Focus on APS Topical Groups

Plasma Astrophysics

By Calla Cofield

The APS Group on Plasma Astrophysics (GPAP) bridges two bodies of physics that are deeply and intricately linked. Astrophysics offers new examples of plasma physics phenomena not seen anywhere else, and many of the most important questions in astronomy and astrophysics have plasma physics at their core. Finding answers to these questions will require astrophysicists with an up-to-date knowledge of plasma physics, and the group aims to create a community where that knowledge can be shared.

APS has a Division of Astrophysics (DAP) and a Division of Plasma Physics (DPP), but the two fields are large and there is a need for specific focus to be given to the overlapping areas found in plasma astrophysics. GPAP’s current chair Steven Spangler of the University of Iowa says that one of group’s goals is to increase the interaction between these two divisions.  

In addition to participating in the April Meeting, GPAP hosts a mini-symposium at the annual meetings of the DPP. The symposium offers GPAP members the chance to discuss the issues that are central to the advancement of the field. The symposium also informs plasma physicists about applications of their discipline to astronomical objects. Last year’s symposium was on momentum transport in laboratory and astrophysical plasmas. Among other things, momentum transport in plasmas can explain how matter orbiting in the accretion disks around black holes can transfer its angular momentum outward and spiral into the black hole. Previous symposium topics have included shock acceleration in space, astrophysical explosions, and the dynamics of magnetic flux tubes in space.

One of the most visible, and magnificent, examples of plasma astrophysics phenomena is the northern and southern lights. The auroras are theorized to be the result of a process called magnetic reconnection, in which plasmas containing magnetic fields are pushed together and the fields cancel, converting a portion of their energy into fast electrons which enter the upper atmosphere and cause the air to glow during the auroras. Magnetic reconnection may also be the driving force behind solar flares and coronal mass ejections, both of which can impact life on Earth. Plasma astrophysicists are also searching for evidence of magnetic reconnection in accretion disks and around black holes.

In the past ten years, scientists have created the first laboratory results clearly showing magnetic reconnection occurring. However, there is controversy over how the onset of this process occurs, how it proceeds, and exactly how the charged particles and electromagnetic fields in plasma interact with each other. “Plasma astrophysicists need to remain in close communication with basic plasma physicists to be aware of the current understanding of magnetic reconnection, as well as limitations to this understanding,” says Spangler.

GPAP was formed in 1999, with key leadership from Amitava Bhattacharjee, then of the University of Iowa, and now of the University of New Hampshire. GPAP’s 381 members are involved in active discussion about ways to advance the field of plasma astrophysics. Their current aims include improving relations with other APS units, primarily the DPP and DAP, and other scientific societies, including the American Geophysical Union and the American Astronomical Society.

Group on Plasma Astrophysics web site