Scientists discover mysterious cosmic filaments at the heart of Milky Way galaxy

"It was a surprise to suddenly find a new population of structures that seem to be pointing in the direction of the black hole."
Mrigakshi Dixit
Two populations of filaments, perpendicular and parallel to the galactic plane, which runs horizontally.
Two populations of filaments, perpendicular and parallel to the galactic plane, which runs horizontally.

Farhad Yusef-Zadeh 

Farhad Yusef-Zadeh, an astrophysicist, has studied mysterious filament-like structures at the heart of the Milky Way galaxy since 1984. 

These massive cosmic filaments come from the cosmic monster Sagittarius A*, a supermassive black hole at the center of our galaxy.

While studying them, Yusef-Zadeh and colleagues discovered an entirely new population of these cosmic filaments. 

"It was a surprise to suddenly find a new population of structures that seem to be pointing in the direction of the black hole," said Yusef-Zadeh of Northwestern University in a statement

The discovery of new cosmic threads

In 1984, what Yusef-Zadeh discovered was a long, one-dimensional filaments dangling vertically near the black hole.

The newly identified filament population appears much shorter and spreads out horizontally or radially from the black hole. Vertical filaments can reach 150 light-year heights, while horizontal filaments resemble "dots and dashes of Morse code."

The South African Radio Astronomy Observatory's (SARAO) MeerKAT telescope, which has enhanced radio astronomy capabilities, identified the new population. The team was studying known vertical filaments when this new population was spotted in the data.  

"We found that these filaments are not random but appear to be tied to the outflow of our black hole. By studying them, we could learn more about the black hole’s spin and accretion disk orientation. It is satisfying when one finds order in a middle of a chaotic field of the nucleus of our galaxy,” added Yusef-Zadeh. 

The team estimates that the newly found filaments are about 6 million years old.

The differences between the two populations 

Aside from being vertical and horizontal to the galactic plane, the filaments exhibit some unique properties. 

In comparison to magnetized vertical filaments, the newly discovered horizontal filaments emit thermal radiation. Vertical filaments accelerate particles at close to the speed of light. Horizontal filaments, on the other hand, "accelerate thermal material in a molecular cloud."

Horizontal filaments are only 5 to 10 light-years long when compared to vertical filaments, which are relatively longer. Vertical filaments wrap around the galaxy's nucleus, while horizontal threads extend only to one side, pointing toward the black hole. 

The authors state that there are still many unknowns regarding the newly identified population, including the origin. “We think they must have originated with some kind of outflow from an activity that happened a few million years ago. It seems to be the result of an interaction of that outflowing material with objects near it," said Yusef-Zadeh.

Yusef-Zadeh concluded by saying: "Our work is never complete. We always need to make new observations and continually challenge our ideas and tighten up our analysis.”

The research results have been published in The Astrophysical Journal Letters.

Study abstract:

We have examined the distribution of the position angle (PA) of the Galactic center filaments with lengths L > 66'' and <66'' as well as their length distribution as a function of PA. We find bimodal PA distributions of the filaments, and long and short populations of radio filaments. Our PA study shows the evidence for a distinct population of short filaments with PA close to the Galactic plane. Mainly thermal, short-radio filaments (<66'') have PAs concentrated close to the Galactic plane within 60° < PA < 120°. Remarkably, the short filament PAs are radial with respect to the Galactic center at l < 0° and extend in the direction toward Sgr A*. On a smaller scale, the prominent Sgr E H ii complex G358.7-0.0 provides a vivid example of the nearly radial distribution of short filaments. The bimodal PA distribution suggests a different origin for two distinct filament populations. We argue that the alignment of the short-filament population results from the ram pressure of a degree-scale outflow from Sgr A* that exceeds the internal filament pressure, and aligns them along the Galactic plane. The ram pressure is estimated to be 2 × 106 cm−3 K at a distance of 300 pc, requiring biconical mass outflow rate 10−4M⊙ yr−1 with an opening angle of ∼40°. This outflow aligns not only the magnetized filaments along the Galactic plane but also accelerates thermal material associated with embedded or partially embedded clouds. This places an estimate of ∼6 Myr as the age of the outflow.

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