(ORDO NEWS) — Using the 4.1-meter SOAR telescope in Chile, astronomers have discovered the first known case of a binary system where a star in the process of becoming a white dwarf orbits a neutron star that has just completed its transformation into a rapidly spinning pulsar.
This pair, discovered initially with the help of the Fermi space gamma-ray observatory (“Fermi”), is the “missing link” in the evolution of such binary systems.
The bright, mysterious gamma-ray source turned out to be a rapidly spinning neutron star – called a millisecond pulsar – that orbits the star as it evolves into an extremely low-mass white dwarf. Astronomers call such binary systems “spiders”, because the pulsar “eats” the outer parts of the companion star, while the latter gradually turns into a white dwarf.
In their work, astronomers studied a source called 4FGL J1120.0-2204, previously discovered using the Fermi observatory, which has so far remained unidentified. This source, however, was the second brightest gamma-ray source in the sky among all unidentified sources.
In their work, the researchers were able to identify the source 4FGL J1120.0-2204 and showed that it is a binary system consisting of a millisecond pulsar, which is the precursor of an extremely low mass white dwarf. The pair is located at a distance of about 2600 light years from us.
The lines of the optical spectra of the future white dwarf, which is part of the 4FGL J1120.0-2204 system, showed a Doppler shift, indicating a revolution around the pulsar with a period of 15 hours.
“These spectra also allowed us to estimate the mass of the companion star,” said study lead author Samuel Swihart of the US Naval Research Laboratory. – This star will eventually form a white dwarf of extremely low mass, no more than 17 percent of the mass of the Sun. Temperatures on the surface of this white dwarf reach about 8200 degrees Celsius.”
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