Skip to main content

Binary neutron star mergers: a jet engine for short gamma-ray burst

Picture: These images show the merger of two neutron stars simulated using a new supercomputer model. Redder colors indicate lower densities. Green and white ribbons and lines represent magnetic fields. The orbiting neutron stars rapidly lose energy by emitting gravitational waves and merge after about three orbits, or in less than 8 milliseconds. The merger amplifies and scrambles the merged magnetic field. A black hole forms and the magnetic field becomes more organized, eventually producing structures capable of supporting the jets that power short gamma-ray bursts. Credit: NASA/AEI/ZIB/M. Koppitz and L. Rezzolla


The LIGO and Virgo Collaborations recently reported the first direct detection of a gravitational-wave (GW) signal and demonstrated that it was produced by the inspiral and coalescence of a binary black hole (BHBH) system.


This breakthrough marks the beginning of the era of GW astrophysics.

GW signals are expected to be generated not only by BHBH binaries but also by neutron star-neutron star (NSNS) and black hole-neutron star (BHNS) binaries.
Merging NSNSs and BHNSs are not only important sources of GWs but also the two most popular candidate progenitors of short gamma-ray bursts (sGRBs)

NSNSs and BHNSs may also generate other detectable, transient electromagnetic (EM) signals prior to merger. Combining GW and EM signals from these mergers could test relativistic gravity and constrain the NS equation of state (EOS).

Credit: P.J.T. Leonard (NASA/GSFC)
In a recent paper (Ruiz et al. 2016) the authors perform magnetohydrodynamic simulations in full general relativity (GRMHD) of quasicircular, equal-mass, binary neutron stars that undergo merger.

The initial stars are irrotational, n=1 polytropes and are magnetized.

The authors explore two types of magnetic-field geometries: one where each star is endowed with a dipolar magnetic field extending from the interior into the exterior, as in a pulsar, and the other where the dipolar field is initially confined to the interior.


 In both cases the adopted magnetic fields are dynamically unimportant initially.

The merger outcome is a hypermassive neutron star that undergoes delayed collapse to a black hole immersed in a magnetized accretion disk. About 60(MNS/1.625M⊙) ms following merger, the region above the black hole poles becomes strongly magnetized, and a collimated, mildly relativistic outflow - an incipient jet - is launched.

Image: State-of-the-art supercomputer models show that merging neutron stars can power a short gamma-ray burst. Credit: NASA's Goddard Space Flight Center

The lifetime of the accretion disk, which likely equals the lifetime of the jet, is Δt∼0.1(MNS/1.625M⊙) s. In contrast to black hole-neutron star mergers, they find that incipient jets are launched even when the initial magnetic field is confined to the interior of the stars.

  • Ruiz et al. 2016 (preprint) -  Binary neutron star mergers: a jet engine for short gamma-ray burst (arXiv)

Etichette:

Comments

Post a Comment

Popular posts from this blog

ORBITAL PERIODS OF THE PLANETS

For orbital period generally we refer to the sidereal period, that is the temporal cycle that it takes an object to make a full orbit, relative to the stars. This is the orbital period in an inertial (non-rotating) frame of reference (365,25 days for the earth).
Post a Comment
Read more

ALMA'S IMAGE OF A NEW PLANET FORMATION IN A BINARY STARS SYSTEM

A composite image of the HD 142527 binary star system from data captured by ALMA shows a distinctive arc of dust (red) and a ring of carbon monoxide (blue and green). The red arc is free of gas, suggesting the carbon monoxide has "frozen out", forming a layer of frost on the dust grains in that region. Astronomers speculate this frost provides a boost to planet formation. The two dots in the center represent the two stars in the system. Credit: Andrea Isella/Rice University; B. Saxton (NRAO/AUI/NSF); ALMA (NRAO/ESO/NAOJ) The Atacama Large Millimeter/submillimeter Array (ALMA) has observed a new very early stage of planet formation around the binary star system HD 142527 (in the costellation of Lupus) and has provided fresh insights into the planet-forming potential of a binary system.
Post a Comment
Read more

Fermi Bubbles

Image: A giant gamma-ray structure was discovered in 2010 by processing Fermi all-sky data at energies from 1 to 10 billion electron volts, shown here. The dumbbell-shaped feature (center) emerges from the galactic center and extends 50 degrees north and south from the plane of the Milky Way, spanning the sky from the constellation Virgo to the constellation Grus. Credits: NASA/DOE/Fermi LAT/D. Finkbeiner et al. At a time when our earliest human ancestors mastered walking upright the heart of our Milky Way galaxy underwent a titanic eruption, driving gases and other material outward at 2 million miles per hour.
Post a Comment
Read more