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This chart of the position of a nova (marked in red) that appeared in the year 1670 was recorded by the famous astronomer Hevelius and was published by the Royal Society in England in their journal Philosophical Transactions.

New observations made with APEX and other telescopes have now revealed that the star that European astronomers saw was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later.

Credit:
Royal Society

Colliding Stars Explain Enigmatic Seventeenth Century Explosion

APEX observations help unravel mystery of Nova Vulpeculae 1670


New observations made with APEX and other telescopes reveal that the star that European astronomers saw appear in the sky in 1670 was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later. The results appear online in the journal Nature on 23 March 2015.

This chart of the position of a nova (marked in red) that appeared in the year 1670 was recorded by the famous astronomer Hevelius and was published by the Royal Society in England in their journal Philosophical Transactions. New observations made with APEX and other telescopes have now revealed that the star that European astronomers saw was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later. Credit: Royal Society
This chart of the position of a nova (marked in red) that appeared in the year 1670 was recorded by the famous astronomer Hevelius and was published by the Royal Society in England in their journal Philosophical Transactions.
New observations made with APEX and other telescopes have now revealed that the star that European astronomers saw was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later.
Credit:
Royal Society

Some of seventeenth century’s greatest astronomers, including Hevelius — the father of lunar cartography — and Cassini, carefully documented the appearance of a new star in the skies in 1670. Hevelius described it as nova sub capite Cygni — a new star below the head of the Swan — but astronomers now know it by the name Nova Vulpeculae 1670 [1]. Historical accounts of novae are rare and of great interest to modern astronomers. Nova Vul 1670 is claimed to be both the oldest recorded nova and the faintest nova when later recovered.

The lead author of the new study, Tomasz Kamiński (ESO and the Max Planck Institute for Radio Astronomy, Bonn, Germany) explains: “For many years this object was thought to be a nova, but the more it was studied the less it looked like an ordinary nova — or indeed any other kind of exploding star.”

When it first appeared, Nova Vul 1670 was easily visible with the naked eye and varied in brightness over the course of two years. It then disappeared and reappeared twice before vanishing for good. Although well documented for its time, the intrepid astronomers of the day lacked the equipment needed to solve the riddle of the apparent nova’s peculiar performance.

During the twentieth century, astronomers came to understand that most novae could be explained by the runaway explosive behaviour of close binary stars. But Nova Vul 1670 did not fit this model well at all and remained a mystery.

Even with ever-increasing telescopic power, the event was believed for a long time to have left no trace, and it was not until the 1980s that a team of astronomers detected a faint nebula surrounding the suspected location of what was left of the star. While these observations offered a tantalising link to the sighting of 1670, they failed to shed any new light on the true nature of the event witnessed over the skies of Europe over three hundred years ago.

This picture shows the remains of the new star that was seen in the year 1670. It was created from a combination of visible-light images from the Gemini telescope (blue), a submillimetre map showing the dust from the SMA (green) and finally a map of the molecular emission from APEX and the SMA (red). The star that European astronomers saw in 1670 was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later. Credit: ESO/T. Kamiński
This picture shows the remains of the new star that was seen in the year 1670. It was created from a combination of visible-light images from the Gemini telescope (blue), a submillimetre map showing the dust from the SMA (green) and finally a map of the molecular emission from APEX and the SMA (red).
The star that European astronomers saw in 1670 was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later.
Credit:
ESO/T. Kamiński

 

Tomasz Kamiński continues the story: “We have now probed the area with submillimetre and radio wavelengths. We have found that the surroundings of the remnant are bathed in a cool gas rich in molecules, with a very unusual chemical composition.”

As well as APEX, the team also used the Submillimeter Array (SMA) and the Effelsberg radio telescope to discover the chemical composition and measure the ratios of different isotopes in the gas. Together, this created an extremely detailed account of the makeup of the area, which allowed an evaluation of where this material might have come from.

What the team discovered was that the mass of the cool material was too great to be the product of a nova explosion, and in addition the isotope ratios the team measured around Nova Vul 1670 were different to those expected from a nova. But if it wasn’t a nova, then what was it?

The answer is a spectacular collision between two stars, more brilliant than a nova, but less so than a supernova, which produces something called a red transient. These are a very rare events in which stars explode due to a merger with another star, spewing material from the stellar interiors into space, eventually leaving behind only a faint remnant embedded in a cool environment, rich in molecules and dust. This newly recognised class of eruptive stars fits the profile of Nova Vul 1670 almost exactly.

Co-author Karl Menten (Max Planck Institute for Radio Astronomy, Bonn, Germany) concludes: “This kind of discovery is the most fun: something that is completely unexpected!”

Notes
[1] This object lies within the boundaries of the modern constellation of Vulpecula (The Fox), just across the border from Cygnus (The Swan). It is also often referred to as Nova Vul 1670 and CK Vulpeculae, its designation as a variable star.

Source: ESO News

 

This artist’s impression depicts the formation of a galaxy cluster in the early Universe. The galaxies are vigorously forming new stars and interacting with each other. Such a scene closely resembles the Spiderweb Galaxy (formally known as MRC 1138-262) and its surroundings, which is one of the best-studied protoclusters.

Credit:

ESO/M. Kornmesser

Construction Secrets of a Galactic Metropolis

Astronomers have used the APEX telescope to probe a huge galaxy cluster that is forming in the early Universe and revealed that much of the star formation taking place is not only hidden by dust, but also occurring in unexpected places. This is the first time that a full census of the star formation in such an object has been possible.


This artist’s impression depicts the formation of a galaxy cluster in the early Universe. The galaxies are vigorously forming new stars and interacting with each other. Such a scene closely resembles the Spiderweb Galaxy (formally known as MRC 1138-262) and its surroundings, which is one of the best-studied protoclusters. Credit: ESO/M. Kornmesser
This artist’s impression depicts the formation of a galaxy cluster in the early Universe. The galaxies are vigorously forming new stars and interacting with each other. Such a scene closely resembles the Spiderweb Galaxy (formally known as MRC 1138-262) and its surroundings, which is one of the best-studied protoclusters.
Credit:
ESO/M. Kornmesser

Galaxy clusters are the largest objects in the Universe held together by gravity but their formation is not well understood. TheSpiderweb Galaxy (formally known as MRC 1138-262 [1]) and its surroundings have been studied for twenty years, using ESO and other telescopes [2], and is thought to be one of the best examples of a protocluster in the process of assembly, more than ten billion years ago.

But Helmut Dannerbauer (University of Vienna, Austria) and his team strongly suspected that the story was far from complete. They wanted to probe the dark side of star formation and find out how much of the star formation taking place in the Spiderweb Galaxy cluster was hidden from view behind dust.

The team used the LABOCA camera on the APEX telescope in Chile to make 40 hours of observations of the Spiderweb Cluster at millimetre wavelengths — wavelengths of light that are long enough to peer right through most of the thick dust clouds. LABOCA has a wide field and is the perfect instrument for this survey.

Carlos De Breuck (APEX project scientist at ESO, and a co-author of the new study) emphasises: “This is one of the deepest observations ever made with APEX and pushes the technology to its limits — as well as the endurance of the staff working at the high-altitude APEX site, 5050 metres above sea level.

The APEX observations revealed that there were about four times as many sources detected in the area of the Spiderweb compared to the surrounding sky. And by carefully comparing the new data with complementary observations made at different wavelengths they were able to confirm that many of these sources were at the same distance as the galaxy cluster itself and must be parts of the forming cluster.

Helmut Dannerbauer explains: “The new APEX observations add the final piece needed to create a complete census of all inhabitants of this mega star city. These galaxies are in the process of formation so, rather like a construction site on Earth, they are very dusty.”

But a surprise awaited the team when they looked at where the newly detected star formation was taking place. They were expecting to find this star formation region on the large filaments connecting galaxies. Instead, they found it concentrated mostly in a single region, and that region is not even centred on the central Spiderweb Galaxy in the protocluster [3].

Helmut Dannerbauer concludes: “We aimed to find the hidden star formation in the Spiderweb cluster — and succeeded — but we unearthed a new mystery in the process; it was not where we expected! The mega city is developing asymmetrically.

To continue the story further observations are needed — and ALMA will be the perfect instrument to take the next steps and study these dusty regions in far greater detail.

Notes

[1] The Spiderweb Galaxy contains a supermassive black hole and is a powerful source of radio waves — which is what led astronomers to notice it in the first place.

[2] This region had been intensively observed by a variety of ESO telescopes since the mid-1990s. The redshift (and hence the distance) of the radio galaxy MRC1138-262 (the Spiderweb Galaxy) was first measured at La Silla. The first visitor modeFORS observations on the VLT discovered the protocluster and afterwards further observations were made with ISAAC,SINFONIVIMOS and HAWK-I. The APEX LABOCA data complement optical and near-infrared datasets from ESO telescopes. The team also used a 12-hour VLA image to cross-identify the LABOCA sources in the optical images.

[3] These dusty starbursts are thought to evolve into elliptical galaxies like those seen around us today in nearby galaxy clusters.

More information

This research was presented in a paper, “An excess of dusty starbursts related to the Spiderweb galaxy”, by Dannerbauer, Kurk, De Breuck et al., to appear online in the journal Astronomy & Astrophysics on 15 October 2014.

APEX is a collaboration between the Max Planck Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO. Operation of APEX at Chajnantor is entrusted to ESO.

The team is composed of H. Dannerbauer (University of Vienna, Austria), J. D. Kurk (Max-Planck-Institut für extraterrestrische Physik, Garching, Germany), C. De Breuck (ESO, Garching, Germany), D. Wylezalek (ESO, Garching, Germany), J. S. Santos (INAF–Osservatorio Astrofisico di Arcetri, Florence, Italy), Y. Koyama (National Astronomical Observatory of Japan, Tokyo, Japan [NAOJ]; Institute of Space Astronomical Science, Kanagawa, Japan), N. Seymour (International Centre for Radio Astronomy Research, Curtin University, Perth, Australia), M. Tanaka (NAOJ; Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, Japan), N. Hatch (University of Nottingham, United Kingdom), B. Altieri (Herschel Science Centre, European Space Astronomy Centre, Villanueva de la Cañada, Spain [HSC]), D. Coia (HSC), A. Galametz (INAF–Osservatorio di Roma, Italy), T. Kodama (NAOJ), G. Miley (Leiden Observatory, the Netherlands), H. Röttgering (Leiden Observatory), M. Sanchez-Portal (HSC), I. Valtchanov (HSC), B. Venemans (Max-Planck Institut für Astronomie, Heidelberg, Germany) and B. Ziegler (University of Vienna).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

Source: ESO