A group of international researchers, led by the National Institute for Astrophysics (Inaf), has made a revolutionary discovery regarding neutron stars, the remains of massive stars that ended their life cycle with a supernova explosion. These celestial bodies, also known as “compact objects” due to their enormous mass concentrated in a small volume, can exist alone or form X-ray binary systems, in which a neutron star attracts matter from a companion star.
During the accretion process, the matter accumulated on the surface of the neutron star can trigger thermonuclear explosions of These explosions not only consume matter, but also expel some of it in the form of collimated jets of matter, observable in the radio band of the electromagnetic spectrum.
The jets, launched both from binary systems with neutron stars and black holes, have been the subject of study for decades, but many questions remain open, such as their launch mechanism and the speed with which they are emitted. Now, thanks to simultaneous observations in the radio and of launch.
Thomas Russell, researcher at INAF in Palermo and first author of the study, underlines the importance of understanding how the jets are launched, since they can influence star formation by releasing enormous amounts of energy into the surrounding environment. The neutron stars under study, 4U 1728-34 and 4U 1636-536, show frequent type I X-ray bursts. The X-band observations were conducted with ESA’s Integral satellite, while those in the radio band with the Australia Telescope Compact Array (ATCA), managed by the Australian National Science Agency (CSIRO).
The researchers observed increases in radio brightness, called “flares,” a few minutes after each thermonuclear explosion, indicating a close correlation between the explosions and the evolution of the jets. Erik Kuulkers, co-author of the study, highlights the dramatic impact of the “bursts” on the brightness of the jets, which increases with the addition of further matter.
The speed of the jets of the binary system 4U 1728-34 was measured through observations at two different radio frequencies, resulting in it being equal to 0.38 c, or one third of the speed of light. This discovery offers a new method to understand the mechanism of jet launch, which could be based on the rotation of the neutron star or its accretion disk.
In conclusion, the discovery of the influence of type I power. With more than 120 neutron stars in our galaxy producing I-type X-ray bursts, researchers will be able to compare the speed of the jets to the properties of the binary system to determine the mechanism behind their launch.
