What might LOFAR see of the first stars?

One of the main science drivers for LOFAR is the detection of the point in the history of the Universe when the first stars turned on.

We know that the Universe formed in a Big Bang, after which it was filled a hot soup (plasma) of elementary particles (like electrons, protons, neutrons and photons as well as much more exotic things). When the Universe cooled sufficiently, the electrons combined with the protons to make hydrogen atoms. At that point the photons which had previously been stuck bumping around between the particles could finally stream across the universe - and we see from that time the first light in the Universe - now cooled to microwave radiation (what we call the cosmic microwave background, or CMB).

After the CMB not much happened for a long time. There still wasn't a lot of structure in the Universe - no stars or galaxies. There was nothing to create any light - so we call this period the "dark ages". During this time the material in the Universe ever so slowly collects together under its gravity. Eventually parts of the Universe start getting more and more dense, and the first stars turn on in the densest parts. Suddenly there is light in the Universe once more, and all these new photons hit the hydrogen atoms and strip them of their electrons (ionizing them, but since they started before the CMB as separate protons and electrons, we like to call it "reionization").

As I described in a previous blog post "LOFAR in Sky and Telescope", and you can read about in the May 2011 issue of Sky and Telescope, neutral hydrogen emits a characteristic spectral line at 21cm (1.4 GHz), due to hyperfine splitting of it's ground state. The neutral hydrogen that was around in the Universe just before the first stars turned on was emitting this line, which is now redshifted to much lower frequencies (which we think should be in the range that LOFAR can detect). Suddenly at the redshift which the first stars turned on, the amount of this 21cm emission will drop dramatically. It is this phase change in the Universe which LOFAR hopes to detect.

A slice through a simulation of the reionization of the Universe. Credit Illian Illiev, SEPnet/Sussex

Exactly when and how the first stars turn on in the Universe is an important measurement to further our understanding of cosmology. Researchers involved in LOFAR (and LOFAR-UK) are working on models of what LOFAR and other telescopes like it might see. One such researcher is SEPnet Fellow Dr. Illian Illiev at the University of Sussex. It was his images and animations of what reionization might look like which were used to illustrate the Sky and Telescope article.

Reionization Animation.

Here's a description of the image and animation provided by Illian:

This is what a giant radio telescope like LOFAR is expected to see as it looks deeper into the past (going right) - a sea of neutral hydrogen atoms (yellow) gently excited into emission by the cosmic microwave background photons.

As the very first stars and galaxies form in the universe, some of their radiation is energetic enough to kick out the electron out of the hydrogen atom (a process called ionization), which leads to the gas 'disappearing' from point of view of the radion telescope, illustrated by the blue regions above, growing with time (going left) as more stars form over time.

The variation in the intensity of the yellow across the image indicates regions with different density, the higher the density, the more intensive the colour (since there is higher concentration of emitting atoms there). This is a manifestation of the 'Cosmic Web' of structures - a honeycomb-like structure which forms due to gravity.

How does LOFAR Work Part 6 (from the KAIRA blog)

And they've been busy over at KAIRA, here's also Part 6 in the series in how LOFAR works. Seems this is the end of the preamble, the real details will start soon.

Squinted Vision (about the need to steer radio dishes).

How does LOFAR Work Part 5 (from the KAIRA blog)

The next installment in how LOFAR works from KAIRA - a reminder about how traditional radio astronomy dishes work.

The Parabolic Dish.

How Does LOFAR Work Part 4 (from the KAIRA blog)

Part 4 of the KAIRA blog series on how LOFAR works: 


From radio waves to electrical signals

LOFAR in Sky and Telescope

One of the feature articles in the May 2011 edition of Sky & Telescope is "The End of the Cosmic Dark Ages" (or "Cosmic Enlightenment - the first stars") which covers how the International LOFAR Telescope plans to try to detect the "phase change" in the early universe when most of the hydrogen changes from neutral to ionized (called "reionization"). This is detectable by low frequency radio telescopes as a sudden decrease in (redshifted) 21cm emission. It works like this.... Neutral hydrogen emits a characteristic spectral line at 1.4 GHz (or 21cm) due to hyperfine splitting in its ground state. Ionized hydrogen does not emit this line. Because of the expansion of the universe, 21cm emission from very early in the universe has been redshifted to much longer wavelengths (detectable by LOFAR hopefully), and the amount of the redshift tells you how far back in the universe you're looking. LOFAR plans to look for a frequency at which redshifted 21cm emission suddenly stops being present (ie. the emission is there at longer wavelengths, but not at shorter ones).  This would provide a time stamp for when the phase change happened which is an important measurement to further our understand of the evolution of the universe.

Anyway check out the article to learn more. It features a series of images (and a link to an animation) from a simulation of the universe being reionized done by LOFAR-UK member Illian Illiev (the SEPnet LOFAR fellow at the University of Sussex) and quotes from LOFAR-UK member Steve Rawlings (from the University of Oxford).

It is a very nice article, and I'm very grateful to Sky and Telescope for sending me a preview version (we helped them locate some nice images of LOFAR stations). There are a couple of small corrections I would like to point out though. The first is that the image shown on Page 28 called "LOFAR First Light", described as being the first image taken by the whole array isn't quite that. That image is described in an earlier blog post "First Images from LOFAR Including Chilbolton" and was taken as part of observations which included the Dutch core and remote stations, as well as Chilbolton, Nancay and Tautenberg (but not the other German stations, or the Swedish one), and as I understand it that image actually only included data from the Dutch stations - it's the zoom in shown in our blog post which included data from the LOFAR-UK station). Also as we have discussed it's not the separation of the array, but the number of antennas and collecting area which make the International LOFAR Telescope the largest telescope in the world (at the moment). Finally Steve Rawlings is not leading LOFAR-UK (although he is very heavilly involved). Rob Fender (Southampton) is our current leader, soon to be replaced by Phil Best (Edinburgh).

How Does LOFAR work Part 3 (from KAIRA blog).

The third installment in the series on how LOFAR works from the KAIRA (LOFAR-Finland) blog.

Part 3 : Start with the radio waves

How Does LOFAR Work Part 2 (from the KAIRA blog)

The next post in the series from KAIRA on how LOFAR works: "What is a LOFAR system?".

Tuning into the Universe in Portsmouth

Dr. David Bacon, of the Institute of Cosmology and Gravitation at the University of Portsmouth (and SEPnet) gave a talk for National Science and Engineering week entitled "Tuning into the Universe". It was covered by the University of Portsmouth student news channel.

06. CCi Live_18-03-11 from CCi Live on Vimeo.

Coverage of the lecture starts at about 9.5 minutes in.

How Does LOFAR Work? (from the KAIRA blog)

Over at the KAIRA blog, they're posting a series of articles on how LOFAR works. We'll be linking them all from here.

Here's the first: "Part 1 : Introduction"

LOFAR-UK, the LOFAR Superterp and the Lovell Telescope observe pulsars together

Tom Hassell

Today we have a guest post by Tom Hassall - a PhD student at the University of Manchester. Tom is going to tell us about observations he ran of some pulsars using the LOFAR-UK station, the LOFAR core in the Netherlands, and the Lovell Telescope near Manchester. 

Tom was born in Stoke-on-Trent. He got his undergraduate degree (an Mphys Physics) at Manchester University in 2008. He continued on at Manchester to study for a PhD in Astronomy and is currently in his final year. His research has been focussed on using LOFAR to observe pulsars.

You can follow Tom on Twitter to hear more about his exploits with LOFAR. Take it away Tom: 

On Wednesday night LOFAR was used to take observations of five pulsars at three different frequencies. The LOFAR superterp was used to observe at 50 MHz, the LOFAR UK station was used in "standalone" mode to observe at 150 MHz and the Lovell was used to observe at 5 GHz. Pulsars are the dense, compact objects left over when a star dies. They rotate very quickly and whilst doing this they emit beams of light from their magnetic poles. As the pulsar rotates the beams sweep past the Earth and we observe a pulse of light for every rotation the pulsar completes, like looking at a VERY distant lighthouse!

The Lovell Telescope

The emission from pulsars is extremely regular (some pulsars are as regular as atomic clocks) so these observations are great for testing how well all of the clocks and delays within LOFAR work. We also hope to do some real science with these observations by testing how well the pulses at different frequencies line up with each other and what effect travelling through 10,000,000,000,000,000 miles of Space has on the shape of the pulses we see at different frequencies.

Jocelyn Bell Burnell wins award for lifetime contributions to radio astronomy

Jocelyn Bell Burnell at the LOFAR-UK station in Chilbolton in September 2010. Credit: James West, SEPnet.

Prof. Jocelyn Bell-Burnell, who opened the LOFAR-UK station back in September has been awarded the 2011 Grote Reber Gold Medal for lifetime innovative contributions to radio astronomy from the US National Radio Astronomy Observatory. The full story from NRAO is reproduced below and can be read on their website here. 




2011 Grote Reber Gold Medal
Ken Kellerman

The 2011 Grote Reber Gold Medal for lifetime innovative contributions to radio astronomy will be awarded to Dr. Jocelyn Bell Burnell who is currently a Professor of Astrophysics at Oxford University in England.  Burnell is being honored for her dramatic 1967 discovery of pulsars, which has had a major impact on 20th century astrophysics, and her continuing contributions to astrophysics and education.

Jocelyn Bell Burnell received her first degree in Physics in 1965 from Glascow University in Scotland and her PhD from the University of Cambridge in 1968.  Following a two year Science Research Council Fellowship, she held a Teaching Fellowship at the University of Southampton followed by research and management positions at the University College, London and the Royal Observatory in Edinburgh. After a ten year period as a Professor of Physics at the Open University of the United Kingdom where she studied X-ray sources, she served as Dean of Science at the University of Bath.

Bell-Burnell is best known for her role in the discovery of pulsars. As a research student in Cambridge she was heavily involved in the construction and operation of a long wavelength radio telescope built to study interplanetary scintillations at 4 m wavelength.  Later, while inspecting the output chart records, she noticed a peculiar signal form that had a periodic pulse rate close to one second. Like Grote Reber, she initially had to convince her better-established colleagues that her observations were important for astronomy and not due to external interference or a spurious instrumental effect.

She has previously been honored by many prizes and recognitions, including the Albert Michelson Medal of the Philadelphia Franklin Institute, the J. Robert Oppenheimer Memorial Prize from the Miami Center for Theoretical Studies, the Tinsley Prize from the American Astronomical Society, and the Herschel Medal from the Royal Astronomical Society.  She has served as President of the Royal Astronomical Society, is a Fellow of the Royal Society, is currently the President of the Institute of Physics, and in June 2007, she was made Dame Commander of the British Empire (DBE) by Queen Elizabeth II.  

The 2011 Reber Medal will be presented to Dame Jocelyn in August 2011 at the XXX URSI General Assembly in Istanbul, Turkey.

The Reber Medal was established by the Trustees of the Grote Reber Foundation to honor the achievements of Grote Reber and is administered by the Queen Victoria Museum in Launceston, Tasmania.  Nominations for the 2012 Medal may be sent to Martin George, Queen Victoria Museum, Wellington St, Launceston, Tasmania 7250, Australia or by e-mail to: martin@qvmag.tas.gov.au to be received no later than 15 October 2011.http://science.nrao.edu/enews/4.3/index.shtml#groterebermedal

Studying Black Holes with LOFAR at the IoP

Another LOFAR talk for NSEW next week:

IoP talk: Studying Black Holes, Pulsars and the Explosive Universe with The Low Frequency Array (LOFAR)

Wednesday 16th March 2011. 7-8pm. LTM University of Surrey. 

Open to the public, admission free

by Martin Bell (Southampton PhD Student who helped to build LOFAR-UK)

The Low Frequency Array (LOFAR) is Europe's newest and most sophisticated radio telescope. It is also one of Europe's largest radio telescopes; it consists of a network of small radio telescopes – or 'ears' - spread out across Europe, which are connected together via the internet. When connected together this network forms a European size radio telescope and is the largest on Earth. The UK has just completed its contribution to the European LOFAR project with the construction of the LOFAR Chilbolton telescope (30 minutes North of Southampton). Using this network of telescopes we can 'listen in' on the most explosive and energetic events in the Universe. In this talk we will find out how the LOFAR radio telescope works; how we can use it to study Black Holes and Pulsars; and also what the future holds for radio astronomy.  

LOFAR UK is supported by SEPnet.

More details.

Tuning into the Universe in Portsmouth

As part of National Science and Engineering Week, (11-20th March 2011) there are several LOFAR related talks happening next week. For example:

Tuning into the Universe

Wednesday 16 March 2011, 6.00-7.00 pm, Portland Building, Portland Street, Portsmouth PO1 3AH

A public lecture by Dr David Bacon, Senior Research Fellow at the Institute of Cosmology and Gravitation, University of Portsmouth. Billions of light years away, galaxies have given out radio waves that speed across the Universe. Light now, some of them have reached a humble field a few miles outside Winchester, where they are being received by some of the antennae of the new LOw Frequency ARray (LOFAR). This is an astonishing Europe-wide radio telescope, which will be used to try to make important discoveries about galaxies and the Universe as a whole. In this talk, I will describe LOFAR and the attempts we are making to use it to probe the furthest reaches of the Universe. David Bacon is a research fellow at the Institute of Cosmology and Gravitation, Portsmouth University. He is co-ordinator for Cosmology in the Surveys Key Science Project with LOFAR.

AUDIENCE: General public and school groups are welcome to this free event, book through events@port.ac.uk

More details.

Test observations at Chilbolton

Observations to test the system are ongoing at Chilbolton, both when the station is linked to the full LOFAR array and controlled from ASTRON, but also with it running in its "standalone" mode, (ie. controlled locally, and using it as a single telescope).

At the end of last week observations were run in standalone mode to test some new parameters. The lastest tests involved pointing at three different places in the sky at once (using the multi-beam capacity - since LOFAR stations are pointed entirely in software, by adding three sets of different delays in the antennas can be used to point 3 places at once), and also testing if data could be taken at 1 Hz frequency resolution across a full band 36 MHz wide.

This kind of data will be useful for all sorts of observations in single station mode, but in particular this observations was used as a dry run for SETI observations as part of Project Dorothy.

The aims of Project Dorothy (for a nice description of the goals and some quotes from Frank Drake here) are to co-ordinate world-wide observations of nearby stars with planetary systems to search for signals of possible extra-terrestrial origin.

In practice the observations last week were no different from any other kind of commissioning (or test) observations which have been run at Chilbolton, except that the time and targets were set to co-ordinate with Project Dorothy at the request of the LOFAR-UK SETI group.