Scientists have long wondered exactly how spiral galaxies, like our Milky Way, get their shape. New observations of a distant galaxy are shedding light on that question. Researchers from the Stratospheric Observatory for Infrared Astronomy say that magnetic fields play a strong role in the shaping of these spiral galaxies.
The team says that magnetic fields are invisible, but may influence the evolution of a galaxy. The team points out that while scientists have a “pretty good understanding” of how gravity affects galactic structures, they are just starting to learn the role magnetic fields play. The magnetic field in spiral galaxies is aligned with the spiral arms across the entire galaxy, which is more than 24,000 light-years across.
The scientists measure magnetic fields along the arms of the spiral galaxy NGC 1068 or M77. The fields are shown as streamlines that closely follow the circling spiral arms. Magnetic field alignment with the star formation implies that gravitational forces that create the spiral shape are also compressing the magnetic field. The team notes that the alignment supports a leading theory of how arms are forced into their spiral shape known as “density wave theory.”
Galaxy M77 is 47 million light-years away from Earth in the constellation Cetus. It has an active supermassive black hole at its center said to be twice as active as the black hole at the center of the Milky Way galaxy. The arms of M77 are filled with dust, gas, and areas of intense star formation.
Using Infrared observations the team was able to determine that the magnetic fields closely follow the newborn-star-filled spiral arms. That closely supports the density wave theory. That theory suggests that gas and stars in the arms aren’t fixed in place like blades on a fan. Rather the material moves along the arms as gravity compresses it.