Will Dunham
WASHINGTON, Feb 28 (Reuters) – The largest stars in the universe live the lives of rock stars – they are born to shine, live fast and die young. If so, the star named WOH G64 might be considered the stellar equivalent of Jimi Hendrix.
WOH G64 is 28 times more massive than the Sun and is located in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. It is one of the few largest known stars, like Hendrix in rock music. More than three decades of observations have shown that it behaves unlike any star seen before.
Astronomers have an incomplete understanding of the life histories of the largest stars, and observations of WOH G64 provide new insights.
Researchers observed a color change in the star in 2014, as it evolved from red to yellow, corresponding to an increase in its surface temperature. The star was once classified as an extreme red supergiant, but soon became a yellow supergiant. From a cosmic perspective, this transformation happened quickly and there was no evidence of an eruption or explosion.
“Stellar evolution typically occurs on timescales of billions of years. On human timescales, we only observe more sudden and violent events, such as eruptions, the merger of two stars, or their explosive death,” said astronomer Gonzalo Muñoz-Sanchez, lead author of the study published this week in the journal Nature Astronomy.
“No current stellar model can fully explain this transition in WOH G64,” said Munoz-Sánchez, who conducted the research at the National Observatory of Athens.
Compared with the sun, its luminosity is about 300,000 times that of the sun, and its diameter is about 1,500 times that of the sun. If it were located at the position of the Sun, its surface would extend to the distance between the orbits of Jupiter and Saturn (the fifth and sixth planets of the Solar System). Traveling at the speed of light, it takes six hours to circle the surface of a star.
WOH G64 is approximately 10 million years old and appears to be nearing the end of its lifespan. By comparison, the Sun is about 4.5 billion years old, with an estimated 5 billion years left. WOH G64 is about 160,000 light-years away from Earth. A light year is the distance that light travels in one year, or 5.9 trillion miles (9.5 trillion kilometers).
“WOH G64 is a massive star that is very different from the Sun,” Muñoz-Sanchez said.
Stars with a mass of about 8 to 23 times the sun are expected to evolve into red supergiants and eventually explode as supernovae.
For stars with 23 to 30 times the mass of the Sun, their fate is less certain. It is unclear whether they will explode as supernovae, collapse directly to form a black hole, or evolve from a red to yellow supergiant stage before ending their lives. Black holes are extremely dense objects whose gravity is so strong that not even light can escape.
“So WOH G64 could be the solution to this problem,” Muñoz-Sanchez said.
Another layer of complexity is added to understanding WOH G64, as observations indicate that it is gravitationally bound to another star in a so-called binary star system. Researchers cannot determine the size or characteristics of the companion star, but say the two may merge at some point.
The researchers hypothesized about recent changes in WOH G64. They said it may have experienced a violent event before observational data turned it red, and is now returning to its usual yellow resting state. They say it’s also possible that interactions between WOH G64 and its companion star temporarily mimicked the appearance of red supergiants.
“As astronomers continue to monitor this remarkable system, WOH G64 promises to reshape our understanding of how the most massive stars live and die,” Muñoz-Sanchez said.
(Reporting by Will Dunham; Editing by Daniel Wallis)
