What happens when you take observations of a gas cloud, a protostar, and a pre-star dense core of gas, and model them with turbulence? A downright hypnotizing model at how multiple star systems may form.

A gas cloud 450 light years away in the constellation Taurus hosts not just a newborn protostar, but a dense core of gas that will likely become a star in the near future. Observations of this system have led to new simulations on the role of turbulence in the formation of multiple star systems.

We know the conditions necessary to form stars: clouds with a few solar masses worth of gas and dust contained within a tenth of a light-year, enough time for things to clomp together, and sooner or later fusion will start. What we aren't so sure about is the distribution and kinematics of that gas and dust leading up to core formation and the birth of a protostar. The only way to pin those conditions down are to observe brand-new protostars, and hopefully find a few almost-star gas cores before they kick off fusion. Protostars only last a few hundred thousand years swaddled in gas and dust before they either incorporate the material or blow it away, entering the next stage of its multi-billion year lifetime.


Multi-wavelength composite of MC27: low-density (green, ALMA) and high-density emission (red, ALMA) of the dust and gas cloud, and the protostar's infrared emission (blue, Spitzer). Credit: Kazuki Tokuda (Osaka Prefecture University) / ALMA (ESO/NAOJ/NRAO) / NASA / JPL-Caltech

From infrared observations by the Spitzer Space Telescope, researchers already knew that a low-luminosity protostar was lurking within gas cloud MC27. A team of researchers at Osaka Prefecture University led by Kazuki Tokuda and Toshikazu Onishi booked time on the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to peer at the gas cloud, observing conditions around the protostar and looking for any likely clumps of gas that could turn become stars.


Tokuda and Onishi used ALMA to peer at MC27/L1521F, a high-density gas cloud in the constellation Taurus. They already knew that MC27 was a baby star, but soon spotted two nearby gas condensations. These cores of high-density gas aren't quite protostars yet, but one of them (MMS-2) is the highest-density non-star gas core ever observed in low-mass star forming regions. That makes it the best candidate yet for a pre-protostar, a core of gas that will eventually kick off fusion.

Artist's conception of the MC27 cloud core. Image credit: NROJ

The twists and trails of the gas are also proving fascinating. Clouds of gas don't last long around protostars — within a few hundred thousand years, the gas is either incorporated into the star, or blown away. This makes it pretty exciting to find a protostar still surrounded by high-density gas. In an ALMA press release, researcher Tokuda gushes:

"It was very exciting when we found a star-forming gas condensation right next to the protostar. We might say we are witnessing star-forming gas at the very moment of birth of a star. We will study further and gain better understanding of star formation mechanism."

From eyeballing the gas distribution around the protostar, it looks like we caught it within decades to up to a couple of centuries after formation. That's not just young in astronomical terms, that's even young within a human historical context! Not only that, but the almost-star MMS-2 has a swooping tail of gas, an indicator of turbulence within the gas cloud.

The researchers used the combination of observations — a protostar, a not-quite-star, and a relatively low-density but turbulent gas cloud — to run computer simulations. They found that by yanking the gas around with more than one gravitational core, denser patches could form and grow, producing multiple stars in complex orbits.

Computer simulation of multiple star formation in a turbulent gas cloud. Credit Tomoaki Matsumoto (Hosei University)

In the computer simulation of turbulence-assisted multiple star formation, the complex motion of newborn stars produce wave-like ripples in the gas. These ripples result in bow-shaped gas structures, similar to the tail observed on MMS-2 in the MC27 gas cloud. While it's going to take more observations and more systems to confirm the role of turbulence in stellar formation, for now it's a nice, plausible concept for thinking about how multiple star systems may form.