Astronomers Discover Most Metal-Deficient Extreme Helium Star Using SALT

Astronomers have used the Southern African Large Telescope (SALT) to observe the recently discovered extreme helium star, EC 19529-4430. This star is the most metal-deficient extreme helium star found to date, marking a significant milestone in the field of astronomy.

What are Extreme Helium Stars?

Extreme helium stars, or EHe stars, are supergiants with low mass and are devoid of most hydrogen. These stars are unique in their composition and behavior, making them a fascinating subject for astronomers worldwide.

The Discovery of EC 19529-4430

EC 19529-4430 is located in the Galactic halo, a spherical region of space around galaxies that extends beyond their main, visible component. This star is at a staggering distance of 15,500 light years from Earth. Despite its distance, astronomers have been able to study it in detail thanks to the capabilities of SALT.

The star has an effective temperature of 20,700 K, and its surface is primarily composed of carbon-nitrogen-oxygen (CNO)-processed helium. This composition is a result of the CNO cycle, a set of fusion reactions by which stars convert hydrogen into helium, releasing energy in the process.

Interestingly, EC 19529-4430 is on a retrograde orbit and belongs to the Galactic halo. This is consistent with its low metallicity, a term astronomers use to describe the abundance of elements heavier than helium in a star.

Unique Characteristics of EC 19529-4430

One of the intriguing aspects of EC 19529-4430 is that no pulsations have been detected from this star. Pulsations, or variations in a star's brightness, are common in many types of stars and can provide valuable information about a star's internal structure.

Moreover, EC 19529-4430 is also the coolest known carbon-poor and nitrogen-rich EHe star. This unique combination of characteristics sets it apart from other known EHe stars and provides astronomers with a unique opportunity to study this type of star in more detail.

The Origin and Future of EC 19529-4430

The most likely origin of EC 19529-4430 is a merger of two helium white dwarfs in a binary system about 11 billion years ago. White dwarfs are the remnants of stars that have exhausted their nuclear fuel. When two of these remnants come together in a binary system, they can merge to form a new star, as is likely the case with EC 19529-4430.

Looking ahead, it is predicted that EC 19529-4430 will likely evolve into a core helium-burning EHe subdwarf. This evolution will mark another phase in the star's life cycle, offering further opportunities for study and discovery.