When neutron stars collide, there is a massive explosion. Contrary to what was thought, it apparently has the shape of a sphere, as researchers from Copenhagen and Darmstadt have found out. Their findings could help to measure the universe more precisely.
The explosion of two colliding neutron stars is called a kilonova. What does such a cosmic major event look like? An international team led by the University of Copenhagen with physicists from the GSI Helmholtz Center for Heavy Ion Research in Darmstadt has now come a step closer to answering this question. Scientists examined a kilonova observed in 2017 and concluded that, contrary to expectations, it had the shape of a near-perfect sphere.They published their results in the journal „Nature“.
The star collision, the data from which the researchers evaluated, occurred at a distance of 140 million light years. The research team analyzed the propagation of the explosion using, among other things, the Doppler effect, which leads to a change in the properties of light depending on the movement of its source.
Sphericity a mystery
Surprisingly, according to the results, the explosion spread in all directions at the same rate. This was not expected because the neutron stars orbited each other a hundred times per second before the collision. Because of the enormous angular momentum, it would have been assumed that the explosion cloud was asymmetrically shaped, says Albert Sneppen, first author of the study. How the kilonova could be spherical is a mystery. According to the GSI researchers, no mechanism can be derived from simulations and theoretical considerations that would inevitably lead to a spherical explosion. However, some models fit the observation quite well.
more on the subject
Observations of further neutron star mergers must show whether the spherical shape is really the norm. If the measurements are confirmed, kilonovae could be used in the future as an additional way to determine the expansion rate of the universe. Bright, spherical objects are suitable for this.Regardless of this, the latest research results can help to better understand the processes involved in neutron star collisions. Such events produce heavy elements such as gold and iodine.
