Mapped ‘local bubble’ magnetic field

Astronomers of the Center for Astrophysics | Harvard & Smithsonian (CfA) have presented a unique map that could answer decades-old questions about star formation and the influence of magnetic fields in the cosmos.

The map shows the magnetic field structure of the Local call – a huge cavity a thousand light years wide in the space around our sun. Our galaxy, the Milky Way, is full of such “super bubbles”, created by the violent explosions of massive stars. These so-called supernovae sweep gas and dust – the raw material for the formation of new stars and planets – to the edges of the bubbles.

Our knowledge of superbubbles is still very incomplete. With the new 3D map of the field’s magnetic fields, astronomers now have new information that can better explain the evolution of superbubbles and their effects on star formation and galaxies as a whole.

The local bubble has become a hot topic in astrophysics because it is the superbubble in which the sun and our solar system now reside. In 2020, its spatial geometry has been extensively mapped by Greek and French researchers. A year later, the surface of the local bubble was found to be the source of all nearby young stars.

These studies and the new three-dimensional map of the magnetic field are partly based on data from the European space telescope Gaia, which measures the positions and movements of a large number of stars, but also maps the local concentrations of cosmic dust and thus defines largely the limits of the local bell.

These data have now been combined with those from Planck, another European space telescope, which between 2009 and 2013 measured the so-called cosmic background radiation, and also detected dust in the Milky Way. These were mostly observations of polarized light, that is, light that vibrates in a certain direction. This polarization is caused by magnetically aligned dust particles in space. The dust alignment, in turn, reveals the orientation of the magnetic field acting on the dust particles.

By mapping the magnetic field lines in this way, the researchers were able to create a two-dimensional map of the magnetic field: its projection on the sky as we observe it from Earth. To convert this map into three spatial dimensions, the researchers made two key assumptions: first, that most of the interstellar dust causing the observed polarization is located on the surface of the local bubble, and second, that the theories predicting that the magnetic field will be “swept” towards the edge of the bubble as it expands are correct.

The research team then compared the resulting map to features found along the outer boundaries of the local bubble, including the well-known star-forming region in the constellation Orion. Future research will also examine the relationships between magnetic fields and these and other structures.

The new findings were presented today by Theo O’Neill of the University of Virginia (USA) at the 241st annual meeting of the American Astronomical Society, to be held this week in Seattle. (EE)