LOFAR sees ‘exoplanet aurorae’ near distant red dwarf suns.
A powerful new method may help to detect exoplanets, via the aurorae they induce on their host star. The finding was announced recently from ASTRON’s Low Frequency Array radio telescope (LOFAR), based out of Exloo in the Netherlands, and sprawled across sites in Europe.
The Low-Frequency Array (LOFAR) is a different kind of radio telescope. Although radio light has the longest wavelengths and lowest frequencies of the electromagnetic spectrum, much of radio astronomy has focused on the higher frequency end. Observatories such as ALMA study radio light at frequencies of hundreds of Gigahertz, and the VLA studies the fifty Gigahertz range, LOFAR captures radio signals below 250 Megahertz, which is in the range of the lowest radio frequencies that can be seen from Earth.
Brown dwarfs are interesting objects. They are generally defined as bodies massive enough to trigger the fusion of deuterium or lithium in their cores (and are thus not a planet) but too small to fuse hydrogen in their cores (and therefore not a star). They are the middle children of cosmic bodies.
A cluster of galaxies is nothing trivial. The shocks, the turbulence, the energy, as all of that matter and energy merges and interacts. And we can watch all the chaos and mayhem as it happens.
A team of astronomers are looking at the galaxy cluster Abell 2255 with the European Low-Frequency Array (LOFAR) radio telescope, and their images are showing some never-before-seen details in this actively merging cluster.
At present, scientists can only look for planets beyond our Solar System using indirect means. Depending on the method, this will involve looking for signs of transits in front of a star (Transit Photometry), measuring a star for signs of wobble (Doppler Spectroscopy), looking for light reflected from a planet’s atmosphere (Direct Imaging), and a slew of other methods.
Based on certain parameters, astronomers are then able to determine whether a planet is potentially-habitable or not. However, a team of astronomers from the Netherlands recently released a study in which they describe a novel approach for exoplanet-hunting: looking for signs of aurorae. As these are the result of interaction between a planet’s magnetic field and a star, this method could be a shortcut to finding life!
The Milky Way galaxy has its own magnetic field. It’s extremely weak compared to Earth’s; thousands of times weaker, in fact. But astronomers want to know more about it because of what it can tell us about star formation, cosmic rays, and a host of other astrophysical processes.
Pulsars are what remains when a massive star undergoes gravitational collapse and explodes in a supernova. These remnants (also known as neutron stars) are extremely dense, with several Earth-masses crammed into a space the size of a small country. They also have powerful magnetic fields, which causes them to rotate rapidly and emit powerful beams of gamma rays or x-rays – which lends them the appearance of a lighthouse.
In some cases, pulsars spin especially fast, taking only milliseconds to complete a single rotation. These “millisecond pulsars” remain a source of mystery for astronomers. And after following up on previous observations, researchers using the Low Frequency Array (LOFAR) radio telescope in the Netherlands identified a pulsar (PSR J0952?0607) that spins more than 42,000 times per minute, making it the second-fastest pulsar ever discovered.
This study was part of an ongoing LOFAR survey of energetic sources originally identified by NASA’s Fermi Gamma-ray space telescope. The purpose of this survey was to distinguish between the gamma-ray sources Fermi detected, which could have been caused by neutron stars, pulsars, supernovae or the regions around black holes. As Elizabeth Ferrara, a member of the discovery team at NASA’s Goddard Space Center, explained in a NASA press release:
“Roughly a third of the gamma-ray sources found by Fermi have not been detected at other wavelengths. Many of these unassociated sources may be pulsars, but we often need follow-up from radio observatories to detect the pulses and prove it. There’s a real synergy across the extreme ends of the electromagnetic spectrum in hunting for them.”
Their follow-up observations indicated that this particular source was a pulsar that spins at a rate of 707 revolutions (Hz) per second, which works out to 42,000 revolutions per minute. This makes it, by definition, a millisecond pulsar. The team also confirmed that it is about 1.4 Solar Masses and is orbited every 6.4 hours by a companion star that has been stripped down to less than 0.05 Jupiter masses.
The presence of this lightweight companion is a further indication of how the spin of this pulsar became so rapid. Over time, matter would have been stripped away from the star, gradually accreting onto PSR J0952?0607. This would not only raise its spin rate but also greatly increase its electromagnetic emissions. The process continues to this day, with the star becoming increasingly smaller as the pulsar becomes more energetic.
Because of the nature of this relationship (which can only be described as “cannibalistic”), systems like PSR J0952?0607 are often called “black widow” or “redback” pulsars. Most of these systems were found by following up on sources identified by the Fermi mission, since the process has been known to result in a considerable amount of electromagnetic radiation being released.
Beyond the discovery of this record-setting pulsar, the LOFAR discovery could also be an indication that there is a new population of ultra-fast spinning pulsars in our Universe. As Dr. Bassa explained:
“LOFAR picked up pulses from J0952 at radio frequencies around 135 MHz, which is about 45 percent lower than the lowest frequencies of conventional radio searches. We found that J0952 has a steep radio spectrum, which means its radio pulses fade out very quickly at higher frequencies. It would have been a challenge to find it without LOFAR.”
The fastest spinning pulsar known, PSR J1748-2446ad, spins just slightly faster than PSR J0952?0607 – reaching a rate of nearly 43,000 rpm (or 716 revolutions per second). But some theorists think that pulsars could spin as fast as 72,000 rpm (almost twice as fast) before breaking up. This remains a theory, since rapidly-spinning pulsars are rather difficult to detect.
But with the help of instrument like LOFAR, that could be changing. For instance, both PSR J1748-2446ad and PSR J0952?0607 were shown to have steep spectra – much like radio galaxies and Active Galactic Nuclei. The same was true of J1552+5437, another millisecond pular detected by LOFAR which spins at 25,000 rpm.
As Ziggy Pleunis – a doctoral student at McGill University in Montreal and a co-author on the study – indicated, this could be a sign that the fastest-spinning pulsars are just waiting to be found.
“There is growing evidence that the fastest-spinning pulsars tend to have the steepest spectra,” he said. “Since LOFAR searches are more sensitive to these steep-spectrum radio pulsars, we may find that even faster pulsars do, in fact, exist and have been missed by surveys at higher frequencies.”
As with many other areas of astronomical research, improvements in instrumentation and methodology are allowing for new and exciting discoveries. As expected, some of the things we are finding are forcing astronomers to rethink more than a few previously-held assumptions about the nature and limits of certain phenomena.
Be sure to enjoy this NASA video that explains “black widow” pulsars and the ongoing search to find them:
In 1888, astronomer Simon Newcomb uttered now infamous words, stating that “We are probably nearing the limit of all we can know about astronomy.” This was an age just prior to identifying faint nebulae as separate galaxies, Einstein’s theory of special and general relativity, and an era when a hypothetical substance called the aether was said to permeate the cosmos.
Newcomb would scarcely recognize astronomy today. Modern observatories span the electromagnetic spectrum and are unlocking the secrets of a universe both weird and wonderful. Modern day astronomers rarely peer through an eyepiece, were it even possible to do so with such bizarre instruments. What follows are some of the most unique professional ground-based observatories in operation today that are pushing back our understanding of the universe we inhabit.
VERITAS: Based at the Fred Lawrence Whipple Observatory in southern Arizona, the Very Energetic Radiation Imaging Telescope Array System (VERITAS) is an observatory designed to observe high energy gamma-rays. Its array consists of four 12-metre aperture reflectors each comprised of 350 mirror scintillators. Each VERITAS array has a 3.5° degree field of view and the array has been fully operational since 2007. VERITAS has been used to study active galactic nuclei, gamma-ray bursts, and the Crab Nebula pulsar.
IceCube: Not the rapper, IceCube is a neutrino detector in based at the Amundsen-Scott South Pole Station in Antarctica. IceCube watches for neutrino interactions by use of thousands of photomultipliers suspended up to 2.45 kilometres down into the Antarctic ice sheet. With a total of 86 detector strings completed in 2011, IceCube is currently the world’s largest neutrino observatory and is part of the worldwide Supernova Early Warning System. IceCube will also complement WMAP and Planck data and can actually “see” the shadowing effect of the Moon blocking cosmic ray muons.
Liquid Mirror Telescopes: One of the more bizarre optical designs out there in the world of astronomy, liquid mirror telescopes employ a large rotating dish of mercury to form a parabolic mirror. The design is cost effective but does have the slight drawback of having to aim directly at the zenith while a swath of sky passes over head. NASA employed a 3-metre liquid mirror telescope as part of its Orbital Debris observatory based near Cloudcroft, New Mexico from 1995-2002. The largest one in the world (and the 18th largest optical telescope overall) is the 6-metre Large Zenith Telescope in the University of British Columbia’s Malcolm Knapp Research Forest.
LIGO: Designed to detect incoming gravity waves caused by pulsar-black hole mergers, the Laser Interferometer Gravitational-Wave Observatory (LIGO) is comprised of a pair of facilities with one based in Hanford, Washington and another in Livingston, Louisiana. Each detector is consists of a pair of 2 kilometre Fabry-Pérot arms and measures a laser beam shot through them with ultra-high precision. Two geographically separate interferometers are needed to isolate out terrestrial interference as well as give a direction of an incoming gravity wave on the celestial sphere. To date, no gravity waves have been detected by LIGO, but said detection is expected to open up a whole new field of astronomy.
The Very Long Baseline Array: A series of 10 radio telescopes with a resolution the size of a continent, the Very Long Baseline Array (VLBA) employs observatories across the continental United States, Saint Croix in the U.S. Virgin Islands, and Mauna Kea, Hawaii. This is effectively the longest radio interferometer in the world with a baseline of over 8,600 kilometres and a resolution of under one milliarcseconds at 4 to 0.7 centimetre wavelengths. The VLBA has been used to study H2O megamasers in Active Galactic Nuclei and measure ultra-precise positions and proper motions of stars and galaxies.
LOFAR: Located just north of the town of Exloo in the Netherlands, The LOw Frequency Radio Array is a phased array 25,000 antennas with an effective collection area of 300,000 square metres. This makes LOFAR one of the largest single connected radio telescopes in existence. LOFAR is also a proof on concept for its eventual successor, the Square Kilometre Array to be built jointly in South Africa, Australia & New Zealand. Key projects involving LOFAR include extragalactic surveys, research into the nature of cosmic rays and studies of space weather.
The Pierre Auger Observatory: A cosmic ray observatory located in Malargüe, Argentina, the Pierre Auger Observatory was completed in 2008. This unique instrument consists of 1600 water tank Cherenkov radiation detectors spaced out over 3,000 square kilometres along with four complimenting fluorescence detectors. Results from Pierre Auger have thus far included discovery of a possible link between some of the highest energy events observed and active galactic nuclei.
GONG: Keeping an eye on the Sun is the goal of the Global Oscillation Network Group, a worldwide network of six solar telescopes. Established from an initial survey of 15 sites in 1991, GONG provides real-time data that compliments space-based efforts to monitor the Sun by the SDO, SHO, and STEREO A & B spacecraft. GONG scientists can even monitor the solar farside by use of helioseismology!
The Allen Telescope Array: Located at Hat Creek 470 kilometres northeast of San Francisco, this array will eventually consist of 350 Gregorian focus radio antennas that will support SETI’s search for extraterrestrial intelligence. 42 antennas were made operational in 2007, and a 2011 budget shortfall put the status of the array in limbo until a preliminary financing goal of $200,000 was met in August 2011.
The YBJ Cosmic Ray Observatory: Located high on the Tibetan plateau, Yangbajing International Cosmic Ray Observatory is a joint Japanese-Chinese effort. Much like Pierre-Auger, the YBJ Cosmic Ray Observatory employs scintillators spread out along with high speed cameras to watch for cosmic ray interactions. YBJ observes the sky in cosmic rays continuously and has captured sources from the Crab nebula pulsar and found a correlation between solar & interplanetary magnetic fields and the Sun’s own “cosmic ray shadow”. The KOSMA 3-metre radio telescope is also being moved from Switzerland to the YBJ observatory in Tibet.
Our Universe is full of surprises. Sometimes those surprises come in packages so overwhelmingly huge that it’s almost impossible for us to comprehend the size. Thus is the case of a newly discovered “giant galaxy”. It’s a galaxy which extends millions of light years across intergalactic space, covering an area as much as a half degree of sky. It’s a new class of monster – one called a Giant Radio Galaxy.
Thanks to the work of an international team of astronomers made up of about fifty members from various institutes and led by ASTRON astronomer, Dr. George Heald, there’s a new discovery which can be credited to the powerful International LOFAR Telescope (ILT). During a perpetual all-sky radio survey – the Multi-frequency Snapshot Sky Survey (MSSS) – the team captured some images which revealed a new radio source. This wasn’t just a weak signal that showed a new blotch. It was a source the size of the full Moon projected on the sky! The huge new radio emission appears to have originated up to hundreds of million of years ago from a single member of a interacting triple galaxy system and spread itself across a vast expanse of space.
Cataloged as UGC 09555, the parent galaxy system is located some 750 million light years from our solar system. Its central galaxy had been studied before and was known to have a flat radio spectrum – a signature of giant radio galaxies. Astronomers speculate when the trio interacted, material was released – spreading out over millions of light years and releasing very low radio frequencies. It’s a source that’s either very powerful, or it’s very old.
Enter LOFAR and the MSSS Survey…
As part of a well orchestrated attempt to image the expanse of the northern night sky at frequencies between 30 and 150 MHz, the radio researchers have taken a initial “shallow scan” image set. This new survey will allow astronomers to fashion an all-sky model which will eventually assist with much deeper observations. Thanks to LOFAR’s extreme sensitivity, ability to operate at low frequencies and suitability to observe old sources, the survey was able to reveal this gargantuan galaxy. Picture its size again in your mind. This Giant Radio Galaxy covers as much sky as the Moon, yet it’s 750 million light years away! As the MSSS Survey continues to scan the skies, who knows what may yet be discovered?
With capabilities as sensitive as some of the world’s greatest radio telescopes, such as the Very Large Array (VLA) in the USA, ASTRON’s Westerbork Synthesis Radio Telescope (WSRT), and the Giant Metrewave Radio Telescope (GMRT) in India, LOFAR will take discoveries such as Giant Radio Galaxies to the next level. It will reveal objects missed by previous surveys and the broad bandwidth coverage may show us even more cosmic wonders.
An array of radio telescopes has connected for the first time to its various locations across Europe, creating the largest telescope in the world at almost 1000 km wide. With the connection, the LOFAR telescope has delivered its first ‘radio pictures’. The images of the 3C196 quasar, a black hole in a distant galaxy, were taken in January 2011 by the International LOFAR Telescope (ILT). LOFAR is a network of radio telescopes designed to study the sky at the lowest radio frequencies accessible from the surface of the Earth with unprecedented resolution.
The UK based telescope at Chilbolton Observatory in Hampshire, was added to the network, and is the western most ‘telescope station’ in LOFAR.
“This is a very significant event for the LOFAR project and a great demonstration of what the UK is contributing”, said Derek McKay-Bukowski, STFC/SEPnet Project Manager at LOFAR Chilbolton. “The new images are three times sharper than has been previously possible with LOFAR. LOFAR works like a giant zoom lens – the more radio telescopes we add, and the further apart they are, the better the resolution and sensitivity. This means we can see smaller and fainter objects in the sky which will help us to answer exciting questions about cosmology and astrophysics.”
“This is fantastic”, said Professor Rob Fender, LOFAR-UK Leader from the University of Southampton. “Combining the LOFAR signals together is a very important milestone for this truly international facility. For the first time, the signals from LOFAR radio telescopes in the Netherlands, France, Germany and the United Kingdom have been successfully combined in the LOFAR BlueGene/P supercomputer in the Netherlands. The connection between the Chilbolton telescope and the supercomputer requires an internet speed of 10 gigabits per second – over 1000 times faster than the typical home broadband speeds,” said Professor Fender. “Getting that connection working without a hitch was a great feat requiring close collaboration between STFC, industry, universities around the country, and our international partners.”
“The images show a patch of the sky 15 degrees wide (as large as a thousand full moons) centred on the quasar 3C196”, said Dr Philip Best, Deputy LOFAR-UK leader from the University of Edinburgh. “In visible light, quasar 3C196 (even through the Hubble Space Telescope) is a single point. By adding the international stations like the one at Chilbolton we reveal two main bright spots. This shows how the International LOFAR Telescope will help us learn about distant objects in much more detail.”
LOFAR was designed and built by ASTRON in the Netherlands and is currently being extended across Europe. As well as deep cosmology, LOFAR will be used to monitor the Sun’s activity, study planets, and understand more about lightning and geomagnetic storms. LOFAR will also contribute to UK and European preparations for the planned global next generation radio telescope, the Square Kilometre Array (SKA).