For astrophysicists, the interplay of hydrogen -- the most common molecule¹ in the universe -- and the vast clouds of dust that fill the voids of interstellar space has been an intractable puzzle of stellar evolution. The dust, astronomers² believe, is a key phase in the life cycle of stars, which are formed in dusty nurseries throughout the cosmos³. But how the dust interacts with hydrogen and is oriented by the magnetic fields in deep space has proved a six-decade-long theoretical challenge.

 

Now, an international team of astronomers reports key observations that confirm a theory devised by University of Wisconsin-Madison astrophysicist Alexandre Lazarian and Wisconsin graduate student Thiem Hoang. The theory describes how dust grains in interstellar space, like soldiers in lock-drill formation, spin and organize themselves in the presence of magnetic fields to precisely⁴ align⁵ in key astrophysical environments.

 

The effort promises to untangle a theoretical logjam about key elements of the interstellar medium and underpin⁶ novel observational tactics to probe magnetic fields in space.

 

The new observations, conducted by a team led by B-G Andersson of the Universities Space Research Association (USRA), and their theoretical implications are to be reported in the Oct. 1, 2013 edition of the Astrophysical Journal. The observations were conducted using a variety of techniques -- optical and near infrared⁷ polarimetry, high-accuracy optical spectroscopy and photometry（光度测定）, and sensitive imaging in the near infrared -- at observatories⁸ in Spain, Hawaii, Arizona and New Mexico.

 

"We need to understand grain alignment⁹ if we want to make use of polarimetry as a means of investigating interstellar magnetic fields," says Lazarian, who was encouraged to attack the problem by the renowned¹⁰ astrophysicist Lyman Spitzer. "Spitzer himself worked on the problem extensively."

 

Scientists have long known that starlight becomes polarized as it shines through clouds of neatly¹¹ aligned¹², rapidly spinning grains of interstellar dust. And the parsing¹³ of polarized light is a key observational technique. But how the grains of dust interact with hydrogen, become aligned so that starlight shining through becomes polarized, and are set spinning has been a mystery.

 

"While interstellar polarization has been known since 1949, the physical mechanisms¹⁴ behind grain alignment have been poorly understood until recently," explains Andersson. "These observations form part of a coordinated¹⁵ effort to -- after more than 60 years -- place interstellar grain alignment on a solid theoretical and observational footing."

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