Pinpointing the Distance to a Pulsar

Image credit: NSF

Astronomers have used the accuracy of the National Science Foundation’s Very Long Baseline Array (VLBA) to pinpoint the distance to a pulsar. The object, called PSR B0656+14, was previously thought to be up to 2,500 light-years away but it was at the same location in the sky as a supernova remnant which is only 1,000 light years away. This was thought to be a coincidence, but the new measurement from the VLBA pegs the pulsar at 950 light years away; the same distance as the remnant – they were both created by the same supernova blast.

Location, location, and location. The old real-estate adage about what’s really important proved applicable to astrophysics as astronomers used the sharp radio “vision” of the National Science Foundation’s Very Long Baseline Array (VLBA) to pinpoint the distance to a pulsar. Their accurate distance measurement then resolved a dispute over the pulsar’s birthplace, allowed the astronomers to determine the size of its neutron star and possibly solve a mystery about cosmic rays.

“Getting an accurate distance to this pulsar gave us a real bonanza,” said Walter Brisken, of the National Radio Astronomy Observatory (NRAO) in Socorro, NM.

The pulsar, called PSR B0656+14, is in the constellation Gemini, and appears to be near the center of a circular supernova remnant that straddles Gemini and its neighboring constellation, Monoceros, and is thus called the Monogem Ring. Since pulsars are superdense, spinning neutron stars left over when a massive star explodes as a supernova, it was logical to assume that the Monogem Ring, the shell of debris from a supernova explosion, was the remnant of the blast that created the pulsar.

However, astronomers using indirect methods of determining the distance to the pulsar had concluded that it was nearly 2500 light-years from Earth. On the other hand, the supernova remnant was determined to be only about 1000 light-years from Earth. It seemed unlikely that the two were related, but instead appeared nearby in the sky purely by a chance juxtaposition.

Brisken and his colleagues used the VLBA to make precise measurements of the sky position of PSR B0656+14 from 2000 to 2002. They were able to detect the slight offset in the object’s apparent position when viewed from opposite sides of Earth’s orbit around the Sun. This effect, called parallax, provides a direct measurement of distance.

“Our measurements showed that the pulsar is about 950 light-years from Earth, essentially the same distance as the supernova remnant,” said Steve Thorsett, of the University of California, Santa Cruz. “That means that the two almost certainly were created by the same supernova blast,” he added.

With that problem solved. the astronomers then turned to studying the pulsar’s neutron star itself. Using a variety of data from different telescopes and armed with the new distance measurement, they determined that the neutron star is between 16 and 25 miles in diameter. In such a small size, it packs a mass roughly equal to that of the Sun.

The next result of learning the pulsar’s actual distance was to provide a possible answer to a longstanding question about cosmic rays. Cosmic rays are subatomic particles or atomic nuclei accelerated to nearly the speed of light. Shock waves in supernova remnants are thought to be responsible for accelerating many of these particles.

Scientists can measure the energy of cosmic rays, and had noted an excess of such rays in a specific energy range. Some researchers had suggested that the excess could come from a single supernova remnant about 1000 light-years away whose supernova explosion was about 100,000 years ago. The principal difficulty with this suggestion was that there was no accepted candidate for such a source.

“Our measurement now puts PSR B0656+14 and the Monogem Ring at exactly the right place and at exactly the right age to be the source of this excess of cosmic rays,” Brisken said.

With the ability of the VLBA, one of the telescopes of the NRAO, to make extremely precise position measurements, the astronomers expect to improve the accuracy of their distance determination even more.

“This pulsar is becoming a fascinating laboratory for studying astrophysics and nuclear physics,” Thorsett said.

In addition to Brisken and Thorsett, the team of astronomers includes Aaron Golden of the National University of Ireland, Robert Benjamin of the University of Wisconsin, and Miller Goss of NRAO. The scientists are reporting their results in papers appearing in the Astrophysical Journal Letters in August.

The VLBA is a continent-wide system of ten radio- telescope antennas, ranging from Hawaii in the west to the U.S. Virgin Islands in the east, providing the greatest resolving power, or ability to see fine detail, in astronomy. Dedicated in 1993, the VLBA is operated from the NRAO’s Array Operations Center in Socorro, New Mexico.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Original Source: NRAO News Release

SMART-1 Launch Pushed Back

Image credit: ESA

The launch of the European Space Agency’s SMART-1 mission to explore the Moon was pushed back because of delays with its Ariane 5 launcher. The mission was originally scheduled for August 28, but now it’s been pushed into September. Once SMART-1 does get into space, it will use its ion engine to make larger and larger orbits around the Earth over the course of 16 months until it finally reaches the Moon. It will remain in orbit around the moon for over 2 years analyzing the surface and searching for evidence of water ice near the southern pole.

Europe is going to the Moon for the first time! In just over two weeks the European Space Agency’s (ESA) lunar probe, SMART-1, begins its journey to the Moon. Due to be launched from Kourou in French Guiana on 3rd September (12.04 a.m. 4th September BST) SMART-1 will be powered only by an ion engine which Europe will be testing for the first time as the main spacecraft propulsion. Onboard will be D-CIXS, an X-ray spectrometer built by scientists in the UK, which will provide information on what the Moon is made of.

SMART-1 represents a new breed of spacecraft. It is ESA’s first Small Mission for Advanced Research in Technology – designed to demonstrate innovative and key technologies for future deep space science missions. As well as the ion propulsion mechanism SMART-1 will test miniaturised spacecraft equipment and instruments, a navigation system which in the long term will allow spacecraft to autonomously navigate through the solar system, and a space communication technique whereby SMART-1 will establish a link with the Earth using a laser beam.

Once it has arrived at the Moon (expected to be in January 2005), SMART-1 will perform an unprecedented scientific study of the Moon- providing valuable information which will shed light on some of the unanswered questions. The spacecraft will search for signs of water-ice in craters near the Moon’s poles, provide data on the still uncertain origin of the Moon and reconstruct its evolution by mapping and the surface distribution of minerals and key chemical elements.

Commenting on the mission Prof. Ian Halliday, Chief Executive of PPARC said,” This mission to our only natural satellite is a masterpiece of miniaturisation and UK scientists have played a leading role in providing one of the spacecraft’s key instruments – testament to the UK’s expertise in space science.” Halliday added, “SMART-1 is packed with innovative technology that promises to revolutionise our future exploration of neighbouring planets whilst answering some fundamental questions about the Moon – how did the Moon form and how did it evolve?”

UK scientists have a lead role in the mission. D-CIXS, a compact X-ray Spectrometer, which will make the first ever global X-ray map of the Moon’s surface, has been built by a team led by Principal Investigator Professor Manuel Grande from the CCLRC Rutherford Appleton Laboratory near Oxford. Scientists from a number of other UK institutions are involved in D-CIXS (see notes to editors for further details).

Professor Grande explains how D-CIXS works,

“When the Sun shines on the Moon, its surface fluoresces and D-CIXS will measure the resulting X-rays to determine many of the elements found on its surface. This will provide us with vital clues which will help understand the origins of our Moon.”

Weighing just 4.5 kilograms and the size of a toaster, one of the challenges for the D-CIXS team has been to fit all the necessary components into the instrument. This has been achieved through clever miniaturisation and the development of new technology such as novel X-ray detectors – based on new swept charge devices (similar to the established charged couple devices found in much of today’s technology) and microfabricated collimators with walls no thicker than a human hair.

Lord Sainsbury, Minister for Science and Innovation at the Department of Trade and Industry said:

“SMART-1 is an unprecedented opportunity to provide the most comprehensive study ever of the surface of the Moon. The UK is playing a key role in this important European mission by providing technology that demonstrates excellent collaboration between engineering and science in this country. This mission will also give the European Space Agency the opportunity to develop new technology for future missions, demonstrating once again the effectiveness of joint working between the UK and our European partners in space.”

Detector Will Measure the Mass of Neutrinos

Image credit: PPARC

On August 14, a new detector designed to determine the mass of neutrinos began operations in an old mine in Minnesota, USA. The Main Injector Neutrino Oscillation Search (MINOS) detector is 30-metres long and consists of 486 massive octagonal plates, each of which is 8-metres across. MINOS will initially measure neutrinos coming from Sun, but in August 2004 it will measure man-made neutrinos created in a laboratory more than 700 km away. If the experiment is successful it will help solve the mystery of dark matter, which some astronomers believe comes from the mass of neutrinos.

Today, (August 14th), sees the start of data collection on the Main Injector Neutrino Oscillation Search (MINOS) detector, situated in the Soudan iron mine, Minnesota, USA. UK particle physicists, working within an international collaboration, will use the MINOS detector to investigate the phenomenon of neutrino mass – a puzzle that goes to the heart of our understanding of the Universe.

Neutrinos are pointlike, abundant particles with very little mass. They exist in three types or ‘flavours’ and recent experiments (including those at SNO – the Sudbury Neutrino Observatory) have demonstrated that neutrinos are capable of oscillating between these flavours (electron, tau and muon). This can only happen if one or more of the neutrino flavours does have mass, in contradiction to the Standard Model of particle physics.

The MINOS detector will start measurements of cosmic ray showers penetrating the Earth. It is situated in the Soudan Mine, Minnesota. The 30-metre-long detector consists of 486 massive octagonal planes, lined up like the slices of a loaf of bread. Each plane consists of a sheet of steel about 8 metres high and 2 ? cm thick, covered on one side with a layer of scintillating plastic that emits light when struck by a charged particle.

“MINOS can separate neutrino interactions from their antimatter counterparts – the antineutrinos.” explains UK MINOS spokesperson, Jenny Thomas from University College London. “The data taken now from neutrinos produced in cosmic ray cascades may provide new insight into why the Universe is made of more matter than antimatter. At least, for the first time we will be able to compare the characteristics of neutrinos and anti-neutrinos coming from the atmosphere.”

However, MINOS has more ambitious plans in place for August 2004. Whilst most experiments like SNO measure neutrinos coming from the Sun, when complete, MINOS will instead study a beam of man-made neutrinos, all of the same type or ‘flavour’ – the muon neutrino flavour. This beam will be created at Fermi National Accelerator Laboratory (Fermilab) and sent straight through the Earth to Soudan – a distance of 735 kilometres. No tunnel is needed because neutrinos interact so rarely with matter. A detector is currently being built just outside Fermilab, known as the ‘near’ detector, similar but smaller than the now operational MINOS detector, known as the ‘far’ detector. The ‘near’ detector will act as a control, studying the beam as it leaves Fermilab, then the results will be compared with those from the ‘far’ detector to see if the neutrinos have oscillated into electron or tau neutrinos during their journey.

A million million neutrinos will be created at Fermilab each year, but only 1,500 will interact with the nucleus of an atom in the far detector and generate a signal; the others will pass straight through.

“The realisation that neutrinos oscillate, first demonstrated by the Super Kamiokande experiment in Japan, has been one of the biggest surprises to emerge in particle physics since the inception of the Standard Model more than 30 years ago.” says Jenny Thomas. “The MINOS experiment will measure the oscillation parameters of these neutrinos to an unprecedented accuracy of a few percent; an amazing feat considering neutrinos can usually pass directly through the Earth without interacting at all and that their inferred masses are estimated to be less than 1eV. (The weight ratio of a neutrino to a 1kg bag of sugar is the same as the ratio of a grain of sand to the weight of the earth!). The parameter measurement will open up an entire new field of particle physics, to understand what effect on the universe this tiny neutrino mass has.”

Within two years of turning on the neutrino beam, MINOS should produce an unequivocal measurement of the oscillation of muon neutrinos with none of the uncertainties associated with the atmospheric or solar neutrino source. If indeed the findings are positive, then a new era in particle physics will begin. Theorists will have to incorporate massive neutrinos into the Standard Model, which will have exciting implications. Furthermore cosmologists will have a strong candidate for the ‘missing mass’ of the Universe (which dynamical gravitational measurements show must exist). The experimental side will be just as exciting as we plan new experiments to measure precisely how the different neutrinos change their flavour.

Original Source: PPARC News Release

These Microbes Can Take the Heat

Microbes taken from a deep sea vent at the bottom of the Pacific Ocean can survive in an environment that would kill anything else on Earth – they live, and thrive, in water that is 130 degrees Celsius. The scientists who discovered the microbes, called Strain 121, put the creature in an autoclave, which is designed to kill all bacteria; not only did it survive, but it kept on multiplying in the high heat. The discovery helps scientists develop new theories of how life could have originated on an early Earth that was much hotter than it is today.

Chandra Sees Horseshoe Nebula

Image credit: Chandra

The latest image released from the Chandra X-Ray Observatory shows the centre of M17, (a.k.a. the Horseshoe Nebula) in the constellation of Sagittarius. The resolution of Chandra is so high that it can pick out the group of massive young stars which are heating the surrounding gas from 1.5 million to 7 million degrees Celsius. The stars in the nebula are only a million years old, so the nebula is too young for one of its stars to have exploded as a supernova and heated the gas.

The Chandra image reveals hot gas flowing away from massive young stars in the center of the Horseshoe Nebula, a.k.a. M17, a.k.a. the Omega Nebula. The gas temperatures range from 1.5 million degrees Celsius (2.7 million degrees Fahrenheit) to about 7 million degrees Celsius (13 million degrees F).

A group of massive young stars responsible for the activity in the nebula is located in the bright pink region near the center of the image. Chandra’s resolving power enabled astronomers to separate the contribution from these and other stars in the nebula from the diffuse emission.

Infrared Close-Up of M17
An infrared image of the Horseshoe Nebula reveals a cloud of much cooler gas and dust shaped like a horseshoe that gives the nebula its name. The hot gas shown by the Chandra image fits inside the cool gas cloud, and appears to have formed the horseshoe shape by carving a cavity in the cool gas. This activity could lead to the formation of new stars in the Horseshoe.

The stars in the Horseshoe Nebula are only about a million years old, so the nebula is too young for one of its stars to have exploded as a supernova and heated the gas. Collisions between high-speed winds of particles flowing away from the massive stars could heat the gas, or the hot gas could be produced as these winds collide with cool clouds to form bubbles of hot gas. This hot gas appears to be flowing out of the Horseshoe like champagne flows out of a bottle when the cork is removed, so it has been termed an “X-ray champagne flow.”

A comparison with other young star clusters confirms that massive young stars are responsible for hot gas clouds like the one seen in the Horseshoe Nebula. The Arches cluster, which contains many massive young stars shows this type of cloud, whereas the central regions of the Orion Nebula, which has few massive young stars, does not.

Original Source: Chandra News Release

Three Fates for Hubble

Image credit: NASA

A NASA panel released three options for the future of the Hubble Space Telescope after its last servicing mission in 2004 or 2005 which will extend its life to 2010. The first idea is to do another servicing mission in 2010 and keep Hubble operating as long as possible. The second option is to just do the single servicing mission around 2006 and install a propulsion device which would allow NASA to de-orbit the telescope by remote control. And the third possibility is to launch a robotic mission that will attach a propulsion device so Hubble can be de-orbited later.

An independent panel of astronomers identified three options for NASA to consider for planning the transition from the Hubble Space Telescope (HST) to the James Webb Space Telescope (JWST) at the start of the next decade.

The panel, chaired by Prof. John Bahcall, Institute for Advanced Study, Princeton, N.J., chartered by NASA earlier this year, submitted their report to the agency this week.

NASA’s current plans are to extend the life of the HST to 2010 with one Space Shuttle servicing mission (SM 4) in 2005 or 2006. The plan is tentative pending the agency’s return to flight process and the availability of Shuttle missions. NASA plans to eventually remove the HST from orbit and safely bring it down into the Pacific Ocean.

“NASA is deeply appreciative to Prof. Bahcall and the panel for getting this thoughtful report to us ahead of schedule,” said Dr. Ed Weiler, NASA’s Associate Administrator for Space Science. “We have a big job to do to study the panel’s findings and consider our options, and we will respond as soon as we have time to evaluate their report,” Weiler said.

The three options presented by the HST-JWST Transition Plan Review Panel, listed in order of priority, are:

“1. Two additional Shuttle servicing missions, SM4 in about 2005 and SM5 in about 2010, in order to maximize the scientific productivity of the Hubble Space Telescope. The extended HST science program resulting from SM5 would only occur if the HST science was successful in a peer-reviewed competition with other new space astrophysics proposals.”

“2. One Shuttle servicing mission, SM4, before the end of 2006, which would include replacement of HST gyros and installing improved instruments. In this scenario, the HST could be de-orbited, after science operations are no longer possible, by a propulsion device installed on the HST during SM4 or by an autonomous robotic system.”

“3. If no Shuttle servicing missions are available, a robotic mission to install a propulsion module to bring the HST down in a controlled descent when science is no longer possible.”

In addition, the panel described various ways to ensure maximum science return from the HST if none, one or two Shuttle servicing missions are available.

“A lot of astronomers and NASA officials were astonished, when we said our report was ready just one week after our public meeting. This was possible because we reached unanimous agreement on our conclusions very quickly; remarkable when you consider there were six independent-minded scientists on the panel. Our secret is we did our homework very thoroughly. Many people helped to educate us,” Bahcall said.

For information about NASA and space science on the Internet, visit:

The HST-JWST Transition Panel report is available on the Internet at:

Information about the panel, including membership and charter, is available at:

For information about the Hubble Space Telescope on the Internet, visit:

For information about the James Webb Space Telescope on the Internet, visit:

Original Source: NASA News Release

Northeast Blackout Seen From Space

The National Oceanic and Atmospheric Administration posted satellite images online that showed the extent of the power blackout that affected more than 50 million people late last week. The photos show the areas both before and after the lights went out and demonstrate the dramatic change in power. The images were acquired by the agency’s Defense Meteorological Satellite Program (DMSP) on August 14 at 9:03 pm EDT.

Fuel Leak Delays Titan Launch

The launch of a Titan 4B rocket was delayed after 200 litres of toxic nitrogen tetroxide propellant spilled out and created a dangerous gas cloud. Fortunately, none of the workers were injured by the cloud, and it dissipated before it reached the adjacent Kennedy Space Center. It’s unknown when the Titan rocket will be ready again to launch its cargo of a National Reconnaissance Office satellite. Investigators are still determining what caused the accident.

Ultrasound is the Coolest Thing Ever

My wife and I went for our second ultrasound last week to see how our second child is coming along. We were originally booked into a terrible ultrasound clinic (we’d been there before) but we begged our midwife to get us into a place that would treat us a little better, so we ended up at a hospital without a maternity ward – they never get a chance to look at babies. We ended up giving the ultrasound technicians a welcome break from the more boring stuff they usually have to look at. They spent almost an hour with us, examining our next baby in detail; showing us the face, the heart, and every little part of the body. If you’ve never watched an ultrasound before, I can’t recommend it enough. A static photo doesn’t do justice to the little images you see of your unborn child squirming around in the womb.

Oh yeah… we’re having a boy. 🙂

Fraser Cain
Universe Today

P.S. I’m headed away for vacation on Friday and won’t be back until Tuesday afternoon so there’ll be a little break in the news.

Gamma Ray Bursts May Propel Fast Moving Particles

Image credit: NASA

Astronomers believe that gamma-ray bursts, the most powerful explosions in the Universe, may be generating ultrahigh-energy cosmic rays, the most energetic particles in the Universe. These cosmic rays have baffled astronomers because they’re moving faster than if they were thrown out of a supernova. Evidence gathered by NASA’s de-orbited Compton Gamma-Ray Observatory showed that in one instance of a gamma ray burst, these high-energy particles dominated the area giving a connection between them, but this is hardly enough evidence to say they’re conclusively linked.

The most powerful explosions in the universe, gamma-ray bursts, may generate the most energetic particles in the universe, known as the ultrahigh-energy cosmic rays (UHECRs), according to a new analysis of observations from NASA’s Compton Gamma-Ray Observatory.

Researchers report in the August 14 edition of Nature of a newly identified pattern in the light from these enigmatic bursts that could be explained by protons moving within a hair’s breadth of light speed.

These protons, like shrapnel from an explosion, could be UHECRs. Such cosmic rays are rare and constitute an enduring mystery in astrophysics, seemingly defying physical explanation, for they are simply far too energetic to have been generated by well-known mechanisms such as supernova explosions.

“Cosmic rays ‘forget’ where they come from because, unlike light, they are whipped about in space by magnetic fields,” said lead author Maria Magdalena Gonzalez of the Los Alamos National Laboratory in New Mexico and graduate student at the University of Wisconsin. “This result is an exciting chance to possibly see evidence of them being produced at their source.”

Gamma-ray bursts — a mystery scientists are finally beginning to unravel — can shine as brilliantly as a million trillion suns, and many may be from an unusually powerful type of exploding star. The bursts are common yet random and fleeting, lasting only seconds.

Cosmic rays are atomic particles (for example, electrons, protons or neutrinos) moving close to light speed. Lower-energy cosmic rays bombard the Earth constantly, propelled by solar flares and typical star explosions. UHECRs, with each atomic particle carrying the energy of a baseball thrown in the Major Leagues, are a hundred-million times more energetic than the particles produced in the largest human-made particle accelerators.

Scientists say the UHECRs must be generated relatively close to the Earth, for any particle traveling farther than 100 million light years would lose some of its energy by the time it reached us. Yet no local source of ordinary cosmic rays seems powerful enough to generate a UHECR.

The Gonzalez-led paper focuses not specifically on UHECR production but rather a new pattern of light seen in a gamma-ray burst. Digging deep into the Compton Observatory archives (the mission ended in 2000), the group found that a gamma-ray burst from 1994, named GRB941017, appears different from the other 2,700-some bursts recorded by this spacecraft. This burst was located in the direction of the constellation Sagitta, the Arrow, likely ten billion light years away.

What scientists call gamma rays are photons (light particles) covering a wide range of energies, in fact, over a million times wider than the energies our eyes register as the colors in a rainbow. Gonzalez’s group looked at the higher-energy gamma-ray photons. The scientists found that these types of photons dominated the burst: They were at least three times more powerful on average than the lower-energy component yet, surprisingly, thousands of times more powerful after about 100 seconds.

That is, while the flow of lower-energy photons hitting the satellite’s detectors began to ease, the flow of higher-energy photons remained steady. The finding is inconsistent with the popular “synchrotron shock model” describing most bursts. So what could explain this enrichment of higher-energy photons?

“One explanation is that ultrahigh-energy cosmic rays are responsible, but exactly how they create the gamma rays with the energy patterns we saw needs a lot of calculating,” said Dr. Brenda Dingus of LANL, a co-author on the paper. “We’ll be keeping some theorists busy trying to figure this out.”

A delayed injection of ultrahigh-energy electrons provides another way to explain the unexpectedly large high-energy gamma-ray flow observed in GRB 941017. But this explanation would require a revision of the standard burst model, said co-author Dr. Charles Dermer, a theoretical astrophysicist at the U.S. Naval Research Laboratory in Washington. “In either case, this result reveals a new process occurring in gamma-ray bursts,” he said.

Gamma-ray bursts have not been detected originating within 100 million light years from Earth, but through the eons these types of explosions may have occurred locally. If so, Dingus said, the mechanism her group saw in GRB 941017 could have been duplicated close to home, close enough to supply the UHECRs we see today.

Other bursts in the Compton Observatory archive may have exhibited a similar pattern, but the data are not conclusive. NASA’s Gamma-ray Large Area Space Telescope (GLAST), scheduled for launch in 2006, will have detectors powerful enough to resolve higher-energy gamma-ray photons and solve this mystery.

Co-authors on the Nature report also include Ph.D. graduate student Yuki Kaneko, Dr. Robert Preece, and Dr. Michael Briggs of the University of Alabama in Huntsville. This research was funded by NASA and the Office of Naval Research.

UHECRs are observed when they crash into our atmosphere, as is illustrated in the figure. The energy from the collision produces an air shower of billions of subatomic particles and flashes of ultraviolet light, which are detected by special instruments.

The National Science Foundation and international collaborators have sponsored instruments on the ground, such as the High Resolution Fly’s Eye in Utah ( and the Auger Observatory in Argentina ( In addition, NASA is working with the European Space Agency to place the Extreme Universe Space Observatory ( on the International Space Station. The proposed OWL mission would, from orbit, look downward towards air showers, viewing a region as large as Texas.

These scientists record the flashes and take a census of the subatomic shrapnel, working backward to calculate how much energy a single particle needs to make the atmospheric cascade. They arrive at a shocking figure of 10^20 electron volts (eV) or more. (For comparison, the energy in a particle of yellow light is 2 eV, and the electrons in your television tube are in the thousand electron volt energy range.)

These ultrahigh-energy particles experience the bizarre effects predicted by Einstein’s theory of special relativity. If we could observe them coming from a remote corner of the cosmos, say a hundred million light years away, we’d have to be patient — it will take a hundred million years to complete the journey. However, if we could travel with the particles, the trip is over in less than a day due to the dilation of time of rapidly moving objects as measured by an observer.

The highest energy cosmic rays cannot even reach us if produced from distant sources, because they collide and lose energy with the cosmic microwave photons left over from the big bang. Sources of these cosmic rays must be found relatively close to us, at a distance of several hundred million light years. Stars that explode as gamma-ray bursts are found within this distance, so intensive observational efforts are underway to find gamma-ray burst remnants distinguished by radiation halos made by the cosmic rays.

Few kinds of celestial objects possess the extreme conditions required to blast particles to UHECR speeds. If gamma-ray bursts produce UHECRs, they probably do so by accelerating particles in jets of matter ejected from the explosion at close to the speed of light. Gamma-ray bursts have the power to accelerate UHECRs, but the gamma-ray bursts observed so far have been remote, billions of light years away. This doesn’t mean they can’t happen nearby, within the UHECR cutoff distance.

A leading contender for long-lived kinds of gamma-ray bursts like GRB941017 is the supernova/collapsar model. Supernovae happen when a star many times more massive than the Sun exhausts its fuel, causing its core to collapse under its own gravity while its outer layers are blown off in an immense thermonuclear explosion. Collapsars are a special type of supernova where the core is so massive it collapses into a black hole, an object so dense that nothing, not even light, can escape its gravity within the black hole’s event horizon. However, observations indicate black holes are sloppy eaters, ejecting material that passes near, but does not cross, their event horizons.

In a collapsar, the star’s core forms a disk of material around the newly formed black hole, like water swirling around a drain. The black hole consumes most of the disk, but some matter is blasted in jets from the poles of the black hole. The jets tear through the collapsing star at close to the speed of light, and then punch through gas surrounding the doomed star. As the jets crash into the interstellar medium, they create shock waves and slow down. Internal shocks also form in the jets as their leading edges slow and are slammed from behind by a stream of high-speed matter. The shocks accelerate particles that generate gamma rays; they could also accelerate particles to UHECR speeds, according to the team.

“It’s like bouncing a ping pong ball between a paddle and a table,” said Dingus. “As you move the paddle closer to the table, the ball bounces faster and faster. In a gamma-ray burst, the paddle and the table are shells ejected in the jet. Turbulent magnetic fields force the particles to ricochet between the shells, accelerating them to almost the speed of light before they break free as UHECRs.”

Detection of neutrinos from gamma-ray bursts would clinch the case for cosmic ray acceleration by gamma-ray bursts. Neutrinos are elusive particles made when high-energy protons collide with photons. Neutrinos have no electrical charge, so still point back to the direction of their source.

The National Science Foundation is currently building IceCube (, a cubic kilometer detector located in the ice under the South Pole, to search for neutrino emission from gamma-ray bursts. However, the characteristics of nature’s highest-energy particle accelerators remain an enduring mystery, though acceleration by the exploding stars that make gamma-ray bursts has been in favor ever since Mario Vietri (Universita di Roma) and Eli Waxman (Weizmann Institute) proposed it in 1995.

The team believes that while other explanations are possible for this observation, the result is consistent with UHECR acceleration in gamma-ray bursts. They saw both low-energy and high-energy gamma rays in the GRB941017 explosion. The low-energy gamma rays are what scientists expect from high-speed electrons being deflected by intense magnetic fields, while the high-energy rays are what’s expected if some of the UHECRs produced in the burst crash into other photons, creating a shower of particles, some of which flash to produce the high-energy gamma rays when they decay.

The timing of the gamma-ray emission is also significant. The low-energy gamma rays faded away relatively quickly, while the high-energy gamma rays lingered. This makes sense if two different classes of particles – electrons and the protons of the UHECRs – are responsible for the different gamma rays. “It’s much easier for electrons than protons to radiate their energy. Therefore, the emission of low-energy gamma rays from electrons would be shorter than the high-energy gamma rays from the protons,” said Dingus.

The Compton Gamma Ray Observatory was the second of NASA’s Great Observatories and the gamma-ray equivalent to the Hubble Space Telescope and the Chandra X-ray Observatory. Compton was launched aboard the Space Shuttle Atlantis in April 1991, and at 17 tons, was the largest astrophysical payload ever flown at that time. At the end of its pioneering mission, Compton was deorbited and re-entered the Earth’s atmosphere on June 4, 2000.

Original Source: NASA News Release