This could radically change our understanding of the gas conditions in the Milky Way.
According to Australian researchers, there may be invisible structures shaped like noodles, lasagna sheets, or hazelnuts lurking around in our galaxy. Dr. Keith Bannister, CSIRO astronomer and lead author of the paper released in Science, said these structures appear to be lumps in the thin gas between the stars.
“They could radically change ideas about this interstellar gas, which is the Galaxy's star recycling depot, housing material from old stars that will be refashioned into new ones,” Bannister said in a press release.
Amazingly, Bannister and his colleagues observed these lumps, allowing them to make the first estimate of their shape. These observations were made possible by an innovative new technique using CSIRO’s Compact Array telescope in eastern Australia.
These mysterious objects were hinted to exist 30 years ago when astronomers saw radio waves from a bright and distant galaxy called a quasar varying in strength. It turns out this varying strength was the work of an invisible atmosphere — a thin gas of electrically charged particles which fills the space between the stars.
“Lumps in this gas work like lenses, focusing and defocusing the radio waves, making them appear to strengthen and weaken over a period of days, weeks or months,” Bannister said. However, these lenses are so hard to find that researchers had given up looking for them.
Bannister and his colleagues soon realized they could find them using CSIRO’s Compact Array. They pointed the telescope at a quasar called PKS 1939-315 in the constellation Sagittarius, where they observed a lensing event that continued for one year.
Astronomers believe these lenses are about the size of Earth’s orbit around the sun, and lie approximately 3,000 light-years away, which is 1,000 times further than the nearest star, Proxima Centauri.
Until recently, astronomers really did not know anything about the shape of the lenses, however Bannister’s team has shown that they could be one of several different shapes. “We could be looking at a flat sheet, edge on,” CSIRO team member Dr. Cormac Reynolds said. “Or we might be looking down the barrel of a hollow cylinder like a noodle, or at a spherical shell like a hazelnut.”
Getting more observations will "definitely sort out the geometry," he said.
Since this lensing event occurred for over a year, Bannister and his team observed it with other radio and optical telescopes as well — techniques used to search for these invisible objects before the use of the Compact Array. The light from the quasar did not vary while the radio telescopes were pointed toward the lensing, meaning earlier optical surveys that looked for these dark lumps in space could not have found the one his team discovered.
So what exactly are these lenses? One theory is that they are cold clouds of gas that stayed together by the force of their own gravity. However, nobody actually knows how the invisible lenses form. “But these structures are real, and our observations are a big step forward in determining their size and shape,” Bannister said.