“Milky Way’s X-Ray Thread” — Hints at a Previously Unknown Violent Phenomenon

 

Milky Way Center

 

A new map reveals the extremely violent center of our Milky Way Galaxy. New research and images by University of Massachusetts Amherst astronomer Daniel Wang reveals, with unprecedented clarity, an X-ray thread, G0.17-0.41, which hints at a previously unknown interstellar mechanism that may govern the energy flow and potentially the evolution of the Milky Way.

“The galaxy is like an ecosystem,” says Wang, whose findings are a result of more than two decades of research. “We know the centers of galaxies are where the action is and play an enormous role in their evolution.” 

The Milky Way’s Opaque Center

And yet, whatever has happened in the center of our own galaxy is hard to study, despite its relative proximity to Earth, because, as Wang explains, it is obscured by a dense,  opaque fog of gas and dust. Researchers simply can’t see the center, even with an instrument as powerful as the famous Hubble Space Telescope. 

Wang, however, has used a different telescope, NASA’s Chandra X-Ray Observatory, capable of penetrating the obscuring fog—and the results shown at the top of the page are stunning.

 

 

Wang’s findings, supported by NASA, give the clearest picture yet of a pair of X-ray-emitting plumes that are emerging from the region near the massive black hole lying at the center of our galaxy. 

Only the Tip of the Reconnection Iceberg

Even more intriguing is the discovery of an X-ray thread called G0.17-0.41 (below), located near the southern plume. “This thread reveals a new phenomenon,” says Wang. “This is evidence of an ongoing magnetic field reconnection event.” The thread, writes Wang, probably represents “only the tip of the reconnection iceberg.”

 

X-Ray Thread

A Hyper-Violent Event

A magnetic field reconnection event is what happens when two opposing magnetic fields are forced together and combine with one another, releasing an enormous amount of energy. 

Story of the Milky Way’s Fermi Bubbles –“As Large as the Galaxy Itself”

“It’s a violent process,” says Wang, and is known to be responsible for such well-known phenomena as solar flares, which produce space weather powerful enough to disrupt power grids and communications systems here on Earth. They also produce the spectacular Northern Lights. Scientists now think that magnetic reconnection also occurs in interstellar space and tends to take place at the outer boundaries of the expanding plumes driven out of our galaxy’s center.

The Strange Events at Our Milky Way’s Supermassive Black Hole

In an email, The Daily Galaxy asked Professor Wang about the durations of these magnetic reconnections. He responded, “Reconnection events are like solar flares. They come and go, just on much longer time scales because of the much greater physical scales.” Wang added, “One may estimate the age (or sound crossing time) of the thread from its length, which is on the order of 10^4 years.”

The Daily Galaxy also asked Professor Wang about the relationship between these X-ray threads, the supermassive black hole Sgr A*, and the large Fermi Bubbles of gamma-rays within the central regions of our Milky Way. Wang replied in an email, “Gamma-ray-emitting particles in the Fermi Bubbles could be accelerated by reconnection events. Magnetic fields could also largely be responsible for the energy transport from the central region of the Galaxy. The magnetic energy does not have to be directly related to any eruption from Sgr A*.”

Known Unknowns

It is still unknown how these magnetic reconnection events affect the central regions of our Milky Way, “What is the total amount of energy outflow at the center of the galaxy? How is it produced and transported? And how does it regulate the galactic ecosystem?” asks Wang.

These, says Wang, are the fundamental questions whose answers will help to unlock the history of our galaxy. Though much work remains to be done, Wang’s new map points the way. 

Source: Q Daniel Wang, Chandra large-scale mapping of the Galactic Centre: probing high-energy structures around the central molecular zone, Monthly Notices of the Royal Astronomical Society (2021). DOI: 10.1093/mnras/stab801

The Daily Galaxy, Maxwell Moe, astrophysicist, NASA Einstein Fellow, University of Arizona via U Mass Amherst and Daniel Wang.

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