Galaxies are classified, according to their shape, into three main types : spiral galaxies, like ours; lenticular galaxies, shaped like a disc; and irregular galaxies, which do not respond to any kind of defined shape.
The reason for the elegant spiral shape with long arms that our galaxy, the Milky Way, has is a mystery that has haunted the heads of scientists for decades. But the Space Research Universities Association (URSA) published new observations in late 2019 that shed light on how spiral galaxies take their shape.
One of the elements that plays a fundamental role in the shape of galaxies, in addition to gravity (the latter, more studied), is the magnetic field, an element from which astronomers are learning new data .
“Magnetic fields are invisible, but they can influence the evolution of a galaxy,” as Enrique López-Rodríguez, a USRA scientist at NASA’s SOFIA Science Center, in Silocon Valley, California, explains. “We have a good understanding. of how gravity affects galactic structures, but now we are beginning to understand the role that magnetic fields play, ”he continues.
Image: NASA / SOFIA; NASA / JPL-Caltech / Roma Tre Univ.
The galaxy in the photograph illustrated in this article is called M77 , located 47 million light-years away in the constellation Cetus. It has a supermassive active black hole at its center that is twice the size of Sagittarius A, the black hole at the heart of the Milky Way. The rotating arms are filled with dust, gas, and areas of intense star formation called starbursts.
As we mentioned, magnetic fields are invisible, but SOFIA’s infrared observations revealed what human eyes cannot.
By measuring magnetic fields across the 24,000 light-years in diameter of the M77 galaxy, astronomers observed that these magnetic fields are aligned with its spiral arms , filled with newborn stars. This means that the gravitational forces that created the spiral shape are also compressing the magnetic field.
The researchers’ hypothesis is that the arms of the galaxy are “forced” to bend in their spiral shape due to what is known as the “density wave theory”.
Density wave theory
Density Wave Theory states that the dust, gas, and stars in the arms of a spiral galaxy are not fixed in place, as the blades of a fan would be. Instead, the material moves along the arms as gravity compresses it , much like the elements on a conveyor belt would.
According to the researchers published in a press release prepared by the URA, this is the first time that we have seen magnetic fields aligned with the birth of stars in the spiral arms of a galaxy on such large scales. The results were published in the Astrophysical Journal .
The SOFIA space telescope’s ability is essential for detecting other “invisible” magnetic fields. The hope of astronomers is that, in the future, similar observations will help to understand how galaxies of other types, such as the unknown irregular galaxies, form.
Reference:
“ SOFIA / HAWC + Traces the Magnetic Fields in NGC 1068 ” E. Lopez-Rodriguez et al., 2019, to appear in the Astrophysical Journal, arxiv.org/abs/1907.06648
