The time it takes for this deceased star to complete one rotation is equivalent to 72 Earth years.

In the end, this may uncover the process of how stars smaller than Jupiter come into existence.

Astronomers have identified an exceptional binary system where a white dwarf, known as a “dead star,” orbits its scorching hot and diminutive stellar partner so rapidly that it condenses nearly 72 years into a single Earth day.

The system, named TMTS J0526, was detected by a team from Tsinghua University utilizing the Tsinghua University-Ma Huateng Telescope for Survey (TMTS) and is positioned approximately 2,760 light-years away from our planet.

TMTS J0526 consists of a white dwarf star rich in carbon and oxygen, with a mass equivalent to about 74% of the sun’s mass. It revolves around a hot subdwarf star with a mass roughly one-third that of our sun, and is only about 7 times wider than Earth, making it smaller than Jupiter and one of the tiniest stars observed in terms of volume.
The constituents of TMTS J0526 complete one full orbit approximately every 20.5 minutes. This sets a new record for this type of binary system, although it still falls short compared to HM Cancri, which features two white dwarfs completing an orbit every 5.4 minutes.

Despite its thin hydrogen atmosphere, the diminutive star remains larger and more visible than its white dwarf counterpart. Nevertheless, the white dwarf has the ability to distort the small star into an ellipsoidal shape due to its significant gravitational pull as the two stars swiftly revolve around each other.

Furthermore, the detection of TMTS J0526 is not only noteworthy due to its remarkably brief orbital period, but also because it may provide insights into the formation of such minuscule subdwarf stars.

Mini-stellar marvels

White dwarfs form when stars similar in size to the sun deplete their hydrogen supplies in their cores, leading to a collapse of the stellar cores due to gravity. This process causes the stars to evolve into red giants before cooling down to become white dwarfs, surrounded by gas and dust envelopes. White dwarfs are stabilized by degeneracy pressure, preventing further collapse. In some cases, white dwarfs can evolve into neutron stars or black holes if they have enough mass. After the sun becomes a white dwarf in approximately 5 billion years, it will lead to the destruction of inner planets, including Earth. While some white dwarfs exist in isolation, others are part of binary systems with another star, sharing a common envelope of gas. The Binary Population Synthesis theory suggests that during a common envelope phase, a thermonuclear explosion called a helium flash can lead to the ejection of the common envelope, transforming the stellar companion into a subdwarf star.

Following the expulsion of the common envelopes, the resultant hot subdwarf and remaining white dwarf revolve around each other, emitting gravitational waves. These waves are distortions in the very structure of spacetime, as initially theorized by Albert Einstein in 1915.

These gravitational waves carry off angular momentum, leading to the white dwarf and the diminutive hot subdwarf star drawing nearer to each other, spiraling around at an accelerated pace and emitting gravitational waves with increased intensity in the process.

This culminates in the establishment of a compact hot subdwarf and white dwarf binary with orbital periods of approximately 20 minutes. The remarkably brief orbital period binary system of TMTS J0526 serves as the primary observational proof for the emergence of a small hot subdwarf through the expulsion of a secondary common envelope.

The team’s research was published in February in the journal Nature Astronomy. 

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