Artist’s impression of how gravitational lensing works. Image Credit: Bill Saxton, NRAO/AUI/NSF; NASA, Hubble Heritage Team, (STScI/AURA), ESA, S. Beckwith (STScI). Additional Processing: Robert Gendler
Astronomers have been able to measure the magnetic field of a galaxy that lies nearly five billion lightyears from Earth.
The observations are helping scientists learn more about the nature and origin of magnetic fields, which affect how galaxies develop over time.
The astronomers used the Very Large Array telescope to study a star-forming galaxy that lies between Earth and a more distant quasar, 8 billion lightyears away.
They were able to use a technique called gravitational lensing, which involves using a massive object in space in order to study a more distant object.
The closer object is so massive that its gravity bends and warps space-time, like a giant cosmic lens.
In this case, the galaxy’s gravity spilt light travelling from the more distant quasar on its way to Earth, which astronomers observed as two separate images of the quasar.
“The polarization of the waves coming from the background quasar, combined with the fact that the waves producing the two lensed images traveled through different parts of the intervening galaxy, allowed us to learn some important facts about the galaxy’s magnetic field,” says Sui Ann Mao, Minerva Research Group Leader for the Max Planck Institute for Radio Astronomy.
The study is based on the fact that magnetic fields affect radio waves travelling through them.
By studying the two images of the quasar, the team could spot a difference in how the waves’ polarisation had changed.
This suggests that the different regions in the galaxy affected the waves coming from the quasar in different ways.
“The difference tells us that this galaxy has a large-scale, coherent magnetic field, similar to those we see in nearby galaxies in the present-day Universe,” Mao says.
A Hubble Space Telescope image of the galaxy and gravitationally-lensed images. Image Credit: Mao et al., NASA
“The similarity is both in the strength of the field and in its arrangement, with magnetic field lines twisted in spirals around the galaxy’s rotation axis.”
Further, since the galaxy is five billion lightyears away, astronomers are observing it as it existed five billion years ago, since that is how long it takes light from the galaxy to reach Earth.
These observations allow scientists to look back in time and learn more about how magnetic fields form and evolve over time.
“The results of our study support the idea that galaxy magnetic fields are generated by a rotating dynamo effect, similar to the process that produces the Sun’s magnetic field,” Mao says.
“However, there are other processes that might be producing the magnetic fields.
To determine which process is at work, we need to go still farther back in time – to more distant galaxies – and make similar measurements of their magnetic fields.”