius) emit this kind of radiation from interstellar space.

Pathfinder backlit by the sun just below the horizon at dusk: The Atacama Pathfinder Experiment had already begun operation in the Atacama Desert in Summer 2005. With an antenna diameter of 12 metres, it was the largest submillimetre telescope in the Earth’s southern hemisphere. The camera flash is reflected off the adjustment screws of the individual panels, which permit the surface of the dish to be very precisely set. Zoom Image

Pathfinder backlit by the sun just below the horizon at dusk: The Atacama Pathfinder Experiment had already begun … [more]
© APEX

 

In the interior of these clouds of gas and dust, new stars are born. The researchers use the submillimetre-light region to investigate the physical and chemical properties of the clouds. Seen in the visible portion of the spectrum, these cosmic regions appear opaque due to the high content of dust. In the millimetre and submillimetre spectrum by contrast, the veil lifts to reveal brightly glowing, emerging structures.

Even the most distant and youngest galaxies are visible for the most part in this region of the spectrum – not because they are particularly cold, but because the wavelengths of light that they emit have lengthened due to the expansion of the universe. The radiation thereby shifts from visible to the long-wavelength submillimetre or millimetre regions.

ALMA does not just display the birth scenarios of stars, baby galaxies, or the evolution of new planets around distant suns in unprecedented sharpness. The scientists also want to analyse the distribution of known molecules – many of which are necessary for life – in interstellar space, and discover new molecules.

The history of the observatory goes back to the 1980s. At that time, astronomers in Europe, the USA, and Japan discussed their separate plans; only ten years later did their plans combine into a single project. Construction began then in 2003. The total costs for ALMA run to1.4 billion dollars, of which the European Southern Observatory (ESO) carries 37.5 per cent.

Before ALMA went into operation, the Atacama Pathfinder Experiment (APEX) saw its first light in June 2005 – with an antenna 12 metres in diameter, the largest submillimetre telescope in the southern hemisphere of the Earth at that time. The APEX dish possesses an extremely precisely shaped surface: The maximal deviation of the dish from parabolic is less than 17 micrometres (17 thousandths of a millimetre). That is smaller than one-fifth the diameter of a human hair.

Parallel to the design and construction of the APEX telescope, researchers began a costly developmental phase for the best-possible detectors. High-resolution, wideband FFT spectrometers developed by the Department of Millimetre and Submillimetre Astronomy at the Max Planck Institute for Radio Astronomy in Bonn were used for the initial observations.

In a few months, the scientists would like to equip APEX with a new receiver that also originated from the workshop of the radio astronomers in Bonn. They built the telescope in collaboration with the Onsala Space Observatory and the ESO and obtained some important results over the past years, such as measuring the distribution of a rarely occurring molecule (D2H+) and observing the details of the compact disk of dust around the massive star known as IRAS 13481-6124.

HOR

Stellar Baby Boom

Stellar baby boom

Astronomers observe starburst galaxies in early space with the ALMA telescope – and discover the most distant detection of water published to date

March 13, 2013

The most vigorous bursts of star birth in the cosmos took place at least one billion years earlier than previously thought. These new insights were the result of observations with the Atacama Large Millimetre/submillimetre Array (ALMA), which will be officially opened on March 14, 2013. The findings are published in a set of three papers which also report on the most distant detection of water to date. Axel Weiß from the Max Planck Institute for Radio Astronomy in Bonn is first author of one of the publications.

Montage, combining data from ALMA with images from the NASA/ESA Hubble Space Telescope, for five distant galaxies. The ALMA images, represented in red, show the distant, background galaxies, being distorted by the gravitational lens effect produced by the galaxies in the foreground, depicted in the Hubble data in blue. The background galaxies appear warped into rings of light known as Einstein rings, which encircle the foreground galaxies. Zoom Image

Montage, combining data from ALMA with images from the NASA/ESA Hubble Space Telescope, for five distant galaxies. The … [more]
© ALMA (ESO/NRAO/NAOJ), Y. Hezaveh et al.

 

The most intense bursts of star birth are thought to have occurred in the early Universe, in massive, bright galaxies. These starburst galaxies convert vast reservoirs of cosmic gas and dust into new stars at a furious pace — many hundreds of times faster than in stately spiral galaxies like our own galaxy, the Milky Way. By looking far into space, at galaxies so distant that their light has taken many billions of years to reach us, astronomers can observe this busy period in the Universe’s youth.

“The more distant the galaxy, the further back in time one is looking, so by measuring their distances we can piece together a timeline of how vigorously the Universe was making new stars at different stages of its 13.7 billion year history,” said Joaquin Vieira (California Institute of Technology, USA), who led the team and is lead author of the paper in the journal Nature.

The international team of researchers first discovered these distant and enigmatic starburst galaxies with the US National Science Foundation’s 10-metre South Pole Telescope (SPT) and then used ALMA to zoom in on them to explore the stellar baby boom in the young Universe. They were surprised to find that many of these distant dusty star-forming galaxies are even further away than expected. This means that, on average, their bursts of star birth took place 12 billion years ago, when the Universe was just under 2 billion years old — a full billion years earlier than previously thought.

This schematic image represents how light from a distant galaxy is distorted by the gravitational effects of a nearer foreground galaxy, which acts like a lens and makes the distant source appear distorted, but brighter, forming characteristic rings of light, known as Einstein rings. An analysis of the distortion has revealed that some of the distant star-forming galaxies are as bright as 40 trillion Suns, and have been magnified by the gravitational lens by up to 22 times. Zoom Image

This schematic image represents how light from a distant galaxy is distorted by the gravitational effects of a nearer … [more]
© ALMA (ESO/NRAO/NAOJ), L. Calçada (ESO), Y. Hezaveh et al.

 

Two of these galaxies are the most distant of their kind ever seen — so distant that their light began its journey when the Universe was only one billion years old. What’s more, in one of these record-breakers, water is among the molecules detected, marking the most distant observations of water in the cosmos published to date.

The team used the unrivalled sensitivity of ALMA to capture light from 26 of these galaxies at wavelengths of around three millimetres. Light at characteristic wavelengths is produced by gas molecules in these galaxies, and the wavelengths are stretched by the expansion of the Universe over the billions of years that it takes the light to reach us. By measuring the stretched wavelengths, astronomers can calculate how long the light’s journey has taken, and place each galaxy at the right point in cosmic history.

“ALMA’s sensitivity and wide wavelength range mean we could make our measurements in just a few minutes per galaxy — about one hundred times faster than before,” said Axel Weiss (Max Planck Institute for Radio Astronomy in Bonn, Germany), who led the work to measure the distances to the galaxies. “Previously, a measurement like this would have been a laborious process of combining data from both visible-light and radio telescopes.”

In the majority of cases, the ALMA observations alone could pinpoint the distances, but for a few galaxies the team combined the ALMA data with measurements from other telescopes, including the Atacama Pathfinder Experiment (APEX) and ESO’s Very Large Telescope [1].

A number of ALMA antennae bathed in red light seen against the Chajnantor night sky. In the background there is the southern Milky Way on the left and the Magellanic Clouds at the top. Zoom Image

A number of ALMA antennae bathed in red light seen against the Chajnantor night sky. In the background there is the … [more]
ESO/C. Malin

 

The astronomers were using only a partial array of 16 of ALMA’s full complement of 66 giant antennas, as the observatory was still under construction at an altitude of 5000 metres on the remote Chajnantor Plateau in the Chilean Andes. When complete, ALMA will be even more sensitive, and will be able to detect even fainter galaxies. For now, astronomers targeted the brighter ones. They took advantage of a helping hand from nature, too: using gravitational lensing, an effect predicted by Einstein’s general theory of relativity, where light from a distant galaxy is distorted by the gravitational influence of a nearer foreground galaxy, which acts like a lens and makes the distant source appear brighter.

To understand by precisely how much this gravitational lensing brightened the view of the galaxies, the team made sharper images of them using more ALMA observations at wavelengths of around 0.9 millimetres.

“These beautiful pictures from ALMA show the background galaxies warped into multiple arcs of light known as Einstein rings, which encircle the foreground galaxies,” said Yashar Hezaveh (McGill University, Montreal, Canada), who led the study of the gravitational lensing. “We are using the massive amount of dark matter surrounding galaxies half-way across the Universe as a cosmic telescope to make even more distant galaxies appear bigger and brighter.”

Analysis of the distortion reveals that some of the distant star-forming galaxies are as bright as 40 trillion (40 million million) Suns, and that gravitational lensing has magnified this by up to 22 times.

“Only a few gravitationally lensed galaxies have been found before at these submillimetre wavelengths, but now SPT and ALMA have uncovered dozens of them.” said Carlos De Breuck (ESO), a member of the team. “This kind of science was previously done mostly at visible-light wavelengths with the Hubble Space Telescope, but our results show that ALMA is a very powerful new player in the field.”

“This is a great example of astronomers from around the world collaborating to make an amazing discovery with a state-of-the-art facility,” said team member Daniel Marrone (University of Arizona, USA). “This is just the beginning for ALMA and for the study of these starburst galaxies. Our next step is to study these objects in greater detail and figure out exactly how and why they are forming stars at such prodigious rates.”

HOR / NJ