Galactic Puzzle: Faint ‘Threads’ Discovered in the Milky Way

A UCLA astronomer has discovered faint “threads” weaving their way through the center of the Milky Way galaxy that are more than 600 trillion miles long, opening a new page in astronomical research.

The “threads” have never been seen before and no one is certain what they are, where they came from or what they mean.

“It was quite unexpected,” says the astronomer, Mark Morris, who made the discovery with a colleague, Farhad Yusef-Zadeh of Columbia University.

“There is nothing known in the astrophysical realm that can account for them. It took awhile to convince ourselves that they are real,” Morris said.

But real they are, according to “radiographs” the two scientists produced with the Very Large Array, a giant radio telescope near Socorro, N.M. Radiographs are similar to photographs except that they use electromagnetic radiation emitted by the subject rather than visible light to produce pictures.

The “threads” are far too faint to reproduce in most publications. But they appear in the high-resolution graphs produced by the scientists as narrow, uniform threads arching across the center of the Milky Way.

“They look like streaks, and we wondered at first if they were photographic defects,” like scratches on a piece of film, Morris said in an interview. But when the “threads” showed up on radiographs produced with two different radio frequencies, the two scientists were convinced they had found something real.

But they aren’t sure just what that “something” is. At this point, they are more convinced of what the “threads” are not than of what they are.

One possibility that they have rejected is the suggestion that the “threads” are a “jet-like phenomena,” which is not at all rare in the universe.

“A lot of galactic nuclei send out jets of plasma that create enormous radio sources,” Morris said. “But the problem is, there is no source. These things meander through the galactic center and they don’t seem to be connected with anything. There’s nothing you can point to and say, ‘That’s the source.’ ”

“Another possibility,” he said, “is that shock fronts (like those produced by exploding stars) propagating through the interstellar medium would light up the region . . . and the edge of it would be the brightest.”

But if the threads are shock fronts, according to Morris, “you would expect to see them get broken up into little segments” by other forces in the galaxy. “Yet these are remarkably uniform,” extending more than 100 light years long, said Morris, a professor of astronomy at UCLA.

“So that’s not a viable hypothesis,” he concluded.

“The other possibility is that these are wakes of something moving through the interstellar medium, but you have a hard time coming up with a candidate (for some object large enough to have caused such a wake). So all those fairly reasonably are out,” Morris said.

So what are they?

The most likely explanation, Morris suggested, is that the threads are “hot radiating plasma that is flowing and confined by the magnetic field” of the galaxy.

But even then, the “threads” should not be as long as they are, according to Morris.

“I’m pretty convinced that’s what they are,” he added. “But I harbor a wild-eyed speculation independent of that. I’m wondering if these aren’t related to cosmic strings, defects in the fabric of space that were created in the very, very early universe.”

Morris and Yusef-Zadeh have been at the forefront of research on the galactic center, using the relatively young field of radio astronomy to look through the galactic dust that obscures the center from optical telescopes.

In 1984, they won wide recognition when they reported the first evidence of a large-scale magnetic field at the galactic center. They are publishing their latest findings in the current issue of the Astronomical Journal.

Nobody has ever seen “cosmic strings,” but their existence has been theorized. The theory is that the universe must have gone through a series of phases during its early history, and some of those phases should show up as “flaws.”

“It would be like if you were to suddenly freeze the ocean,” Morris said. “That would be a phase change. Yet there would have to be boundaries in that frozen ocean along which the crystalline structure didn’t match (because of differences in ocean salinity or other factors). Between those two boundaries there would have to be a wall, where the orientation of the crystals didn’t match.”

Similarly, according to Morris, “When you try to sew the parts of the universe together you find that you cannot do it neatly without these boundaries.”

Theoretically, those boundaries could show up as long “threads.”

If the “threads” are “cosmic strings,” it “could provide the answer to a lot of puzzles, like galaxy formation,” Morris said.