Messier 77 is a relatively nearby and well-known bright spiral galaxy with a supermassive black hole at its center.
Messier 77 concept by artist. It is characterized by its powerful black hole and accretion disk, as well as the polarized light of water masers located outside the Milky Way. Image credit: NSF / AUI / NRAO / S. Dagnello.
Messier 77 is a barred spiral galaxy located 62 million light-years away in the constellation Cetus.
Also known as NGC 1068, LEDA 10266, and Cetus A, it has an apparent magnitude of 9.6.
Messier 77 was discovered in 1780 by French astronomer Pierre Méchain, who initially identified it as a nebula. Méchain then relayed this discovery to his colleague, the French astronomer Charles Messier.
Messier believed that the extremely bright objects he saw were clusters of stars, but as technology advanced, their true status as a galaxy was recognized.
At 100,000 light-years in diameter, Messier 77 is one of the largest galaxies in the Messier catalog, and its gravity is enough to twist and distort other galaxies nearby.
It is also one of the closest galaxies to active galactic nuclei (AGNs).
These active galaxies are among the brightest objects in the universe, emitting light in many if not all wavelengths, from gamma rays and X-rays to microwaves and radio waves.
But Messier 77's accretion disk is hidden by a thick cloud of dust and gas, despite being a popular target for astronomers.
Several light-years in diameter, the outer accretion disk is dotted with hundreds of different water maser sources that have been hinting at deeper structures for decades.
Masers are clear beacons of electromagnetic radiation that shine at microwave or radio wavelengths. In radio astronomy, water masers, observed at a frequency of 22 GHz, are particularly useful because they can shine through many of the dusts and gases that block the wavelengths of light.
Bucknell University astronomer Jack Gallimore and his colleagues began observing Messier 77 with two goals in mind: astronomical mapping of the galaxy's radio continuum and measuring the polarization of water masers.
“Messier 77 is a bit of a VIP among active galaxies,” says Dr. CM Violette Impellizzeri, an astronomer at the Leiden Observatory.
“There's an accretion disk right next to the black hole, and it's unusually powerful. And because it's so close, it's been studied in great detail.”
But the study authors looked at Messier 77 in an entirely new way.
Their observations were recently upgraded High sensitivity array (HSA) consists of the Karl G. Jansky Very Large Array, the Very Long Baseline Array, and NSF's NRAO telescope at the Green Bank Telescope.
By measuring the water maser's polarization and the continuous radio emission from Messier 77, they reveal the compact radio source, now known as NGC 1068*, and the mysterious extended structure of the fainter emission. I created a map to
Mapping the astronomical distribution of galaxies and their water masers reveals that they are spread along structural filaments.
“These new observations reveal that the maser spot filaments are actually arranged like beads on a string,” Dr. Gallimore said.
“We were stunned to see that there was an apparent offset, or displacement angle, between the radio continuum, which describes the structure of the galaxy's core, and the position of the maser itself.”
“The configuration is unstable, so we're probably looking at a magnetically ejected source.”
Measuring the polarization of these water masers with HSA revealed significant evidence of a magnetic field.
“No one has ever seen polarization in water masers outside of our galaxy,” Dr. Gallimore said.
“Similar to the loop structures seen as prominences on the Sun's surface, the polarization patterns of these water masers clearly indicate that there is also a magnetic field at the root of these light-year-scale structures.”
“Looking at the filaments and making sure the polarization vector is perpendicular to the filaments is key to confirming that they are magnetically driven structures. It's exactly what you expected. It’s a thing.”
Previous studies of the region have suggested patterns, usually related to magnetic fields, but such conclusions were until recently beyond the scope of observational techniques.
The discovery reveals evidence for a compact central radio source (the galaxy's supermassive black hole), distinct polarization of water masers indicating structure within Messier 77's magnetic field, and spectacular extended signatures across the radio frequency continuum. It became.
Taken together, these findings indicate that magnetic fields are the underlying driving force for these phenomena.
However, many mysteries remain. For example, within the radio continuum map there is a diffuse, faint protrusion that the team has dubbed the foxtail foxtail, extending northward from the central region.
“When we set out on this, we said to ourselves, 'Let's really push the limits and see if we can get good continuum and polarization data,' and those goals were both It was a success,” Dr. Gallimore said.
“Using the NSF NRAO High Sensitivity Array, we detected the polarization of a water megamaser for the first time. We also created a very surprising continuum map, which we are still trying to understand.”
a paper The results will be explained today. Astrophysics Journal Letter.
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Jack F. Gallimore others. 2024. Discovery of polarized water vapor megamaser emission in molecular accretion disks. APJL 975, L9; doi: 10.3847/2041-8213/ad864f
Source: www.sci.news
