Hubble Catches Heavyweight Runaway Star Speeding from 30 Doradus

30 Doradus Nebula

Credit for Hubble Image: NASA, ESA, J. Walsh (ST-ECF), and ESO

Acknowledgment: Processing by Z. Levay (STScI)
Acknowledgment: J. Alves (Calar Alto, Spain), and B. Vandame and Y. Beletski (ESO)

Processing by B. Fosbury (ST-ECF)

A heavy runaway star is rushing away from a nearby stellar nursery at more than 250,000 miles an hour, a speed that will get you to the Moon and back in two hours. The runaway is the most extreme case of a very massive star that has been kicked out of its home by a group of even heftier siblings.

The homeless star is on the outskirts of the 30 Doradus nebula, a raucous stellar breeding ground in the nearby Large Magellanic Cloud. The finding bolsters evidence that the most massive stars in the local universe reside in 30 Doradus, making it a unique laboratory for studying heavyweight stars. 30 Doradus, also called the Tarantula Nebula, is roughly 170,000 light-years from Earth.

Tantalizing clues from three observatories, including the Hubble Space Telescope's newly installed Cosmic Origins Spectrograph (COS), and some old-fashioned detective work, suggest that the star may have traveled about 375 light-years from its suspected home, a giant star cluster called R136. Nestled in the core of 30 Doradus, R136 contains several stars topping 100 solar masses each.

The observations offer insights into how massive star clusters behave.

"These results are of great interest because such dynamical processes in very dense, massive clusters have been predicted theoretically for some time, but this is the first direct observation of the process in such a region," says Nolan Walborn of the Space Telescope Science Institute in Baltimore and a member of the COS team that observed the misfit star. "Less massive runaway stars from the much smaller Orion Nebula Cluster were first found over half a century ago, but this is the first potential confirmation of more recent predictions applying to the most massive young clusters."

Runaway stars can be made in a couple of ways. A star may encounter one or two heavier siblings in a massive, dense cluster and get booted out through a stellar game of pinball. Or, a star may get a 'kick' from a supernova explosion in a binary system, with the more massive star exploding first.

"It is generally accepted, however, that R136 is sufficiently young, 1 million to 2 million years old, that the cluster's most massive stars have not yet exploded as supernovae," says COS team member Danny Lennon of the Space Telescope Science Institute. "This implies that the star must have been ejected through dynamical interaction."

The runaway star research team, led by Chris Evans of the Royal Observatory Edinburgh, published the study's results May 5 in the online edition of The Astrophysical Journal Letters.

Astronomers have been on the trail of this rogue star since 2006 when a team led by Ian Howarth of University College London spotted it with the Anglo-Australian Telescope at Siding Spring Observatory. The observation revealed that the stellar misfit was an exceptionally hot, massive, blue-white star and relatively far from any cluster in which such stars are usually found.

Hubble astronomers unexpectedly picked up another clue when they used the star as a target to calibrate the COS instrument, installed in May 2009 during Servicing Mission 4. Those ultraviolet spectroscopic observations, made in July 2009, showed that the wayward star is unleashing a fury of charged particles in one of the most powerful stellar winds known, a clear sign that it is extremely massive, perhaps as much as 90 times heavier than the Sun. The star, therefore, also must be very young, about 1 million to 2 million years old, because extremely massive stars live only a few million years.

Sifting through Hubble's archive of images, astronomers found another important piece of evidence. An optical image of the star taken by the Wide Field Planetary Camera 2 in 1995 revealed that it is at one end of an egg-shaped cavity. The cavity's glowing edges stretch behind the star and point in the direction of its home in 30 Doradus.

Another spectroscopic study from the European Southern Observatory's Very Large Telescope (VLT) at the Paranal Observatory in Chile revealed that the star's velocity is constant and not a result of orbital motion in a binary system. Its velocity corresponds to an unusual motion relative to the star's surroundings, evidence that it is a runaway star.

The study also confirmed that the light from the runaway is from a single massive star rather than the combined light of two lower-mass stars. In addition, the observation established that the star is about 10 times hotter than the Sun, a temperature that is consistent with a high-mass object.

The VLT observations are part of a legacy program called the FLAMES (VLT multi-object spectrograph) Tarantula Survey. The survey, conducted by an international team led by Evans of the Royal Observatory, comprises more than 900 stars in the 30 Doradus region. Like the COS observations of the star, the FLAMES results also were serendipitous. The star's location is far from the nebula's central region, placing it at the edge of the FLAMES survey field.

The renegade star may not be the only runaway in the region. Two other extremely hot, massive stars have been spotted beyond the edges of 30 Doradus. Astronomers suspect that these stars, too, may have been ejected from their home. They plan to analyze the stars in detail to determine whether 30 Doradus might be unleashing a barrage of massive stellar runaways into the surrounding neighborhood.

The wayward star will continue to streak across space, says team member Paul Crowther of the University of Sheffield in England, and will eventually end its life in a titanic supernova explosion, likely leaving behind a remnant black hole.

CONTACT

Donna Weaver
Space Telescope Science Institute, Baltimore, Md.
410-338-4493
dweaver@stsci.edu

Nolan Walborn
Space Telescope Science Institute, Baltimore, Md.
410-338-4915
walborn@stsci.edu

Danny Lennon
Space Telescope Science Institute, Baltimore, Md.
410-338-4909
lennon@stsci.edu

Herschel finds a hole in space

NGC 1999 is the green tinged cloud towards the top of the image. The dark spot to the right was thought to be a cloud of dense dust and gas until Herschel looked at it. It is in fact a hole that has been blown in the side of NGC 1999 by the jets and winds of gas from the young stellar objects in this region of space.

This image combines Herschel PACS 70 and 160 micron data, and 1.6 and 2.2 micron data with the NEWFIRM camera on the Kitt Peak 4 meter. Credits: ESA/HOPS Consortium

ESA’s Herschel infrared space telescope has made an unexpected discovery: a hole in space. The hole has provided astronomers with a surprising glimpse into the end of the star-forming process.

Stars are born in dense clouds of dust and gas that can now be studied in unprecedented detail with Herschel. Although jets and winds of gas have been seen coming from young stars in the past, it has always been a mystery exactly how a star uses these to blow away its surroundings and emerge from its birth cloud. Now, for the first time, Herschel may be seeing an unexpected step in this process.

A cloud of bright reflective gas known to astronomers as NGC 1999 sits next to a black patch of sky. For most of the 20th century, such black patches have been known to be dense clouds of dust and gas that block light from passing through.

When Herschel looked in its direction to study nearby young stars, the cloud continued to look black. But wait! That should not be the case. Herschel’s infrared eyes are designed to see into such clouds. Either the cloud was immensely dense or something was wrong.

Investigating further using ground-based telescopes, astronomers found the same story however they looked: this patch looks black not because it is a dense pocket of gas but because it is truly empty. Something has blown a hole right through the cloud. “No-one has ever seen a hole like this,” says Tom Megeath, of the University of Toledo, USA. “It’s as surprising as knowing you have worms tunnelling under your lawn, but finding one morning that they have created a huge, yawning pit.”

The astronomers think that the hole must have been opened when the narrow jets of gas from some of the young stars in the region punctured the sheet of dust and gas that forms NGC 1999. The powerful radiation from a nearby mature star may also have helped to clear the hole. Whatever the precise chain of events, it could be an important glimpse into the way newborn stars disperse their birth clouds.

Contacts

Tom Megeath
University of Toledo, Ohio
Tel: +1 419 530 7812
Email: tommegeath @ gmail.com

Caption: A Hubble Space Telescope image of the galaxy studied by Marianne Heida. The white circle marks the centre of the galaxy and the red circle marks the position of the suspected offset black hole. Image: STScI / NASA

Undergraduate student Marianne Heida of the University of Utrecht has found what appears to be a supermassive black hole leaving its home galaxy at high speed. As part of an international team of astronomers, this extraordinary discovery appears in a paper in the journal Monthly Notices of the Royal Astronomical Society.

For her final year project, Marianne worked at the SRON Netherlands Institute for Space Research, used the Chandra Source Catalog (made using the orbiting Chandra X-ray Observatory) to compare hundreds of thousands of sources of X-rays with the positions of millions of galaxies. Normally each galaxy contains a supermassive black hole at its centre. The material that falls into black holes heats up dramatically on its final journey and often means that black holes are strong X-ray sources.

X-rays are also able to penetrate the dust and gas that obscures the centre of a galaxy, giving astronomers a clear view of the region around the black hole, with the bright source appearing as a starlike point. Looking at one galaxy in the Catalog, Marianne noticed that the point of light was offset from the centre and yet was so bright that it could well be associated with a supermassive black hole.

The black hole appears to be in the process of being expelled from its galaxy at high speed. Given that these objects can have masses equivalent to 1 billion Suns, it takes a special set of conditions to cause this to happen.

Marianne’s newly-discovered object is probably the result of the merger of two smaller black holes. Supercomputer models suggest that the larger black hole that results is shot out away at high speed, depending on the direction and speed in which the two black holes rotate before their collision. In any case, it provides a fascinating insight into the way in which supermassive black holes develop in the centre of galaxies.

Marianne’s research – which was carried out under the supervision of SRON researcher Peter Jonker - suggests this discovery may be only the tip of the iceberg, with others subject to future confirmation using the Chandra Observatory. She comments: "We have found many more objects in this strange class of X-ray sources. With Chandra we should be able to make the accurate measurements we need to pinpoint them more precisely and identify their nature."

Finding more recoiling black holes will provide a better understanding of the characteristics of black holes before they merge. In future, it might even be possible to observe this process with the planned LISA satellite, an instrument capable of measuring the gravity waves that the two merging black holes emit. Ultimately this information will let scientists know if supermassive black holes in the cores of galaxies really are the result of many lighter black holes merging together.

CONTACTS

Dr. Peter Jonker
SRON Netherlands Institute for Space research
Tel: +31 88 777 5877
E-mail: p.jonker@sron.nl

Marianne Heida
E-mail: marianneheida@gmail.com

Dr Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7734 3307 x. 214
Mob: +44 (0)794 124 8035
E-mail: rm@ras.org.uk

IMAGE

An image of the system observed by Marianne Heida can be found at http://www.sron.nl/index.php?option=com_content&task=view&id=2709&Itemid=588

NOTES FOR EDITORS

The research results have been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society, under the title "A bright off-nuclear X-ray source: a type IIn supernova, a bright ULX or a recoiling super-massive black hole in CXO J122518.6+144545". The authors are: Peter G. Jonker (SRON), Manuel A.P. Torres (Harvard-Smithsonian Center for Astrophysics), Andy C. Fabian (Cambridge), Marianne Heida (Utrecht), Giovanni Miniutti (Centro de Astrobiologia), Dave Pooley (Wisconsin). A preprint of this paper can be seen at http://arxiv.org/abs/1004.5379

Marianne Heida carried out her research at SRON Netherlands Institute for Space Research in Utrecht under the supervision of Dr Peter Jonker.

The Royal Astronomical Society (RAS: www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

Invisible light discovers the most distant cluster of galaxies - Dr. Masayuki Tanaka

The image is 3.4 arcmin on a side (1 arcmin is 1/60th of a degree), which corresponds to 5,700,000 light years in the universe 9.6 billion light years away. The arrows indicate galaxies that are likely located at approximately the same distance, and these galaxies cluster around the center of the image. The cluster emits X-rays as shown by the contours. The circles show galaxies whose distances are accurately measured from the near-infrared observations and have been confirmed to be at 9.6 billion light years away. Though the number of the confirmed members may be small, the combination of the X-ray detection and the confirmation of massive galaxies unequivocally prove a real, gravitationally bound cluster.

The universe hosts a multitude of galaxies. Galaxies are not uniformly distributed in the universe, but are arrayed in filamentary structures. Filaments permeate the universe and form a gigantic cosmic spider web. Galaxies clusters, where many galaxies live together, are often located at the knots of the filaments. The most distant cluster known – at least until now – is located some 9.2 billion light years away. A team of astronomers from Japan and Germany has discovered an even more distant cluster of galaxies using light invisible to human eyes.

The universe is a time machine; that is, you can go back in time as you look deeper into the universe. Astronomers have used this principle in search of clusters in a distant past. But, the expansion of the universe forces distant galaxies away from Earth at large velocities, shifting their light away from visible wavelengths to infrared wavelengths. This shift makes the light from the distant universe invisible, which has impeded progress over the years. The powerful capability of Subaru's near-infrared eye MOIRCS, though, now enables astronomers to peer deeper back into the early universe.

Tanaka and collaborators found a candidate in a very distant cluster of galaxies in the constellation of Cetus. MOIRCS was used to measure the distances to massive galaxies in the candidate cluster. "MOIRCS has an extremely powerful capability of measuring distances to galaxies. This is what made our challenging observation possible," says Tanaka. The team succeeded in measuring the distances and confirmed that several galaxies actually have congregated at a distance as far as 9.6 billion light years away. He adds, "Though we confirmed only several massive galaxies at that distance, there is convincing evidence that the cluster is a real, gravitationally bound cluster."

Galaxy clusters host a vast amount of matter heated to extreme temperatures. Every material emits light; but at such high temperatures, the emission is so blue that the light is not visible to the human eye. The team used the orbiting X-ray observatory XMM-Newton to search for invisible light from the cluster. According to Finoguenov, X-ray expert on the team, "Despite the difficulties in collecting X-ray photons with a small effective telescope size similar to the size of a backyard telescope, we detected a clear signature of hot gas in the cluster."

The combination of observations in invisible wavelengths – near-infrared and X-ray – has led to the discovery of the cluster at 9.6 billion light years away, making it the most distant cluster known today some 400 million more light years away. The cluster is an ideal laboratory for studying the evolution of galaxies. Also, a collection of such distant clusters can be a sensitive probe of the origin of the universe. The team is continuing their search for more distant clusters.

Dr. Masayuki Tanaka of the Institute for the Physics and Mathematics of the Universe (IPMU), Dr. Alexis Finoguenov of the Max Planck Institute for Extraterrestrial Physics, and Dr. Yoshihiro Ueda of Kyoto University discovered the most distant cluster of galaxies in the universe 9.6 billion light years away using light invisible to our eyes.

The paper has been accepted for publication in The Astrophysical Journal Letters.

Publication: The Astrophysical Journal Letters
Title: "A spectroscopically confirmed X-ray cluster at z=1.62 with a possible companion
in the Subaru/XMM-Newton deep field"
Authors: M. Tanaka, A. Finoguenov, and Y. Ueda

References

European Space Agency
Subaru Telescope
Subaru/XMM-Newton Deep Field
XMM-Newton Satellite

Contacts - For more details

Masayuki Tanaka - IPMU Researcher
tel: +81-4-7136-6525
e-mail: masayuki.tanaka@ipmu.jp

Alexis Finoguenov - Max-Planck-Institut fur extraterrestrische Physik, Germany
tel: +49-89-30000-3644
e-mail: alexis@mpe.mpg.de

Media Contact

Fusae Miyazoe - IPMU Press Officer
tel: +81-4-7136-5977
e-mail: press@ipmu.jp

Making the invisible visible

Fig. 1: A snapshot of a stellar nursery in our home galaxy, the Milky Way: a high-mass star forming region inside the giant molecular cloud S255, about 8,000 light-years away from Earth (1 light-year is roughly 10 trillion kilometers). Such clouds are typically opaque to visible light. However, infrared light can penetrate the dust, so that the LUCIFER image reveals the cluster of newly born stars and its complex environment in all their splendour. Image: Arjan Bik

LUCIFER’s innovative design allows astronomers to observe in unprecedented detail, for example, star forming regions which are commonly hidden by dust clouds. The instrument provides unrivaled flexibility, with features such as a unique robotic arm that can replace spectroscopic masks within the instrument’s extreme sub-zero environment.

LUCIFER and its twin are mounted at the focus points of the LBT’s two giant 8.4-metre (27.6 foot) diameter telescope mirrors. Each instrument is cooled to a chilly -213 degrees Celsius in order to observe in the near-infrared (NIR) wavelength range. Near-infrared observations are essential for understanding the formation of stars and planets in our galaxy as well as revealing the secrets of the most distant and very young galaxies.

Fig. 2: The faint irregular dwarf galaxy NGC 1569, located 6.2 million light-years from Earth. This galaxy contains several large stellar clusters with episodic star formation at a rate of more than 100 times faster than we observe in our own galaxy. In visible light, the core of the galaxy shows only three large stellar clusters, each containing more than one million stars. With LUCIFER it became possible to peer through the cosmic dust and to reveal many more compact star forming regions. Image: Anna Pasquali

LUCIFER is a remarkable new multi-purpose instrument with great flexibility combining a large field of view with a high resolution. It provides three exchangeable cameras for imaging and spectroscopy in different resolutions according to observational requirements. Besides its outstanding imaging capability which presently makes use of 18 high-quality filters, LUCIFER allows the simultaneous spectroscopy of about two dozen objects in the infrared through laser-cut slit-masks. For highest flexibility the masks can be changed even at the cryogenic temperatures, through the innovative development of a unique robotic mask grabber which places the individual masks with absolute precision into the focal plane.

"Together with the large light gathering power of the LBT, astronomers are now able to collect the spectral fingerprints of the faintest and most distant objects in the universe." says Richard Green, the Director of the LBT. "After completion of the LBT adaptive secondary mirror system to correct for atmospheric perturbation, LUCIFER will show its full capability by delivering images with a quality that are otherwise only obtained from space-based observatories."

"Already the very first LUCIFER observations of star forming regions are giving us an indication of the enormous potential of the new instrument," said Thomas Henning, the chair of the German LBT-Partners.

Fig. 3: A cut-out of a multi-object spectrum obtained with LUCIFER showing the tell-tale signs of gas heated by young stars at unimaginably distances of billions of light-years. Such a spectrum is the decomposition of light into its different wavelengths (colors). At certain wavelengths, emission lines can be found depending on the chemical composition and physical conditions of an object. For distant galaxies, the most interesting lines are found in the near-infrared, where observations were less efficient until now. With LUCIFER and the LBT, large samples of galaxies can now be studied using its multi-object capability. Image: Jaron Kurk

The instruments have been built by a consortium of five German institutes led by the Center for Astronomy of Heidelberg University (Landessternwarte Heidelberg, LSW) together with the Max Planck Institute for Astronomy in Heidelberg (MPIA), the Max Planck Institute for Extraterrestrial Physics in Garching (MPE), the Astronomical Institute of the Ruhr-University in Bochum (AIRUB) as well as the University of Applied Sciences in Mannheim (Hochschule Mannheim).

Walter Seifert (LSW), Nancy Ageorges (MPE) and Marcus Jütte (AIRUB), responsible for the successful commissioning, spent more than half a year in several runs at the LBT site to make the telescope/instrument combination work efficiently. Holger Mandel, the Principal Investigator of LUCIFER said: "From the very beginning, there was uniform excitement about the promise of this instrument for cutting-edge science. Now, the amazing results speak for themselves."

********

The Large Binocular Telescope (LBT) is a collaboration among the Italian astronomical community (National Institute of Astrophysics - INAF), The University of Arizona, Arizona State University, Northern Arizona University, the LBT Beteiligungsgesellschaft in Germany (Max Planck Institute for Astronomy in Heidelberg, Zentrum fur Astronomie der Universität Heidelberg, Astrophysikalisches Institut in Potsdam, Max Planck Institute for Extraterrestrial Physics in Garching (Munich), and Max Planck Institute fϋr Radio Astronomy in Bonn), The Ohio State University and Research Corporation (Ohio State University, University of Notre Dame, University of Minnesota, and University of Virginia).

Related links:

[1] Images, detailed image captions and additional technical background information

PDF (361 KB)

Contact:

Prof. Dr. Thomas Henning
Max Planck Institute for Astronomy, Heidelberg
Tel.: +49 6221 528-201
E-mail: henning@mpia.de

Dr. Klaus Jäger
Max Planck Institute for Astronomy, Heidelberg
Tel.: +49 6221 528-379
E-mail: jaeger@mpia.de

Dr. Holger Mandel
Landessternwarte Heidelberg
Tel.: +49 6221 541-734
E-mail: h.mandel@lsw.uni-heidelberg.de

Dr. Walter Seifert
Landessternwarte Heidelberg
Tel.: +49 6221 541-732
E-mail: wseifert@lsw.uni-heidelberg.de

Herschel's HIFI follows the trail of cosmic water

Herschel's HIFI instrument was especially designed to follow the water trail in the Universe over a wide range of scales, from the Solar System out to extragalactic sources. Early results, presented this week at the Herschel First Results Symposium, demonstrate how HIFI uses water to probe the physical and chemical conditions in different regions of the cosmos.

Water is an extremely important molecule in the Universe, abundant in a large variety of cosmic environments — from our own blue planet and its neighbourhood, the Solar System, through interstellar clouds where new stars and planets are formed, and even beyond the Milky Way, in star-forming galaxies. Due to the large amount of water vapour present in the Earth's atmosphere, however, astronomical observations of water from ground-based facilities are virtually impossible, even from the driest and highest deserts; they need to be carried out with space observatories.

Depicts: Water lines toward low-mass protostars in the NGC 1333 star-forming region

Copyright: ESA and the HIFI consortium; L.E. Kristensen for the WISH Key Programme. Background image: NASA/JPL-Caltech/R. Gutermuth (Harvard-Smithsonian CfA)

Depicts: Water lines toward the intermediate-mass protostar NGC 7129

Copyright: ESA and the HIFI consortium; D. Johnstone for the WISH Key Programme. Background image: NASA/JPL-Caltech/S.T. Megeath (Harvard-Smithsonian CfA)

The presence of water in a celestial object is revealed through its very distinctive fingerprints, or lines, in the object's spectrum at far-infrared and sub-millimetre wavelengths. Only high resolution spectrographs, such as HIFI on board ESA's Herschel Space Observatory, are able to obtain spectra sufficiently precise to track down the abundance of water in great detail.

HIFI, or the Heterodyne Instrument for the Far Infrared, was designed with the quest of water and other molecules very much in mind. Based on the heterodyne detection principle, it basically translates, without loss of information, the high-frequency signal received from astronomical sources to a lower frequency, where measurements are easier to perform. "With its superb spectral resolution, HIFI is ideally suited to detect and characterize molecular lines, and is currently performing a chemical census of the cosmos," says Göran Pilbratt, Herschel Project Scientist.

"Water is an excellent diagnostic tool to probe the chemical and physical structure of the interstellar medium," explains Alexander Tielens from Leiden University. "Early detection of this important molecule on all cosmic scales highlights that HIFI is working extremely well."

With its superb resolution, HIFI can target about 40 different lines, each coming from a different transition of the water molecule and thus sensitive to a different temperature. This plethora of water lines in the spectra is anything but redundant information: it actually helps to overcome one of the natural drawbacks of astronomical observations, which yield two-dimensional images due to the projection on the celestial vault. As each line comes from a slightly different area in the interstellar clouds, putting all the information together gives a three-dimensional view of them. "HIFI data represent a sort of MRI scan through these regions, examining them slice-by-slice in a tomographic approach," explains Frank Helmich, Principal Investigator for Herschel-HIFI.

The role of water is crucial in the processes of star formation, because this molecule contributes to the cooling of the gas and dust mixture from which stars are born. Early results, reported this week at the Herschel First Results Symposium, demonstrate the detection of water in various proto-stellar systems. Along with upcoming data from star-forming clouds throughout the Milky Way, these data will help astronomers understand the mechanisms of star formation in great detail. Beyond our Galaxy, water signatures have been found in nearby galaxies which are known to be undergoing intense bursts of star formation.

Water trails go all the way from vast star-forming clouds down to stars and planets on much smaller scales. In the proto-planetary discs surrounding stars in the process of forming, water vapour may in fact freeze onto dust grains; these cold grains would then condense into icy planetesimals, the seeds of planet formation.

"In our very own planetary system, HIFI has observed a handful of comets, which are dusty conglomerates held together by icy water," notes Tielens. These cosmic 'ice balls' are living fossils in the Solar System, since they spend most of their lifetime at its boundaries and their chemical composition closely reflects the pristine conditions when the planets were formed about 4.5 billion years ago. "Further analysis of these early data collected by HIFI will shed new light on the early history of the Solar System," Tielens adds.

Notes for editors:

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia, with important participation from NASA.

HIFI, a high resolution spectrometer was designed and built by a nationally-funded consortium led by SRON Netherlands Institute for Space Research. The consortium includes institutes from France, Germany, USA, Canada, Ireland, Italy, Poland, Russia, Spain, Sweden, Switzerland, and Taiwan.

The distribution of water and its related species is the primary focus of the Key Programme WISH: Water In Star-forming regions with Herschel, led by Principal Investigator E.F. van Dishoeck. This programme is dedicated to studying the physical and chemical structure of star-forming regions through combined HIFI and PACS spectroscopy.

Other HIFI Key Programmes with a water theme are: HIFISTARS, led by Principal Investigator Valentín Bujarrabal, which studies the role of water in the ejecta from stars in the latest stages of their evolution when they return most of their material back to the interstellar medium; HSSO, led by Principal Investigator Paul Hartogh, which studies the role of water in Solar System objects, in particular Mars, the giant planets and comets; and HEXGAL, led by Principal Investigator Rolf Güsten, which among other things follows the water trail on a galactic scale in nearby galaxies.

Contacts:

Göran Pilbratt, Herschel Project Scientist
Research and Scientific Support Department
Science and Robotic Exploration Directorate, ESA, The Netherlands
Email: gpilbrattr@ssd.esa.int
Phone: +31-71-565-3621

Alexander Tielens, HIFI Project Scientist
Leiden University, The Netherlands
Email: tielens@strw.leidenuniv.nl
Phone: +31-71-527-8465

Ewine van Dishoeck, Principal Investigator of the WISH Key Programme
Leiden University, The Netherlands
Email: ewine@strw.leidenuniv.nl
Phone: +31-71-527-5814

Frank Helmich, Principal Investigator for HIFI
SRON Netherlands Institute for Space Research, The Netherlands
Email: F.P.Helmich@sron.nl
Phone: + 31-50-363-8320
Mobile phone: +31-6-49423644

Herschel unveils rare massive stars in the act of forming

New images from ESA's Herschel space observatory reveal high-mass protostars around two ionised regions in our Galaxy. The detection of these rare stars in an early phase of evolution is key to understanding the mysterious formation of massive stars.

This is one of the many discoveries presented this week at the Herschel First Results Symposium, ESLAB 2010, held at the European Space Research and Technology Centre, Noordwijk, The Netherlands.

Massive stars are the rare birds of astrophysics. With a mass over eight times that of the Sun, these stars are much less common than their lower-mass counterparts. In addition, they are short-lived, consuming their nuclear fuel at a rapid rate before ending their life in spectacular manner as a supernova. Their scarcity means that observations of these rare giants can prove difficult to obtain, but characterising these elusive objects is essential for understanding the chemical and dynamical evolution of galaxies.

The mechanism leading to the formation of massive stars is still largely debated. Detecting these objects in their earliest phases is a highly challenging task, since they are embedded in dusty cocoons that hide them from view. However, the dust that absorbs their light re-emits it at infrared wavelengths, making an infrared observatory such as Herschel a unique tool for locating newborn massive stars in their natal nests.

RCW 120 as seen by Herschel. Credit: ESA, PACS & SPIRE Consortia, A. Zavagno (Laboratoire d'Astrophysique de Marseille) for the Herschel HOBYS and Evolution of Interstellar Dust Key Programmes

One theory that has been put forward predicts that massive stars form at the outskirts of HII regions. An HII region is a bubble of hot hydrogen gas which has been ionised by the powerful radiation emitted by a central massive star formed in a previous generation. Temperature differences between the interior (up to 10 000 Kelvin) and the surrounding material (cooler than 100 Kelvin) cause these bubbles to expand and to reach supersonic speeds. This expanding bubble sweeps up a layer of neutral material around it, which then fragments into the dense seeds of a new generation of high-mass stars.

New data from Herschel targeting two distinct HII regions in our Galaxy, namely RCW 120 and N49, yield strong evidence in favour of this scenario. Thanks to its unprecedented resolution and sensitivity over a wide range of infrared wavelengths, ESA's new space observatory has imaged, for the first time, a handful of very young, massive stars on the border of both regions. These objects, which came to life less than a few tens of thousands of years ago, have never before been observed.

"We can finally witness the long-sought-after triggered formation of massive stars," says Annie Zavagno from Laboratoire d'Astrophysique de Marseille. "The high density of the material surrounding these bubbles and the intense motions due to stellar winds might be responsible for this particularly efficient star-forming process, leading to a new population of more massive stars around them."

The 'collect and collapse' model.

Credit: Deharveng & Zavagno

"Exploiting the unique combination of PACS and SPIRE, the two cameras on board Herschel, with a total spectral coverage that extends beyond the far-infrared into the sub-millimetre, the newly released images have refined our view on the birth of stars around expanding HII regions," says Göran Pilbratt, Herschel Project Scientist. "As a result of this new data, astronomers have been able not only to spot previously undetected young stars, but also to characterise their physical properties."

Particularly striking is the discovery, around RCW 120, of a massive protostar with a mass 8-10 times larger than the Sun's. "This object appears to be surrounded by a huge envelope of about 2000 solar masses, and it will continue to grow into an even more massive fully-fledged star," adds Zavagno.

Over the course of the next few months, PACS and SPIRE will target several other galactic HII regions that exhibit evidence of triggered star formation, in order to study this process in greater detail and to shed new light on the mechanisms producing high-mass stars in our Galaxy.

Notes to Editors

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia, with important participation from NASA.

PACS is an imaging photometer and integral field line spectrometer covering wavelengths between 57 and 210 µm. PACS was built by a consortium of institutes and university departments from across Europe, and is led by Albrecht Poglitsch of the Max-Planck-Institute for Extraterrestrial Physics, Garching, Germany. Consortium members are: Austria: UVIE; Belgium: IMEC, KUL, CSL; France: CEA, OAMP; Germany: MPE, MPIA; Italy: IFSI, OAP/OAT, OAA/CAISMI, LENS, SISSA; Spain: IAC.

The SPIRE instrument comprises an imaging photometer (camera) and an imaging spectrometer. The camera operates in three wavelength bands centred on 250, 350 and 500 μm, and so can make images of the sky simultaneously in three submillimetre “colours”. The spectrometer covers the range 200 – 670 μm, allowing the spectral features of atoms and molecules to be measured. SPIRE has been developed by a consortium of institutes led by Cardiff Univ. (UK) and including Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC (UK); and NASA (USA). The SPIRE consortium is led by Prof. Matt Griffin of Cardiff University, United Kingdom.

The results reported here are based on a subset of observations from the following Herschel Key Programmes: HOBYS: the Herschel imaging survey of OB Young Stellar objects, led by Principal Investigator Frédérique Motte (SAp/CEA Saclay, France); Evolution of Interstellar Dust, led by Principal Investigator Alain Abergel (Institut d'Astrophysique Spatiale, IAS, France); and Hi-GAL: the Herschel Infrared Galactic Plane Survey, led by Principal Investigator Sergio Molinari (IFSI-INAF, Italy).

Related publications

Zavagno, A., et al., "Star formation triggered by the Galactic HII region RCW 120", 2010
Zavagno, A., et al., "Star formation triggered by HII regions in our Galaxy", 2010

Both papers will appear in a special issue of the journal Astronomy & Astrophysics dedicated to Herschel's first results.

Contacts

Annie Zavagno
Laboratoire d'Astrophysique de Marseille, France
Email: annie.zavagno@oamp.fr
Phone: +33-4-95-04-41-55

Göran Pilbratt, Herschel Project Scientist
Research and Scientific Support Department
Science and Robotic Exploration Directorate, ESA, The Netherlands
Email: gpilbratt@rssd.esa.int
Phone: +31-71-565-3621

Herschel reveals galaxies in the GOODS fields in a brand new light

The discovery of a previously unresolved population of galaxies in the GOODS fields and the first measurements of properties of galaxies in the almost unexplored far-infrared domain are among the first exciting scientific results achieved by Herschel's PACS and SPIRE instruments. These findings confirm the extraordinary capabilities of ESA's new infrared space observatory to investigate the formation and evolution of galaxies.

These are some of the many discoveries presented this week at the Herschel First Results Symposium, ESLAB 2010, held at the European Space Research and Technology Centre, Noordwijk, The Netherlands.

Understanding the details of how galaxies formed and evolved throughout cosmic history is one of the main goals of current astrophysical research. ESA's Herschel space observatory has begun to address this issue by joining in GOODS - the Great Observatories Origins Deep Survey - an ambitious project conceived to shed new light on this open topic.

Two carefully selected regions of the northern and southern sky, centred on the Hubble Deep Field North and the Chandra Deep Field South, have been the target of deep surveys conducted during the past decade over an extremely broad wavelength range, by means of ESA's and NASA's space observatories and the foremost ground-based telescopes. The GOODS fields, each measuring 10 by 16 arc minutes, are ideal for studying galaxies out to very high redshifts, as they do not contain any bright star and are not contaminated by strong emission coming from the Milky Way.

"Although both GOODS fields have been the object of extensive observations in the past, they have not yet been explored in the far-infrared region of the electromagnetic spectrum," explains Göran Pilbratt, Herschel Project Scientist. "Exploiting Herschel's powerful infrared eye and its broad wavelength coverage, we are now in the process of revealing some of the secrets that have been concealed until now."

Depicts: GOODS-South field

Copyright: ESA/PACS Consortium/PEP Key Programme Consortium

Depicts: PACS composite image of the GOODS-North field

Copyright: ESA/PACS Consortium/PEP Key Programme Consortium

With both the wavelength coverage and the technical characteristics required to resolve this 'cosmic fog' into individual galaxies, Herschel's PACS has isolated the sources of about a half of the CIB in the GOODS fields. "Thanks to the wealth of complementary data available for these fields, we have also studied how many of these galaxies are to be found at various epochs in cosmic history," adds Stefano Berta, who led this study. In fact, most of these galaxies are located at relatively low redshifts, their light having travelled less than 8000 million years before reaching us.

GOODS-N as viewed by SPIRE.

Credit: ESA/SPIRE Consortium/ HerMES Key Programme Consortium

"We know that the energy we receive from galaxies directly is roughly as much as the energy we receive from them after it has been reprocessed by dust," says Seb Oliver from the University of Sussex and leader of the HerMES Key Programme which probes galaxy evolution. "Thanks to SPIRE and PACS, we can finally explore how the population of obscured galaxies has evolved over cosmic time."

The true power of Herschel is unleashed when the images from both instruments are studied together. As a result of this synergy, observations of galaxies made by SPIRE on the GOODS-North field complement the studies on the CIB performed with PACS data. "A significant fraction of galaxies contributing to the CIB has also been resolved by SPIRE," comments Oliver. "This population of galaxies is dominated by sources at z~1, demonstrating that most of the infrared background radiation is emitted at low redshifts," adds Steve Eales from Cardiff University.

By sampling galaxies at the peak of their far-infrared emission, Herschel allows also a better understanding of the star-forming processes taking place within them. "The properties of galaxies in these new PACS and SPIRE images appear surprisingly uniform over the last 10 billion years of cosmic history, even for those galaxies harbouring an active nucleus," says David Elbaz from Laboratoire AIM-Paris-Saclay. This finding suggests that the history of star formation in the Universe is governed by simple, universal mechanisms. "This is only a first step, since a new window on the GOODS fields has just been opened with the GOODS-Herschel Open Time Key Programme. This will push Herschel to its ultimate limits in terms of depth," adds Elbaz.

And it is clear that much more is in store when placing Herschel data in the broader context of the wider electromagnetic spectrum. Some interesting results have already arisen when comparing Herschel data with radio observations of the GOODS-North field performed by the Very Large Array. "We have revealed tantalising signs of an evolution of the famous (and surprisingly strong) correlation between infrared emission and radio emission," notes Rob Ivison from UK Astronomy Technology Centre at the Royal Observatory in Edinburgh.

Notes to Editors

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia, with important participation from NASA.

PACS is an imaging photometer and integral field line spectrometer covering wavelengths between 57 and 210 µm. PACS was built by a consortium of institutes and university departments from across Europe, and is led by Albrecht Poglitsch of the Max-Planck-Institute for Extraterrestrial Physics, Garching, Germany. Consortium members are: Austria: UVIE; Belgium: IMEC, KUL, CSL; France: CEA, OAMP; Germany: MPE, MPIA; Italy: IFSI, OAP/OAT, OAA/CAISMI, LENS, SISSA; Spain: IAC.

The SPIRE instrument comprises an imaging photometer (camera) and an imaging spectrometer. The camera operates in three wavelength bands centred on 250, 350 and 500 μm, and so can make images of the sky simultaneously in three submillimetre "colours". The spectrometer covers the range 200 – 670 μm, allowing the spectral features of atoms and molecules to be measured. SPIRE has been built by a consortium of 18 institutes in eight countries (UK, France, Italy, Spain, Sweden, USA, and China), and is led by Prof. Matt Griffin of Cardiff University. The instrument was assembled at the STFC's Rutherford Appleton Laboratory in the UK.

The PACS data on the GOODS fields have been obtained within the PACS Evolutionary Probe (PEP) collaboration, a Herschel Guaranteed Time Key Programme extragalactic survey, led by Dieter Lutz (Max Planck Institute for extraterrestrial Physics). PEP aims at studying galaxies up to redshift z~3 over a large total area in the sky, including the COSMOS field, the Lockman Hole and fields centred on lensing galaxy clusters. PEP is coordinated with SPIRE observations of the same fields in the Herschel Multi-tiered Extragalactic Survey (HerMES), another Guaranteed Time Key Programme probing galaxy evolution at high redshift. HerMES is led by Seb Oliver (University of Sussex).

Related publications

Berta, S., et al., "Dissecting the Cosmic Infra-Red Background with Herschel/PEP", 2010

Oliver, S.J., et al., "HerMES: SPIRE galaxy number counts at 250, 350 and 500 µm", 2010

Eales, S., et al."First results from HerMES on the evolution of the submillimetre luminosity function", 2010

Elbaz, D., et al., "Herschel unveils a puzzling uniformity of distant dusty galaxies", 2010

Ivison, R.J., et al., "The far-infrared/radio correlation as probed by Herschel", 2010

These papers will appear in a special issue of the journal Astronomy & Astrophysics dedicated to Herschel's first results.

Contacts

Göran Pilbratt, Herschel Project Scientist
Research and Scientific Support Department
Science and Robotic Exploration Directorate, ESA, The Netherlands
Email: gpilbrattr@ssd.esa.int
Phone: +31-71-565-3621

Dieter Lutz
Max Planck Institute for extraterrestrial Physics, Germany
Phone: +49 89 300003614
Email: lutz@mpe.mpg.de

Stefano Berta
Max Planck Institute for extraterrestrial Physics, Germany
Phone: +49-89-300003616
Email: berta@mpe.mpg.de

Seb Oliver

University of Sussex, United Kingdom

Phone: +44-1273-678852; mobile number: +44-7971-019161

Email: Oliver@sussex.ac.uk

Steve Eales
Cardiff University, United Kingdom
Phone: +44-29-208-76168
Email: Steve Eales@astro.cf.ac.uk

David Elbaz
Laboratoire AIM-Paris-Saclay, France
Phone: + 33-1-69085439
Email: delbaz@cea.fr

Rob Ivison
UK Astronomy Technology Centre at the Royal Observatory Edinburgh, part of the Science and Technology Facilities Council, United Kingdom
Phone: +44-131-668-8361
Email: rji@roe.ac.uk

A Cluster and a Sea of Galaxies

PR Image eso1019a

The Cluster of Galaxies Abell 315

PR Image eso1019b

Around Abell 315

PR Video eso1019a

Zooming in on Abell 315

A new wide-field image released today by ESO displays many thousands of distant galaxies, and more particularly a large group belonging to the massive galaxy cluster known as Abell 315. As crowded as it may appear, this assembly of galaxies is only the proverbial “tip of the iceberg”, as Abell 315 — like most galaxy clusters — is dominated by dark matter. The huge mass of this cluster deflects light from background galaxies, distorting their observed shapes slightly.

When looking at the sky with the unaided eye, we mostly only see stars within our Milky Way galaxy and some of its closest neighbours. More distant galaxies are just too faint to be perceived by the human eye, but if we could see them, they would literally cover the sky. This new image released by ESO is both a wide-field and long-exposure one, and reveals thousands of galaxies crowding an area on the sky roughly as large as the full Moon.

These galaxies span a vast range of distances from us. Some are relatively close, as it is possible to distinguish their spiral arms or elliptical halos, especially in the upper part of the image. The more distant appear just like the faintest of blobs — their light has travelled through the Universe for eight billion years or more before reaching Earth.

Beginning in the centre of the image and extending below and to the left, a concentration of about a hundred yellowish galaxies identifies a massive galaxy cluster, designated with the number 315 in the catalogue compiled by the American astronomer George Abell in 1958 [1]. The cluster is located between the faint, red and blue galaxies and the Earth, about two billion light-years away from us. It lies in the constellation of Cetus (the Whale).

Galaxy clusters are some of the largest structures in the Universe held together by gravity. But there is more in these structures than the many galaxies we can see. Galaxies in these giants contribute to only ten percent of the mass, with hot gas in between galaxies accounting for another ten percent [2]. The remaining 80 percent is made of an invisible and unknown ingredient called dark matter that lies in between the galaxies.

The presence of dark matter is revealed through its gravitational effect: the enormous mass of a galaxy cluster acts on the light from galaxies behind the cluster like a cosmic magnifying glass, bending the trajectory of the light and thus making the galaxies appear slightly distorted [3]. By observing and analysing the twisted shapes of these background galaxies, astronomers can infer the total mass of the cluster responsible for the distortion, even when this mass is mostly invisible. However, this effect is usually tiny, and it is necessary to measure it over a huge number of galaxies to obtain significant results: in the case of Abell 315, the shapes of almost 10 000 faint galaxies in this image were studied in order to estimate the total mass of the cluster, which amounts to over a hundred thousand billion times the mass of our Sun [4].

To complement the enormous range of cosmic distances and sizes surveyed by this image, a handful of objects much smaller than galaxies and galaxy clusters and much closer to Earth are scattered throughout the field: besides several stars belonging to our galaxy, many asteroids are also visible as blue, green or red trails [5]. These objects belong to the main asteroid belt, located between the orbits of Mars and Jupiter, and their dimensions vary from some tens of kilometres, for the brightest ones, to just a few kilometres in the case of the faintest ones.

This image has been taken with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. It is a composite of several exposures acquired using three different broadband filters, for a total of almost one hour in the B filter and about one and a half hours in the V and R filters. The field of view is 34 x 33 arcminutes.

Notes

[1] The Abell catalogue from 1958 comprised 2712 clusters of galaxies, and was integrated with an additional 1361 clusters in 1989. Abell put together this impressive collection by visual inspection of photographic plates of the sky, seeking those areas where more galaxies than average were found at approximately the same distance from us.

[2] Ten percent of a galaxy cluster’s mass consists of a very hot mixture of protons and electrons (a plasma), with temperatures as high as ten million degrees or more, which makes it visible to X-ray telescopes.

[3] Astronomers refer to these slight distortions as weak gravitational lensing, as opposed to strong gravitational lensing, characterised by more spectacular phenomena such as giant arcs, rings and multiple images.

[4] A weak lensing study of the galaxy cluster Abell 315 has been published in a paper that appeared in Astronomy & Astrophysics in 2009 (“Weak lensing observations of potentially X-ray underluminous galaxy clusters”, by J. Dietrich et al.).

[5] The blue, green or red tracks indicate that each asteroid has been detected through one of the three filters, respectively. Each track is composed of several, smaller sub-tracks, reflecting the sequence of several exposures performed in each of the filters; from the length of these sub-tracks, the distance to the asteroid can be calculated.

More information

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, 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 VISTA, the world’s largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Contacts

Henri Boffin
ESO, VLT Press Officer
Garching, Germany
Tel: +49 89 3200 6222
Cell: +49 174 515 43 24
Email: hboffin@eso.org

Additional Eyes for Pulsar Astronomers

Figure 1: Simultaneous detection of pulses from pulsar PSR B1133+16 in four widely spaced bands, using the Effelsberg telescope at 3.5 cm wavelength, the Lovell telescope at 21 cm wavelength, and LOFAR high-band (HBAs) and low-band antennas (LBAs) at 170 cm and 430 cm wavelength, respectively. The figure shows the pulse intensity as a function of time for the four observed wavelengths. The shape of the pulsar's pulsed emission maps the spreading of magnetic field lines above the pulsar's magnetic poles. Image: Aris Karastergiou, University of Oxford

Figure 2: A part of the 96 LBA dipole antennas of the LOFAR station Effelsberg can be seen in the foreground, in close proximity to the giant 100-m radio telescope. Image : Wolfgang Reich (MPIfR)

Combination of new technology telescope with existing facilities promises new insight into extreme stars

An international team of astronomers including scientists from the Max Planck Institute for Radio Astronomy has set a new world record in wavelength coverage for observing the enigmatic radio emitting stars called pulsars. They used the new European LOFAR telescope, in combination with two of the world's largest radio telescopes, the Effelsberg telescope in Germany and the Lovell telescope in the United Kingdom. This unique combination of telescopes allowed them to simultaneously observe the radio light from six different pulsars across wavelengths from only 3.5 centimetres up to 7 meters - a factor of 200 difference. These different wavelengths of radio light are analogous to the different colours perceived by the human eye and provide an unprecedented view of how radio pulsars shine.

Pulsars are rapidly rotating neutron stars, which measure only about 20 kilometers across and yet are more massive than the Sun. They produce beams of radio light from their magnetic poles, which are observable over a wide range of wavelengths.

For the last 40 years astronomers have been studying pulsars and they are getting closer and closer to understanding the mechanism that generates these intense beams. They hypothesize that the emission seen at the different wavelengths emerges from different heights above the highly magnetized pulsar surface. Emission seen at a particular radio wavelength therefore provides a slice through the pulsar's surrounding "magnetosphere" (magnetized atmosphere). The magnetic field lines that accelerate particles spread apart as one moves further and further away from the pulsar's surface. Experimental support for this hypothesis is the observation that the pulses of some pulsars become stretched out at long wavelengths (Fig. 1). The shape of the pulsar's pulsed emission is seen to evolve quite drastically as a function of wavelength and maps the spreading of magnetic field lines above the pulsar's magnetic poles.

With any single telescope, a pulsar can only be observed in a relatively narrow range of wavelengths at any given time. By combining the traditional large Effelsberg and Lovell telescopes, observing at wavelengths of centimetres, with the next generation telescope LOFAR, observing at wavelengths of meters, the astronomers were able to observe a set of six pulsars, each simultaneously across a range of nearly 8 octaves. "For comparison, consider that we have simultaneously observed these pulsars over a range equivalent to all the tones spanned by a piano," says Jason Hessels of ASTRON Netherlands Institute for Radio Astronomy. "By simultaneously observing these pulsars at such a wide range of wavelengths, we can make many snapshots of what the pulsar's emission looks like at a range of heights above the star's magnetic poles," he adds.

Key to these observations was the use of the new LOFAR telescope, which has a collection of thousands of radio antennas in stations that are centred near Exloo, in the Netherlands, and that spread from there over distances of hundreds of kilometers into neighbouring countries, such as France, Germany, Sweden, and the United Kingdom. The data taken on all stations are brought together for data analysis via high-speed networks to a BlueGene/P supercomputer and powerful cluster computers at the University of Groningen Centre for Information Technology. LOFAR is operated as an integrated facility from the ASTRON headquarters in Dwingeloo, the Netherlands. The LOFAR telescope is currently being prepared for full-scale scientific observations, and the astronomers were excited to make such high-quality, pulsar measurements even in the testing phase.

Michael Kramer, director at the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, is excited about the enormous extension in wavelength coverage provided by LOFAR, of which the first international antenna station was built next to the Effelsberg telescope in Germany. "These observations show how LOFAR complements the existing radio telescopes in Europe, like the 100-m Effelsberg telescope, in a nearly perfect way" (see Fig. 2).

These observations have the primary goal of better understanding how pulsars pulse. However, there is also much to be learned beyond studying just the pulsar itself. "Not only do such observations give us a fantastic handle on understanding the emission of pulsars, they are also a powerful probe of the interstellar gas that is between us and the pulsar," says Ben Stappers of the University of Manchester.

"We are really excited to have the first international LOFAR station operating here in direct vicinity to the giant 100-m Effelsberg radio telescope", says Kosmas Lazaridis from MPIfR. "The combination of both, large parabolic dishes for the centimetre regime, and new digital technology for the longer wavelengths provides a wealth of new data for our pulsar research programs."

The LOFAR telescope, spanning more than 1000 kilometres in Europe, will be completed in the next year and will be the most powerful telescope on Earth for observing the Universe at the longest possible radio wavelengths visible from the Earth's surface: 1-30 meters. It is expected that this will produce a flood of exciting new scientific results.

The Supernovae of Triangulum

An optical image of the Triangulum Galaxy.

Scientists have used the Chandra X-ray Observatory to study and characterize all of the known supernova remnants in this galaxy. Credit: Paul Mortfield, Stefano Cancelli

The Triangulum Galaxy, at a distance of only 2.6 million light-years, is one of the closest spiral galaxies to earth. It is also the third largest member of our galactic neighborhood (after Andromeda and our own Milky Way). Because we see it nearly face on and so have such a clear view of its stars, it has long been an obvious choice for astronomers wanting to characterize the complete population of supernovae in a galaxy.

Supernovae are the explosive deaths of massive stars. These cataclysms disburse into space all the chemical elements produced by the nuclear reactions inside the progenitor stars, and chemical enrichment alone is reason enough to make supernovae objects of intense study. In addition, though, supernovae are so bright that they can be seen at very large (cosmological) distances. If a supernova's intrinsic brightness is known from its basic character, its distance (and the distance of its host galaxy) can be determined from its apparent brightness. This presumes that we understand supernovae and their possible varieties. By studying the character of an entire population of supernovae in a single galaxy, like the Triangulum, and the remnants they leave behind, astronomers can test and refine their understanding of supernovae.

In the Milky Way there have been at least five supernovae in the last thousand years or so. All of their remnants are detectable today as X-ray sources, and their differing properties reflect their diverse characters. For example, while four these five remnants have comparatively modest gas temperatures, the Crab Nebula remnant hosts a pulsar and its gas is much hotter. CfA astronomers Terrance Gaetz, Bob Kirshner, Paul Plucinsky, and Ralph Tullmann, together with a team of twelve colleagues, used the Chandra X-ray Observatory to undertake the first deep X-ray study of the Triangulum Galaxy.

The scientists detected eighty-two of the 137 known supernova remnants, making this the largest sample of supernova remnants detected both in optical and X-rays in any galaxy, including the Milky Way. They developed a new morphological classification scheme to relate optical and X-ray sources, reported that they find no direct analogs to some of the bright, recent remnants in the Milky Way, and concluded that there are no strong correlations between the X-ray brightness of these remnants and their brightnesses at other wavelengths. The results refine our basic understanding of supernovae, and help clarify the range of X-ray properties they have.