Collection |

Kilonovae, short gamma-ray bursts & neutron star mergers

This Collection of research and comment from Nature Research focuses on the electromagnetic counterparts to the gravitational wave event GW 170817 from the merger of two neutron stars. LIGO’s first three gravitational wave detections, and LIGO-Virgo’s first, all originated from mergers of black holes. These momentous black-hole clashes produced gravitational waves that were audible to LIGO-Virgo but there was nothing to see. But a neutron star merger is different. Following GW 170817, a short gamma ray burst and kilonova occurred, releasing photons across a wide electromagnetic spectrum: from radio waves to infrared to visible to X-rays to gamma rays. The Research papers published in Nature and Nature Astronomy cover some of these counterpart signals. Welcome to the era of gravitational wave astrophysics.

 

Related Collections: 2017 Nobel Prize in Physics, Gravitational Waves

 

News and comment

Merging neutron stars are potential sources of gravitational waves and have long been predicted to produce jets of material as part of a low-luminosity transient known as a 'kilonova'. There is growing evidence that neutron-star mergers also give rise to short, hard gamma-ray bursts. A group of papers in this issue report observations of a transient associated with the gravitational-wave event GW170817—a signature of two neutron stars merging and a gamma-ray flash—that was detected in August 2017. The observed gamma-ray, X-ray, optical and infrared radiation signatures support the predictions of an outflow of matter from double neutron-star mergers and present a clear origin for gamma-ray bursts. Previous predictions differ over whether the jet material would combine to form light or heavy elements. These papers now show that the early part of the outflow was associated with lighter elements whereas the later observations can be explained by heavier elements, the origins of which have been uncertain. However, one paper (by Stephen Smartt and colleagues) argues that only light elements are needed for the entire event. Additionally, Eleonora Troja and colleagues report X-ray observations and radio emissions that suggest that the 'kilonova' jet was observed off-axis, which could explain why gamma-ray-burst detections are seen as dim.

News & Views | | Nature

Krzysztof Belczynski et al. present numerical simulations of the formation of binary black holes that provide a framework for interpreting the recent detection of the first gravitational-wave source (known as GW150914) — a merger of two massive black holes. Their models imply that these events take place in an environment where the metallicity is less than 10 per cent of that of the Sun, and that the progenitors are stars with initial masses of 40–100 solar masses that interact through mass transfer and a common-envelope phase. The calculations predict detections of about a thousand black-hole mergers per year once gravitational-wave observatories reach full sensitivity.

News & Views | | Nature

The general theory of relativity predicts that all accelerating objects produce gravitational waves — analogous to electromagnetic waves — that should be detectable for instance in the case of extremely massive objects such as black holes undergoing acceleration. The existence of such waves has been inferred indirectly, but an important goal in physics is their direct observation, a feat that would both validate Einstein's theory and lead to new areas of cosmology. Now early results from LIGO (the Laser Interferometer Gravitational-Wave Observatory), one of the handful of detectors searching for gravity waves, have provided a starting point for further gravity hunts by deriving an upper limit for the stochastic background of gravitational waves of cosmological origin. The data rule out models of early Universe evolution with a relatively large equation-of-state parameter, as well as cosmic (super)string models with relatively small string tension that are favoured in some string theory models.

News & Views | | Nature

The first detection of electromagnetic emission from a gravitational wave source bridges the gap between one of the most energetic phenomena in the Universe and their dark, difficult to detect progenitors.

News & Views | | Nature Astronomy

Kilonovae and short gamma-ray bursts

Merging neutron stars are potential sources of gravitational waves and have long been predicted to produce jets of material as part of a low-luminosity transient known as a 'kilonova'. There is growing evidence that neutron-star mergers also give rise to short, hard gamma-ray bursts. A group of papers in this issue report observations of a transient associated with the gravitational-wave event GW170817—a signature of two neutron stars merging and a gamma-ray flash—that was detected in August 2017. The observed gamma-ray, X-ray, optical and infrared radiation signatures support the predictions of an outflow of matter from double neutron-star mergers and present a clear origin for gamma-ray bursts. Previous predictions differ over whether the jet material would combine to form light or heavy elements. These papers now show that the early part of the outflow was associated with lighter elements whereas the later observations can be explained by heavier elements, the origins of which have been uncertain. However, one paper (by Stephen Smartt and colleagues) argues that only light elements are needed for the entire event. Additionally, Eleonora Troja and colleagues report X-ray observations and radio emissions that suggest that the 'kilonova' jet was observed off-axis, which could explain why gamma-ray-burst detections are seen as dim.

Letter | | Nature

Merging neutron stars are potential sources of gravitational waves and have long been predicted to produce jets of material as part of a low-luminosity transient known as a 'kilonova'. There is growing evidence that neutron-star mergers also give rise to short, hard gamma-ray bursts. A group of papers in this issue report observations of a transient associated with the gravitational-wave event GW170817—a signature of two neutron stars merging and a gamma-ray flash—that was detected in August 2017. The observed gamma-ray, X-ray, optical and infrared radiation signatures support the predictions of an outflow of matter from double neutron-star mergers and present a clear origin for gamma-ray bursts. Previous predictions differ over whether the jet material would combine to form light or heavy elements. These papers now show that the early part of the outflow was associated with lighter elements whereas the later observations can be explained by heavier elements, the origins of which have been uncertain. However, one paper (by Stephen Smartt and colleagues) argues that only light elements are needed for the entire event. Additionally, Eleonora Troja and colleagues report X-ray observations and radio emissions that suggest that the 'kilonova' jet was observed off-axis, which could explain why gamma-ray-burst detections are seen as dim.

Letter | | Nature

Merging neutron stars are potential sources of gravitational waves and have long been predicted to produce jets of material as part of a low-luminosity transient known as a 'kilonova'. There is growing evidence that neutron-star mergers also give rise to short, hard gamma-ray bursts. A group of papers in this issue report observations of a transient associated with the gravitational-wave event GW170817—a signature of two neutron stars merging and a gamma-ray flash—that was detected in August 2017. The observed gamma-ray, X-ray, optical and infrared radiation signatures support the predictions of an outflow of matter from double neutron-star mergers and present a clear origin for gamma-ray bursts. Previous predictions differ over whether the jet material would combine to form light or heavy elements. These papers now show that the early part of the outflow was associated with lighter elements whereas the later observations can be explained by heavier elements, the origins of which have been uncertain. However, one paper (by Stephen Smartt and colleagues) argues that only light elements are needed for the entire event. Additionally, Eleonora Troja and colleagues report X-ray observations and radio emissions that suggest that the 'kilonova' jet was observed off-axis, which could explain why gamma-ray-burst detections are seen as dim.

Letter | | Nature

Merging neutron stars are potential sources of gravitational waves and have long been predicted to produce jets of material as part of a low-luminosity transient known as a 'kilonova'. There is growing evidence that neutron-star mergers also give rise to short, hard gamma-ray bursts. A group of papers in this issue report observations of a transient associated with the gravitational-wave event GW170817—a signature of two neutron stars merging and a gamma-ray flash—that was detected in August 2017. The observed gamma-ray, X-ray, optical and infrared radiation signatures support the predictions of an outflow of matter from double neutron-star mergers and present a clear origin for gamma-ray bursts. Previous predictions differ over whether the jet material would combine to form light or heavy elements. These papers now show that the early part of the outflow was associated with lighter elements whereas the later observations can be explained by heavier elements, the origins of which have been uncertain. However, one paper (by Stephen Smartt and colleagues) argues that only light elements are needed for the entire event. Additionally, Eleonora Troja and colleagues report X-ray observations and radio emissions that suggest that the 'kilonova' jet was observed off-axis, which could explain why gamma-ray-burst detections are seen as dim.

Letter | | Nature

Merging neutron stars are potential sources of gravitational waves and have long been predicted to produce jets of material as part of a low-luminosity transient known as a 'kilonova'. There is growing evidence that neutron-star mergers also give rise to short, hard gamma-ray bursts. A group of papers in this issue report observations of a transient associated with the gravitational-wave event GW170817—a signature of two neutron stars merging and a gamma-ray flash—that was detected in August 2017. The observed gamma-ray, X-ray, optical and infrared radiation signatures support the predictions of an outflow of matter from double neutron-star mergers and present a clear origin for gamma-ray bursts. Previous predictions differ over whether the jet material would combine to form light or heavy elements. These papers now show that the early part of the outflow was associated with lighter elements whereas the later observations can be explained by heavier elements, the origins of which have been uncertain. However, one paper (by Stephen Smartt and colleagues) argues that only light elements are needed for the entire event. Additionally, Eleonora Troja and colleagues report X-ray observations and radio emissions that suggest that the 'kilonova' jet was observed off-axis, which could explain why gamma-ray-burst detections are seen as dim.

Letter | | Nature

LIGO and fundamental physics

The gravitational-wave signature of merging black holes or neutron stars yields the distance to the merger. If a counterpart is observed and its recession velocity arising from the Hubble flow is known, then a calibration of the Hubble constant that is entirely independent of the usual 'distance ladder' is possible. The gravitational-wave event of 17 August 2017 (GW170817) corresponded to the merger of two neutron stars, and an associated 'kilonova' was seen. Daniel Holz and the LIGO–Virgo collaboration, along with a group of astronomers involved with the search for the counterpart, have determined that the Hubble constant calculated this way is about 70 kilometres per second per megaparsec. This is consistent with other determinations, but independent of them.

Letter | | Nature

The general theory of relativity predicts that all accelerating objects produce gravitational waves — analogous to electromagnetic waves — that should be detectable for instance in the case of extremely massive objects such as black holes undergoing acceleration. The existence of such waves has been inferred indirectly, but an important goal in physics is their direct observation, a feat that would both validate Einstein's theory and lead to new areas of cosmology. Now early results from LIGO (the Laser Interferometer Gravitational-Wave Observatory), one of the handful of detectors searching for gravity waves, have provided a starting point for further gravity hunts by deriving an upper limit for the stochastic background of gravitational waves of cosmological origin. The data rule out models of early Universe evolution with a relatively large equation-of-state parameter, as well as cosmic (super)string models with relatively small string tension that are favoured in some string theory models.

Letter | | Nature

Black holes present a profound challenge to our current foundations of physics, and an exciting era of astronomy is just opening in which gravitational-wave observation and very-long-baseline interferometry may provide important hints about the new principles of physics needed.

Comment | | Nature Astronomy