What’s Going On in 30 Doradus?


30 Doradus in the X-Ray Spectrum (a/k/a The Tarantula Nebula)

30 Doradus in the X-Ray Spectrum (a/k/a the Tarantula Nebula)

For astronomers, the Milky Way, our local galaxy, can be a bit of a disappointment. Most of the stars it currently produces are red M-dwarfs. With masses less than half that of the Sun, these stars will burn fuel contentedly for a couple of trillion years and then gradually fade. Boring. Really massive stars, with 10 or more times the mass of the Sun, the kind that will explode and possibly leave an exotic object like a black hole behind? They’re pretty rare around here.

But over in our neighboring galaxy, the Large Magellanic Cloud, which orbits the Milky Way, there’s a region called 30 Doradus, also known as the Tarantula Nebula. And 30 Doradus has an astonishingly large number of young stars, including many very large ones—possibly including the largest star ever observed.

Of the 452 stars the astronomers were able to observe with the Very Large Telescope, 247 were bigger than 15 solar masses, which means that all of them are destined to explode in a supernova.

If this data holds up, it breaks astronomy’s models for star formation.

Current theory says if you survey a large-enough portion of the galaxy and then plot the number of stars against their masses, you should see a steady decline in number as the mass goes up. Simulations of star formation have allowed scientists to estimate the rate of that decline. Implicit in the theory is the conclusion – the end point, if you will – that for a massive enough star, the incidence should be zero.

The theory predicts that 150 solar masses would be the upper limit, but the researchers found one in 30 Doradus that’s more than 200 solar masses. Other researchers have claimed a star in the area is about 300 solar masses. And the 30 Doradus data can only rule out stars of 500 solar masses with a 90-percent confidence level.

Is it something unique to the star formation region of 30 Doradus? Is it just experimental error?

Assuming the data are accurate and 30 Doradus is not somehow unique, that implies there should be a lot more supernovae and black hole collisions than astronomy has observed.

WC loves these moments in science, when the paradigm shifts, when existing theories no longer support the data and the theory – the paradigm – shifts to a new approach.

As Joni Mitchell said, “We are stardust.” These are the stars that make that stardust.

 

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