Introduction

In a groundbreaking discovery, an international team of astronomers has announced the identification of three new helium-enriched hot subdwarf stars that possess strong magnetic fields. This exciting finding, conducted using the Southern African Large Telescope (SALT), was detailed in a research paper published on October 3 on the preprint server arXiv.

What Are Hot Subdwarf Stars?

Hot subdwarf O stars, commonly known as helium-rich subdwarf O stars (He-sdOs), are intriguing celestial bodies. They represent a crucial phase in stellar evolution, specifically in the pre-white dwarf state. These stars predominantly consist of helium and are characterized by their incredibly high temperatures, typically ranging between 40,000 and 50,000 K. Notably, He-sdOs are believed to be formed through double helium white dwarf mergers, providing a fascinating insight into the life cycles of stars.

A Rare Class of Stars

But here's the twist: recent observations have unveiled a rare class of magnetic helium-rich hot subdwarfs, which feature magnetic fields ranging from 300 to 500 kilogauss (kG). While it's hypothesized that these magnetic fields result from white dwarf mergers, a puzzling mystery remains: why do most He-sdOs lack detectable magnetic fields, even though they are thought to originate from similar merger processes?

The Discoverers

Leading the charge in this discovery is Matti Dorsch from the University of Potsdam, who together with his team, has identified these three new magnetic He-sdOs among a sample of 592 stars observed with SALT's Robert Stobie Spectrograph (RSS). The new additions have been designated as J123359.44−674929.11, J125611.42−575333.45, and J144405.79−674400.93, bringing the total count of known magnetic hot subdwarfs to seven.

Characteristics of the New Stars

Interestingly, the magnetic fields of these newly discovered stars are measured at around 200 kG, which is somewhat lower than the stronger fields recorded in previously known magnetic He-sdOs. Among this trio, J123359.44−674929.11 stands out as the least massive star, with an estimated mass of about 0.48 solar masses, while J125611.42−5753333.45 and J144405.79−674400.93 are approximately 0.74 and 0.56 solar masses, respectively. Remarkably, all three stars have similar radii, fluctuating between 0.175 and 2.1 solar radii, coupled with effective temperatures ranging from 46,000 to 47,680 K.

Insight into Stellar Evolution

The team’s research provides essential insights into the origins of these magnetic He-sdOs. Their analysis led them to propose that these stars likely arise from the merger of a helium white dwarf with a hydrogen/helium white dwarf. As these stars merge, the hydrogen/helium white dwarf is effectively annihilated, leading to a mixing of materials that results in a substantial portion of the mass condensing onto the surface of the helium white dwarf.

Conclusion

This remarkable research not only deepens our understanding of stellar evolution but also raises exciting questions about the nature of magnetic fields in stars. What else might we discover as technology and our observation capabilities improve? Stay tuned for further astronomical revelations!