In a groundbreaking discovery, Dr. Varsha Ramachandran and her team from the Center for Astronomy at Heidelberg University have revealed the existence of the first “stripped” star of intermediate-mass.
This remarkable finding bridges a crucial gap in our understanding of stellar evolution, particularly in relation to systems involving merging neutron stars.
These systems play a vital role in unraveling the mysteries behind the origin of heavy elements like silver and gold.
The research, conducted at ZAH’s Astronomisches Rechen-Institut (ARI), has been published in the esteemed journal Astronomy & Astrophysics.
For years, astronomers have been aware of stripped stars belonging to both the low-mass category, known as subdwarfs, and the high-mass group known as Wolf-Rayet stars.
However, until now, the so-called “intermediate-mass stripped stars” had remained elusive, raising questions about the accuracy of existing theoretical models.
By utilizing high-resolution spectroscopy devices mounted on the Very Large Telescope (VLT) of the European Southern Observatory in Chile, Dr. Ramachandran and her colleagues scrutinized hot and luminous stars.
Their meticulous analysis led to the detection of intriguing signatures in the spectrum of a previously classified hot, massive star.
Further investigation revealed that the object was, in fact, a binary system comprising an intermediate-mass stripped star and a fast rotating companion called a Be star.
The Be star had acquired its high rotation speed by accreting mass from the stripped-star progenitor.
Remarkably, this system was found in the Small Magellanic Cloud (SMC), a nearby dwarf galaxy.
The stars in this galaxy possess lower levels of heavier elements, known as metals, compared to those found in our own Milky Way.
Consequently, the metal-poor massive stars in the SMC provide astronomers with valuable insights into the early stages of galactic evolution and the chemical composition of the universe.
Dr. Ramachandran, who completed her undergraduate studies in India before pursuing her Ph.D. in Potsdam, Germany, explained the significance of their discovery.
While confirming the presence of the long-sought population of stripped stars, their findings also revealed unexpected characteristics.
Rather than being completely devoid of outer layers, these partially stripped stars retain a small but crucial amount of hydrogen above their helium cores.
This feature makes them appear larger and cooler than their true nature.
The term “partially stripped stars” has been coined to describe this newfound population.
Dr. Andreas Sander emphasized that the remaining hydrogen mantle serves as a form of disguise, allowing partially stripped stars to masquerade as normal, non-stripped hot stars.
Unveiling their true nature requires the combination of high-resolution data, spectral analysis, and detailed computer models.
The uniqueness of the discovered stripped star lies not only in its existence but also in its future.
Dr. Jakub Klencki, an independent research fellow at the European Southern Observatory (ESO), explained that this system serves as a vital link in the evolutionary chain connecting various extraordinary objects.
Stellar evolution models suggest that the stripped star will eventually explode as a stripped-envelope supernova, leaving behind a neutron star remnant.
What makes this discovery truly remarkable is that it represents the first identification of a stripped star in a metal-poor galaxy.
Should the binary system survive the impending supernova explosion, the roles of the two stars will reverse.
The Be-star companion will then donate mass to the accreting neutron star, transforming the system into a Be X-ray binary.
These captivating systems are believed to be the precursors to double neutron star merger events, which are some of the most awe-inspiring cosmic phenomena ever observed.
Furthermore, they hold the key to understanding the origins of valuable chemical elements like silver and gold.
Unraveling their formation process poses a significant challenge for modern astrophysics, and observing intermediate evolutionary stages is critical to achieving this goal.
Dr. Ramachandran concluded that their discovery provides vital insights into the mass transfer evolution of massive star systems, offering direct constraints on this intricate process.
With each new piece of the puzzle, we come closer to comprehending the complex and captivating journey of stellar evolution.
The Astonishing Revelation of Partially Stripped Stars
Astronomers have long been captivated by the mysteries of stellar evolution and the intricate processes that shape celestial objects.
In a breakthrough study, Dr. Varsha Ramachandran and her team at Heidelberg University’s Center for Astronomy have uncovered a celestial enigma—the existence of partially stripped stars.
These peculiar stars challenge existing theories and reveal new insights into the evolution of massive star systems.
Stripped stars are stars that have shed most of their outer layers, exposing their dense and hot helium-rich cores. These cores are formed through nuclear fusion, where hydrogen is converted into helium. Stripped stars can be classified into various categories based on their mass, including low-mass subdwarfs and high-mass Wolf-Rayet stars.
Intermediate-mass stripped stars are a newly discovered population of stars that have lost their outer layers but have retained a small amount of hydrogen on top of their helium cores. This unique characteristic sets them apart from other stripped stars and challenges existing theoretical models of stellar evolution.
Dr. Varsha Ramachandran and her colleagues used high-resolution spectroscopy devices on the Very Large Telescope (VLT) of the European Southern Observatory in Chile to examine hot and luminous stars. They identified suspicious signatures in the spectrum of a previously classified hot, massive star, which led to the discovery of the binary system consisting of an intermediate-mass stripped star and a fast rotating companion.
The Small Magellanic Cloud is a nearby dwarf galaxy with lower metallicity compared to our Milky Way galaxy. The metal-poor environment of the SMC provides valuable insights into the early stages of galactic evolution and the chemical composition of the universe. Discovering stripped stars in the SMC allows astronomers to study the formation and evolution of these stars in a different context.
Partially stripped stars retain a small amount of hydrogen on top of their helium cores, whereas other stripped stars have lost their hydrogen completely. This retention of hydrogen gives partially stripped stars a larger and cooler appearance compared to their true nature. The presence of this hydrogen mantle makes it challenging to distinguish them from normal, non-stripped hot stars without careful spectral analysis and detailed computer modeling.
According to stellar evolution models, the stripped star in the discovered system will eventually explode as a stripped-envelope supernova, leaving behind a neutron star remnant. If the binary system survives the supernova explosion, the roles of the two stars will reverse, with the Be-star companion donating mass to the accreting neutron star, creating a Be X-ray binary. This system provides a unique opportunity to study the various stages of stellar evolution and the mechanisms behind the formation of extraordinary objects in the universe.
More information: Astronomy & Astrophysics (2023). DOI: 10.1051/0004-6361/202346818