A faint red glow at the central bar region of the Milky Way has been detected for the first time by scientists on Earth.  While the actual source of the “flag” is still under speculation, astronomers say it may provide an insight into the driving force of the galaxy’s spiral nature.
It was detected using the WHAM (Wisconsin H-Alpha Mapper), a telescope located in Chile, and while it’s just barely visible from this part of the universe, the discovering team believes it may be a sign of ionized hydrogen gas emitted from the formation of new stars. Details of their findings were published in the journal Science Advances. 
The glow had first appeared to be a moving object, but further observation revealed it was a tight cluster of ionized gases. By analyzing other colors coming from the emission of nitrogen and hydrogen, the researchers were able to pinpoint the source. They subsequently named the glow the Tilted Disk, since it appears close to the nucleus of the galaxy and seems tilted compared to the rest of it.
According to co-author Dr. Lawrence Haffner of Embry-Riddle Aeronautical University, Florida: “Without an ongoing source of energy, free electrons usually find each other and recombine to return to a neutral state in a relatively short amount of time. ‘Being able to see ionized gas in new ways should help us discover the kinds of sources that could be responsible for keeping all that gas energized.”
Now nicknamed “The Red Flag”
The Tilted Disk was first spotted when Haffner’s colleague, Professor Bob Benjamin of the University of Wisconsin-Whitewater, was analyzing over twenty years’ worth of data from WHAM recordings. The configuration of the flag couldn’t be explained by any known physical laws or phenomena. Scientists believe it’s moving toward our planet because it was found on an elliptical orbit interior to the Milky Way’s spiral arm.
“Being able to make these measurements in optical light allowed us to compare the nucleus of the Milky Way to other galaxies much more easily,” Dr. Haffner said. “Many past studies have measured the quantity and quality of ionized gas from the centers of thousands of spiral galaxies throughout the universe. For the first time, we were able to directly compare measurements from our galaxy to that large population.”
To determine exactly how much gas makes up the Tilted Disk, Lead author Dhanesh Krishnarao, a graduate student at the University of Wisconsin-Madison, used an existing model to predict the parameters until he arrived at an approximate 3D representation.
Scientists have always known about the presence of non-ionized gases in the central bar region, and this makes the appearance of the red flag a true novelty at best.
“Close to the nucleus of the Milky Way,” Mr. Krishnarao explained. “Gas is ionized by newly forming stars, but as you move further away from the center, things get more extreme, and the gas becomes similar to a class of galaxies called LINERs, or low ionization (nuclear) emission regions.”
It could lead to a better understanding of our galaxy, the Milky Way
Previous reports estimate that roughly a third of all known galaxies in their samples are classified as LINERs. The Milky Way is a LINER-type galaxy, and they are characterized by centers with more radiation than galaxies where stars are still beginning to form. They are also known to have less radiation than galaxies whose supermassive black holes are consuming enormous amounts of material.
“Before this discovery by WHAM, the Andromeda Galaxy was the closest LINER spiral to us,” said Dr. Haffner. “But it’s still millions of light-years away. With the nucleus of the Milky Way only tens of thousands of light-years away, we can now study a LINER region in more detail. Studying this extended ionized gas should help us learn more about the current and past environment in the center of our Galaxy.”
The researchers plan to use this discovery to analyze the source of energy at the center of the Milky Way.
“In the next few years, we hope to build WHAM’s successor, which would give us a sharper view of the gas we study,” Dr. Haffner said. “Right now, our map `pixels’ are twice the size of the full moon. WHAM has been a great tool for producing the first all-sky survey of this gas, but we’re hungry for more details now.”
- “Scientific ‘red flag’ reveals new clues about our galaxy.” Science Daily. Retrieved July 6, 2020.
- “Discovery of Diffuse Optical Emission Lines from the Inner Galaxy.” Science Mag. Krishnarao et al. Retrieved July 6, 2020.