Looking deep into the heart of Orion

Photo: This spectacular image of the Orion Nebula star-formation region was obtained from multiple exposures using the HAWK-I infrared camera on ESO’s Very Large Telescope in Chile. This is the deepest view ever of this region and reveals more very faint planetary-mass objects than expected. Credit: ESO/H. Drass et al.
This spectacular image of the Orion Nebula star-formation region was obtained from multiple exposures using the HAWK-I infrared camera on ESO’s Very Large Telescope in Chile. This is the deepest view ever of this region and reveals more very faint planetary-mass objects than expected. Credit: ESO/H. Drass et al.

ESO’s HAWK-I infrared instrument on the Very Large Telescope (VLT) in Chile has been used to peer deeper into the heart of Orion Nebula than ever before. The spectacular picture reveals about ten times as many brown dwarfs and isolated planetary-mass objects than were previously known. This discovery poses challenges for the widely-accepted scenario for Orion’s star formation history.

An international team has made use of the power of the HAWK-I infrared instrument on ESO’s Very Large Telescope (VLT) to produce the deepest and most comprehensive view of the Orion Nebula to date. Not only has this led to an image of spectacular beauty, but it has revealed a great abundance of faint brown dwarfs and isolated planetary-mass objects. The very presence of these low-mass bodies provides an exciting insight into the history of star formation within the nebula itself.

The famous Orion Nebula spans about 24 light-years within the constellation of Orion, and is visible from Earth with the naked eye, as a fuzzy patch in Orion’s sword. Some nebulae, like Orion, are strongly illuminated by ultraviolet radiation from the many hot stars born within them, such that the gas is ionised and glows brightly.

The relative proximity of the Orion Nebula makes it an ideal testbed to better understand the process and history of star formation, and to determine how many stars of different masses form.

Amelia Bayo (Universidad de Valparaíso, Valparaíso, Chile; Max-Planck Institut für Astronomie, Königstuhl, Germany), a co-author of the new paper and member of the research team, explained why this is important: “Understanding how many low-mass objects are found in the Orion Nebula is very important to constrain current theories of star formation. We now realise that the way these very low-mass objects form depends on their environment.”

This new image has caused excitement because it reveals a unexpected wealth of very-low-mass objects, which in turn suggests that the Orion Nebula may be forming proportionally far more low-mass objects than closer and less active star formation regions.

Astronomers count up how many objects of different masses form in regions like the Orion Nebula to try to understand the star-formation process. Before this research the greatest number of objects were found with masses of about one quarter that of our Sun. The discovery of a plethora of new objects with masses far lower than this in the Orion Nebula has now created a second maximum at a much lower mass in the distribution of star counts.

These observations also hint tantalisingly that the number of planet-sized objects might be far greater than previously thought. Whilst the technology to readily observe these objects does not exist yet, ESO’s future European Extremely Large Telescope (E-ELT), scheduled to begin operations in 2024, is designed to pursue this as one of its goals.

Lead scientist Holger Drass (Astronomisches Institut, Ruhr-Universität Bochum, Bochum, Germany; Pontificia Universidad Católica de Chile, Santiago, Chile) enthused: “Our result feels to me like a glimpse into a new era of planet and star formation science. The huge number of free-floating planets at our current observational limit is giving me hope that we will discover a wealth of smaller Earth-sized planets with the E-ELT.”

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ESO’s Very Large Telescope finds hottest and most massive touching double star

Image: Artist's impression of two contacting stars. Credit: ESO
This artist’s impression shows VFTS 352 — the hottest and most massive double star system to date where the two components are in contact and sharing material. The two stars in this extreme system lie about 160,000 light-years from Earth in the Large Magellanic Cloud. Credit: ESO/L. Calçada

ESO News Release

The double star system VFTS 352 is located about 160,000 light-years away in the Tarantula Nebula. This remarkable region is the most active nursery of new stars in the nearby universe and new observations from ESO’s VLT have revealed that this pair of young stars is among the most extreme and strangest yet found.

VFTS 352 is composed of two very hot, bright and massive stars that orbit each other in little more than a day. The centers of the stars are separated by just 12 million kilometers. In fact, the stars are so close that their surfaces overlap and a bridge has formed between them. VFTS 352 is not only the most massive known in this tiny class of “overcontact binaries” — it has a combined mass of about 57 times that of the Sun — but it also contains the hottest components — with surface temperatures above 40,000 degrees Celsius.

Extreme stars like the two components of VFTS 352, play a key role in the evolution of galaxies and are thought to be the main producers of elements such as oxygen. Such double stars are also linked to exotic behavior such as that shown by “vampire stars,” where a smaller companion star sucks matter from the surface of its larger neighbor.

In the case of VFTS 352, however, both stars in the system are of almost identical size. Material is, therefore, not sucked from one to another, but instead may be shared. The component stars of VFTS 352 are estimated to be sharing about 30 percent of their material.

Such a system is very rare because this phase in the life of the stars is short, making it difficult to catch them in the act. Because the stars are so close together, astronomers think that strong tidal forces lead to enhanced mixing of the material in the stellar interiors.

“The VFTS 352 is the best case yet found for a hot and massive double star that may show this kind of internal mixing,” explains lead author Leonardo A. Almeida of the University of São Paulo, Brazil. “As such it’s a fascinating and important discovery.”

Astronomers predict that VFTS 352 will face a cataclysmic fate in one of two ways. The first potential outcome is the merging of the two stars, which would likely produce a rapidly rotating, and possibly magnetic, gigantic single star. “If it keeps spinning rapidly it might end its life in one of the most energetic explosions in the universe, known as a long-duration gamma-ray burst,” says the lead scientist of the project, Hugues Sana, of the University of Leuven in Belgium.

The second possibility is explained by the lead theoretical astrophysicist in the team, Selma de Mink of University of Amsterdam: “If the stars are mixed well enough, they both remain compact and the VFTS 352 system may avoid merging. This would lead the objects down a new evolutionary path that is completely different from classic stellar evolution predictions. In the case of VFTS 352, the components would likely end their lives in supernova explosions, forming a close binary system of black holes. Such a remarkable object would be an intense source of gravitational waves.”

Proving the existence of this second evolutionary path would be an observational breakthrough in the field of stellar astrophysics. Regardless of how VFTS 352 meets its demise, this system has already provided astronomers with valuable new insights into the poorly understood evolutionary processes of massive overcontact binary star systems.

Phenominal new view of our galaxy’s core

Photo: Central bulge of the Milky Way Galaxy. ESO/VVV Consortium Acknowledgement: Ignacio Toledo, Martin Kornmesser
Central portion of the Milky Way: ESO/VVV Consortium – Acknowledgement: Ignacio Toledo, Martin Kornmesser

Using a whopping nine-gigapixel image from the VISTA infrared survey telescope at ESO’s Paranal Observatory, an international team of astronomers has created a catalogue of more than 84 million stars in the central parts of the Milky Way. This gigantic dataset contains more than ten times more more stars than previous studies and is a major step forward for the understanding of our home galaxy. The image gives viewers an incredible, zoomable view of the central part of our galaxy. It is so large that, if printed with the resolution of a typical book, it would be 9 meters long and 7 meters tall.

“By observing in detail the myriads of stars surrounding the centre of the Milky Way we can learn a lot more about the formation and evolution of not only our galaxy, but also spiral galaxies in general,” explains Roberto Saito (Pontificia Universidad Católica de Chile, Universidad de Valparaíso and The Milky Way Millennium Nucleus, Chile), lead author of the study.

Most spiral galaxies, including our home galaxy the Milky Way, have a large concentration of ancient stars surrounding the centre that astronomers call the bulge. Understanding the formation and evolution of the Milky Way’s bulge is vital for understanding the galaxy as a whole. However, obtaining detailed observations of this region is not an easy task.
“Observations of the bulge of the Milky Way are very hard because it is obscured by dust,” says Dante Minniti (Pontificia Universidad Catolica de Chile, Chile), co-author of the study. “To peer into the heart of the galaxy, we need to observe in infrared light, which is less affected by the dust.”

Photo: Center of the Milky Way with VISTA region indicated. ESO/Nick Risinger (skysurvey.org)
Central portion of the Milky Way with VISTA region indicated. ESO/Nick Risinger (skysurvey.org)

The large mirror, wide field of view and very sensitive infrared detectors of ESO’s 4.1-meter Visible and Infrared Survey Telescope for Astronomy (VISTA) make it by far the best tool for this job. The team of astronomers is using data from the VISTA Variables in the Via Lactea program (VVV), one of six public surveys carried out with VISTA. The data have been used to create a monumental 108 200 by 81 500 pixel color image containing nearly nine billion pixels. This is one of the biggest astronomical images ever produced. The team has now used these data to compile the largest catalogue of the central concentration of stars in the Milky Way ever created.

To help analyze this huge catalog the brightness of each star is plotted against its color for about 84 million stars to create a color–magnitude diagram. This plot contains more than ten times more stars than any previous study and it is the first time that this has been done for the entire bulge. Color–magnitude diagrams are very valuable tools that are often used by astronomers to study the different physical properties of stars such as their temperatures, masses and ages.

“Each star occupies a particular spot in this diagram at any moment during its lifetime. Where it falls depends on how bright it is and how hot it is. Since the new data gives us a snapshot of all the stars in one go, we can now make a census of all the stars in this part of the Milky Way,” explains Dante Minniti.

The new color–magnitude diagram of the bulge contains a treasure trove of information about the structure and content of the Milky Way. One interesting result revealed in the new data is the large number of faint red dwarf stars. These are prime candidates around which to search for small exoplanets using the transit method.

“One of the other great things about the VVV survey is that it’s one of the ESO VISTA public surveys. This means that we’re making all the data publicly available through the ESO data archive, so we expect many other exciting results to come out of this great resource,” concludes Roberto Saito. For access to much larger versions of these images, visit the ESO Web site.

Source: ESO News Release

Earth-sized planet discovered in Alpha Centauri system

European astronomers have discovered a planet with about the mass of the Earth orbiting a star in the Alpha Centauri system — the nearest to Earth. It is also the lightest exoplanet ever discovered around a star like the Sun. The planet was detected using the HARPS instrument on the 3.6-metre telescope at ESO’s La Silla Observatory in Chile. The results appeared online in the journal Nature on October 17, 2012.

Alpha Centauri is one of the brightest stars in the southern skies and is the nearest stellar system to our Solar System — only 4.3 light-years away. It is actually a triple star — a system consisting of two stars similar to the Sun orbiting close to each other, designated Alpha Centauri A and B, and a more distant and faint red component known as Proxima Centauri. Since the 19th century astronomers have speculated about planets orbiting these bodies, the closest possible abodes for life beyond the Solar System, but searches of increasing precision had revealed nothing. Until now.

“Our observations extended over more than four years using the HARPS instrument and have revealed a tiny, but real, signal from a planet orbiting Alpha Centauri B every 3.2 days,” says Xavier Dumusque (Geneva Observatory, Switzerland and Centro de Astrofisica da Universidade do Porto, Portugal), lead author of the paper. “It’s an extraordinary discovery and it has pushed our technique to the limit!”

The European team detected the planet by picking up the tiny wobbles in the motion of the star Alpha Centauri B created by the gravitational pull of the orbiting planet. The effect is minute — it causes the star to move back and forth by no more than 51 centimetres per second (1.8 km/hour), about the speed of a baby crawling. This is the highest precision ever achieved using this method.

Alpha Centauri B is very similar to the Sun but slightly smaller and less bright. The newly discovered planet, with a mass of a little more than that of the Earth, is orbiting about six million kilometres away from the star, much closer than Mercury is to the Sun in the Solar System. The orbit of the other bright component of the double star, Alpha Centauri A, keeps it hundreds of times further away, but it would still be a very brilliant object in the planet’s skies.

The first exoplanet around a Sun-like star was found by the same team back in 1995 and since then there have been more than 800 confirmed discoveries, but most are much bigger than the Earth, and many are as big as Jupiter. The challenge astronomers now face is to detect and characterise a planet of mass comparable to the Earth that is orbiting in the habitable zone around another star. The first step has now been taken.

“This is the first planet with a mass similar to Earth ever found around a star like the Sun. Its orbit is very close to its star and it must be much too hot for life as we know it,” adds Stéphane Udry (Geneva Observatory), a co-author of the paper and member of the team, “but it may well be just one planet in a system of several. Our other HARPS results, and new findings from Kepler, both show clearly that the majority of low-mass planets are found in such systems.”

Source: European Southern Observatory