Supermassive stars burn brighter than the sun
By Amanda Jermyn



Back in 2010 I wrote about the discovery of a star 265 times the mass of our Sun, shining about 9 million times as brightly. This star, known as R136a1, is about 165,000 light years from our Milky Way, in the super star cluster, R136, near the center of the Tarantula Nebula in the Large Magellanic Cloud galaxy. It was discovered by a team led by astrophysicist Paul Crowther of the University of Sheffield, England, using the European Southern Observatoryís Very Large Telescope in Chile, as well as data from the Hubble Space Telescope.

R136a1 still holds the record as the most massive star ever discovered. To give you an idea of how massive it is, the Sun is about 332,950 times the mass of the Earth. This seems pretty big, until you try to imagine something 265 times that mass! Some stars, such as Red Giants, are larger in size, but they weigh far less. It is estimated that at its birth the star R136a1 had 320 times the mass of our Sun, before shedding some of its mass over the past million years. However, current theories hold that stars cannot be born above 150 solar masses, suggesting that supermassive stars like this one formed through mergers of multiple stars. R136a1 has actually been shedding its mass very rapidly, far more so than our Sun. In fact it sheds an entire Sunís worth of mass every hundred thousand years. Such massive stars, known as Wolf-Rayet stars, lose their mass by means of a very strong stellar wind, with speeds of up to 1,243 miles per second. By comparison, the speed of the solar wind is about 249 miles per second.

Massive stars tend to be less stable than smaller ones, burning more brightly, and generating more pressure that ejects gas outward into space. The largest of them suffer from rapid burnout, lasting a mere three million years, compared to the 14 billion year life expectancy of our Sun. Stars between about 8 and 150 solar masses explode at the end of their lives as supernovae, leaving in their wake neutron stars or black holes. It is now thought that supermassive stars such as R136a1, with solar masses between 150 and 300 solar masses, may die as hypernovae, stellar explosions with the energy of more than 100 supernovae.

A star forms when clouds of dust and gas are drawn together under the force of gravity, becoming hotter and denser, until the atoms begin fusing together, setting off a nuclear reaction. Because the formation of supermassive stars requires a huge amount of dust and gas, it used to be thought that they could only form in very dense star clusters containing stellar nurseries, with plenty of raw materials to go round. However, in a study led by L. M. Oskinova of the University of Potsdam, Germany, published in the October 1st, 2013 issue of the Monthly Notices of the Royal Astronomical Society, the researchers describe a surprising discovery. A star named WR102ka, near the center of the Milky Way, was discovered floating in space, away from any other nearby stars. At about 100 times the mass of our Sun, it is one of the most massive and luminous stars in our galaxy. From infrared observations the researchers were able to determine that the star was not moving fast, and therefore canít have traveled far from where it was formed. Also, the star is very young, about 2 million years old, and there is no stellar nursery it could have come from in the short time since it was born. They therefore suggest that it formed in relative isolation, away from any massive star cluster, and that the region close to the center of our galaxy provided a suitable environment. However, where exactly the raw materials required for its formation came from remains a mystery. There is still so much we donít know about the formation of supermassive stars.

Join the Springfield Stars Club on Tuesday, November 26th at 7.30pm at the Springfield Science Museum for a Mission to Mars panel discussion by Stars Club members. Paul Cardone will provide an introduction to the red planet, followed by Alan Rifkin explaining the orbital mechanics of getting a spacecraft to Mars. Crystal Mengele will report on the findings of the Mars Curiosity Rover, and Dr. David Wexler will talk on the medical implications of sending humans to Mars. A ten-minute video of the Curiosity landing in August 2012 will be shown. Refreshments will be served, and the public is welcome free of charge.

Also, on Friday, December 6th, the Stars Club and the Springfield Science Museum will host ďStars over Springfield.Ē Paul Cardone will speak on Whatís New in our Solar System? A fee of $3 for adults and $2 for children under 18 will be charged.