* Astronomy

Flaring black holes may solve cosmic ray puzzle

Gamma-ray bursts are usually created by exploding stars, which produce neutrinos. So last April, when the IceCube neutrino detector in Antarctica saw no neutrinos accompanying high-energy cosmic rays, astronomers favoured galaxies with active supermassive black holes at their cores as the source of the rays. But a more recent study found that only one galaxy was powerful enough to have produced cosmic rays with such high energies. The rest appear to come from galaxies that seem too weak.
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Killer black hole devours star in a flash

One of the biggest and brightest bangs ever recorded by astronomers came from a massive black hole at the centre of a distant galaxy. The black hole appears to have ripped apart a star that wandered too close, creating a powerful beam of energy that crossed the 3.8 billion light years to Earth.
The observations, published in the journal Science, were carried out by an international team including STFC-funded astronomers from the universities of Warwick, Leicester and Hertfordshire. They used an array of space and ground based facilities including the Hubble, UKIRT (UK Infrared Telescope) and Gemini telescopes to witness this catastrophic event.
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Black hole kills star and blasts 3.8 billion light year beam at Earth

Observations led by astronomers at the University of Warwick have shown that the flash from one of the biggest and brightest bangs yet recorded by astronomers comes from a massive black hole at the centre of a distant galaxy. The black hole appears to have ripped apart a star that wandered too close, creating a powerful beam of energy that crossed the 3.8 billion light years to Earth.
Their research is published today 16th June, in the Journal Science, in a paper entitled "An Extremely Luminous Panchromatic Outburst from the Nucleus of a Distant Galaxy".
The high energy X-rays and gamma-rays persisted at an extremely bright level for weeks after the event, with bright flares arising when further chunks of the star apparently fell into the black hole, while at optical and infrared wavelengths it is as bright as a hundred billion suns. The extreme brightness of this event comes from the fact that it created a powerful beam of energy pointing a jet of light towards the Milky Way and thus concentrated into only a small fraction of the sky and which was detected at Earth 3.8 billion years after the star was ripped apart.
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Title: Quark-Novae in Low-Mass X-ray Binaries as a model for G87-7 and for GRB 110328A
Authors: Rachid Ouyed (1), Jan E. Staff (2), Prashanth Jaikumar (3 and 4) ((1) Physics&Astronomy, University of Calgary, AB, Canada, (2) Physics&Astronomy, Louisiana State University, LA, USA, (3) Physics&Astronomy, California State University Long Beach, CA, USA, (4) Institute of Mathematical Sciences, India)

We propose a simple model explaining two outstanding astrophysical problems related to compact objects: (1) that of stars such as G87-7 (alias EG 50) that constitute a class of relatively low-mass white dwarfs which nevertheless fall away from the C/O composition and (2) that of GRB 110328A/Swift J164449.3+57345 which showed spectacularly long-lived strong X-ray flaring, posing a challenge to standard GRB models. We argue that both these observations may have an explanation within the unified framework of a Quark-Nova occurring in a low-mass X-ray binary (neutron star-white dwarf). For LMXBs where the binary separation is sufficiently tight, ejecta from the Neutron Star triggers nuclear burning in the white dwarf on impact, leading to alpha-rich and Fe-rich composition compact white dwarfs reminiscent of G87-7. Under slightly different conditions, the white dwarf is ablated and its ashes raining down on the Quark star leads to accretion-driven X-ray luminosity with energetics and duration reminiscent of GRB 110328A. We predict additional flaring activity towards the end of the accretion phase if the Quark star turns into a Black Hole.

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