Astronomers are amazed by a binary system, formed by a white dwarf and its companion star, located 1,950 light years away from Earth. It’s just that, according to current theoretical models, the white dwarf should synchronize its rotation with the other star — but it didn’t. I wonder why?
- Is there a planet in this white dwarf’s habitable zone?
- “Polluted” white dwarfs can show when planets formed
Cataclysmic variable stars are those in a binary system that change their brightness with a certain frequency. In all of them, the white dwarf is “sucking” matter from its companion, increasing its own mass.
As matter gains on its surface, the white dwarf increases its brightness by a large factor and then reverts to its previous state. But not all cataclysmic variables are created equal: white dwarfs of one of the subclasses (known as polar), exhibit a very strong magnetic field.
Theoretical models say that white dwarfs in cataclysmic variables can synchronize their rotational frequency with that of their companion. For this, it is enough for the white dwarf to have a magnetic field greater than 10 MG.
But that’s not what astronomers found in the SDSS system J134441.83+204408.3 (or J1344 for short). Using data from NASA’s Transiting Exoplanet Survey Satellite (TESS) space observatory, they observed that this system has a 56 MG white dwarf that was out of orbit.
Another characteristic of the white dwarf in J1344 is that its orbital period is 114 minutes, indicating that it is very close to its companion. This would also be more than enough reason to conclude that its rotation is synchronized (or synchronous), but the star has decided to be a bit “rebellious”.
This discovery calls into question some of the scientific convictions about this type of star system. Until then, astronomers thought that a white dwarf with magnetism greater than 10 MG and close enough to its companion would cause the orbit to be synchronous. Now, they will have to review the theoretical models.
In addition, it will be necessary to analyze data from other synchronous cataclysmic variable systems, since they all obey a theoretical model that, apparently, is wrong. If the J1344 system is at odds with theory, others may also just be “disguised” as synchronous systems.
The study is available at arXiv.org and has been accepted for publication in The Astrophysical Journal.
Source: arXiv.org; via: phys.org