One cosmic pretzel for two baby stars

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When astronomers looked at this new ALMA image, it reminded them of a pretzel – a pastry shaped
like a knot. But there are no real pretzels in space, of course. So what does the image really show?
And what are the two bright spots in the center of the cosmic pretzel?

In fact, this is a picture of the growth of stellar twins: two stars that are born at the same time, out of
the same cloud of gas and dust. The ALMA observations reveal how gas from the surrounding cloud
ends up in the two stars.

In the case of a single star, the gas accretes into a flattened, rotating disk. At the very center of the
disk, the gas falls onto the forming star. Such a ‘circumstellar disk’ is shaped more like a pizza than a
pretzel.

With this particular binary star, things are different. Yes, both baby stars are surrounded by a disk.
The two disks can be seen as the bright spots in the ALMA image. But because the two stars orbit
each other, they stir up the gas and dust in their vicinity.

As a result, gas from the surrounding cloud does not accrete evenly into the two disks. Instead, the
gas flows in huge loops and spirals: the pretzel-shaped structure.

Earlier observations of the young stellar twins could only discern one large blob of radiation. Thanks
to the sharp vision of ALMA, astronomers have now also imaged the two disks, and revealed the
funny shape of the larger structure.

The new result will help scientists to understand the birth of binary stars. An important goal, since
most of the stars in the universe are part of a binary system.

What?

The cosmic pretzel surrounds a young binary star known as [BHB2007] 11. The binary star sits in a
dark, dusty cloud known as Barnard 59 (after astronomer Edward Barnard). Barnard 59 is part of the
much larger Pipe Nebula in the constellation Ophiuchus, the Serpent Bearer. The nebula is between
600 and 700 light-years away. The two stars orbit each other at a distance of some 4.2 billion
kilometers – about the distance between the Sun and the outermost planet Neptune. Each star is
surrounded by a circumstellar disk of gas and dust about the size of the asteroid belt in our own solar
system: some 800 million kilometers across.

Who?

The ALMA observations of the young binary star [BHB2007] 11 in the Pipe Nebula were carried out
by a team of seven astronomers, led by Felipe Alves of the Max Planck Institute of Extraterrestrial
Physics in Germany. Felipe worked together with colleagues from Germany, Spain and Brazil. The
team published their results in Science.

ALMA URL