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Astronomers discover helium-burning white dwarf


Still Waters

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A white dwarf star can explode as a supernova when its mass exceeds the limit of about 1.4 solar masses. A team led by the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching and involving the University of Bonn has now found a binary star system in which matter flows onto the white dwarf from its companion.

The system was found due to bright, so-called super-soft X-rays, which originate in the nuclear fusion of the overflowed gas near the surface of the white dwarf. The unusual thing about this source is that it is helium and not hydrogen that overflows and burns. The measured luminosity suggests that the mass of the white dwarf is growing more slowly than previously thought possible, which may help to understand the number of supernovae caused by exploding white dwarfs. 

https://phys.org/news/2023-03-astronomers-helium-burning-white-dwarf.html

The results have been published in the journal Nature.

https://www.nature.com/articles/s41586-023-05714-4

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High-resolution optical spectra taken at three epochs with the High Resolution Spectrograph (HRS) at SALT show a double-peaked profile of all lines (Fig. 3), thus demonstrating their origin in an accretion disk. ...

assuming Keplerian rotation, we infer a projected velocity of the outer disk of vK × sin(i) ≈ 60 km s−1. ...

The full width at zero intensity in the He I lines suggests a maximum projected velocity of 120 ± 10 km s−1, with that of the He II 4686 line clearly being different, about 200 ± 20 km s−1. ...

The peak separation of all the main lines is similar, including that of He II. The vertical dotted lines indicate a peak separation of ±60 km s−1. ...

the accreting white dwarf and the donor are both hidden under this disk flux. ...

A Lomb–Scargle periodogram shows the largest power at a period of 1.1635 days and a secondary lower-power peak at 2.327 days.

https://www.nature.com/articles/s41586-023-05714-4

 

I have my doubts about this 'binary star'. Allegedly neither star has been discerned.

If there is no binary star, there cannot be an accretion disk.

If there is no accretion disk, all the observed characteristics must originate in the white dwarf.

The double peaks clearly indicate rotation. What if this is the rotation of the white dwarf? Or possibly that of a whirlpool / cyclone in the outer layers of the white dwarf?

I cannot explain the maximum projected velocities. If a whirlpool / cyclone exists, mabe it is rotating faster in its depths than at the surface of the white dwarf?

The power periods in my opinion are indicative of magnetic polarity reversals; I would suspect not of the star itself, but of the hypothetical whirlpool / cyclone.

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