What we’re looking at here is a bubble in a star-forming nebula about 4300 light years from Earth. But how did the bubble get there?
The European Space Agency’s Herschel Space Observatory, an orbiting telescope that is about to celebrate its one-year anniversary, sees the cosmos in infrared light, meaning it can see deep into places visible wavelengths cannot penetrate. In this case, Herschel is studying a bubble called RCW 120 that would otherwise be obscured by the surrounding nebulous gas and dust.
SLIDE SHOW: Want to see more star-forming nebulae? Browse the Discovery News “Best of Hubble” 20th anniversary slide show.
Invisible to Herschel, there’s a young, hot 2.5 million year old star right in the center of the bubble, blasting the nebula with intense radiation. The pressure of this radiation is enough to hollow out this empty cavity inside the nebula.
Although this looks very interesting, RCW 120 has a surprise hiding inside the shell of dense gas surrounding the bubble. Right at the bottom of the bubble is a very bright star. It turns out that this is the Goliath of stars with the potential to become one of the biggest and brightest stars in our galaxy.
BIG PIC: Herschel Sees Big Stellar Babies: The infrared space observatory has a habit of spotting star nurseries and this image of the Rosette Nebula is something to shout about.
This massive star didn’t appear by chance. Because the nebula bubble-blowing star has created a cavity, pushing the gas to the bubble’s outermost edge, secondary star birth has been sparked. The gas has become so dense that clouds of the dense material have collapsed, kick-starting fusion and started up a new generation of stars.
Scientists using Herschel have concluded that this unexpectedly large embryonic star is already 8-10 times the mass of our sun, with the potential to grow a lot bigger. They also estimate that the surrounding star-feeding region contains as much as 2000 solar masses-worth of gas. This thing could grow a lot bigger.
Image of RCW 120 (ESA), annotation by me.
Although all this gas wont be eaten by the star in one sitting, it does pose an interesting question. The biggest stars in our galaxy have been observed to not exceed 150 solar masses, but according to theory, they shouldn’t grow more than 8 solar masses. At this size, the star becomes so hot and so bright that it blasts any surrounding gas away. If the 8 solar mass star blows all the surrounding matter away (much like the star that is creating the bubble, above), how can the most massive stars grow?
For now, this question remains open, but it is hoped that Herschel will continue to return stunning imagery deep inside star-forming nebulae so a potential answer can be found. But if I had to place a bet, I reckon the most massive stars are force-fed dense gas by smaller young stars on the edges of ‘bubbles’ like RCW 120. It looks like Herschel scientists are suggesting the same mechanism too.