Study investigates the evolution of X-ray binary system GX 301-2

Astronomers from Argentina and France have investigated the evolutionary historical past of an eccentric high-mass X-ray binary often known as GX 301-2. Outcomes of the research, printed December 22 on the arXiv pre-print repository, ship vital insights into the origin of this object and will assist scientists to higher perceive the evolution of X-ray binaries usually.

X-ray binaries are composed of a standard star or a white dwarf transferring mass onto a compact neutron star or a black hole. Based mostly on the mass of the companion star, astronomers divide them into low-mass X-ray binaries (LMXBs) and high-mass X-ray binaries (HMXBs).

Situated some 10,000 light years away from the Earth, GX 301-2 is an XRB found in 1973, which consists of a compact object and an optical star designated Wray 977. Observations of Wray 977 have discovered that it’s a hypergiant star with mass bigger than 31 solar masses, making GX 301-2 an HMXB.

GX 301-2 showcases X-ray pulsations with a interval of 11.6 minutes and skilled speedy spin-up episodes. It is without doubt one of the most eccentric techniques amongst all of the HMXBs recognized thus far and its orbital period was measured to be about 41.5 days. Usually, GX 301-2 seems to be a singular object, whose particular person properties are notably completely different from each different recognized XRB.

A bunch of astronomers led by Adolfo Simaz Bunzel of the Argentine Institute of Radio Astronomy in Buenos Aires, Argentina, examined the peculiar properties of GX 301-2, focusing primarily on the origin and evolution historical past of this method. For this function they utilized the detailed stellar-evolution code MESA.

“We used the publicly out there stellar-evolution code MESA to evolve binaries from their preliminary levels till the core-collapse situation. We included a natal kick distribution based mostly on observations to proceed the evolution through the X-ray binary phase and seek for candidates matching present observations of GX 301-2,” the researchers defined.

The research discovered that the GX 301-2 system requires the progenitor of the neutron star to have transferred most of its envelope to the companion (Wray 977), in a extremely accretion-efficient situation. The astronomers estimate that the progenitor had a mass inside the vary of 23–30 solar lots and that the preliminary mass ratio of the system was 0.8–0.9. They added that greater preliminary lots would probably produce a black hole.

The discovering concerning the mass of progenitor stars means that the preliminary orbital interval was beneath 5 days. Above this restrict, the accretion isn’t adequate sufficient to extend the mass of the companion to be contained in the vary derived for Wray 977. Furthermore, the preliminary orbital interval of lower than two days can be disfavored because the star would then fail to succeed in the core-collapse stage.

The researchers additionally investigated the power of the so-called natal kick of the neutron star in GX 301-2. It’s assumed that neutron stars obtain a major velocity kick at beginning—reaching even 1,500 km/s. In response to the research, the natal kick power for the investigated system is more likely to have been about 450 km/s.

Summing up the outcomes, the authors of the paper underlined how distinctive the properties of GX 301-2 are, which was confirmed by their analysis.

“Weighting our outcomes with generally used distributions of preliminary binary parameters, we estimate that the possibilities of having HMXBs with properties just like those present in GX 301–2 are very low, that’s lower than two out of 100,000 binaries. We thus don’t look forward to finding one other binary with comparable properties within the Milky Way,” the scientists concluded.

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