Category: Astronomy

Low-frequency radio sky at the time of a cosmic ray hit. Image credit: MPIFR. Click to enlarge.
Using the LOPES experiment, a prototype of the new high-tech radio telescope LOFAR to detect ultra-high energy cosmic ray particles, a group of astrophysicists, in collaboration of Max-Planck-Gesellschaft and Helmholtz-Gemeinschaft, has recorded the brightest and fastest radio blasts ever seen on the sky. The blasts, whose detection are reported in this week’s issue of the journal Nature, are dramatic flashes of radio light that appear more than 1000 times brighter than the sun and almost a million times faster than normal lightning. For a very short moment these flashes – which had gone largely unnoticed so far – become the brightest light on the sky with a diameter twice the size of the moon.

The experiment showed that the radio flashes are produced in the Earth atmosphere, caused by the impact of the most energetic particles produced in the cosmos. These particles are called ultra-high energy cosmic rays and their origin is an ongoing puzzle. The astrophysicists now hope that their finding will shed new light on the mystery of these particles.

The scientists used an array of radio antennas and the large array of particle detectors of the KASCADE-Grande experiment at Forschungszentrum Karlsruhe. They showed that whenever a very energetic cosmic particle hit the Earth atmosphere a corresponding radio pulse was recorded from the direction of the incoming particle. Using imaging techniques from radio astronomy the group even produced digital film sequences of these events, yielding the fastest movies ever produced in radio astronomy. The particle detectors provided them with basic information about the incoming cosmic rays.

The researchers were able to show that the strength of the emitted radio signal was a direct measure of the cosmic ray energy. “It is amazing that with simple FM radio antennas we can measure the energy of particles coming from the cosmos” says Prof. Heino Falcke from the Netherlands Foundation for Research in Astronomy (ASTRON) who is the spokesperson of the LOPES collaboration. “If we had sensitive radio eyes, we would see the sky sparkle with radio flashes”, he adds.

The scientists used pairs of antennas similar to those used in ordinary FM radio receivers. “The main difference to normal radios is the digital electronics and the broad-band receivers, which allow us to listen to many frequencies at once”, explains Dipl. Phys. Andreas Horneffer, a graduate student of the University of Bonn and the International Max-Planck Research School (IMPRS), who installed the antennas as part of his PhD project.

In principle some of the detected radio flashes are in fact strong enough to wipe out conventional radio or TV reception for a short time. To demonstrate this effect the group has converted their radio reception of a cosmic ray event into a sound track (see below). However, since the flashes only last for some 20-30 nanoseconds and bright signals happen only once a day, they would be hardly recognisable in everyday life.

The experiment also showed that the radio emission varied in strength relative to the orientation of the Earth magnetic field. This and other results verified basic predictions that had been made in theoretical calculations earlier by Prof. Falcke and his former PhD student Tim Huege, as well as by calculations of Prof. Peter Gorham from the University of Hawaii.

Cosmic ray particles constantly bombard the earth causing little explosions of elementary particles which form a beam of matter and anti-matter particles rushing through the atmosphere. The lightest charged particles, electrons and positrons, in this beam will be deflected by the geomagnetic field of the Earth which causes them to emit radio emission. This type of radiation is well known from particle accelerators on Earth and is called synchrotron radiation. In analogy, the astrophysicists now speak of “geosynchrotron” radiation due to the interaction with the Earth magnetic field.

The radio flashes were detected by the LOPES antennas installed at the KASCADE-Grande cosmic ray air shower experiment at Forschungszentrum Karlsruhe, Germany. KASCADE-Grande is a leading experiment for measuring cosmic rays. “This shows the strength of having a major astroparticle physics experiment directly in our neighbourhood – this gave us the flexibility to also explore unusual ideas as this one” says Dr. Andreas Haungs, spokesperson of KASCADE-Grande.

The radio telescope LOPES (LOFAR Prototype Experimental Station) uses prototype antennas of the largest radio telescope of the world, LOFAR, to be built after 2006 in the Netherlands and parts of Germany. LOFAR has a radical new design, combining a multitude of cheap low-frequency antennas which collect the radio signals from the entire sky at once. Connected by high-speed internet a supercomputer then has the ability to detect unusual signals and make images of interesting regions on the sky without moving any mechanical parts. “LOPES achieved the first major scientific results of the LOFAR project already in the development phase. This makes us confident that LOFAR will indeed be as revolutionary as we had hoped it will be.” explains Prof. Harvey Butcher, director of the Netherlands Foundation for Research in Astronomy (ASTRON) in Dwingeloo, The Netherlands, where LOFAR is currently being developed.

“This is indeed an unusual combination, where nuclear physicists and radio astronomers work together to create a unique and highly original astroparticle physics experiment”, states Dr. Anton Zensus, director at the Max-Planck-Institut f?r Radioastronomie (MPIfR) in Bonn. “It paves the way for new detection mechanisms in particle physics as well as demonstrating the breathtaking capabilities of the next generation telescopes such as LOFAR and later the Square Kilometer Array (SKA). Suddenly major international experiments in different research areas come together”

As a next step the astrophysicists want to use the upcoming LOFAR array in the Netherlands and Germany for radio astronomy and cosmic ray research. Test are under way to integrate radio antenna into the Pierre Auger Observatory for cosmic rays in Argentina and possibly later in the second Auger Observatory in the Northern hemisphere. “This may be a major breakthrough in detection technology. We hope to use this novel technique for detecting and understanding the nature of the highest energy cosmic rays and also to detect ultra-high energy neutrinos from the cosmos”, says Prof. Johannes Bl?mer, Astroparticle Physics programme director of the Helmholtz Association and at Forschungszentrum Karlsruhe.

The detection has been confirmed in part by a French group using the large radio telescope of the Paris observatory at Nan?ay. Historically, work on radio emission from cosmic rays was first done in the late 1960ies with the first claims of detections. However, no useful information could be extracted with the technology of these days, and the work ceased quickly. The main shortcomings were the lack of imaging capabilities (now implemented by software), the low time resolution, and the lack of a well-calibrated particle detector array. All of this has been overcome with the LOPES experiment.

Original Source: MPI News Release

Hubble deep field view. Image credit: Hubble. Click to enlarge.
Cosmologists from Princeton University announced a new method to understand why the expansion of the universe is speeding up. The proposed technique will be able to determine if the cosmic acceleration is due to a yet unknown form of Dark Energy in the universe or if it is a signature of a breakdown of Einstein’s theory of General Relativity at very large scales of the universe. The result is being presented today by the principal investigator, Dr. Mustapha Ishak-Boushaki, a research associate at Princeton University in New Jersey, to the Canadian Astronomical Society meeting in Montreal, QC.

“The accelerating expansion of the universe constitutes one of the most intriguing and challenging problems in astrophysics. Moreover, it is related to problems in many other fields of physics. Our research work is focused on constraining different possible causes of this acceleration.” says Dr. Ishak-Boushaki.

During the last 8 years, several independent astronomical observations have demonstrated that the expansion of the universe has entered a phase of acceleration. The discovery of this acceleration came as a surprise to astrophysicists who were expecting to measure a slowing down of the expansion caused by the gravitational attraction of ordinary matter in the universe.

In order to explain the cosmic acceleration, theoretical cosmologists introduced the notion of a new energy component that would constitute two thirds of the entire energy density of the universe and that is gravitationally repulsive rather than attractive. This component has been termed Dark Energy.

Is Dark Energy real? “We don’t know,” comments Professor David Spergel from Princeton. “It could be a whole new form of energy or the observational signature of the failure of Einstein’s theory of General Relativity. Either way, its existence will have profound impact on our understanding of space and time. Our goal is to be able to distinguish the two cases.”

The simplest case of Dark Energy is the cosmological constant that Einstein introduced 80 years ago in order to reconcile his theory of General Relativity with his prejudice that the universe is static. He had to withdraw the cosmological constant a few years later when the expansion of the universe was discovered. The discovery of the cosmic acceleration has revived the debate about the cosmological constant in a new context.

Another fundamentally different possibility is that the cosmic acceleration is a signature of a new theory of gravity that enters at very large scales of the universe rather than the product of Dark Energy. Some of the recently proposed modified gravity models are inspired by Superstring theory and extra dimensional physics.

Could we distinguish between these two possibilities? The proposed procedure shows that the answer is yes. The general idea is as follows. If the acceleration is due to Dark Energy then the expansion history of the universe should be consistent with the rate at which clusters of galaxies grow. Deviations from this consistency would be a signature of the breakdown of General Relativity at very large scales of the universe. The procedure proposed implements this idea by comparing the constraints obtained on Dark Energy from different cosmological probes and allows one to clearly identify any inconsistencies.

As an example, a universe described by a 5-dimensional modified gravity theory was considered in this study and it was shown that the procedure can identify the signature of this theory. Importantly, it was shown that future astronomical experiments can distinguish between modified gravity theories and Dark Energy models.

The research work on the results presented was led by Dr. Mustapha Ishak-Boushaki in collaboration with Professor David Spergel, both from the Department of Astrophysical Sciences at Princeton University, and Amol Upadhye, a graduate student at the Physics Department at Princeton University.

Original Source: Princeton News Release

Gemini North image of stellar nursery RY Tau. Image credit: Gemini. Click to enlarge.
Using a giant telescope on Mauna Kea Hawaii is a dream for most amateur sky watchers. Recently a Canadian amateur astronomy group took advantage of a rare opportunity and used one of the largest telescopes in the world, the Gemini 8-meter telescope, to look more deeply into the remains of a particular stellar nursery than anyone ever has.

The observations of a star emerging from its cocoon were the result of a proposal submitted as part of a nationwide contest in Canada. The winning group from Quebec received its data/images during a special ceremony at the annual meeting of the Canadian Astronomical Society at the University of Montreal on May 15, 2005.

“Our group knew that this object was unique and hadn’t been observed in detail with a big telescope like Gemini,” said Gilbert St-Onge, the club member who submitted the proposal. “I feel like we’ve not only made a pretty picture, but probably provided some new and valuable data for the pros!”

Gemini Astronomer Tracy Beck, who studies these stellar incubators, agrees. “This object is a classic, and one of the first-known examples of this type of young star,” she said. “I believe this is by far the deepest and most detailed image ever taken of this object and scientists will no doubt use these data for important research in the future.”

The object, known as RY Tau is part of a class of objects known as T Tauri stars. These stars represent the very youngest of low-mass stellar specimens that have only recently emerged from the cocoon of gas and dust in which they formed. The new Gemini image of RY Tau displays a striking array of wispy gas filaments that glow from scattering caused by radiation from the nearby star. Over the next few million years this gas will be blown away by the central star leaving a normal star and perhaps a family of planets that also formed from gas and dust in the cloud.

The observations, which took a total of about one hour using the Gemini Multi-Object Spectrograph (GMOS), were challenging to make. The central star is so bright that it can overwhelm the faint glowing clouds around it. To overcome this, a series of many short exposures were obtained and stacked to produce the final image. A selection of four filters were also used to bring out specific color features in the dynamic cloud.

The program was sponsored by the team of scientists who coordinate Gemini observations for Canada (through the Canadian Gemini Office) at the National Research Council of Canada’s Herzberg Institute of Astrophysics (HIA) in Victoria. B.C. The contest, which began in 2004, solicited proposals from more than a hundred amateur astronomy clubs throughout Canada as a way to thank them for the work they do to support and excite the public about astronomy. The winning proposal was selected by a process similar to that used by professional astronomers, where selection criteria include scientific merit and an assessment of the uniqueness of the observation.

“When we first worked on scheduling these observations, we jokingly referred to the program as the “amateur hour” since it allows amateur astronomers to get an hour of time on a large telescope,” said Doug Welch, Canadian Gemini Project Scientist. “However, the caliber of the proposals and scientific potential of this data has shown that it is more like a pro-am golf tournament where the hobbyists work directly with the pros!”

The contest also included an hour of time on Gemini’s neighbor on Mauna Kea, the Canada-France-Hawaii Telescope (CFHT). The winning observation at CFHT was from a group in Alberta, Canada who used the wide-field capability of the telescope to image a large field of the Pleiades star cluster with the MegaPrime imager.

Original Source: Gemini News Release

A negative image of the Sun showing the active region. Image credit: PPARC. Click to enlarge.
Solar physicists have observed the smallest ever coronal mass ejection (CME) – a type of explosion where plasma from the Sun is thrown out into space, sometimes striking the Earth and damaging orbiting satellites. The observation has come as a great surprise to scientists and has turned previous ideas up-side-down.

To date studies of these phenomena have focussed on large explosions which are easier to detect and which have massive footprints on the Sun, sometimes covering thousands of millions of square miles. But in a paper published in the May edition of Astronomy and Astrophysics, an international team from the UK, Argentina, Finland, France and Hungary showed that CMEs can also be produced from regions as small as the Earth, around 10,000 miles across. This still may sound large but it is tiny by cosmic standards.

CMEs are believed to be caused by the destabilisation of twisted loops in the Sun’s magnetic field, which contain lots of energy, settling into more stable positions (like a twisted rubber band unwinding suddenly). Until now, the events have been traced back to large areas of magnetic activity on the Sun, but the new observations relate to an area much smaller than anything seen before. However, even though the event was small it was still energetic enough to reach the Earth and amazingly the magnetic field lines were ten times more twisted than is usually seen in the larger areas.

Understanding CMEs and the mechanisms that power them is important because the plasma and accelerated particles they throw into space can damage satellites, cause harm to astronauts and even affect the Earth itself, causing beautiful aurora but also power black outs and problems to radio signals. This is the science of space weather.

Dr Lucie Green of UCL’s Mullard Space Science Laboratory said “Previously coronal mass ejections were thought to be huge, involving massive portions of the Sun’s magnetic field and all the theoretical models are based around this assumption. However, this one was amazing in that it came from a tiny magnetic region on the Sun which would normally have been overlooked in the search for CME source regions. This will be an exciting area for further study.”

Existing models for CMEs are based on the type of large event previously observed and the team cannot yet say how frequent such mini CMEs are or whether they represent a significant part of space weather. The event was so small that is was almost at the limit of what we can see with current instruments. Future missions studying the Sun will be able to ‘see’ in much better detail, such as the UK-US-Japanese mission called Solar-B.

The research used data from NASA/ESA’s SOHO spacecraft, NASA’s TRACE satellite and from the now defunct Japanese/US/UK Yohkoh satellite. UK involvement was funded by PPARC.

Original Source: PPARC News Release

An artist’s impression of merging neutron stars, one of the theoretical progenitors of gamma-ray bursts. Image credit: NASA E/PO, Sonoma State University, Aurore Simonnet. Click to enlarge.
Gamma Ray bursters (GRBs) are almost a daily occurrence – so you’d think follow-up on such things would be routine by now – but that’s just not the case. Imagine a fire department having to respond to a new fire every day: they’d still have to pull on hats and heavy raincoats, slide down shiny metallic poles, and jump onto their fire engine as fast as possible.

And on Monday, May 9th, 2005 there were two fires; one reported earlier in the day by NASA’s HETE-2, and then another by its even more sophisticated associate SWIFT.

So even as we were working on a previous story for Universe Today readers about a dark Gamma Ray Burster detected by HETE-2 in August 2002, two new bursts occurred overhead. Both events sounded the alarm and astronomers worldwide scrambled to capture the rapidly diminishing optical afterglow (OAs) that might help explain one of the deepest mysteries in the Universe: how can so much energy be packed into those tiny, massless photons?

GRB events themselves are of two types. Some are “hard and fast” while others are “soft and slow”. When a “hard-fast” event occurs, astronomical fire fighters have to work quickly.

It all begins when HETE-2 or SWIFT detects an outburst from their lonely perches in low Earth orbit. Once a burst is detected, instruments aboard the craft swing around to make a determination of just where in space that event has occurred and capture whatever lingering x-ray data may still be available. Here SWIFT has the advantage over HETE-2 due to its smaller “error circle” – the satellite’s best guess as to the location of the event in the heavens. Data related to location, burst strength, and duration is then beamed to NASA instrument teams on Earth where the data is integrated and advisories are published to enlist available astronomers and instruments.

All this is comparable to an “all points bulletin” going out so astronomers anywhere can scramble to capture what is now the rapidly diminishing afterglow of the main event. Typically only small instruments associated with major observatories respond first, since larger instruments are scheduled months in advance for other projects. You’ll never see the mighty Hubble Space Telescope swing around for one of these events.

Even as available scopes turn to the sky, astronomers look for detailed survey charts of the region associated with the error circle. Why? Because images and data may already be available to simplify afterglow identification along with baseline spectra, and recessionary distances of host galaxies to assist their analysis.

As time passes, larger and larger instruments are made available for use. This is essential since dark GRBs fade quickly and more and more optical depth is needed to pick up the trail. In the case of GRB020819 detected by HETE-2 in 2002 not even the 10-meter Keck ESI instrument (capturing 26th magnitude light) was able to image an afterglow even though it swung around within 15 days of the initial high energy burst. But with SWIFT’s rapid response and tighter error circles its now becoming possible to catch a dark GRB in the act of disappearing for good.

Of the two GRB events of the day, GRB050509B is most promising because its optical light afterglow is relatively dim (fainter than the 20th magnitude) and galaxy is relatively bright (the 15th). And it is because roughly 1 in 10 GRBs are optically impoverished that makes them specially interesting to astrophysicists. Basically current models used to explain dark GRB events predict that a broad range of photon-energy levels should be seen to accompany any gamma-ray outburst. The fact that some GRBs don’t happen to map well against theory is troublesome, and therein lies the itch behind GRB020819’s (and now GRB050509B’s) scratch.

One theory of GRBs is that gamma rays somehow “muscle their way” through intervening matter in space while optical light – the “afterglow” of such an event – does not. This optical extinction scenario has yet to be demonstrated and several dark GRBs show no sign of the kind of massive clouds of intervening matter needed to support it.

Meanwhile there are three theories of the fireball-shock type postulated by astrophysicists to account for all rapidly diminishing short-time scale GRBs. The fireball scenario typically involves an explosion that hurls extremely hot gases at exceedingly high speeds into space after some kind of a cataclysmic event. These gases then interact with other material already present in the interstellar medium (ISM) or material previously ejected into space by the same object at lower velocities. One theory postulates a “relativistic jet” of hot gases penetrating either a stratified “onion” of other slower moving gases or a simple homogeneously filled-“bubble” of gases. The others assume either a rapidly expanding sphere of hot gases into the same type “bubble” or “onion”.

According to an international team of astronomers, data analyzed across the EM spectrum from GRB020819 supports the expanding sphere into homogeneous medium fireball-shock model. Those findings have been documented in a paper entitled “The Radio Afterglow and Host Galaxy of the Dark GRB020819” published May 2, 2005. The related Universe Today article is an online companion to this article entitled “Shedding Light on Dark Gamma Ray Bursters“.

Meanwhile – at this very moment – astronomical “firefighters and fire marshals” are gathering data associated with SWIFT’s detection of GRB 050509B. This process may continue in one form or another for as long as six months. Several years hence a team of investigators – such as that associated with GRB020819 – may attempt to make sense of how a little understood paroxysm of matter and energy occuring some 2.5 billion years ago in the direction of the springtime constellation Coma Berenices could ever have happened in the first place.

To make all this possible numerous and ever larger “eyes on the skies” will have to collect and focus radio, near-infrared, optical, and near-ultraviolet light. All of that information will be sifted through with infinite patience in an effort to forensically determine not “who done it” but “what”.

Written by Jeff Barbour

Dark gamma ray burst GRB020819. Image credit: Keck. Click to enlarge.
Virtually everything we know about the Universe comes to us through the agency of light. Unlike matter, light is uniquely suited to travel the vast distances across space to our instruments. Most astronomical phenomena however are persistent and repeatable – we can rely on them to “hang around” for long-term observation or “come back around” on a regular basis. But this isn’t so for gamma ray bursts (GRB’s) – those mysterious cosmological events that supercharge photons (and sub-atomic particles) with absurdly high energy levels.

The first detected celestial GRB occurred during nuclear arms treaty monitoring in 1967. That event required years of analysis before its extraterrestrial origin was confirmed. After this discovery, primitive triangulation methods were put in place using detectors located on various space probes within the Interplanetary Network (IPN). Such methods required a great deal of number crunching and made instant follow-up using Earth-based instruments impossible. Despite the delays involved, hundreds of gamma ray sources were catalogued. Today – even using the Internet – it would still require several days to respond using an IPN-type detection approach.

All this began to change in 1991 when NASA put the Compton Gamma Ray Observatory (CGRO) into space using space shuttle Atlantis as part of its “Great Observatories” program. Within four months of scanning the sky, CGRO made it clear to astronomers that the Universe underwent sporadic and widely distributed gamma ray paroxysms on an almost daily basis – paroxysms caused by cataclysmic events that hurl vast quantities of gamma and other high-energy radiation across the abyss of space-time.

But CGRO had one main limitation – although it could detect gamma rays and alert astronomers quickly, it wasn’t particularly accurate as to where such events happened in space. Because of this large “error circle”, astronomers were unable to locate the visible light “afterglow” of such events. Despite this limitation, CGRO went on to detect hundreds of continuous, periodic, and episodic gamma ray sources – including supernovae, pulsars, black holes, quasars, and even the Earth itself! Meanwhile CGRO also discovered something unsuspected – certain pulsars acted as narrow band transmitters of gamma rays without accompanying visible light – and therein lay astronomer?s first sense of “dark” GRBs.

Today we know that “dark pulsars” are not the only “dark” sources of gamma rays in the Universe. Astronomers have determined that some small portion of episodic (one-time-only) GRBs are also low in visible light, and they – like anyone tickled by the unusual and inexplicable – want to know why. In fact GRB’s are so unique that aficionados may often be heard saying “When you’ve seen one GRB, you’ve seen one GRB”.

The first satellite to simplify optical detection of GRB afterglows was BeppoSAX. Developed by the Italian Space Agency in the mid 1990’s, BeppoSAX launched April 30, 1996 from Cape Canaveral and continued to detect and pinpoint X-ray emission sources until 2002. BeppoSax’s error circle was small enough to enable optical astronomers to rapidly track down many GRB afterglows for detailed study in visible light using earth-based instruments.

BeppoSAX re-entered the Earth’s atmosphere April 29, 2003, but by this time NASA’s replacement (HETE-2 the High Energy Transient Explorer-2) was already several years on station in low-earth orbit. Instrument’s on HETE-2 (its first incarnation HETE failed to separate from the third stage of its Pegasus rocket in 1996) expanded the range of X-ray detection and provided even tighter error circles – just the thing astronomers needed to improve their response time in locating GRB afterglows.

Two years and a few months later (Monday, August 19, 2002) HETE-2 set off the bells and whistles as a strong gamma ray source was detected somewhere near the head of the constellation Pisces the Fishes. That event (designated GRB 020819) caused a series of astronomical observatories to begin capturing radio-frequency, near-infrared, and visible light photons in an effort to determine just where the event occurred and help make sense of the phenomenon driving it.

According to the paper “The Radio Afterglow and Host Galaxy of the Dark GRB 020819” published May 2, 2005 by an international team of investigators (including Pall Jakobsson of the Niels Bohr Institute, Copenhagen Denmark who proofed this article), within 4 hrs of detection the 1 meter Siding Spring Observatory (SSO) telescope in Australia was turned to a region of space less than 1/7th the apparent diameter of the Moon. 13 hours later, a second, slightly larger instrument – the 1.5 meter P60 unit at Mt. Palomar – also joined the chase. Neither instrument – despite capturing light as faint as magnitude 22 – caught anything unusual for that region of space. However a large and extremely photogenic 19.5 magnitude face-on barred spiral galaxy fell nicely within the grasp of their instruments.

Fifteen days later, the 10 meter Keck ESI instrument on Mauna Kea, Hawaii imaged the same region in blue and red light down to magnitude 26.9. At this optical depth, a distinct 24th magnitude “blob” (suspected to be an HII star-formation region) could be seen 3 arc seconds north of the spiral galaxy. A final attempt to detect anything further was made January 1, 2003 – again using the Keck 10 meter. No change was seen in optical light emanating from the region of GRB 020819. All this confirmed that no visible afterglow accompanied the gamma ray outburst detected by HETE-2 some 134 days earlier. The investigating team had their “dark gamma ray burster”. Later would come the task of figuring out just what the heck it was – or at least was not…

Periodically throughout the cycle of optical and near-infrared inspection, the region of the burst was monitored in radio-wave frequencies. Using the VLA (Very Large Array – consisting of 27 Y-configured 25 meter dishes located fifty miles west of Socorro, New Mexico) the team succeeded in capturing a dwindling trail of 8.48 Ghz radiation and identified its locale.

First radio waves from GRB 020819 were collected 1.75 days after the HETE-2 alert. By day 157, rf energy levels flattened to the point where the source could no longer be seen with confidence. However by this time, its location had been pinpointed to the “blob” three arc-seconds north of the core of the previously uncharted spiral galaxy. Unfortunately – due to its faintness – the distance to the blob itself could not be determined spectrographically – however the galaxy was found to lie some 6.2 BLY away and enjoys “high-confidence” in terms of having a relationship with the source.

As a result of such investigations astronomers are now learning more and more about a class of cataclysmic events that results in massive fluxes of high and low energy photons while almost completely skipping intermediate frequencies – such as ultraviolet, visible, and near-infrared of light. Is there anything that could account for this?

Based on learning from GRB 020819, the team explored three fireball-shock models of how dark GRBs might occur. Of the three (an even expansion of high energy gases into a homogenous medium, even expansion into a stratified medium, and a collimated jet penetrating either type medium), the best fit against GRB 020819 behaviors was that of an even expansion of high energy gases into a homogenous medium of other gases (a model first proposed by the astrophysicist R. Sari et al in 1998). The virtue of this isotropic-expansion model being (in the words of the investigating team) that “only a modest amount of extinction must be invoked” to account for the absence of visible light.

In addition to narrowing the range of possible scenarios associated with dark GRBs, the team concluded that “GRB 020819, a relatively nearby burst, is only one of two of the 14 GRB’s localized to within (2 arc minutes using) HETE-2 that does not have a reported OA. This lends support to the recent proposition that the dark burst fraction is far lower than previously suggested, perhaps as small as 10%.”

Written by Jeff Barbour

Artist illustration of a superflare on a young star. Image credit: NASA. Click to enlarge.
New results from NASA’s Chandra X-ray Observatory imply that X-ray super-flares torched the young Solar System. Such flares likely affected the planet-forming disk around the early Sun, and may have enhanced the survival chances of Earth.

By focusing on the Orion Nebula almost continuously for 13 days, a team of scientists used Chandra to obtain the deepest X-ray observation ever taken of this or any star cluster. The Orion Nebula is the nearest rich stellar nursery, located just 1,500 light years away.

These data provide an unparalleled view of 1400 young stars, 30 of which are prototypes of the early Sun. The scientists discovered that these young suns erupt in enormous flares that dwarf – in energy, size, and frequency — anything seen from the Sun today.

“We don’t have a time machine to see how the young Sun behaved, but the next best thing is to observe Sun-like stars in Orion,” said Scott Wolk of Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. “We are getting a unique look at stars between one and 10 million years old – a time when planets form.”

A key result is that the more violent stars produce flares that are a hundred times as energetic as the more docile ones. This difference may specifically affect the fate of planets that are relatively small and rocky, like the Earth.

“Big X-ray flares could lead to planetary systems like ours where Earth is a safe distance from the Sun,” said Eric Feigelson of Penn State University in University Park, and principal investigator for the international Chandra Orion Ultradeep Project. “Stars with smaller flares, on the other hand, might end up with Earth-like planets plummeting into the star.”

According to recent theoretical work, X-ray flares can create turbulence when they strike planet-forming disks, and this affects the position of rocky planets as they form. Specifically, this turbulence can help prevent planets from rapidly migrating towards the young star.

“Although these flares may be creating havoc in the disks, they ultimately could do more good than harm,” said Feigelson. “These flares may be acting like a planetary protection program.”

About half of the young suns in Orion show evidence for disks, likely sites for current planet formation, including four lying at the center of proplyds (proto-planetary disks) imaged by Hubble Space Telescope. X-ray flares bombard these planet-forming disks, likely giving them an electric charge. This charge, combined with motion of the disk and the effects of magnetic fields should create turbulence in the disk.

The numerous results from the Chandra Orion Ultradeep Project will appear in a dedicated issue of The Astrophysical Journal Supplement in October, 2005. The team contains 37 scientists from institutions across the world including the US, Italy, France, Germany, Taiwan, Japan and the Netherlands.

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate, Washington. Northrop Grumman of Redondo Beach, Calif., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

Original Source: Chandra News Release

Two of the four H.E.S.S. telescopes in Namibia. Image credit: HESS. Click to enlarge.
Our planet is exposed to almost four dozen octaves of electro-magnetic radiation from the Universe around us. Of those, half-a-dozen octaves can be detected from the Earth’s surface. During the 1990’s several extraordinary new octaves were added with the advent of high-sensitivity CCD imagers and modern computing systems. Today we can track super-high energy gamma rays back to their sources in space ? even while safely ensconced in the Earth?s protective mantle of air.

Well before the turn of the third millennium, it was realized that high-energy photons penetrating the air causes a secondary form of light known as Cherenkov Radiation (CR). CR was first observed by Pierre and Marie Curie when investigating radioactivity at the turn of the 20th century. It wasn’t until the mid-1930s that the hauntingly beautiful “blue-white” glow given off by glass in the presence of radioactivity was studied in detail.

CR was first fully investigated by the Russian experimentalist P. A. Cherenkov in 1936. Cherenkov found that whenever high-energy photons (or particles) pass through a transparent gas, liquid, or glass at velocities greater than the speed of light for that substance, a shower of secondary light is created. In terms of the Earth’s atmosphere, such showers typically occur as gamma rays approach within 10 km’s of sea level and the resulting luminosity projects a light cone (or “light pool”) roughly 250ms in diameter.

Enter the Max Plank Institute of Physics (MPIK) of Heidelberg, Germany in the early 1990s.

In 1992 MPIK tested the first in a series of prototypes intended to develop a full scale IACT (Imaging Atmospheric Cherenkov Telescopes) system. That instrument (CT1) proved that CR showers could be detected using CCDs. It also showed that computers could accurately log a CR shower’s time and position in the sky. A later instrument (CT2) increased CR sensitivity and resolution by adding aperture. Meanwhile improvements were made to associated imaging, data processing, and sky sensing components. By combining four CT2-class instruments together, the first full IACT system was developed in 1995 (CT3). Because of this progress, MPIK’s own website could later say that “Ground-based Imaging Atmospheric Cherenkov Telescopes have become the most efficient experimental technique for the observation of cosmic gamma rays in the TeV energy range.”

IACT systems monitor for CR showers using two or more widely spaced light-collecting mirror assemblies pointed at the same part of the sky. Because CR originates in the Earth’s atmosphere – not well-off in the Universe itself – each mirror sees a shower from a different perspective. The resulting “stereoscopic vision” works like eye and brain to precisely determine the path a gamma ray takes after entering the atmosphere. Based on that data – along with laws governing the way photons move – computers calculate the location of gamma ray source in space. Each ray effectively acts like a luminous finger pointing back toward a distant cosmic source.

By 1998 the first purely astronomical IACT (HEGRA – High Energy Gamma Ray Astronomy) was put into service by MPIK on La Palma in the Canary Islands. HEGRA confirmed dozens of high energy gamma ray sources – many hurling photons of more than 1 terra-electron-volts of energy (the amount of force stored in a single electron accelerated by a trillion volts of electricity). Among them were the Crab Nebula pulsar in Taurus and the giant elliptical galaxy M87 – regent of the Coma-Virgo galaxy cluster.

Today even more advanced IACT systems collect CR. One of the most sophisticated instruments (H.E.S.S – High Energy Stereoscopic System) was developed by MPIK along with a consortium of European scientific and educational organizations. Currently HESS consists of four separate 12m diameter IACTS gathering faint CR light in the dark skies above the 1.8km high Khomas Highlands of Namibia, Africa.

Named after Nobel Prize winning physicist Victor Hess (who discovered cosmic rays in 1912), HESS uses an array of four IACT mirror systems. Each spherical IACT mirror consists of 382, 60cm diameter individually-adjustable sub-mirrors reflecting CR light into a large electronic “camera”. Light focused on the camera is detected by a honeycomb of 960 “smartpixel” photo-multiplier tubes (PMTs). The four IACTs are placed in a square and spaced by 120 meters to give an optimally stereoscopic view of the sky within the 250m light pool caused by a CR event.

Each HESS IACT is ten times more sensitive than its corresponding HEGRA unit – and has to be, for the total amount of CR light in the sky is 10 stellar magnitudes fainter than starlight. HESS IACTS can resolve CR showers caused by photons as “weak” as .1 TeV while discriminating between high-energy particles and photons. Using a pair of IACTS, gamma ray sources can be isolated to less than 5 arc-minutes of angular resolution – roughly 1/6th the apparent size of the full moon. To simplify detection, HESS IACTS can scan 5 degrees of the sky at a time.

One of the fundamental questions before astrophysicists is to determine just how nature manages to pack so much punch into those mass-less, charge-less photons. Currently no terra-electron-volt particle accelerators are on line – and such devices only work with charged particles – not photons. It may fall to IACTS like HESS to lead the way.

In a paper entitled “Observation of the giant radio galaxy M87 at TeV energies using H.E.S.S”, M Beilicke of the Institute for Expermental Physics, Hamburg Germany and associates have used HESS to determine that the giant elliptical galaxy M87 is a strong and possibly periodically variable source of high-energy gamma ray photons.

According to the paper, “M87 is of particular interest for observations of TeV energies. The large jet angle makes it different from the so far observed TeV emitting AGN of the blazar type.” Using HESS, the team determined that high-energy photons originate from a point source centered in the midst of M87 – precisely where it’s AGN is thought to be. Unlike blazars however, M87’s relativistic jets do not point at the Earth.

Meanwhile the team may have also discovered that gamma ray output from M87’s AGN is variable “on time scales of years.” According to M. Bielecke et al, “Such a result would be very important since various models for the TeV gamma-ray production in M87 could be ruled out.” The team goes on to say that “Mechanisms correlated with cosmic rays, large scale jet structures, and exotic dark matter particle annihilation could not explain variability in the TeV gamma ray emission on these time-scales.”

As in many areas of contemporary astronomical investigation, observing M87 across a wide-range of the em band may be essential to understanding how those tiny mass-free wave-particles of light can carry so much ?weight?. There is no doubt that capturing the ‘blue-white” glow of Cherenkov radiation put off by our Earth’s very own atmosphere will play a critical role in making this possible.

Written by Jeff Barbour

Near perfect “Einstein Ring” gravitational lens. Image credit: ESO/VLT. Click to enlarge.
This is Einstein’s Year. One-hundred years ago a little known Swiss patent clerk in the very early years of a scientific career was confronted with a series of paradoxes related to time and space, energy and matter. Gifted with a profound intuition and a powerful imagination, Albert A. Einstein rose out of obscurity to present an entirely new way of looking at natural phenomenon. Einstein showed us all that time had very little to do with clocks, energy has less to do with quantity and more to do with quality, space was not just ?a big square box to put stuff in”, matter and energy were two sides of the same cosmic coin, and gravity had a profound effect on everything – light, matter, time, and space.

Today we use all these principles ? enunciated a century ago – to probe the most distant things in the Universe. Because of Einstein’s investigation of the photoelectric effect, we now understand why light is not continuous but curiously riddled with dark and bright lines telling us when that light was emitted, what emitted it. and the kinds of things touching it in its travels. Because of Einstein’s insight into the conversion of mass and energy, we now understand how distant suns illuminate the cosmos, and how powerful magnetic fields whip particles up to stupendous speeds later to come crashing down on the Earth’s atmosphere. And because gravity is now understood to influence everything, we have learned how distant objects can capture and focus light from even more distant objects.

Although we have yet to find an absolutely perfect instance of gravitational lensing in the Universe, today we are much closer to that ideal. In a paper entitled “Discovery of a high red-shift Einstein Ring” published April 27, 2005, Remi Cabanac of Canada-France-Hawaii Telescope, in Hawaii and associates “report the discovery of a partial Einstein ring … produced by a massive (and seemingly isolated) elliptical galaxy.” Previous to this find, the most complete Einstein ring discovered was documented in 1996 by S.J. Warren of the Imperial College in London. That ring – also one of the few visible in optical light – is slightly less than a half-circle in circumference (170 degrees).

Remi Cabanac explained that he “discovered the system while observing at the European Southern Observatory Very Large Telescope in Chile with a spectro imager called FORS1.” Remi says he was fullfilling his responsibilties as a service astronomer, “observing for Helmut Jerjen (co-author of the paper) doing deep imaging of nearby dwarf galaxies in the outskirts of a well-known nearby galaxy cluster in Fornax.” Remi continued to say that his “eye got attracted by the very unusual bright arc in the northwest of the field, I knew it was something pretty amazing because lensing arcs are usually very dim, and I was observing in red band whereas arcs are usually blueish.”

To confirm his suspicions of a new discovery Remi “went to the astronomical database but nothing existed under the coordinates.” Later Remi consulted with “Chris Lidman (another co-author and lens expert) and showed him the image. He couldn’t believe it was a lens at first because it was so bright and conspicuous, Chris thought it could be an artefact on the image.” With Chris’ support, Remi “applied for spectroscopic follow-up and realized that it was both a true gravitational lense and a very significant discovery, because the background source was highly amplified and very far away.”

According to the paper, the ring inscribes a “C-shaped” circle of 270 degrees in near-complete circumference with an apparent radius of slightly more than 1 3/4 arc seconds – roughly the size of a star’s “virtual” image seen at high power through a small amateur telescope. The lens galaxy is a giant elliptical similar to M87 in the Virgo-Coma cluster. The lens lies some 7 billion light years distant in the direction of the constellation Fornax (visible from warmer temperate northern hemisphere and southern hemisphere skies). The source galaxy bears a red shift of 3.77 – suggesting a recessionary distance of roughly 11 BLYs. Source and lens galaxy have received the designation FOR J0332-3557 3h32m59s, -35d57m51s and lie proximate to the Fornax galaxy cluster – but well beyond it in terms of real space.

What makes this particular discovery so interesting astronomically is the fact that the lens galaxy is very massive, is in a period of star-birth quiescence, lies at such a great distance from the Earth, and may be isolated from other cluster galaxies in its own spatial locale. Meanwhile the source galaxy is significantly brighter (by one absolute stellar magnitude) than other Lyman break galaxies (galaxies that red-shift the Lyman Break at 912 angstroms into the visible part of the spectrum), is poor in emission line spectra, and recently had completed a cycle of rapid star birth (“starburst”). All these factors combined mean that FOR J0332 could provide a wealth of data concerning galaxy formation before the current inflationary epoch of the Universe.

According to the science team, “One of the key issues in galaxy formation within the current LCDM (Lambda Cold Dark Matter) framework of structure formation is the mass assembly histories of galactic halos.” Current thinking is that galaxies accumulate halo mass – that huge spherical bulge of low luminosity matter surrounding galactic cores – before star formation really kicks in. One way to investigate this idea is to determine how mass-to-light ratios change over time as galaxies evolve. But to do that you need to sample the masses and luminosities of as many galaxies as possible, of a variety of types, over the broadest possible range of space and time.

The discovery of FOR J0332 – and the three other partial Einstein ring objects – helps astronomers by adding examples of galaxies normally undetectable at great distances. From the paper, “Various deep surveys have uncovered different galaxy populations, but the selection criteria produced biased samples: UV-selected and narrow-band selected samples are sensitive to actively star-forming galaxies and biased against quiescent, evolved systems while sub-millimeter and near-infrared surveys select dusty starburst galaxies and very red galaxies respectively.”

What conclusions can we draw based on this discovery?

Remi underscores the significance of this find by saying “The source amplified by the lens is the galaxy with the brightest apparent luminosity ever discovered at such a distance. It will give us unique information on the physical conditions prevailing in the interstellar medium when the universe was only 12% of its present age. The shape of the source is also very important because it gives the amount of mass within the lens at a redshift of z=1. Only a handful of Einstein rings have been discovered at such high redshift. It will give an important measurement at how elliptical galaxy mass evolved through time.”

Written by Jeff Barbour

Applying cutting edge computer science to a wealth of new astronomical data, researchers from the Sloan Digital Sky Survey (SDSS) reported today the first robust detection of cosmic magnification on large scales, a prediction of Einstein’s General Theory of Relativity applied to the distribution of galaxies, dark matter, and distant quasars.

These findings, accepted for publication in The Astrophysical Journal, detail the subtle distortions that light undergoes as it travels from distant quasars through the web of dark matter and galaxies before reaching observers here on Earth.

The SDSS discovery ends a two decade-old disagreement between earlier magnification measurements and other cosmological tests of the relationship between galaxies, dark matter and the overall geometry of the universe.

“The distortion of the shapes of background galaxies due to gravitational lensing was first observed over a decade ago, but no one had been able to reliably detect the magnification part of the lensing signal”, explained lead researcher Ryan Scranton of the University of Pittsburgh.

As light makes its 10 billion year journey from a distant quasar, it is deflected and focused by the gravitational pull of dark matter and galaxies, an effect known as gravitational lensing. The SDSS researchers definitively measured the slight brightening, or “magnification” of quasars and connect the effect to the density of galaxies and dark matter along the path of the quasar light. The SDSS team has detected this magnification in the brightness of 200,000 quasars.

While gravitational lensing is a fundamental prediction of Einstein’s General Relativity, the SDSS collaboration’s discovery adds a new dimension.

“Observing the magnification effect is an important confirmation of a basic prediction of Einstein’s theory,” explained SDSS collaborator Bob Nichol at the University of Portsmouth (UK). “It also gives us a crucial consistency check on the standard model developed to explain the interplay of galaxies, galaxy clusters and dark matter.”

Astronomers have been trying to measure this aspect of gravitational lensing for two decades. However, the magnification signal is a very small effect — as small as a few percent increases in the light coming from each quasar. Detecting such a small change required a very large sample of quasars with precise measurements of their brightness.

“While many groups have reported detections of cosmic magnification in the past, their data sets were not large enough or precise enough to allow a definitive measurement, and the results were difficult to reconcile with standard cosmology,” added Brice Menard, a researcher at the Institute for Advanced Study in Princeton, NJ.

The breakthrough came earlier this year using a precisely calibrated sample of 13 million galaxies and 200,000 quasars from the SDSS catalog. The fully digital data available from the SDSS solved many of the technical problems that plagued earlier attempts to measure the magnification. However, the key to the new measurement was the development of a new way to find quasars in the SDSS data.

“We took cutting edge ideas from the world of computer science and statistics and applied them to our data,” explained Gordon Richards of Princeton University.

Richards explained that by using new statistical techniques, SDSS scientists were able to extract a sample of quasars 10 times larger than conventional methods, allowing for the extraordinary precision required to find the magnification signal. “Our clear detection of the lensing signal couldn’t have been done without these techniques,” Richards concluded.

Recent observations of the large-scale distribution of galaxies, the Cosmic Microwave Background and distant supernovae have led astronomers to develop a ‘standard model’ of cosmology. In this model, visible galaxies represent only a small fraction of all the mass of the universe, the remainder being made of dark matter.

But to reconcile previous measurements of the cosmic magnification signal with this model required making implausible assumptions about how galaxies are distributed relative to the dominant dark matter. This led some to conclude that the basic cosmological picture was incorrect or at least inconsistent. However, the more precise SDSS results indicate that previous data sets were likely not up to the challenge of the measurement.

“With the quality data from the SDSS and our much better method of selecting quasars, we have put this problem to rest,” Scranton said. “Our measurement is in agreement with the rest of what the universe is telling us and the nagging disagreement is resolved.”

“Now that we’ve demonstrated that we can make a reliable measurement of cosmic magnification, the next step will be to use it as a tool to study the interaction between galaxies, dark matter, and light in much greater detail,” said Andrew Connolly of the University of Pittsburgh.

Original Source: SDSS News Release