Vampire stars, known as blue straggler stars (BSS), defy simple models of stellar evolution and show many characteristics of younger stars. Photo: PIB

Team of astronomers from the Indian Institute of Astrophysics (IIA) have made the discovery that a vampire star has been rejuvenating its youth by sucking up material from a companion in the star cluster M67 located in the constellation Cancer.

Vampire stars, known as blue straggler stars (BSS), defy simple models of stellar evolution and show many characteristics of younger stars.

“This anomalous youth is explained theoretically as due to rejuvenation by eating up material from a binary stellar companion. Star clusters are useful test-beds to test this theory as they host a large number of binary stars, some of which can lead to the formation of vampire stars. Once rejuvenated, these stars follow a different path of evolution when compared to Sun-like single stars. So far, detection of sucked up material along with the sighting of their remnant binary companion was elusive,” said the department of science and technology.

However, recently, a team of astronomers from IIA made a groundbreaking discovery of a vampire star in M67, that sheds light on a complex rejuvenation process, known as mass-transfer in a binary system.

The key to this detection was data from the UltraViolet Imaging Telescope, on board AstroSat, India’s first dedicated space observatory.

The scientists studied the surface composition of the vampire star in M67, called WOCS 9005, using spectroscopy, a technique where the light of the star is dispersed into its colors like the rainbow.

“This star is expected to show chemistry very similar to our Sun, but we found that its atmosphere is rich in heavy elements such as barium, yttrium, and lanthanum”, said Harshit Pal, the lead author of the paper.

“The presence of heavy elements in the spectrum pointed to a polluted atmosphere of the vampire star and the source of pollution being an external source. The external source is 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”, said Prof. Annapurni Subramaniam, co-author of the paper and Director IIA.

Prof. Subramaniam added that the blue straggler star that we see now must have eaten up most of this barium-rich material due to its gravitational pull, and is now presenting itself as a rejuvenated star.