Wednesday, January 3, 2024

New ultra-short period binary discovered


Binary evolution theory predicts that the second common envelope (CE) ejection can produce low-mass (0.32-0.36 Msun) subdwarf B (sdB) stars inside ultrashort-orbital-period binary systems, as their helium cores are ignited under nondegenerate conditions.

Here we report the discovery of a 20.5-minute-orbital-period ellipsoidal binary, TMTS J052610.43+593445.1, in which the visible star is being tidally deformed by an invisible carbon-oxygen white dwarf (WD) companion.

The orbital periods of such detached sdB binary systems can be as short as 20 minutes. However, to date only four binaries of this type with orbital periods below one hour have been found.

Now, a team of astronomers led by Jie Lin of the Tsinghua University in Beijing, China, reports the detection of a new sdB binary with an extremely short orbital period...they discovered a dozen such objects, and one of them, which received designation TMTS J052610.43+593445.1 (or J0526 for short) turned out to be an sdB binary with an orbital period of approximately 20.5 minutes.

BNN Breaking:

The white dwarf, although ten times smaller than the sun, has a mass of 0.735 solar masses and an effective temperature of 25,400 K. This binary system presents astronomers with a unique opportunity to study the physics and evolution of stars under extreme conditions.

In about 1.5 million years, the subdwarf will begin transferring mass to the white dwarf at an even shorter orbital period, leading to the formation of an AM CVn star through the helium-star channel. This process is pivotal for understanding binary evolution from the second common envelope ejection to the formation of AM CVn stars. The discovery of TMTS J052610.43+593445.1 could play a significant role in investigating these binary evolution paths.


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