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Blobrana


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Glimpse elusive matter in shattering star

New calculations by a team including Piro and led by David Tsang, also of Caltech, suggest that nature occasionally obliges by shattering neutron stars, allowing us to gain precious information about their innards.
It is not easy to shatter something with 10 billion times the strength of steel, but it seems to happen via the same trick that lets an opera singer shatter a wine glass. In that case, sound waves that equal the glass's resonant frequency are the culprit. A neutron star has a resonant frequency too -  and Tsang's team have shown that it gets shaken at this frequency when a pair of such stars spirals closer together on the way to merging in a black hole.
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Blobrana


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Title: Do Very Short Gamma Ray Bursts originate from Primordial Black Holes? Review
Authors: David B. Cline, Stan Otwinowski, Bozena Czerny, Agnieszka Janiuk

We present the state of current research of Very Short Gamma Ray Bursts (VSGRBs) from seven GRB detectors. We found that VSGRBs form distinct class of GRBs, which in our opinion, in most cases can originate from the evaporating Primordial Black Holes (PBHs). Arguments supporting our opinion: 1. GRBs with time duration (T90) < 100 ms form distinct class: VSGRBs. 2. We observe significant anisotropy in the galactic angular distribution of BATSE VSGRB events. 3. V/Vmax distribution for BATSE VSGRB events indicates the local distance production. 4. VSGBBs have more energetic gamma-ray burst than other GRBs with longer duration (KONUS). 5. We observe small number of afterglows in SWIFT VSGRB sample (25%), in contrast with the noticeable afterglow frequency in SGRB sample (78%). 6. Time profile of rising part BATSE VSGRBs is in agreement with the evaporation PBH model.

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Blobrana


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Neutron Star Collision and Gamma Ray Burst Discovery



Every day or two, on average, satellites detect a massive explosion somewhere in the sky. These are gamma-ray bursts, the brightest blasts in the universe. They're thought to be caused by jets of matter moving near the speed of light associated with the births of black holes. Gamma-ray bursts that last longer than two seconds are the most common and are thought to result from the death of a massive star. Shorter bursts proved much more elusive.



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Blobrana


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Breakthrough Study Confirms Cause of Short Gamma-Ray Bursts

A new supercomputer simulation shows the collision of two neutron stars can naturally produce the magnetic structures thought to power the high-speed particle jets associated with short gamma-ray bursts (GRBs). The study provides the most detailed glimpse of the forces driving some of the universe's most energetic explosions.
The state-of-the-art simulation ran for nearly seven weeks on the Damiana computer cluster at the Albert Einstein Institute (AEI) in Potsdam, Germany. It traces events that unfold over 35 milliseconds -- about three times faster than the blink of an eye.
GRBs are among the brightest events known, emitting as much energy in a few seconds as our entire galaxy does in a year. Most of this emission comes in the form of gamma rays, the highest-energy form of light.
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Blobrana


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Analysis of nine short gamma-ray bursts (GRBs) observed with Gemini, Magellan, and the Hubble Space Telescope reveals that the progenitors of these GRBs may reside in faint host galaxies at redshifts of  z = 1.1 and beyond.  
Unexpectedly, the host galaxies of these short GRBs (with R ~ 23-27 mag) can be more than a 100 times fainter than those of previously known short GRBs (brighter than R ~ 22 mag). Therefore the hosts of the recently observed short GRBs are starkly different from the first few short GRBs hosts, which were all at z < 0.5. It seems that our understanding of the nature of GRB progenitors may be undergoing a paradigm shift.

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Blobrana


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Gamma-ray bursts
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A type of co­los­sal cos­mic ex­plo­sion could beam le­thal ra­di­a­tion across a ga­laxy, fry­ing any life forms in its path, a new anal­y­sis has found.
The blasts are thought to oc­cur rare­ly in our Milky Way gal­axy, but more of­ten in those where stars are born and die more fre­quent­ly. These in­clude ar­eas where as­tro­no­mers hope to find Earth-like plan­ets ripe for life.

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Blobrana


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Hypermassive neutron stars
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Title: Magnetised Hypermassive Neutron Star Collapse: a candidate central engine for short-hard GRBs
Authors: Branson C. Stephens, Matthew D. Duez, Yuk Tung Liu, Stuart L. Shapiro, Masaru Shibta

Hypermassive neutron stars (HMNSs) are equilibrium configurations supported against collapse by rapid differential rotation and likely form as transient remnants of binary neutron star mergers. Though HMNSs are dynamically stable, secular effects such as viscosity or magnetic fields tend to bring HMNSs into uniform rotation and thus lead to collapse. We simulate the evolution of magnetized HMNSs in axisymmetry using codes which solve the Einstein-Maxwell-MHD system of equations. We find that magnetic braking and the magnetorotational instability (MRI) both contribute to the eventual collapse of HMNSs to rotating black holes surrounded by massive, hot accretion tori and collimated magnetic fields. Such hot tori radiate strongly in neutrinos, and the resulting neutrino-antineutrino annihilation could power short-hard GRBs.

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Blobrana


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Title: Last moments in the life of a compact binary system: gravitational waves, gamma-ray bursts and magnetar formation
Authors: S. Rosswog

The first detections of afterglows from short gamma-ray bursts (GRBs) have confirmed the previous suspicion that they are triggered by a different central engine than long bursts. In particular, the recent detections of short GRBs in galaxies without star formation lends support to the idea that an old stellar population is involved. Most prominent are mergers of either double neutron stars or of a neutron star with a stellar-mass black hole companion. Since the final identification of the central engine will only come from an integral view of several properties, we review the observable signatures that can be expected from both double neutron stars and neutron star black hole systems. We discuss the gravitational wave emission, the structure of the neutrino-cooled accretion disks, the resulting neutrino signal and possible mechanisms to launch a GRB. In addition, we address the speculative idea that in some cases a magnetar-like object may be the final outcome of a double neutron star merger. We also discuss possibilities to explain the late-time X-ray activity that has been observed in several bursts.

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Blobrana


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Just a reminder to say that on Wednesday, NASA will announce new findings related to short gamma-ray bursts .

Since the 1980s, the two most popular theories of the origin of gamma-ray bursts postulated stupendous explosions at gigantic distances, either from a supernova caused by the sudden collapse of a massive star's core, or the merger of two neutron stars or a neutron star and a black hole.
The high-speed orbit of these dense binaries causes ripples of energy to radiate out from the system. The energy loss in turn causes the objects to slowly but inevitably spiral inward, eventually crashing together in a cataclysmic explosion.


Steve Thorsett of Princeton University has calculated the consequences if such a merger were to take place within 3,500 light-years of Earth, with its energy aimed at the solar system. The blast would bathe Earth in the equivalent of 300,000 megatons of TNT, 30 times the world's nuclear weaponry, with the gamma-ray and X-ray radiation stripping Earth of its ozone layer.
While scientists cannot yet predict with any precision which nearby stars will go supernova, the merger of neutron star binaries is predictable. Three such binary systems have been discovered, and one, PSR B1534+12, presently sits about 3,500 light-years away and will coalesce in a billion years.

Scientists in the 1990s concluded that gamma-ray bursts lasting longer than 10 seconds appeared linked to unusual supernovas occurring many billions of light-years away.

UPDATE will be posted here.

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