Our scientists claim that Bram Stoker’s Dracula has many cosmic counterparts in the universe, sucking up the energy materials from nearby victim stars through cosmic winds. These ‘Vampire Stars’ are scientifically called ‘Blue Straggler Stars (BSS)’.
Astronomers at the Indian Institute of Astrophysics (IIA) have been investigating the mysterious formation of the blue straggler stars (BSS) aka Vampire Stars. These unique stars appear anomalously younger and energetic than they actually should. It is a phenomenon thought to occur because they “rejuvenate” by absorbing material from a nearby companion star in a binary system.
India is rapidly moving towards a Viksit Bharat when it comes to Astrophysics and Space Science. Let’s break down this significant discovery by Indian astronomers in a point wise, systematic and easy to understand manner.
Discovery by Indian Institute of Astrophysics (IIA)
Recently, the IIA team made a groundbreaking discovery. They found a vampire star in the M67 cluster, located in the constellation Cancer.
Star clusters contain hundreds to thousands of stars with wide range of masses but similar surface chemistry. This makes star clusters ideal to understand how single and binary stars live and die.
The vampire star or the blue straggler, named WOCS 9005, shows clear evidence of having absorbed barium-rich material from its binary companion.
What makes this discovery even more significant and interesting is that the astronomers also directly detected emissions from the remains of that companion star.
This discovery provides rare insights into the complex rejuvenation process known as mass transfer in binary star systems.
Key Detection and Tools Used
The discovery was made possible using data from the UltraViolet Imaging Telescope (UVIT) on AstroSat, India’s first dedicated space observatory.
Spectroscopy, a technique that disperses a star’s light into a rainbow like spectrum, was used to study blue straggler WOCS 9005’s surface composition. The spectra of the star thus formed deciphers their surface and atmosphere chemistry.
Archival data from the Galactic Archaeology with Hermes (GALAH) survey revealed that the WOCS 9005 star’s atmosphere is rich in heavy elements such as barium, yttrium, and lanthanum, which are typically found in asymptotic giant branch (AGB) stars.
This essentially means that the environment of the WOCS 9005 star was “polluted” by that of an external source in the vicinity. This external source being a star which passed it’s AGB phase.
Understanding the Source of the Heavy Elements
AGB Stars are those which have passed their final nuclear burning phase and are moving towards formation of a planetary nebula and ultimately ending up into a white dwarf stage.
The presence of heavy elements in the spectrum of WOCS 9005 star pointed to a polluted atmosphere of this vampire star and the source of it’s ‘pollution’ being an external source.
The external source of this ‘pollution’ was likely to be its binary companion, which must have made the heavy elements when it passed through its AGB phase, and later became a white dwarf star.
The blue straggler star, WOCS 9005 in this case must have eaten up most of the companion star’s barium-rich material due to its gravitational pull, and is now presenting itself as a rejuvenated star
Confirmation of the Companion Star
The WOCS 9005 has a temperature similar to the sun and it was not expected that it will be bright in the ultraviolet (UV) light. However, when analysed there was considerable UV brightness of the WOCS 9005, confirming the presence of the hot, small companion star.
Since there was bright light, there had to be a source as well. White dwarf stars, which are bright in ultraviolet (UV) light but faint in visible light, were suspected to be the companion.
It was theoretically calculated and validated that the two stars WOCS 9005 and the white dwarf were close enough to transfer the matter from the donor star to the vampire star through cosmic winds.
Significance of the Discovery
This is the first time the white dwarf remnant of a companion star has been directly detected in a chemically “polluted” blue straggler star.
The discovery experimentally confirms the theory that blue straggler stars are formed by absorbing material from a companion star.
The rarity of such systems remains a mystery, possibly due to the quick settling of pollutants in the atmosphere of vampire stars.
