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The same physics that makes mushroom clouds might play a key role in making the universe’s most massive stars.

According to simple equations, a star shouldn’t be able to grow to more than 20 times the mass of the sun. As a cloud of gas compresses into a star, it glows even before nuclear fusion kicks off at its core.

The intense radiation it emits should hold back any gas arriving late, keeping it from adding mass to the growing star even as gravity continues to pull that gas down.

But in stellar nurseries, we see baby stars that weigh up to 150 times more than the sun.

Sophisticated simulations show that these stars accomplish the feat by pulling in matter not from all sides, but from a spinning accretion disk in a single plane.

Now, a new simulation shows the most complete account yet of other ways stars suck in gas.

Burst your bubble

As radiation rises from the star, it inflates bubbles that push out into the surrounding gas, holding that material at bay. According to a study led by ��at the University of California, Santa Cruz, those bubbles can pop, letting tendrils of gas penetrate down toward the star.

The process, called a Raleigh-Taylor instability, is the same process responsible for mushroom clouds around nuclear explosions – it happens where thin, hot material pushes against colder, heavier stuff.

“We see these fingers from along the edge of the bubbles coming down and accreting onto the disk,” Rosen says. “Then that material can be incorporated onto the star.”

But not everyone is convinced that bubble-popping really helps build massive stars. , the growth process is a much more orderly affair, with the bubbles holding up to outside pressure and the star plumping up just from a disk.

“The bubble didn’t collapse in our simulation and there was still a healthy star,” says at McMaster University in Ontario, a member of that team.

But Pudritz is hopeful that Rosen’s paper, which also shows how the two teams might agree on whether the radiation bubbles pop if they used the same techniques, will help solve the question. “Bananas to bananas, right? The same methods, the same code,” he says. “That’s a positive step toward trying to compare.”

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