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A gamma ray is a high-energy, short wavelength electromagnetic wave

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APOD: 2013 December 6 - Gamma Ray Earth and Sky

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A different astronomy and space science related image is featured each day, along with a brief explanation.

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Supernovas occur when stars can't handle their nuclear fuel and they explode in a brilliant burst of light.

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Gamma rays have a low ionizing power, so they can pass through most substances

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Gamma Rays, Gamma Rays Uses, Examples of Gamma Rays | Physics@TutorVista.com

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What is electromagnetic radiation and which ray has the smallest of wavelength and highest of energy? Our subject experts can help you with gamma rays and more.

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Short-duration burst-From merging neutron stars
Long-Duration burst-from supernovae

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Late last week, as some staff astronomers embarked on trips to see Monday's solar eclipse, two of NASA's space-based observatories - Hubble and Chandra X-ray - and at least two land-based telescopes scrambled to capture a far more explosive event. The astronomers who stayed behind trained their telescopes on a patch of sky where they hoped to find an astrophysical Rosetta stone: a cataclysmic event capable of producing electromagnetic signals on top of gravitational waves separately detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (Advanced LIGO).

The LIGO collaboration made headlines in February 2016 when it announced it had detected gravitational waves from two colliding black holes. Four months later, while still in its first observing run, the team confirmed the detection of a second black hole merger. A third such merger was detected in January during Advanced LIGO's second observing run, which ended today. This possible newevent could represent something special.

While two merging black holes are thought to produce nothing detectable beyond a crescendo of gravitational waves, events involving two neutron stars or a neutron star and a black hole could also leave behind a glowing wreckage for telescopes to see. LIGO has yet to confirm that such an event has been detected. "Some promising gravitational-wave candidates have been identified in data from both LIGO and Virgo during our preliminary analysis, and we have shared what we currently know with astronomical observing partners," said an announcement posted by the LIGO team this morning.

But there has been speculation on Twitter, in a New Scientist article and on astronomer Peter Coles's blog that such a link has been found, based on publicly available observation logs.

"If the detection is true, it would be transformative for the field and probably one of the greatest discoveries in astronomy," said Enrico Ramirez-Ruiz of the University of California, Santa Cruz, who refused to discuss any specific results.

In recent years, many astrophysicists have become convinced that rare mergers of binary neutron stars offer a solution to multiple open problems in astronomy. The collisions could be the source of mysterious and brief flashes of gamma rays from the distant universe, or the dominant forges of some of the universe's heavy "r-process" elements, such as uranium, platinum and gold. They could also help physicists understand how matter behaves at densities comparable to the nucleus of an atom. An event seen in both gravitational wave and electromagnetic data could answer these questions. "If you get all these different pieces then you can put together the full story," said Duncan Brown, a physics professor at Syracuse University and a member of the LIGO collaboration, who also declined to comment on any new discoveries.

With the combination of gravitational waves and detailed spectra, "we would be able to see the formation of r-process material in real time, calculate the total amount of mass produced in the event, and give a relatively precise estimate of the merger rate," Ramirez-Ruiz said.

Every gravitational wave signal sparks a search with survey telescopes for a matching afterglow. But a close look at the observation logs shows that this time, both survey telescopes and narrow-field observatories were called into action to look at a specific source.

Starting August 17 and continuing every night since, the Visible and Infrared Survey Telescope for Astronomy at Cerro Paranal in Chile has taken survey images intended to spot a kilonova, the proposed observational signature of two colliding neutron stars, based on a LIGO gravitational wave detection. Another instrument on the same mountain took spectra from a part of that region of the sky for over four and a half hours from August 19 to 22.

Up in space, multiple Hubble programs that take visible and infrared data with the telescope's highest-resolution camera shifted to a new target on August 18 and August 22. And the Chandra Observatory began at least one of its own gravitational wave follow-up studies in X-ray wavelengths on August 19.

If astronomers have indeed managed to track down some combination of visible light, infrared radiation, X-rays or gamma rays from the same place as a gravitational wave event, it could be because they got an actionable tip on exactly where to look - perhaps from NASA's gamma-ray-sensitive FERMI telescope, as Nature reports has been rumored, or maybe from the gravitational wave community. LIGO started its second observing run on November 30, 2016 with only two detectors. A third - crucial for triangulating where waves are coming from in the sky - was added on August 1 when the Virgo detector in Italy joined the effort. If a detection took place so soon after Virgo went online, the timing would be fortuitous; after today, LIGO will go on a year-long hiatus to upgrade its detectors.

"It will require time to establish the level of confidence needed to bring any results to the scientific community and the greater public," this morning's LIGO statement said. "We will let you know as soon we have information ready to share."
This article was reprinted in Wired.com.

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For Astronomers, a Neutron Star Merger Could Eclipse the Eclipse

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Late last week, as some staff astronomers embarked on trips to see Monday's solar eclipse, two of NASA's space-based observatories - Hubble and Chandra X-ray - and at least two land-based telescopes scrambled to capture a far more explosive event.

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The combination of a positron and electron produces gamma rays in a process called annihilation

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Combining neutron stars produce a torus (a field of magnetic particles.) The torus spins irregularly causing magnetic instability and gamma ray emission

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Stephan Rosswog, The Oskar Klein Centre for Cosmoparticle Physics, Department of Astronomy, Stockholm University, Stockholm, Sweden

New calculations show that the accretion flows that form after a neutron star collision can eject large amounts of matter that is rich in gold and other heavy elements.

The Begelman group and Steve Burrows/JILA

Gold has long been appreciated for its beauty, its rareness, and a number of astonishing physical properties, like the fact that a single coin can be beaten into an area of more than 30 square meters. As much as gold has been searched for on Earth, there has been a long debate about its cosmic origin. But the detection this past summer of both gravitational waves and an electromagnetic flash from a neutron star merger (see 16 October 2017 Viewpoint) implies that heavy elements are forged around the most extreme objects in the Universe: neutron stars and black holes. A new theoretical study by Daniel Siegel and Brian Metzger from Columbia University, New York [ 1], simulates in detail the postmerger accretion of neutron star matter onto a black hole and confirms earlier, but less sophisticated, studies claiming that such systems are indeed promising production sites for gold and other heavy elements. The results may provide new insights into the recent neutron star merger observations, such as why the electromagnetic flash that accompanied the gravitational waves was so bright.

The heaviest elements are formed through the so-called " r process," in which a nucleus grows larger by rapidly capturing multiple neutrons. Neutrons are favored over protons, whose positive charge repels them from the positively charged nucleus. After capturing a neutron, the nucleus is not generally stable. Instead, it may transform a neutron into a proton in a beta decay, thereby emitting an electron and an antineutrino. The next neutrons need to be captured on a very short time scale, before the next beta decays set in. This is the defining feature of the r process, and its basic workings were already understood in the late 1950s [ 2].

Although it's clear what the r process needs-an explosion with lots of neutrons-where this actually happens has been a mystery for decades. The first suspected culprits were massive stars that explode as core-collapse supernovae. Later on, researchers developed an alternative r-process scenario involving mergers of neutron stars in binary systems, but this idea retained an "exotic" aura as such mergers had never been observed before. It is rather obvious that neutron stars would be an ideal place for the r process; after all, they consist predominantly of neutrons. Much less obvious is whether there is any way to eject the matter in the first place. A neutron star has an enormous gravitational pull, with a gravitational binding energy in excess of 100 MeV/nucleon. By comparison, the most energetic nuclear reactions release less than 10 MeV of energy per nucleon. So nuclear reactions would fall far short of liberating any matter from a neutron star surface. To rip a neutron star apart, it takes a merger with another extreme object, either a black hole [ 3] or another neutron star [ 4]. Besides being potential heavy element sources, these violent collisions were also predicted [ 4] to produce short gamma-ray bursts (GRBs), which are brief and enormously bright flashes of gamma rays.

In the late 1990s, computer simulations [ 5] showed that neutron star mergers can indeed eject a few percent of a solar mass when they come into contact, enough to explain a large fraction, if not all, of the observed r-process matter in the Milky Way. A companion study [ 6] demonstrated that these "dynamic ejecta" forge a broad range of heavy elements up to and beyond gold and platinum. More recently, researchers have identified additional ejection channels, including "neutrino-driven winds" [ 7] and the unbinding of a torus of accreting matter [ 8, 9] in the aftermath of a merger. This latter scenario of torus unbinding is the focus of Siegel and Metzger's work.

An accretion torus is a natural consequence of the merger of two neutron stars or of a black hole and a neutron star (see Fig. 1). The torus contains neutron star debris, a portion of which is destined to fall into the central spinning black hole that emerges from the coalescence. Since neutron stars often have strong magnetic fields, the torus is endowed from its beginning with a seed field. The rotation profile-in which the inner parts spin faster than the periphery-makes the torus prone to a "magnetorotational instability" (MRI) that amplifies the seed field, drives the torus into a turbulent state, redistributes its angular momentum, and leads to continued draining of the neutron star matter into the hole. While the occurrence of the instability can be demonstrated analytically, following its detailed growth has proven to be a serious challenge for computer simulations because very small length scales need to be resolved. As such, previous attempts have often relied on "effective models" that treat the effect of the MRI as a single viscosity parameter.

Siegel and Metzger [ 1] performed three-dimensional relativistic magnetohydrodynamics simulations of such a black hole torus system. Since the torus is very dense (∼1 0 1 0 g/cm 3 ) it emits large amounts of neutrinos while trapping photons. The weak interactions that produce the neutrinos can also change the neutron-to-proton ratio in the torus. Contrary to earlier studies, Siegel and Metzger calculated both relativistic effects and the dissipation inside the torus from first principles rather than via effective models. The new results show how the magnetic fields grow-first by winding through rotational motion, then via the MRI-and how the neutron-to-proton ratio evolves in the torus. Interestingly, the MRI-driven flow manages to eject a significant fraction (over 20%) of the initial torus mass into space. With neutron-to-proton ratios between 3 and 10, the ejecta produce a range of heavy r-process material with a pattern similar to what is observed in the solar system. This is consistent with previous studies, but the predictions are more trustworthy as they are obtained from first principles.

Until very recently, the idea that neutron star mergers produce heavy elements-as well as GRBs and gravitational waves-was supported only by indirect evidence. This changed on August 17, 2017, when researchers detected, for the first time, the gravitational-wave "chirp" from a neutron star merger. This signature was followed 1.7 s later by a GRB and subsequently by a slew of transient signals across the electromagnetic spectrum [ 10], as expected from the decay of freshly forged r-process elements. The long-awaited era of "multimessenger" astrophysics had finally become a reality.

The gravitational-wave window to the Universe has only just opened up and already we have conclusive answers to long-standing puzzles, such as the connection between neutron star mergers and r-process nucleosynthesis. But very soon we may receive answers to questions that we have not yet asked. Therefore, it is crucial that our theoretical models keep up with the observational pace. The new study by Siegel and Metzger is an important element in solidifying our understanding of the physics of multimessenger sources. The authors' result that a large fraction of the accreting torus escapes the final black hole's pull may explain why the first observed multimessenger event was so bright in electromagnetic waves. Whether it was typical or "just" an extreme outlier can only be answered after more such detections. We eagerly await the excitement the next "nuggets" will bring.

This research is published in Physical Review Letters.

References

1. D. Siegel and B. D. Metzger, "Three-Dimensional GRMHD Simulations of the Remnant Accretion Disks from Neutron Star Mergers: Outflows and r-Process Nucleosynthesis," Phys. Rev. Lett. 119, 231102 (2017).

2. E. M. Burbidge, G. R. Burbidge, W. A. Fowler, and F. Hoyle, "Synthesis of the Elements in Stars," Rev. Mod. Phys 29, 547 (1957).

3. J. M. Lattimer and D. N. Schramm, "Black-Hole-Neutron-Star Collisions," Astrophys. J 192, L145 (1974).

4. D. Eichler, M. Livio, T, Piran, and D. N. Schramm, "Nucleosynthesis, Neutrino Bursts and 𝛾 -Rays from Coalescing Neutron Stars," Nature 340, 126 (1989).

5. S. Rosswog, M. Liebendörfer, F.-K. Thielemann, M. B. Davies, W. Benz, and T. Piran, "Mass Ejection in Neutron Star Mergers," Astron. Astrophys. 341, 499 (1999).

6. C. Freiburghaus, S. Rosswog, and F.-K. Thielemann, "r-Process in Neutron Star Mergers," Astrophys. J. Lett. 525, L121 (1999).

7. A. Perego, S. Rosswog, R. M. Cabezon, O. Korobkin, R. Kappeli, A. Arcones, and M. Liebendorfer, "Neutrino-Driven Winds from Neutron Star Merger Remnants," Mon. Not. R. Astron. Soc. 443, 3134 (2014).

8. R. Fernández and B. D. Metzger, "Delayed Outflows from Black Hole Accretion Tori Following Neutron Star Binary Coalescence," Mon. Not. R. Astron. Soc. 435, 502 (2013).

9. O. Just, A. Bauswein, R. Ardevol Pulpillo, S. Goriely, and H.-T. Janka, "Comprehensive Nucleosynthesis Analysis for Ejecta of Compact Binary Mergers," Mon. Not. R. Astron. Soc. 448, 541 (2015).

10. B. P. Abbott et al., "Multi-messenger Observations of a Binary Neutron Star Merger," Astrophys. J. Lett. 848, 12 (2017).

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Viewpoint: Out of Neutron Star Rubble Comes Gold

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Stephan Rosswog, The Oskar Klein Centre for Cosmoparticle Physics, Department of Astronomy, Stockholm University, Stockholm, Sweden New calculations show that the accretion flows that form after a neutron star collision can eject large amounts of matter that is rich in gold and other heavy elements.

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Scientists use solid crystal blocks to produce electric current that can be used to detect gamma radiatio

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The scattering of photons from charged particles is called Compton scattering after Arthur Compton who was the first to measure photon-electron scattering in 1922. When the incoming photon gives part of its energy to the electron, then the scattered photon has lower energy and according to the Planck relationship has lower frequency and longer wavelength.

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                                                                                                                                       Jack Baptist                                                                                                                                         3/14/18                                                                                                                                         Period 3Gamma Ray Bursts from Merging Neutron StarsA gamma ray burst is an electromagnetic wave made of gamma radiation. There are two main types of gamma ray bursts: short duration and long duration. Besides their time of duration, the main difference between these is their origin. Short wavelength rays come from the fusion of two neutron stars, while long duration rays come from the creation of a supernova. For both, gamma rays are given off due to nuclear instability of atoms.This instability, called the metastable state, causes the nucleus of an atom to release a particle known as a positron. The positron has the same mass as an electron, but the opposite charge. After being emitted from the nucleus, it impacts an electron in a process called annihilation, which results in the release of gamma radiation. This occurs in collisions between other matter and antimatter particles as well, all of which produce electromagnetic radiation.The nuclear instability that causes gamma radiation to occur exists due to magnetic instability in a torus. The torus is a ring of matter produced by the merging of two neutron stars or the collapse of a neutron star into a black hole. It, like its parent star, contains magnetic fields. The torus spins more quickly near the center than near the edge, causing the magnetic fields to become irregularly shaped and unstable.Gamma rays are the most energetic, lowest wavelength type of electromagnetic radiation. They have a high penetrating power, or ability to pass through matter. Scientists normally use crystals to detect gamma radiation in a process known as Compton scattering. The gamma ray scatters the electrons in the crystal, which can then be detected by electrical sensors. Due to the damaging effects of gamma radiation, it is one of the possible causes of the Ordovician extinction, an event that occurred about 444 million years ago. In that extinction, the glaciation of the ocean caused the extinction of many species. A gamma ray burst may have damaged the Earth’s atmosphere enough to cause this cooling.

# data[].attributes.subject
                                                                                                                                       Jack Baptist                                                                                                                                         3/14/18                                                                                                                                         Period 3Gamma Ray Bursts from Merging Neutron StarsA gamma ray burst is an electromagnetic wave made of gamma radiation. There are two main types of gamma ray bursts: short duration and long duration. Besides their time of duration, the main difference between these is their origin. Short wavelength rays come from the fusion of two neutron stars, while long duration rays come from the creation of a supernova. For both, gamma rays are given off due to nuclear instability of atoms.This instability, called the metastable state, causes the nucleus of an atom to release a particle known as a positron. The positron has the same mass as an electron, but the opposite charge. After being emitted from the nucleus, it impacts an electron in a process called annihilation, which results in the release of gamma radiation. This occurs in collisions between other matter and antimatter particles as well, all of which produce electromagnetic radiation.The nuclear instability that causes gamma radiation to occur exists due to magnetic instability in a torus. The torus is a ring of matter produced by the merging of two neutron stars or the collapse of a neutron star into a black hole. It, like its parent star, contains magnetic fields. The torus spins more quickly near the center than near the edge, causing the magnetic fields to become irregularly shaped and unstable.Gamma rays are the most energetic, lowest wavelength type of electromagnetic radiation. They have a high penetrating power, or ability to pass through matter. Scientists normally use crystals to detect gamma radiation in a process known as Compton scattering. The gamma ray scatters the electrons in the crystal, which can then be detected by electrical sensors. Due to the damaging effects of gamma radiation, it is one of the possible causes of the Ordovician extinction, an event that occurred about 444 million years ago. In that extinction, the glaciation of the ocean caused the extinction of many species. A gamma ray burst may have damaged the Earth’s atmosphere enough to cause this cooling.

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Science Mission Directorate. "Gamma Rays" NASA Science. 2010. National Aeronautics and Space Administration. [insert date - e.g. 10 Aug. 2016] http://science.nasa.gov/ems/12_gammarays

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Science Mission Directorate. "Gamma Rays" NASA Science. 2010. National Aeronautics and Space Administration. [insert date - e.g. 10 Aug. 2016] http://science.nasa.gov/ems/12_gammarays

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“Gamma Ray Emission.” Cyberphysics, www.cyberphysics.co.uk/topics/radioact/Radio/gamma.html.

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