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When a star with a mass like the Sun runs out of nuclear fuel and sheds its outer layers, an extremely dense core is formed - a white dwarf. Typically, the mass of these stellar remnants, surrounded by a thin hydrogen or helium shell, does not exceed the solar mass. But recently, astronomers have discovered a “pulsating” record holder among them.
Unlike "classical" white dwarfs, their massive counterparts appeared as a result of the evolution of either very massive stars or the merger of two white dwarfs. These objects are about 5-30 percent heavier than the Sun, but do not exceed the solar mass by many times. Some of them belong to the class of pulsating variable stars, the luminosity of which varies (from one to 30 percent) due to non-radial pulsations caused by gravitational waves - hydrodynamic gravitational waves (not to be confused with those arising from the merger of black holes).
Since the study of pulsating white dwarfs is important for understanding the final stages of the evolution of massive stars and the occurrence of type Ia supernovae, the recently discovered object WD J0135+5722 turned out to be a real find: the authors of the study, published on the Cornell University preprint server, recorded a record number in the star.
The star was discovered using the Great Canary Telescope (The Gran Telescopio CANARIAS, GTC) and the Apache Point Astronomical Observatory in the United States. To clarify the properties of the star, an international group of astronomers led by Francisco de Jerónimo (Francisco C. De Gerónimo) from the National University of La Plata in Argentina conducted high-speed photometric observations in ranges sensitive to pulsations.
The results showed that WD J0135+5722, located about 165 light-years from Earth, has 19 different pulsation periods ranging from 137 to 1345 seconds, and the object's mass is about 1,12 times the mass of the Sun. Previously, the record holder was the white dwarf BPM 37093 with eight pulsation periods. Astronomers suggested that a "crystalline" structure is forming in the center of the star. However, detailed asteroseismic analysis can provide accurate information about the chemical composition of the core. Scientists also need to confirm the star's rotation speed.
"The discovery has greater significance for future research, as it provides a key to understanding the final stages of stellar evolution and possible scenarios leading to supernova explosions," the astronomers concluded.
Thus, WD J0135+5722 became not only a new record holder for the number of detected pulsation periods, but also a unique natural laboratory for studying the internal structure of massive white dwarfs and their evolution.
