Hidden within the Large Magellanic Cloud, a nebula located just outside the Milky Way, is potentially the largest star known in the entire universe. This star, named R136a1, is approximately 150,000 light-years away from Earth (according to Phys.org).
R136a1 was originally discovered 62 years ago by a team of astronomers at the Redcliffe Observatory in Pretoria, and it was published in the Monthly Notices of the Royal Astronomical Society in October 1960.
RMC 136a1 is one of the heaviest and brightest stars, with a mass hundreds of times that of the Sun, and a luminosity 6.2 million times that of the Sun. It is also one of the hottest stars, with a temperature reaching 46,000 degrees Celsius. R136a1 is located in a cluster within the Tarantula Nebula, a cloud of dust and gas situated 165,000 light-years from the Milky Way. It was discovered using telescopes from the European Space Observatory located in the Atacama Desert, Chile.
A new study on R136a1 was published in August this year after a team of astronomers led by Venu Kalari from the Gemini Observatory researched the star cluster it resides in. They managed to capture images of this supergiant star, allowing them to provide new estimates regarding the size of R136a1. Their findings, published in the Astrophysical Journal, shed light on the mysteries surrounding this star and its potential representation of how the largest stars in our universe operate.
Professor Paul Crowther from the University of Sheffield (UK) believes that when it was first formed, R136a1 weighed hundreds of times more than the Sun. “Unlike us humans, these stars are very massive at birth and will lose weight over time,” he stated. Crowther also noted that R136a1 is incredibly luminous, with a brightness several million times that of the Sun, and its surface temperature is seven times hotter than that of the Sun.
When R136a1 was first discovered, its mass was initially estimated to be around 250 to 320 times that of our Sun. This was particularly intriguing for scientists at that time, as they believed the maximum mass of a star was much lower until the discovery of R136a1. This maximum mass, known as the Eddington Limit, is the theoretical point at which stars shine so brightly that they blow off their outer layers. According to research published in Nature, the Eddington Limit is estimated to be around 150 times the mass of the Sun.
R136a1 is classified as a Wolf-Rayet star (stars with a mass over 20 times that of the Sun, exhibiting high mass loss through stellar winds at speeds exceeding 2,000 km/s). Over the past million years, R136a1 has lost a mass equivalent to about 50 times that of the Sun. R136a1 is estimated to be around 1.7 million years old, and by reversing its mass loss rate, its initial mass is predicted to have been over 320 times that of the Sun. This finding contradicts some previous models that suggested the mass limit of a star is only 150 times that of the Sun.
According to Phys.org, the new estimates from the research team suggest that this star has a mass ranging from 170 to 230 times that of our Sun, a much more reasonable estimate compared to past research. Nevertheless, it still stands as the largest star ever discovered in our universe (according to the NOIRLab).
R136a1 is not only the largest star discovered in our universe to date, but it may also accurately represent how all stars of this mass function. Stars form in various sizes, ranging from red dwarfs to blue supergiants. According to Phys.org, if astronomers can learn more about supergiant stars like R136a1, including their prevalence, it could help us understand how they form.
Initial evidence that R136a is a star cluster was proposed by Weigelt and Beier in 1985. They used speckle interferometry to demonstrate that R136 consists of eight stars within one arcsecond at the center of the cluster, with R136a1 being the brightest star. The final confirmation of the nature of R136 came after the launch of the Hubble Space Telescope. Its Wide Field and Planetary Camera (WFPC) observed R136 in at least 12 parts, revealing that R136 contains over 200 extremely bright stars. The more advanced Wide Field and Planetary Camera 2 (WFPC2) allowed the study of 46 luminous supergiant stars within a half parsec of R136 and over 3,000 stars within a radius of 4.7 parsecs.
Understanding how large stars like R136a1 operate can help us learn more about some of the heavier celestial bodies in our universe – they are formed through supernova explosions. According to NASA, up to 80% of elements heavier than iron originate from massive supernovae. These new findings about R136a1 could aid astronomers in their search for other massive stars and remnants of past supernovae.
