Mapping the Milky Way's magnetic field in 3D

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The celestial location of the surveyed area is about four square degrees. Left: full-sky map of dust emission Middle: zooming in on the surveyed regions, including a portion of the northern sky polar ring to the east of the map. Right: Close-up view of the surveyed area. The black areas indicate the polarization orientation from the stars in our survey. debt: Astronomy & Astrophysics (2024) DOI: 10.1051/0004-6361/202349015

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The celestial location of the surveyed area is about four square degrees. Left: full-sky map of dust emission Middle: zooming in on the surveyed regions, including a portion of the northern sky polar ring to the east of the map. Right: Close-up view of the surveyed area. The black areas indicate the polarization orientation from the stars in our survey. debt: Astronomy & Astrophysics (2024) DOI: 10.1051/0004-6361/202349015

We are all familiar with the concept of Earth's magnetic field. Most objects in space have magnetic fields, but measuring them is tricky. Astronomers have developed a unique way to measure the Milky Way's magnetic field using polarized light from interstellar dust grains that align themselves with magnetic field lines. A new survey has begun this mapping process and has mapped an area that covers an area 15 times the size of the full moon.

Many people remember experiments in school with iron filings and bar magnets to discover their magnetic field. Capturing the Milky Way's magnetic field is not so easy. The new method of measuring the field relies on tiny dust grains that penetrate the interstellar space.

The grains of dust are similar to smoke particles, but they are not spherical in shape. Like a boat turning itself into a current, the long axis of the dust particles tends to align with the local magnetic field. When they do, they emit a glow at the same frequency as the cosmic background radiation, which is what astronomers are tuning into.

The particles not only glow, but also absorb the starlight that passes through them, like polarizing filters. The polarization of light is well known to photographers, who can use polarizing filters to darken the sky and manage reflections. The phenomenon of polarization refers to the propagation of light. As it moves through a medium it carries energy from one place to another but along the way it exhibits wave-like properties.

Wave nature is made up of alternating displacements of the medium they travel through (imagine a wave in water). Displacement is not always the same as direction of travel; Sometimes it is parallel and other times perpendicular. In polarization, the displacement is in one direction only.

In interstellar particles, polarizing properties trap the magnetic field and polarize light traveling through them, revealing details of the magnetic field. As they are on Earth, magnetic field lines are critical to galactic evolution. They regulate star formation, shape the structure of a galaxy and, like giant interstellar rivers, shape and direct the flow of gas around the galaxy.

Researchers from the Inter-University Institute for High Energies in Belgium used the PASIPHAE survey – an international collaboration to study the magnetic field from polarization in interstellar dust – to start the process. They measured the polarity of more than 1,500 stars, covering an area of ​​the sky no more than 15 times the size of the full moon.

The team used data from the Gaia Astrometry satellite and a new algorithm to map the galaxy's magnetic fields in that region of the sky. Study is Published In the magazine Astronomy & Astrophysics.

This is the first time any large-scale project has attempted to map the Milky Way's gravitational field. It will take some time to complete the entire map, but once it is done it will provide better insight into not only the magnetic field of galaxies but also the evolution of galaxies throughout the universe.

More information:
V. A first-degree-scale starlight-polarization-based tomography map of the magnetized interstellar medium, Belgrims et al. Astronomy & Astrophysics (2024) DOI: 10.1051/0004-6361/202349015

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Astronomy & Astrophysics


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