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

SUPERNOVAE FROM WD-WD DIRECT COLLISIONS

Image: Supernova remnant N 63A. Credit: NASA/ESA/HEIC and The Hubble Heritage Team (STScI/AURA) Models for supernovae (SNe) related to thermonuclear explosions of white dwarfs (WDs) have been extensively studied over the last few decades, mostly focusing on single degenerate (accretion of material of a WD) and double degenerate (WD-WD merger) scenarios.
Post a Comment
Read more

ALMA Discovers Cold Dust Around Nearest Star

This artist’s impression shows how the newly discovered belts of dust around the closest star to the Solar System, Proxima Centauri, may look. ALMA observations revealed the glow coming from cold dust in a region between one to four times as far from Proxima Centauri as the Earth is from the Sun. The data also hint at the presence of an even cooler outer dust belt and indicate the presence of an elaborate planetary system. These structures are similar to the much larger belts in the Solar System and are also expected to be made from particles of rock and ice that failed to form planets. Note that this sketch is not to scale — to make Proxima b clearly visible it has been shown further from the star and larger than it is in reality. Credit: ESO/M. Kornmesser Proxima Centauri is the closest star to the Sun. It is a faint red dwarf lying just four light-years away in the southern constellation of Centaurus (The Centaur). It is orbited by the Earth-sized temperate world Proxima b ...
Post a Comment
Read more

Atmospheric Beacons Guide NASA Scientists in Search for Life

Beacons of life could help researchers identify potentially habitable worlds. Credits: NASA’s Goddard Space Flight Center/Mary Pat Hrybyk Some exoplanets shine brighter than others in the search for life beyond the solar system. New NASA research proposes a novel approach to sniffing out exoplanet atmospheres. It takes advantage of frequent stellar storms — which hurl huge clouds of stellar material and radiation into space — from cool, young dwarf stars to highlight signs of habitable exoplanets. Traditionally, researchers have sought potential biosignatures as ways of identifying inhabited worlds: byproducts from life as we know it such as oxygen or methane that over time accumulate in the atmosphere to detectable amounts. But with current technology, according to Vladimir Airapetian, lead author of a Nature Scientific Reports study published on Nov. 2, 2017, identifying these gases on distant terrestrial exoplanets is time-consuming, requiring days of observation time. The ne...
Post a Comment
Read more