While stars come in pairs, massive ones are rarely seen without a companion and interestingly these twins are usually equal in mass but those which are not turned the attention of the Harvard researchers to look into it to discover that a new class of binary stars are a combination one star fully formed and the other in its infancy.
The massive star always shines brighter making it difficult to identify extreme mass-ratio binaries as it hides the lighter star. To overcome this, Maxwell Moe of the Harvard-Smithsonian Center for Astrophysics (CfA) and his colleague Rosanne Di Stefano looked for eclipsing route, when the two stars line up in such a way that they periodically pass in front of each other causing the clipse effect whenn seen from Earth.
“When the fainter star eclipses the brighter, their combined light drops detectably,” said the researchers as these systems are rare and require a precise alignment when seen from Earth.
After filtering thousands of eclipsing views, Moe and Di Stefano zeroed in on 18 extreme mass-ratio binaries in our neighboring galaxy called the Large Magellanic Cloud, where the stars circle each other in three to nine days. While the massive stars weigh 6 to 16 times bigger than the sun, the less massive stars weigh about one or two times the sun, they said.
The data provided a clue to the younger age of the fainter stars just like the illuminization phases of the moon. The two stars orbit each other and the companion reflects the light of the brighter, and more massive star, they explain.
“We caught them at just the right time. In effect, we’re seeing these stars in the delivery room,” said lead author Maxwell Moe. We only see phases because the fainter, less massive companion is not yet a full-fledged star. Astronomers describe it as being ‘pre-main sequence’.”
A star is born when a giant clump of gas pulls together under its own gravity, and begins to grow denser and hotter until nuclear fusion ignites. This process happens faster for more massive stars than the lighter ones, which are still in their infancy.
“Imagine if a human baby shrank as it got older instead of growing. That’s what happens for young stars,” says Di Stefano. In this case, the young star is puffier than it would be, since it is still contracting, effectively letting the other massive star act as a giant mirror, reflecting its partner’s brilliance.
The discovery of twin stars provides clue to the formation and evolution of massive stars, close binaries, and star nurseries, said the Harvard scientists.
“These 18 systems were culled from millions of stars in the Large Magellanic Cloud observed by the Optical Gravitational Lensing Experiment. Due to their rarity, finding examples in our galaxy likely will require an extensive survey using facilities like the upcoming Large Synoptic Survey Telescope,” explained the researchers further.
The finding will be published in the Astrophysical Journal.