To determine the amount of energy or radiation at the center of the Milky Way, the researchers had to look through a galaxy full of more than 200 billion stars and home to dark patches of dust and interstellar gas. University of Wisconsin-Whitewater professor Bob Benjamin, a leading expert on the structure of stars and gas in the Milky Way, was looking at the value of two decades of data when he saw a scientific red flag, a peculiar shape that protruded from The dark and dusty center of the Milky Way ripples with highly energized ionized hydrogen moving toward Earth.
The rarity was ionized hydrogen gas, which appears in red when captured through the Wisconsin H-Alpha Mapper (WHAM), a Chile-based telescope that was used for the team’s latest study. The WHAM group is studying an important component of the interstellar medium (ISM) in our own Milky Way: where does the energy produced in the star-forming regions of our galaxy go?
Knowing how much energy permeates the center of the Milky Way, a discovery published in the July 3 issue of the journal Science Advances, could provide new clues to the fundamental source of our galaxy’s power, said L. Matthew Haffner of the University Embry-Riddle Aeronautics. .
A new image at the top of the page shows the violent center of the Milky Way spanning a distance of more than 600 light years, revealing details within the dense swirls of gas and dust in high resolution, opening the door for future research. about how massive stars are forming and what is fueling the supermassive black hole at the core of our galaxy.
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The position of the feature, known to scientists as the “Tilted Disk” because it appears to be tilted compared to the rest of the Milky Way, could not be explained by physical phenomena known as galactic rotation. The team had a rare opportunity to study the protruding Incline Disc, a portion behind the Baade Window, a hole in the thick dust near the Galactic center with one of the few lines of sight that is not obscured by dust. In the image below, the region surrounding the bright globular cluster, NGC6522 (center), is surrounded by dark streets of dark dust.
Freed from its usual irregular dust cover, by using optical light, the tilted disk can be studied with radio or infrared light techniques, which allow researchers to make observations through the dust, but limit their ability to learn more about the ionized gas.
“Being able to make these measurements with optical light allowed us to compare the Milky Way nucleus with other galaxies much more easily,” said Haffner. “Many previous studies have measured the quantity and quality of ionized gas at the centers of thousands of spiral galaxies throughout the universe. For the first time, we were able to directly compare the measurements of our galaxy with that large population. “
Optical image of the Milky Way in relation to the Hα emission line associated with the inclined disk. (Axel Mellinger)
Krishnarao took advantage of an existing model to try to predict how much ionized gas should be in the emitting region that had caught Benjamin’s attention. Raw data from the WHAM telescope allowed him to refine his predictions until the team had an accurate three-dimensional image of the structure. Comparing other colors of visible light from hydrogen, nitrogen, and oxygen within the structure gave the researchers more clues about its composition and properties.
At least 48 percent of the hydrogen gas in the inclined disk in the center of the Milky Way has been ionized by an unknown source, the team reported. “The Milky Way can now be used to better understand its nature,” said Krishnarao.
The gaseous and ionized structure changes as it moves away from the center of the Milky Way, the researchers reported. Previously, scientists only knew about the neutral (non-ionized) gas located in that region.
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“Near the core of the Milky Way,” explained astronomer “DK” Krishnarao, “the gas is ionized by the newly formed stars, but as you move away from the center, things become more extreme and the gas becomes similar. to a class of galaxies called LINER, or regions of low (nuclear) ionization. “
The researchers found that the structure seemed to move toward Earth because it was in an elliptical orbit inside the spiral arms of the Milky Way.
LINER-type galaxies, such as the Milky Way, account for about a third of all galaxies. They have centers with more radiation than galaxies that are only forming new stars, but less radiation than those whose supermassive black holes are actively consuming a tremendous amount of material.
“Before this WHAM discovery, the Andromeda galaxy was the closest LINER spiral to us,” said Haffner. “But it is still millions of light years away. With the core of the Milky Way just 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 at the center of our galaxy. “
Next, researchers must discover the energy source at the center of the Milky Way. Being able to classify the galaxy based on its radiation level was an important first step toward that goal.
Now that Haffner has joined Embry-Riddle’s growing Astronomy and Astrophysics program, he and his colleague Edwin Mierkiewicz, an associate professor of physics, have big plans. “In the coming years, we hope to build WHAM’s successor, which would give us a clearer picture of the gas we are studying,” said Haffner. “Right now, our map ‘pixels’ are twice the size of the full moon. WHAM has been a great tool in producing the first sky-wide study of this gas, but now we are hungry for more details. “
In separate research, Haffner and colleagues reported earlier this month on the first visible light measurements of “Fermi Bubbles,” mysterious columns of light that swell from the center of the Milky Way. That work was presented at the American Astronomical Society.
More information: D. Krishnarao el al., “Discovery of diffuse optical emission lines from the inner galaxy: evidence of gas similar to LI (N) ER”, Science Advances (2020). advance.sciencemag.org/lookup
The Daily Galaxy, Sam Cabot, via Embry-Riddle Aeronautical University and Harvard University
Image credit: Optical Milky Way image. Credit: Axel Mellinger
