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Articles on this Page
- 09/28/17--17:00: _Treasures of the Wi...
- 10/01/17--17:00: _RFoF Environmental ...
- 10/02/17--17:00: _Moonset from La Palma
- 10/03/17--17:00: _Understanding the n...
- 10/04/17--17:00: _Photo impression la...
- 10/05/17--17:00: _The Square Kilometr...
- 10/08/17--17:00: _Kick-off in the new...
- 10/09/17--17:00: _Hajee's career move
- 10/10/17--17:00: _Particle Rejuvenati...
- 10/11/17--17:00: _ASTRON proud member...
- 10/12/17--17:00: _Unboxing the GAME
- 10/15/17--17:00: _September 13th: sub...
- 10/16/17--17:00: _Radio telescopes zo...
- 10/17/17--17:00: _CASA VLBI workshop ...
- 10/18/17--17:00: _Recombination lines...
- 10/19/17--17:00: _Dedication of the ...
- 10/22/17--17:00: _Food for thought...
- 10/23/17--17:00: _When a jet hits a c...
- 10/24/17--17:00: _1 + 1 > 2
- 10/25/17--17:00: _Dwingeloo 1 & 2 are...
- 09/28/17--17:00: Treasures of the Wiskunde Boek
- 10/01/17--17:00: RFoF Environmental test
- 10/02/17--17:00: Moonset from La Palma
- 10/03/17--17:00: Understanding the nature of drifting subpulses in pulsars.
- 10/04/17--17:00: Photo impression labs session MSc students RuG at NOVA-ASTRON
- 10/05/17--17:00: The Square Kilometre Array and the origins of life
- 10/08/17--17:00: Kick-off in the new APERTIF room
- 10/09/17--17:00: Hajee's career move
- 10/10/17--17:00: Particle Rejuvenation In Distant Galaxy Clusters
- 10/11/17--17:00: ASTRON proud member of Innovation Cluster Drachten
- 10/12/17--17:00: Unboxing the GAME
- 10/15/17--17:00: September 13th: submission on a dead line
- 10/16/17--17:00: Radio telescopes zoom in gravitational wave counterpart
- 10/17/17--17:00: CASA VLBI workshop 2017
- 10/18/17--17:00: Recombination lines with Apertif
- 10/19/17--17:00: Dedication of the de Bruyn Room at the Kapteyn Institute
- 10/22/17--17:00: Food for thought...
- 10/23/17--17:00: When a jet hits a cloud
- 10/24/17--17:00: 1 + 1 > 2
- 10/25/17--17:00: Dwingeloo 1 & 2 are still there!
© Madroon Community Consultants (MCC)For the ridiculously low price of Eu 14,95 you can buy Het Wiskune Boek (The Mathematics Book(**)). Each of its more than 500 pages explains an important brick of the mighty edifice of mathematics, which was built over the millennia by a long line of rather clever people.
Flipping idly through its pages the other day, I suddenly noticed that the item for 2002 (see picture) described the work(*) of one of our very own ASTRON colleagues. Right there, between giants like Zeno, Euclid, Hypatia, Newton, Leibniz, Huygens, Euler, Fourier, Gauss, Galois, Cantor, Godel, Moron, Russell, Noether, Brouwer, Turing, Ulam, Jones, Mandelbrot, etc, etc.
That is the kind of person you might meet in the corridors of ASTRON, JIVE, NOVA and DOME.
(*) It proves that the 3500 year old African game Awari will always end in a draw if both players play perfectly.
(**) Unfortunately, the book is only available in Dutch. But note that the members of the august Royal Society, only a few centuries ago, learnt Dutch in order to be able to read the letters of Anthonie van Leeuwenhoek.
© Lesley GoudbeekOver the years ASTRON developed and produced many instruments, tools and components. Many of these start their life on a lab-bench at ASTRON. Life on a lab-bench is relaxed (minus some probing with an oscilloscope) and the environmental conditions are very stable. An important step in the development process is to make sure the instrument survives the environment in which it is supposed to operate. Which is why an environmental test with the Radio over Fiber (RFoF) housing seemed appropriate.
The aluminum housing and phosphor bronze caps of the RFoF modules where put inside a pot. On the bottom of this pot resides a mixture of water and salt. The pot is put in a temperature chamber and cycled from 10C to 70C several times a day for around 2 months. The results clearly show that unprotected caps corrode heavily and the unprotected aluminum is affected to by the salt and water mixture (pic.6 close-up, a small part of the original material color is visible). We are glad to see that the coatings on the materials are effective, and to show what harsh climates can do with the instruments.
© Cees BassaOn occasion, radio astronomers observe with, and get to go to, telescopes operating at other wavelengths. When those wavelengths are optical, this usually means remote or exotic mountain tops.
Last December I had the joy of observing with the Isaac Newton Telescope on La Palma, and took my camera and tripod to photograph the night sky. On one of the nights the young Moon was setting, and this image shows a sequence of individual exposures. Moonlight is reflected in the dome of the William Herschel Telescope. Atmospheric refraction dramatically alters the shape and color of the trails of the stars, the Moon and also Mars (in the bottom center), as they near the horizon.
© ASTRONWe performed detailed analysis of archival data of PSR J0815+0939 which revealed that the second component is the only one which exhibits drift in the opposite direction. We proposed a model that shows that the observed bi-drifting phenomenon follows from the insight that the discharging regions, i.e., sparks, do not rotate around the magnetic axis per se, but rather around the point of maximum potential at the polar cap.
We found that a purely dipolar surface magnetic field cannot exhibit bi-drifting behaviour, however, certain non-dipolar configurations can. We can distinguish two types of solutions, with relatively low (~1e12 G) and high (~1e14 G) surface magnetic fields. Depending on the strength of the surface magnetic field, the radius of the curvature of magnetic field lines ranges from 1e5 to 1e7 cm.
Pulsar J0815+0939 allows us to gain an understanding of the polar-cap conditions essential for plasma generation processes in the inner acceleration region, by linking the observed subpulse shift to the underlying spark motion. (Szary & van Leeuwen, ApJ 845, 95).
© Willem JellemaOn Thu 29 Sep 2017, 15 students following the course Basic Detection Techniques (BDT) visited the Optical & IR group at NOVA-ASTRON for a labs session. In 4 groups the students worked on 4 experiments determining the wavefront error of an individual test sample using 4 different wavefront sensing techniques:
- an optical test plate
- a Shack-Hartmann wavefront sensor
- a laser interferometer
- a Foucault knife-edge test
We experienced an enjoyable day, with great enthusiasm, pleasant interaction, good working spirit and look forward receiving great reports!
Thanks to Rik ter Horst, Annemieke Janssen, Joost van den Born, Ronald Roelfsema, and Eddy Elswijk for their help with the experiments, and Ramon Navarro and Albert-Jan Boonstra for the guided tours.
dr. ir. Willem Jellema
on behalf of the NOVA Optical & IR group at ASTRON
© Matthijs van der WielThe symposium Fundamentals of Life in the Universe was held on August 31st and September 1st. Taking place at the Energy Academy building on the Groningen University campus (see bottom left), the symposium featured presenters from a wide range of scientific disciplines, including astronomers, biologists, geologists, chemists, and physicists. The aim of this symposium -- and the freshly started Origins Center -- is to facilitate interdisciplinary connections to tackle fundamental questions about the emergence of life in the Universe and on Earth.
The symposium was attended by a delegation from ASTRON & JIVE (see top left), who had a fruitful time during the reception and poster session , and advertised the capabilities of the planned Square Kilometre Array (SKA) observatory in the context of studying the prerequisites for life . The SKA's capabilities will be ideally suited to study centimetre-size particles in protoplanetary disks, on their way to forming potentially life-bearing terrestrial planets. It will also study prebiotic molecules and exoplanet magnetic fields, map out star and planet forming regions throughout the Galaxy, and take the next step in the search for signals from technological civilizations beyond Earth. At this symposium, we made clear that development of the SKA is important for this field of research, the "Route 4" of the Dutch National Science Agenda.
 From left to right: Huib Jan van Langevelde, Matthijs van der Wiel, Joeri van Leeuwen.
 In addition to the delegation, credits go to Jess Broderick, Michiel van Haarlem, and the SKA Cradle of Life science working group for providing input for the poster presentation.
© Gert KruithofMany things already have been done for APERTIF and many things still are on the to-do-list...
All the effort and hard work of the several groups within ASTRON for these project is highly appreciated. Not only APERTIF requires attention; there are many other projects and actions that need to be taken care of.
Busy weeks for e.g. APERTIF proved to be successful: good for the team spirit and good for the progress. Such a set up stimulates the cooperation and communication cross team, cross departments.
In order to create a similar setting the Reading Room recently has been refurbished into the socalled APERTIF room.
A few people have a permanent working place there for the next couple of months. Others will join them there as much as possible.
The overall goal is to have very short communication lines and efficient collaboration. Everybody working at the same goal: the start of the surveys.
On September 25th, we had the first team meeting in our APERTIF room.
I would like to thank everybody who made this APERTIF room possible at such a short notice: the people of Facility Services and the ICT department, and not to forget the secretaries.
© ASTRONToday we say goodbye to our colleague Hajee (Harm-Jan) Pepping. Hajee has worked at Astron for the past six years. In this period he has developed firmware for the UniBoard and for the APERTIF Beamformer and Correlator. This work concerned writing VHDL for FPGAs and test software in Python. Hajee has been a dedicated firmware engineer and end 2015 this led to the measurement of the first fringes with APERTIF http://www.astron.nl/dailyimage/index.html?main.php?date=20151116 .
Besides technology, Hajee also has a keen interest in personal development and in the interaction between men and women. In this area Hajee has become a trainer and coach, and about two years ago he started his own company called ManKracht (manpower). It is not that easy to combine two careers. Therefore Hajee has decided to now fully pursue his new career and leave Astron.
The photo shows Hajee in a fascinating elevator in a hotel in Sydney, where we went for a meeting on the Correlator and Beamformer for SKA Low. Thanks Hajee, for being our colleague and we wish you all the best with your new endeavours.
© Francesco de Gasperin (Leiden University)A composite (false-colour) image of the galaxy cluster Abell 1033. Optical light from individual galaxies, visible as coloured spots across the image, is obtained by the Sloan Digital Sky Survey, while in blue the X-ray emission observed with the Chandra satellite traces the hot gas. Radio emission from LOFAR and the VLA is shown in orange and traces a complex of radio sources including a tail of particles left behind by the galaxy moving towards the left of the image.
The steep spectrum emission in the central region of the cluster is detected only at the low frequencies to which LOFAR is sensitive. It is thought to have been perturbed and re-energised by the intracluster medium. Sources powered through this proposed mechanism can maintain electrons at higher energies than radiative aging would allow. If this mechanism is common for aged plasma, a population of mildly relativistic electrons can accumulate inside clusters and provide a seed population that can then be reaccelerated by shocks or turbulence to produce the cluster-wide emission that is observed in some massive merging clusters.
© ASTRONSince September 29th, ASTRON officially joins the Innovation Cluster Drachten (ICD). ICD is an internationally active ecosystem of collaborating high-tech companies and knowledge institutes operating at the forefront of innovation and competitive on the global market.
Chairman of ICD, Kor Visscher, proudly mentioned at the signing event at ASTRON: "What we can learn from our new scientific partner reaches beyond stars and planets. ASTRON has a special place in the High-Tech Systems & Materials (HTSM) industry. With knowledge, technology and development, the Institute makes astronomical research possible. ASTRON regularly publishes new discoveries that give a better understanding of the universe. Within the HTSM Top Sector, ASTRON brings knowledge in the area of Big Data handling, algorithmic and cyber-physical programming. With the accession of ASTRON, Innovation Cluster Drachten connects 17 highly innovative high tech companies in the Northern Netherlands."
At the Signing Event on September 29th at ASTRON, Kor Visscher and Carole Jackson signed for the membership. At ICD it is tradition to do this on eachothers back as you can see on the image.
Before having a toast on a fruitful cooperation within the Innovation Cluster Drachten, Kor Visscher said that he was happy to include ASTRON in the ICD: "ASTRON is highly internationally oriented and is in close contact with business, both in the Netherlands and abroad and therefore a wonderful addition to our cluster."
We are proud to be a member of ICD now and we hope that our drive for innovation will get a further boost!
For further information on the Innovation Cluster Drachten and its activities, please take a look at https://www.icdrachten.nl/.
© ASTRON, JIVE, NOVAHave you ever wondered what it takes to make discoveries in astronomy happen, but you couldn't find a short and simple answer very quickly? Or you were searching everywhere on the web and were trying to find but you got lost in the abundance of all the difficult stuff because there was only one piece of information given at a time and not everything at a one go, or in one place? Or in case you could not make heads nor tails from how astronomy relates to engineering ...
Search no further for we have designed a quartet card game especially for YOU!
In this game, you will find the answers to all or at least 52 out of many of your questions you might have that relate to the following:
"What is needed to make discoveries in astronomy happen?"
Short and sweet texts (surely informative!), accompanied by beautiful pictures and appealing illustrations, embedded into 12 quartet themes ranging from instrumentation engineering design,through operations & maintenance, to astronomical observations, sources, phenomena and science. What's more important you will see that none of the domains can fully exist in isolation, they need each other! Already curious?
Just as many of you have already noticed, I love unboxing things, after all who doesn't like to see the fruits of their team's labour? :) without the further ado: let the drums roll!!!
Ladies and Gentlemen, on behalf of the quartet work-group, I proudly present to you:
The first batch of the world's first "Astronomy? That's how it works!" quartet card game! Just in time for the weekend of Science and meant to be distributed during the ASTRON, JIVE, NOVA Open Day last Sunday (8th of October)!
Enthusiastic volunteers from JIVE, NOVA and ASTRON have joined their creative minds in something they haven't done before, a collaboration ... a game development endeavor to be exact! Without their help throughout the whole process, it would be impossible to deliver this game in merely 15 weeks!
Great thanks go to the true Star Team for making the impossible possible:
Ilse van Bemmel (JIVE), Gina Maffey (JIVE), Gabby Kroes (NOVA), Iris Nijman (ASTRON), Mark Ruiter (ASTRON), Roy van der Werp (ASTRON), Aleksandar Shulevski (ASTRON)
I'd love to thank many more colleague-angels who contributed as well in parts of the process:
Gert Kruithof, Monique Sluiman-de Vries, Jason Hessels, Joeri van Leuwen, Johan Pragt, Albert van Duin, Andre Gunst, Gijs Schoonderbeek, Boudewijn Hut, Michel Arts, Jan Kragt and his kids, Lesley Goudbeek - all of them contributed to the text editorials;
Albert van Duin thank you for your photos, other photos you found, and a whole quartet theme you came up with!
Jan Idserda, Sjouke Kuindersma, Dirk Lesman, Henk Mulder, Hiddo Hanenburg - thanks for your input & ideas.
Kids of Ilse, Gabby, Mark - thanks for testing the game (yes, there were some kids who were busy testing the prototypes)!
Tibor Agocs - thank you for the exciting subject of "Ghosts" as optical noise ... it's only a pity that the Dutch translation doesn't sound as exciting as the English equivalent ;-)
And THANKS to many more colleagues who supported the project by sharing their opinion/comments/giving tips.
Naturally, super huge THANK YOU goes to the highest management:
Carole Jackson, Marco de Vos - ASTRON
Huib Jan van Langevelde - JIVE
Ramon Navarro, Wilfried Boland - NOVA
Ronald Halfwerk - AstroTec (Bureau of Technology Transfer)
without their enthusiastic patronage this game would not be published and would not reach you!
Last but definitely not least, you see it on the box as the first thing that catches your eye: think of Niels Tromp when you see the title :). Thanks Niels!
If you missed the game during the open day last Sunday ... visit us in Dwingeloo :)
© SOS TeamIt was Wednesday, the 13th., of September. The wind was howling through the trees, because of the biggest storm this year. It was the day that astronomers from all over the world are preparing for that important deadline: to submit their LOFAR proposal by 2 pm and be granted some precious time at this wonderful telescope. As true astronomers do, some waited for the last moment to prepare and submit their proposal. They are used to this and normally it is not a problem. But not this day. This was the 13th!
Waiting in their office, just after lunch, were three telescope scientists. Eager to see what proposals were coming in, they closely monitored the proposal submission tool, until suddenly, the lights flickered in their office. They had no idea what was going on. They were preparing to go to the Westerbork site, to check the proposals and to sneak out to celebrate the retirement of their dear colleague Geert Kuper, operator. Then the fire-alarm went off, and everybody was summoned to leave the building.
Disaster struck on this 13th, 1.5 hours before the submission deadline. There was a power failure at ASTRON. The servers and network went down, and all the eager astronomers could no longer reach the ASTRON servers and submit their proposals. After all was safe, the remaining telescope scientists left for Westerbork, where they joined their colleagues, avoiding fallen trees on their way. Their primary mission was to inform the LOFAR users of the disaster and reassure them that all was not lost and they would be able to submit their proposal at a later time. This is not an easy task at a radio quiet zone, and with the network also being down at Westerbork. Sadly, the mail servers were down, so firstname.lastname@example.org could not be reached by users, even though the name was never so appropriate. But even if trips had to be made for several kilometers, through the woods, in the storm, nothing could stop the telescope scientists from reaching the users.
In the end, there was nothing left to do, but to celebrate Geert's goodbye party, wait a day for the systems to be brought online by the tremendous effort of ICT, the LOFAR software development and operational support group and a few telescope scientists, and repeat the exercise on Friday, the 15th! This time, without problems, such that cycle 9 preparations are well on their way.
The image shows the team of dedicated telescope scientists at Westerbork, feeling lost without an actual network connection.
© LIGO-Virgo Consortium (image); ASTRON, JIVELast year we learned about the birth of the new field of gravitational wave astronomy, when gravitational waves were first detected from merging stellar-mass black holes. Yesterday, on 16 October 2017, the LIGO-Virgo Consortium (LVC) and various observatories made another major announcement: the first detection of gravitational waves from merging neutron stars. Such events are particularly interesting to astronomers because the matter ejected during this type of merger is expected to become bright in various parts of the electromagnetic spectrum, including at radio wavelengths. That is, we can study these phenomena in detail with observations from our 'ordinary' telescopes.
The LVC was well prepared: they made agreements to a great number of observing facilities and astronomy groups several years ago. When the event GW170817 was detected on 17 August this year, it was immediately followed up by our telescopes. This resulted in another milestone discovery: the detection of an electromagnetic transient counterpart resulting from the explosive processes that followed the inspiral and merging of the two neutron stars. The arXiv preprint server was flooded yesterday by the scientific results from this discovery.
One particular paper summarizes the events from the gravitational wave detection and localization, as well as all the additional observations with different telescopes. This paper was put together in a collaborative effort by approximately 70 contributing groups. This paper has about 3500 authors affiliated to more than 900 institutions, demonstrating how global this collaboration was.
Our JIVE and ASTRON colleagues took part in the follow-up program. The ASTERICS initiated Euro VLBI team has observed the transient at centimetre wavelengths with the UK-based e-MERLIN, and with the European VLBI Network (EVN), at a number of epochs. The LOFAR team observed part of the LVC localization footprint at metre wavelengths. The radio emission is still very faint and we could not detect it with our (very) long baseline interferometers, but we expect the source to brighten in the coming weeks. The image therefore shows the LVC localization of the GW170817 event, together with the localization of the related short gamma-ray burst detected by Fermi, as well as the first optical image (and a pre-discovery image) of the transient now called SSS17a.
Zsolt Paragi for the Euro VLBI team
Jess Broderick and Antonia Rowlinson for the LOFAR team
© JIVEThere is a focused and tense energy radiating from the room. People are sat in pairs at small tables throughout, and fingers are tapping at speed with eyes flicking from screen to screen. Hushed, concentrated discussions occur between tables, and occasionally one will grab the attention of other users leading to an open conversation, before people return their gaze to their own screen.
Welcome to the CASA VLBI workshop. In a glass fronted meeting room individuals from around the world have gathered to test a new toolkit for processing data collected during VLBI experiments. JIVE has been developing the toolkit in CASA, with testing occurring in house – until now. Twenty individuals have come together to spend the week experimenting with using the toolkit on their own datasets.
For Cormac Reynolds from CSIRO the workshop has not only been been a welcome return to familiar territory, but a way to "future proof" and help ensure that "younger students [who are] familiar with CASA do not have to jump through another hoop" to analyse their data in radio astronomy.
The JIVE team have used the workshop to get feedback on the toolkit, while also hearing what wishes there are for future functionality from participants. Which is exactly what Rachael Ainsworth from Jodrell Bank has spent the time doing: "It would be great to just press a button and let [the toolkit] go, but right now it's about understanding and knowing what to look for to troubleshoot."
Ultimately, in developing the toolkit the JIVE team are hoping to open up VLBI data processing in radio astronomy. If this is possible then, as Walter Brisken from the Long Baseline Observatory said, it: "makes VLBI more accessible to a broader side of the radio astronomy community."
© ASTRONThe motivation for building Apertif is to increase the survey speed of the WSRT and to turn it into a radio survey telescope. This is achieved by increasing the field of view by using phased-array feeds to make 39 primary beams on the sky at the same time. This, effectively, creates 39 WSRT's which work in parallel, and makes the WSRT 39 times faster for surveying the sky. However, not everybody is aware that Apertif increases the survey speed of the WSRT by an extra factor two by doubling the bandwidth of the receivers. For spectral line observations of atomic hydrogen this doubles the distance out to which it can be detected.
But there is another application. To illustrate this, the broad observing band of Apertif was used to observe the radio recombination lines coming from the Galactic star forming region W3 (discovered by Gart Westerhout in the mid-fifties using the Dwingeloo telescope, hence the W in W3!!). Radio recombination lines are emitted by ionised hydrogen gas that has a temperature around 10000 degrees C. Because the gas is fairly hot, most of it is ionised (i.e. protons and electrons are freely floating around), but occasionally it happens that a proton and an electron bind to each other (forming a hydrogen atom), a process that is called recombination.
In the initial stages of this recombination, the electron 'sits' in a high energy level of the atom. But every now and then, the electron pops to a lower energy state and every time it does so, it emits a photon with an energy exactly that of the energy transition. This means that over time, many photons are emitted, each with an energy (or frequency) characteristic of the energy jump it did. Other elements, like carbon and sulphur, do similar things.
At the frequencies Apertif operates on, in practise this means that every 24 MHz one can detect a spectral line (a radio recombination line), each line corresponding to a different 'energy jump'. This, in turn, means that in the 300-MHz wide observing band of Apertif, several of these recombination lines can be detected in a single observation (see figure). And, this is the trick of course, they can be averaged to significantly improve the signal-to-noise. This is important because recombination lines are faint.
The figure shows spectra extracted from an Apertif observation of W3 with five of the recombination lines detected. For each row, the hydrogen recombination line is the stronger one on the right. The line on the left-hand side is a combination of similar lines from carbon and sulphur. The improvement of the averaging is obvious. Careful modelling of the hydrogen line shows it comes from a mix of relatively cold (5000 C) and hotter gas (10000 C) and that the carbon and sulphur lines are associated with the colder hydrogen gas, not with the warmer gas. On the single lines such modelling is not possible, but the average gives clear answers.
© ASTRONWith a small and warm ceremony last Thursday, attended by family, friends and colleagues, the De Bruyn Office was dedicated at the Kapteyn Institute in Groningen. As underlined by Leon Koopmans in his dedication speech, for many years Ger de Bruyn played an instrumental role (literally and figuratively) in Dutch radio astronomy. In particular in his dual role as astronomer at Astron and at the Kapteyn Institute, connecting instrument and science in a way only he could do. His abrupt passing has left a large void for the great science to be done with Lofar, but also for many people personally. The de Bruyn Office is a fitting way to keep the memory to his many contributions alive.
© ASTRONIt is rather sad to say but at ASTRON, and also at the R&D department, there are some people (almost) burn-out. On a regular basis in the R&D MT meetings attention has been paid to this: How do we prevent people from getting a burn-out? How do we recognize if someone is reaching the dangerous zone? And how can we help this colleague to recover? Even more important: how do we ensure that we won't get in that zone anyway? Important questions to be answered...
Recently, Ruud Meulenberg, whose job it is to coach (almost) burned out people, has been invited for a special R&D MT meeting. The whole team went outside with him, his colleague and a trainee, as the coaching sessions with Ruud Meulenberg are always in the beautiful woods and fields of Drenthe. The R&D MT has been briefly informed on signals, necessary actions, etc. which was highly appreciated and eventually resulted in an one hour extension of the meeting in the open air. One of the things the R&D MT members learned was that a lot of people suffering/recovering from a burn-out are hard-working people, very dedicated to their job and always striving for the best results. However, not only workload will cause a burn-out. Also other factors, like impressive events in private life, personality, etc. can play a significant role.
A clear advice is: stay as close as possible to who you really are instead of trying to become just like someone else. "An oak will never become a beech".
© AstronIt is thought that every fairly massive galaxy has a super-massive black hole (SMBH) sitting in its centre. Sometimes, such a SMBH is 'active', meaning it ejects ultra-fast plasma jets, almost at the speed of light. These jets plays an important role in the evolution of galaxies because they interact with the gas in the galaxy, and the energy released through this interaction dramatically changes the properties of the gas. The main effect is that fewer stars can form from the gas, because for the gas to form stars again, it first has to settle back to normal conditions. So the galaxy does not grow so big as it should.
The physics of these jet-gas interactions is not yet well understood. One would naively expect that, because of the enormous amounts of energy dumped into the gas reservoir by the jet, the gas affected would become very hot. However, it turns out that this is not the case. One of the big surprises which came out of observations we did some years ago (including some with the WSRT) is that, in fact, the jet interaction makes the gas very cold...
To try resolving this puzzle, we used ALMA to observe the galaxy IC 5063, which harbours one of the nicest cases of jet-gas interactions. In this galaxy, this interaction manifests itself as a very fast outflow of very cold gas, driven by the jet. Such cold gas usually is in the form of molecular which can be best observed with ALMA.
Using observations of several emission lines of the cold, molecular gas, we were able, for the first time, to map in detail the physical properties (kinematics, density, temperature and pressure) of the jet-affected gas and how these relate to the properties of the jet plasma. This provides important new information for models of jet-gas interactions that are being developed. The picture shows the image of the ratio of the intensities of two different emission lines of the molecular gas. The contours show the radio emission coming from the SMBH (the central blob) and the plasma jets (the things sticking out left and right of the SMBH). This ratio gives indications about the density and temperature of the gas. The colours clearly show that very different ratios are found in the region coinciding with the jet compared what is seen for gas outside the jet. From this information one can determine how the gas is affected by the jet and learn more about the processes involved.
All this is in a paper by Tom Oosterloo, J. B. Raymond Oonk, Raffaella Morganti, Francoise Combes, Kalliopi Dasyra, Philippe Salome', Nektarios Vlahakis, and Clive Tadhunter recently accepted by Astronomy & Astrophysics: "Properties of the molecular gas in the fast outflow in the Seyfert galaxy IC 5063"
© AstronAstron will soon operate two world-class telescopes, Lofar and Apertif. In other places in the world, telescopes like Lofar and Apertif are operational (or soon will be). But what is unique to Astron is that Lofar and Apertif are a perfect match to each other and that the combined capabilities are much more powerful than those of each instrument separately.
This is because the relative sensitivities of the two instruments match that of the typical radio source. In other words, the average radio source is imaged by both instruments with the same signal to noise and resolution. This is unique. Because Lofar and Apertif operate in very different frequency bands, such combined images give much more additional information on the nature of the objects compared to the single images.
A corollary of the above is that if a source looks very different in both images, the source is not typical, and is therefore, like atypical people, likely much more interesting. To illustrate this, the movie shown above blinks between a Lofar image and an Apertif image of the same piece of sky (part of the Lockman Hole). Many sources show up in both images, but there are some sources, in particular extended ones, that only Lofar sees. These turn out to be sources that are very old; they have lost most of their energy and only still shine at low frequencies. This is a very interesting class of objects because they give a new view of what happens when radio sources grow old. Because of the large field of view of both telescopes, many many of such sources will be discovered.
© astronEvery weekend Apertif is observing as part of the astronomical commissioning. One of the modes that are regularly tested is spectral line imaging, to see if the changes made to the system were successful. One obvious target to observe for such tests are the galaxies Dwingeloo 1 and 2, the two galaxies named after 'us'.
The two galaxies were discovered in the mid-nineties by Renee Kraan-Korteweg and collaborators when they used the Dwingeloo dish to do a survey called DOGS (Dwingeloo Obscured Galaxy Survey) with the aim to find galaxies hidden behind the Milky Way. The gas and dust in the Milky Way absorbs optical light, so objects that are behind the Milky Way are very hard to see with normal telescopes. However, the Milky Way is transparent for radio waves, so radio telescopes can see right through it and galaxies behind the Milky Way are easily spotted.
Actually, only Dwingeloo 1 was discovered with the Dwingeloo dish. The Dwingeloo dish has very low resolution, it can cannot distinguish objects that are close to each other. So when later Dwingeloo 1 was observed with the WSRT to study the galaxy in detail, it turned out that there was a second, smaller galaxy, right next to Dwingeloo 1. It was named Dwingeloo 2, but perhaps that should have been Westerbork 1...
The left image shows the atomic hydrogen of Dwingeloo 1 and 2 as seen by the 'old' WSRT, the right image as seen with Apertif.