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Composite image of the Whale Galaxy. (Jayanne English/University of Manitoba)

Breathtaking Image Shows Powerful Magnetic 'Ropes' Surrounding The Whale Galaxy

DAVID NIELD
2 JANUARY 2020

Sometimes you just have to stand back in awe at the beauty of the Universe – and that's absolutely the case with this image from the National Radio Astronomy Observatory (NRAO), which captures the side view of a spiral galaxy know as the Whale Galaxy.

 

But if you look closer, the stunning picture also shows something else: the magnetic 'ropes' around the edges of the galaxy's disc.

These filaments, like cosmic strands of hair, show the galaxy's magnetic field extending into its halo.

The green colouring shows filaments with their magnetic field pointing towards the viewer, with the blue colouring showing filaments with their magnetic field pointing away. This phenomenon has never before been directly observed in the halo of a galaxy.

"This is the first time that we have clearly detected what astronomers call large-scale, coherent, magnetic fields far in the halo of a spiral galaxy, with the field lines aligned in the same direction over distances of a thousand light-years," says astrophysicist Marita Krause, from the Max-Planck Institute for Radio Astronomy in Germany.

"We even see a regular pattern of this organised field changing direction."

Some 80,000 light-years across, the Whale Galaxy (also known as NGC 4631 or Caldwell 32), was studied using the Very Large Array radio telescope in New Mexico, and was found to have an unusually strong magnetic field.

 

Because this galaxy – some 25 million light-years away from Earth – is seen side-on from our planet, it's really useful for studying how gas, stars and magnetic fields extend beyond the plane of a galaxy. That side view is also what gives the galaxy its nickname, as it looks somewhat like a swimming whale from our point of view.

What astronomers have now seen here matches existing theoretical models of galaxy behaviour, and in particular the idea of galactic dynamos that can create spiralling magnetic fields in the halo, a continuation of the spiral arms in the galactic disc.

"We are a little bit like the blind men and the elephant, since each time we look at the galaxy in a different way we reach a different conclusion about its nature," says astrophysicist Richard Henriksen, from Queen's University in Canada.

The next stage is to work out how common these types of galactic magnetic fields are in the Universe, and to explore what other shapes they might take.

That in turn should improve our understanding of how galaxies develop magnetic fields in the first place, and how the motion of the celestial objects in a galaxy influence the magnetic field it generates.

Further down the line, astronomers want to figure out how the magnetic fields that stretch between galaxies work, and how they might influence the development of galaxies.

"To understand how stars like the Sun and planets like Earth came to be, we must understand how galaxies, such as our Milky Way, form and evolve," says astrophysicist Matthew Benacquista, from the National Science Foundation.

"This project is an attempt to measure galactic magnetic fields and learn how they influence the way that interstellar gases are ejected from galaxy discs and contribute to galaxy formation and evolution."

The research has been published in Astronomy & Astrophysics.