National Astronomical Observatory of Japan

Electromagnetic Radiation from a Neutron Star Merger


“Neutron stars” are one of the extreme types of celestial objects found in space. Although they have masses 1.4 times that of the Sun, their radii are only about 10 km, making the density 1 trillion kilograms per cubic centimeter. It is believed that these neutron stars often form binary star system together with each other, and before long the binaries stars merge together. What can we see when neutron stars merge? This video is a visualization of simulations conducted to determine how electromagnetic radiation, such as X-rays, visible light, and radio waves, is emitted by a neutron star merger.

Neutron Star Mergers Shine Red

The 1st half of the video depicts the intensity of electromagnetic radiation emitted from matter ejected by the neutron star merger. A merger phenomenon shines through the radioactive decay energy from radioisotopes in the matter ejected at the time of merger. Around 15 days after the merger, the ejected matter becomes dilute and stops emitting electromagnetic waves.

The 2nd half shows the color of the light emitted from the matter scattered by the neutron star merger. This color changes with temperature. Based on this simulation we learned that the electromagnetic radiation emitted by a neutron star merger has wavelengths from visible to infrared, so it would appear red to our eyes.

Neutron Star Mergers as Sources of Gravitational Waves

It is thought that “gravitational waves,” which are predicted by the Theory of General Relativity, are produced when a neutron star merger occurs. Gravitational wave detectors (like KAGRA constructed in Kamioka, Gifu Prefecture, Japan) aim to directly detect the gravitational waves from neutron star mergers. This simulation showed us what kinds of electromagnetic wave observations we should perform after gravitational waves are detected, opening the road to “Multi-Messenger Astronomy” combining gravitational wave observations and electromagnetic observations.

Translation by: Ramsey Lundock (NAOJ)

Video Data

ComputerCray CX30 “ATERUI”
Phenomenon Time Scale15 days
Phenomenon Spatial ScaleExpands from 1015 cm to 1016 cm with time
Simulation byMasaomi Tanaka (NAOJ)
CreditMasaomi Tanaka; Kenta Hotokezaka; 4D2U Project, NAOJ

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