Scientists at the University of Copenhagen have shown that when two neutron stars collide, a kilonova flash occurs, which has the shape of an ideal sphere. The results of the cosmic explosion study are published in the journal Nature .
The researchers analyzed data obtained from observing the kilonova AT2017gfo, which flared up at a distance of 140 million light years and was recorded in 2017. Astronomers captured ultraviolet, optical and infrared radiation from the source using the X-shooter spectrograph mounted on the European Southern Observatory VLT telescope in Chile .
Previous models have shown that the explosion in the collision of two neutron stars should be flattened and asymmetric. However, in the new work, scientists have shown that the expanding cloud is completely symmetrical and has a shape close to a perfect sphere. The phenomenon is explained by the fact that a colossal amount of energy escaped from the epicenter of the collision, which smooths out the shape of the explosion, but this does not fit into the existing theory.
It is assumed that when neutron stars collide, they briefly combine into a single supermassive neutron star, which then collapses into a black hole. Scientists hypothesize that the energy of a hypermassive neutron star’s powerful magnetic field is released when the star collapses into a black hole, with the energy being distributed spherically. However, this contradicts the model, according to which heavy chemical elements should be produced in separate areas of the kilonovae. The spherical explosion model assumes that only lighter elements will be synthesized.
Scientists hope that more data on kilonovae will be obtained in the future, for example, using the LIGO observatory, which registers gravitational waves from collision events of compact supermassive objects.