The international group of astronomers received record-breaking early spectra of the supernova at the first moments after the outbreak – just 6 hours after its explosion. Based on the new data, scientists confirmed that at least several hundred days before the explosion massive red giants significantly increase the rate of mass emissions into the surrounding space. Observations make it possible to clarify the existing models of explosions of such supernovae. The study is published in the journal Nature Physics .
Supernovae are objects that increase their luminosity tens of thousands of times in just a few days. There are several reasons for such large-scale phenomena: the collapse of a star with a mass of eight to ten times greater than that of the Sun or the explosion of a white dwarf in a binary system. Most often the supernova’s predecessors are massive red giants – such objects are called Type II supernovae. Their evolution after the explosion is described quite well thanks to automated tracking systems for the sky – dozens of new outbreaks are opened every year. However, the processes occurring during and immediately before the outbreak are much worse due to a small statistical sample – usually a few days pass between the flash and the discovery of the supernova.
On October 6, 2013, the automated tracking station of the Palomar Observatory discovered a new light source, labeled iPTF 13dqy, in NGC 7610 (166 million light-years from the Earth). Information about this was transferred to a number of other automated observatories and, according to several independent observations, astronomers found out that this object is a type II supernova. Extrapolation of the brightness curve showed that it was detected only three hours after the explosion.
The first optical spectrum of the luminescence of the object was obtained by the Keck observatory six hours after the explosion. After it a number of observatories, including cosmic ones, carried out detailed observations of the object in the infrared, ultraviolet and X-ray ranges. The analysis of optical spectra allowed scientists to investigate not only the propagating blast wave of a supernova, but also the nearest environment of a star.
The optical emission of a supernova is associated not only with the huge temperatures developing in the process of collapse, but also with the processes of ionization in the medium and the excitation of gas atoms. For example, the huge gas velocity in the front of the shock wave leads to a Doppler shift in the frequency of the hydrogen atom and the telescope “sees” a wide peak instead of a narrow emission band. Out of its width, astronomers determined the speed of the wave – about 100 kilometers per second.
Moreover, in the first optical spectra astronomers noticed a large number of bands associated with heavy ionized gases – oxygen and nitrogen. After five days, this radiation was almost completely lost. This behavior indicates that around the star at the time of the explosion there was a large amount of gas, probably dropped to her before the explosion. According to astronomers, the gas disk extends up to distances five times the radius of the orbit of Neptune. Scientists believe that the substance was actively starred at least 500 days before the explosion. The total mass of the ejected gas can reach one thousandth of the total mass of the star.
Similar gas shells were previously predicted only theoretically. The discovery by astronomers of the gas envelope dumped by the supergiant may refer to about half of all the observed supernovae.
Earlier in 2016, an international group of astronomers led by Peter Garnavich (University of Notre Dame in Indiana) found in the Kepler data evidence of two supernova explosions observed by the telescope since the explosion. The space telescope caught the moment of the primary flash, when the shock wave reached the surface of the supergiant. Like iPTF 13dqy, these supernovas are of type II.