Scientists detect magnetic fields in massive stars outside our galaxy for the first time

Most massive star-forming region NGC346 in the Small Magellanic Cloud. Credit: NASA, ESA, A. James (STScI).

For the first time, scientists have detected magnetic fields in three massive, hot stars located in our neighboring galaxies, the Large and Small Magellanic Clouds.

While magnetic fields in massive stars have been found in our galaxy, this discovery is significant because the Magellanic Clouds have many young massive stars.

This allows scientists to study how these stars form and what the upper limit is for a star’s mass before it becomes unstable.

Magnetic fields play a crucial role in the evolution of massive stars, which are those with more than eight times the mass of our Sun.

These stars eventually leave behind neutron stars and black holes. The merging of these compact remnants has been observed by gravitational wave observatories.

Additionally, theoretical studies suggest that magnetic fields are involved in the explosions of massive stars, which can lead to phenomena like gamma-ray bursts, x-ray flashes, and supernovae.

“Studying magnetic fields in massive stars in galaxies with young stellar populations gives us vital information about star formation in the early universe,” says Dr. Swetlana Hubrig from the Leibniz Institute for Astrophysics Potsdam (AIP), the lead author of the study.

To measure stellar magnetic fields, scientists use a technique called spectropolarimetry, which involves recording circularly polarized light from stars and examining small changes in spectral lines.

This method requires high-quality data and is very demanding because it needs a lot of photons. Massive stars in neighboring galaxies, despite their size, do not provide enough light for conventional high-resolution spectropolarimeters and smaller telescopes.

Therefore, the researchers used the FORS2, a low-resolution spectropolarimeter mounted on one of the four 8-meter telescopes of the Very Large Telescope (VLT) of the European Southern Observatory (ESO).

Previous attempts to detect magnetic fields in massive stars outside our galaxy had failed due to the complexity of the measurements and various influencing factors.

The magnetic field detected with circular polarization is called the longitudinal magnetic field, which points towards the observer. Similar to a lighthouse beam, it is only visible when directed at the observer.

The structure of the magnetic field in massive stars usually features a global dipole with the axis inclined to the rotation axis, which can sometimes result in a zero longitudinal magnetic field if the observer looks directly at the magnetic equator.

The team conducted spectropolarimetric observations of five massive stars in the Magellanic Clouds. They detected magnetic fields of around one kiloGauss in two single stars and one binary system in the star-forming region NGC346 in the Small Magellanic Cloud.

On our Sun, such strong magnetic fields are only found in small, highly magnetized regions called sunspots.

These findings suggest that massive star formation in galaxies with young stellar populations, like the Magellanic Clouds, occurs in a similar way to our own galaxy.

The research has been published in the journal Astronomy & Astrophysics.