Institut de Radioastronomie Millimétrique
iram
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To the edge of the universe
Institut de radioastronomie millimétrique
Institut de Radioastronomie Millimétrique
iram
IRAM is an international research institute for radio astronomy. Its overall objective is to explore the universe and to study its origins and evolution.
IRAM was founded in 1979 by the French CNRS (Centre National de la Recherche Scientifique), the German MPG (Max-Planck-Gesellschaft) and the Spanish IGN (Instituto Geográfico Nacional) - initially an associate member, becoming a full member in 1990. Today, the institute is considered a model of scientific multinational cooperation. IRAM’s headquarters are located in Grenoble. With a staff of more than 120 scientists, engineers, technicians and administrative
personnel, IRAM maintains and develops two observatories: the 30-meter telescope located on Pico Veleta near Granada in Spain, and the Plateau de Bure interferometer (an array of six 15-meter antennas) in the French Alps. Both instruments are prime facilities for radio astronomy and the most powerful observatories today operating at millimeter wavelengths.
These radio telescopes play a crucial role in modern astronomy, as they enable the study of cold matter through measuring the emission of molecular gas and dust – key elements in the formation of stars and galaxies and thus for the evolution of the universe. The
Revealing the unseen universe
millimeter wavelength range is essential to astronomy, since dust and gas-enshrouded cosmic objects remain optically invisible. Using radio techniques, astronomers can push the frontiers, penetrate the most distant galaxies, analyse black holes at the edge of the observable universe and trace the cosmological radiation up to its source, the Big Bang.
With their unmatched sensitivity, IRAM telescopes are able to detect these radio emissions from within our solar system and out to the farthest reaches of the universe. IRAM scientists and engineers also develop instrumentation and software for the specific needs of millimeter radio astronomy and for the benefit of the wider astronomical community. The institute’s laboratories cover the complete field of high frequency technology, from ultra-sensitive super-conducting detectors to complex receiver systems, high-speed digital electronics and advanced data reduction software. Providing manufacture and supply of devices to other radio astronomy centers, IRAM has highly valued partnerships with national and international space research organisations such as ESA, NASA and CNES. IRAM is a major
partner in the international ALMA project, a giant radio observatory under construction in the Chilean desert.
Its observatories and in-house technical expertise make IRAM the worldwide leader in millimeter radio astronomy.
The Andromeda galaxy (M31) seen in the visible and in the emission of carbon monoxide tracing the dense and cold molecular gas in which the stars are formed.
Interstellar molecules
Many molecules were first detected in interstellar clouds, such as the famous Horsehead Nebula.
Rotating on their axis, molecules emit at millimeter wavelengths, each of them with their own characteristic frequencies.
The IRAM telescopes operate at wavelengths of 3, 2, 1 and 0.8 millimeters, the four atmospheric windows where the millimeter emission from space reaches the earth. However, the clear transmission of these frequencies is affected by the amount of water vapour in the atmosphere, which is why the IRAM telescopes are built on high and relatively dry mountain sites.
This millimeter image of the famous Horsehead Nebula (named after its optical appearance), which shows the distribution and density of the molecular gas in this dark interstellar cloud, is more reminiscent of a seahorse.
Millimeter radio astronomy is a recent branch of astronomy. It was only in the 1960’s that the first receivers sensitive enough to detect the millimeter waves originating from space were built. Since then, this observing technique has become a key means of investigating the universe.
Radio astronomy in particular has been crucial in detecting numerous interstellar molecules. In addition to the detection of water in space, more than one hundred molecules, many unknown on earth, have so far been identified using millimeter astronomy.
The millimeter radiation of molecules – which contrary to visible light is not absorbed by interstellar clouds of dust – has enabled astronomers to make numerous discoveries. Not only is it possible to study dense, dark clouds, previously uninvestigated – but also to explore cold matter, a few degrees above absolute zero, where stars are formed. Molecules and dust are key elements in the evolution of the matter dispersed between stars: this so-called interstellar matter is continuously transformed in cycles, which are regulated by stellar birth and death. Molecules, which are most abundant in dense
interstellar clouds, play a dominant role in gas cooling and therefore in the evolution of interstellar clouds that, by gradual collapse, can initiate the birth of one or many stars. Any remaining surrounding matter orbits around the newborn star in the form of circumstellar disks. In these disks, the gas and dust continues to evolve in a more and more complex way, eventually forming proto-planets.
Shells of matter that are ejected by a dying star add further molecules and freshly-made dust to the interstellar environment. When exposed to the strong radiation of a nearby star, the surface of interstellar clouds can become the site of numerous chemical processes involving the formation of complex molecular species.
The enrichment of interstellar matter is driven by these various processes. Starting with hydrogen, the most abundant atom in the universe (created in the Big Bang) and less abundant atoms such as carbon, nitrogen and oxygen (synthesized in the stellar interiors), these processes first form simple molecules such as carbon monoxide, methanol or ethanol; then more and more complex
molecular species, including those at the origin of life.
The cosmic cycle of interstellar matter can best be studied using millimeter radio astronomy. The IRAM telescopes, equipped with cutting-edge technology, are ideally adapted to explore the cycle of molecules and dust in space.
Radio astronomy and the cycle of interstellar matter
Carbon monoxide (CO) is one of the most abundant molecules in the interstellar medium. Its emission at millimeter wavelengths enables astronomers to study molecular gas from nearby clouds to the farthest known objects in the universe.
Amino acetonitrile (NH2CH2CN), a molecule that is
close to an amino acid, was detected using the IRAM instruments in a region near the center of the Milky Way.
O
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H N N C C H H HThe 30 meter telescope, Pico Veleta
The 30-meter telescope on Pico Veleta in the Spanish Sierra Nevada is one of the two radio astronomy facilities operated by IRAM. Built in only four years (1980 to 1984) at an elevation of 2850 meters, it is one of today’s largest and most sensitive radio telescopes for tracing millimeter waves.
The telescope is a classic single dish parabolic antenna, which allows the exploration of extended cosmic objects such as nearby galaxies and interstellar clouds. Due to its large surface, the 30-meter telescope is unrivalled in its sensitivity and is well adapted to detect weak sources. The surface of the parabola is adjusted to a precision of 55 micrometers, corresponding to the width of a human hair.
The 30-meter telescope is equipped with a series of single pixel receivers operating at 3, 2, 1 and 0.8 millimeters and with two cameras working at 1 millimeter: HERA with 9 pixels for the mapping of molecular gas in extended nebulae and MAMBO, a camera with 117 pixels, built by the Max-Planck-Institut for Radioastronomy (in Bonn, Germany), dedicated to the observation of dust emission from nearby molecular clouds and also out to the farthest known galaxies and black holes. By pointing the telescope towards a celestial source, and then by scanning and tracking the source, one can build up radio images – whether of complete galaxies or regions of star formation in the Milky Way. With its
ability to observe simultaneously at several wavelengths, the telescope can produce multiple images.
Scientists are therefore able to obtain detailed maps of the millimeter universe, to look for new, hitherto unknown structures or to comb through the spectra of interstellar objects searching for new molecules.
Today, the 30-meter telescope is one of the most sought-after radio telescopes in the world. Each year, more than 250 astronomers come to Pico Veleta to pursue their scientific projects. In fact, the annual number of submitted proposals is so high that only one third of them can be scheduled. The
observatory operates 24 hours a day every day of the year and includes a control room, from which the telescope is operated, along with living quarters for scientists and IRAM staff. At the forefront of radio astronomy, the 30-meter telescope in the Sierra Nevada also allows astronomers to access parts of the southern skies and therefore to observe the center of our galaxy.
The Plateau de Bure Interferometer
The other observatory of IRAM, the Plateau de Bure interferometer, is the most advanced facility existing today for millimeter radio astronomy.
Located in the Hautes-Alpes on the wide and isolated Plateau de Bure at an elevation of 2550 meters, the interferometer consists of six antennas, each 15 meters in diameter. Each antenna is equipped with state-of-the-art high-sensitivity receivers. Two rails, extending on a north-south and east-west axis, enable the antennas to be moved up to a maximum separation of 760 meters.
During observations, the six antennas function as a single telescope, a technique called interferometry. With the antennas pointing towards the same cosmic source, the signals received by each of them are subsequently combined. The angular resolution achieved during observation is that of a single telescope, whose diameter corresponds to the maximum distance between the individual antennas. In the case of the IRAM interferometer, this is equivalent (for the longest baselines) to a telescope with a diameter of 760 meters, which can distinguish two one-cent coins placed next to each other at a distance of 5000 meters.
Due to the complexity of such an advanced antenna array system, only IRAM operators perform the observations.
To obtain a complete image of a cosmic object, interferometry uses the earth’s rotation,
which slowly turns the antennas with respect to the source, thus enabling step by step to scan the source’s structure. Astronomers are able, after several hours of observation, to reconstruct a high angular resolution image of a cosmic object and study its detailed morphology.
The two IRAM facilities can also be combined with other radio telescopes into one giant interferometer with intercontinental baselines (Very Large Baseline Interferometry or VLBI). This global technique is particularly well adapted to the exploration of ultra luminous cosmic phenomena, such as brightly shining matter around black holes (quasars) or shells ejected by dying stars. The angular resolution that is achieved with this technique is such that it would be possible to detect a golf ball on the moon! VLBI is also used to measure the movements of the tectonic plates and to pinpoint the position of a spacecraft.
Thousands of tons of materials and machinery were transported up to the Plateau de Bure to build the interferometer and in particular the east-west and north-south tracks. These tracks enable the antennas to move to their observation configurations where their positions can be measured to within a fraction of a millimeter.
Since the beginning of construction in the early 1990s, the Plateau de Bure interferometer has been constantly upgraded. With only three antennas at the beginning, the number
of antennas was doubled in the next ten years, and the baselines have been extended to about three times their original length. Recently, a new generation of receivers was
installed that has significantly increased the sensitivity and therefore the efficiency of the Plateau de Bure interferometer.
B C D E F H G
The antenna’s reflector panels B collect the cosmic signals A and relay them to the sub-reflector C, which transfers them the the receivers E located inside the antenna
D. Due to the great cosmic distances, the incoming signals are very weak.
To amplify the signals, the receiver starts by converting them to a lower frequency. The cosmic signal is then mixed (inside the mixer-block F, part of the receiver) with a locally produced signal G at a frequency close to that of the original signal. The super-conducting junction H, the active element of the mixer, sends out the difference between the two incoming signals, the so-called intermediate frequency, which is low enough to be amplified.
E
F
Mapping the cosmic signals
Located in the main building I, the correlator J on the Plateau de Bure site collects the signals from the antennas, removing any parasitic background noise. At the 30-meter telescope, an auto-correlator processes the signals.
Finally, astronomers convert the incoming signals into data K and reconstruct radio-images from the cosmic sources such as the Whirlpool galaxy M51 L.
≳10 cm ~1 mm ~10 µm ~500 nm ~10nm ≲1 nm I J J K Radio waves Millimeter Infrared Visible light Ultraviolet X rays L 12CO 2–1 in M51 HERA / IRAM 30m RT NE – Region
Spiral arm near 75” / 80”
Interarm near 100” / 90” Interarm near 50” / 70” 0.2 0.15 0.1 0.05 0 300 350 400 Velocity (km/h) 450 500 550 K
When they reach the surface of an antenna, signals from cosmic sources are extremely weak. Their weakness is such that the IRAM 30-meter telescope would have to collect them during a period spanning the entire age of the universe (13.7 billion years) to obtain enough energy to power a light bulb for one second.
The signals have thus to be amplified before they can be analysed: this is the role of the receiver. However, it is technically very difficult, if not impossible, to directly amplify signals emitted at short wavelengths (or high frequencies) such as in the millimeter range. Therefore, the frequency of the incoming signal is first lowered in the mixer block of the receiver, a device only a few centimeters in size, and only then is it amplified.
Once the signals are collected by the antenna, they are focused onto the receiver, where they reach the horn and are channelled through a narrow, millimeter-sized conduit called the wave-guide, before reaching the mixer itself. Inside the mixer, the signals are combined in the coupler to a signal with a close-by frequency that is produced by the local oscillator. The super-conducting junction sends out the difference between these two signals, the intermediate frequency, which is low enough that the signal can finally be amplified.
The mixer is also equipped with super-conducting circuits in order to separate the two incoming signals and to optimise the super-conducting junction’s performances.
This entire process has been conceived and developed by IRAM engineers, technicians and scientists. Using micro-mechanical manufacturing technologies, the horn, coupler and mixer are designed and manufactured at the institute’s mechanical workshop and assembled in its laboratories.
With a size of less than one micrometer (a thousandth of a millimeter), the super-conducting junction is the core piece of the receiver system, ensuring the transmission of the astronomical signal with as little background noise as possible.
The junction consists of two layers of niobium, a metal which at near absolute zero, becomes super-conducting – without resistance – and therefore without any additional background noise. This is why specially built cryostats, which are cooled by liquid helium, maintain the receivers at a constant temperature of -269C°. The two super-conducting layers are themselves separated by a thin insulating layer of aluminium oxide, one nanometer in size (a thousandth of a thousandth of a millimeter). The cosmic signal triggers electric charges between the two metal layers of the junction. This process, called the photon tunnel effect,
High frequency technology in radio astronomy
The mixer blocks that convert the cosmic signals to lower frequencies are high-precision devices, manufactured in the IRAM workshop with a 5-axis milling machine.
is the actual receiving process in a millimeter system, in other words, collecting and registering of the photons of incoming cosmic signals.
IRAM operates its own laboratory for the development and fabrication of super-conducting junctions, employing modern coating processes under ultra-high vacuum conditions as well as micro-lithographic methods in order to structure the junctions. With its long-time expertise, IRAM is able to build receiver systems, which guarantee a perfect signal transmission, only affected by unavoidable quantum noise. Leader in the field of high frequency technologies, IRAM also develops receiver systems for the ALMA project in the southern hemisphere.
The super-conducting junctions have a size of only one square micron. They are produced in a clean room and incorporated into microchips that are then fixed in the mixer blocks with a glue activated by ultraviolet light.
IRAM’s digital universe
Geometr ic dela y Cable delay CorrelatorLocated in the main building of the observatory, the correlator plays a key role in collecting signals coming from the antennas, in particular in interferometry.
With a processing power of thousands of billions of operations per second, the correlator is able to filter out the smallest signal from the background noise generated by quantum effects and the environment. Unlike these random noises, the cosmic signal usually does not vary. The correlator averages the incoming signal over time, so that noise diminishes and the cosmic signal gradually appears. Simultaneously, the correlator compensates for the signals’ delays caused by the earth’s rotation.
All the electronic circuits required for these operations – including a large number of custom-made silicon chips – are designed and manufactured for this purpose.
By analyzing and classifying thousands of incoming frequencies, the correlator enables astronomers to identify molecules. Using the temporal delay of the signals reaching the antennas, it also provides necessary information about the sources’ positions on the sky. This is why a special electronic device continuously measures to an accuracy of a millimeter the cables’ length between the antennas and the main building.
To optimize both signal and data transmission, the Plateau de Bure is covered with an
underground network of single-mode optical fiber and cables.
Contrary to the Plateau de Bure interferometer, the 30-meter telescope has no correlator, but several spectrometers working on the principles of auto-correlation and using analog filtering and Fourier transforms. The bandwidths used in the millimeter domain are several hundred times larger than those used for the fastest Internet connections to date.
The stream of data delivered by the correlator is subsequently processed by specific software that was developed at IRAM. The institute has become a world leader in the design and development of software in millimeter radio astronomy.
Several control programs – including antenna steering as well as receiver and backend tuning – have been created by engineers and astronomers from IRAM, as well as software for observation management, data reduction and archiving. IRAM has also pioneered dynamic scheduling of astronomical observations. These programs are regularly updated and adapted to scientific needs. The data reduction software of IRAM is freely accessible and currently used by many radio observatories worldwide.
This active technical research and development is at the heart of the cutting edge instrumentation available at the IRAM
telescopes. It also impacts other fields such as medical imaging, high-speed communication technology, precision remote sensing and atmospheric research.
Over the last 30 years, the IRAM telescopes have been at the origin of a large number of spectacular discoveries. They have provided sensational images of stars at birth and at the last stages of their lives, detected the farthest known black holes – formed only 870 million years after the Big Bang - and enabled detailed observations of discs orbiting young stars where rapid chemical evolution is taking place and planets are being formed. The IRAM telescopes have also played an essential role in the detection of molecular gas in galaxies at cosmological distances.
IRAM scientists have not only obtained trailblazing results in how galaxies and stars are formed, but have also detected a large number of the interstellar molecules identified to date – a substantial
contribution to astrochemistry and a crucial step towards exobiology.
Looking 13 billion years into the past
Astrochemistry (from the Greek ‘astron’, starand possibly ‘chymeia’, a mixture of liquids) is the study of the molecular species in space. It is an active branch of modern astronomy where the main focus is to understand how molecules are formed, how they interact with each other and their surrounding matter and how they are destroyed. Ultimately, this research brings new elements to the comprehension of the emergence of life in the universe.
Comets, such as Hale-Bopp, are thought to have had a profound influence on the evolution of planets in the solar system.
The IRAM telescopes have been instrumental in the detection of a large number of molecules in this comet. The diversity and complexity of molecular species in comets is such that their impact with the primitive earth could have brought organic molecules to its surface.
The life cycle of stars
The bipolar outflow of the young star
HH 211
The formation of a star is a fascinating process. When an interstellar cloud of dense molecular gas and dust progressively collapses under its own gravity, a protostar forms at its center. Upon further compression, a star gradually emerges. During this process, the protostar rotates faster and faster and ejects part of its matter in the surrounding medium in the form of bipolar outflows, with velocities of up to 100 km/s. This phenomenon was first observed using millimeter radio telescopes.
A spectacular example of such an outflow has been observed around HH 211, a protostar with only one fourth the mass of the Sun. The observations obtained with the Plateau de Bure interferometer allowed for the first time to obtain a complete and detailed view of this outflow. Embedded in a dense cloud, HH 211 is not visible optically, but is revealed by the dust emission at
millimeter wavelengths (the red contours at the centre of the image). The bipolar outflow of molecular material is ejected by the protostar, impacting the ambient interstellar matter at its ends.
Using the increase in angular resolution of the interferometer, astronomers have recently obtained more detailed images of the bipolar outflow around HH211. These reveal that the outflow is not ejected in a linear fashion, as previously thought. In fact, through interactions with the matter immediately surrounding the protostar, it actually seems to split.
The star TT Cygni
Small to medium mass stars (such as the Sun) eject their outer layers at the end of their lifetime before turning into white dwarves. Obtained by the Plateau de Bure interferometer, this extraordinary image shows the star TT Cygni at the final stage of its evolution. The carbon monoxide emission reveals a large, almost circular envelope of molecular gas, ejected about 2000 years ago and slowly expanding away from the star at velocities of 20 km/s. A more recent ejected envelope can be seen in the center, still close to the star. Once ejected, stellar shells cool off and form molecules as well as dust. At their death, stars become true factories of cosmic dust and are astronomers’ favourite hunting grounds in the search for new molecules.
The circumstellar disk around
GG Tauri
A detailed study of the young binary system GG Tauri has revealed further remarkable results in the process of star formation.
About half of the stellar population consists of binary systems where two stars orbit each other. GG Tauri is a system composed of two very young stars, each about two thirds of the mass of the Sun. The millimeter detection of a disk of dust and gas around this binary system was a surprise for the astronomers at IRAM - it represents the only known circum-binary disk to date. The disk is composed of interstellar matter that was not used for the central stars. Its shape, including the large central void, results from the dynamic sculpting caused by the inner orbital motion of the two stars. It is in disks similar to the one around GG Tauri, best observed at millimeter wavelengths, that planets form. Astronomers can thus explore the origins of planetary formation and analyse the chemical process leading to the creation of solar systems similar to our own.
Galaxies near and far
M51, the Whirlpool galaxy
Along with Andromeda (M31), the Whirlpool galaxy (M51) is one of the closest galaxies, at a distance of only 27 million light-years.
Using the 30-meter telescope, IRAM astronomers made the first detailed map of the molecular gas in M51 by tracing the emission of carbon monoxide over the entire extent of the galaxy. By comparing these remarkable results with maps obtained at other wavelengths, they have been able to derive a complete description of this nearby spiral galaxy from its stellar population to the atomic and molecular matter out of which stars are formed.
The Galaxy SMM J16359
At a distance of more than 5 billion light years away, the galaxy SMM J16359 is hidden behind a galaxy cluster and should not be observable from the earth. However, due to an exceptional astronomical phenomenon, the gravitational lens effect, it becomes visible. The gravitation of the galaxy cluster (seen in the upper right of the optical image) deflects the light of SMM J16359, dividing it into three images and amplifying its emission by a factor of more than 40.
By observing the abundant molecule of carbon monoxide, the Plateau de Bure interferometer detected the amplified triple image of SMM J16359. By analyzing this emission, astronomers could derive the mass and the dynamics of this far galaxy and conclude that it is most likely composed of two galaxies in the process of merging.
Optical image Millimeter image
Location Pico Veleta, Sierra Nevada, Spain Plateau de Bure, Hautes-Alpes, France
Altitude 2850 meters 2550 meters
Longitude / Latitude 03:23:33.7 W / 37:03:58.3 N 05:54:28.5 E / 44:38:02.0 N
Number of antennas 1 6
Antenna diameter 30 meters 15 meters
Antenna weight 800 tons 125 tons
Antenna mount Alt-azimuth, steel on concrete pedestal Alt-azimuth, steel on autonomous bogies
Dish panels 420 aluminium panels on honeycomb back-structure 176 aluminium panels on honeycomb back-structure
Secondary mirror diameter 2 meters 1,5 meters
Surface precision 55 microns 50 microns
Tracking precision during observations < 1/3600° (less than one arcsecond) < 1/3600° (less than one arcsecond) Frequencies / wavelengths 80 to 370 GHz / 3 to 0.8 millimeters 80 to 370 GHz / 3 to 0.8 millimeters
30 meter telescope 6 x 15-meter interferometer
La porte de l’univers Décoder les signaux de l’espace
L’univers digital de l’IRAM De la molécule interstellaire à la galaxie La radioastronomie et les éléments constitutifs de l’espace
Molécules interstellaires Six antennes à l’écoute du cosmos
La technologie des hautes fréquences en radioastronomie
Le cycle des étoiles 13 milliards d’années dans le passé
13 14 15 16 17 18 19 2021 22 23 24 25 26 27 28 29 30 31 39 40 41 42 43 44 4645 36 38 37 32 33 34 35 Photo credits
1: X-ray: NASA/CXC/CfA/D.Evans et al.; Optical/ UV: NASA/STScI; Radio: NSF/VLA/CfA/D.Evans et al., STFC/JBO/MERLIN; 2: IRAM; 3: © Rebus; 4: IRAM; 5, 6, 7: © Rebus; 8: IRAM; 9, 10: © Rebus; 11: Optical: © 1998, 1999, 2000 Celestial Images; millimetric: IRAM
12: © Rebus;13: IRAM; 14: T.A.Rector (NOAO/AURA/ NSF) and Hubble Heritage Team (STScI/AURA/ NASA); 15: 3D representations: Sven Thorwirth (MPIfR) / © Rebus; 16: Alexandre Beelen; 17: © Rebus;
18: © Rebus; 19: Bruno Pissard; 20, 21 22, 23, 24, 25: IRAM; 26: NRAO/AUI/NSF; 27: IRAM; 28: NASA/ JPL-Caltech/ Univ. of AZ/R. Kennicutt; 29: T.A.Rector and Monica Ramirez/NOAO/AURA/NSF; 30: NASA/JPL-Caltech; 31: NASA/CXC/UMd./A.Wilson et al.; 32: IRAM;
33: © Rebus; 34, 35: IRAM; 36, 37, 38: ©Rebus;
39: Wolfgang Brandner (JPL/IPAC), Eva K. Grebel (Univ. Washington), You-Hua Chu (Univ. Illinois Urbana-Champaign), and NASA; 40: Nicolas Biver; 41, 42, 43, 44: IRAM; 45: NASA, ESA, Richard Ellis and Jean-Paul Kneib; 46: IRAM.
Institut de Radioastronomie Millimétrique
C100 M44 Y0 K0 Pantone 300 C Myriad Roman Tracking -20 Solid leading (The iram 'a' is re-drawn)
C100 M44 Y0 K0 Pantone 300 C
C0 M100 Y100 K0 Pantone RED 032 C C0 M0 Y0 K100 Pantone Process Black
