To determine the amount of energy or radiation at the center of the Milky Way, the researchers had to travel through a galaxy filled with more than 200 billion stars and harboring dark patches of dust and interstellar gases. Professor Bob Benjamin of the University of Wisconsin and Whitewater – a leading expert on the structure of stars and gas in the Milky Way – examining the value of two decades of data when he spotted a scientific red flag – a peculiar form emerging from the Dark and dusty center of the Milky Way undulates highly energized ionized hydrogen moving towards the Earth.
The curiosity was ionized hydrogen gas, which appears red when captured by 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 the energy produced in the star-forming regions of our Galaxy goes.
Knowing the amount of energy that permeates the center of the Milky Way – a discovery reported in the July 3 edition of the journal Science Advances – could provide new clues to the fundamental source of power in our galaxy, said L Matthew Haffner of Embry-Riddle Aeronautical University.
A new image at the top of the page shows the violent center of the Milky Way over a distance of more than 600 light years, revealing details in the dense vortices of gas and dust in high resolution, opening the door to future research. on how massive stars are formed and what fuels the supermassive black hole at the heart of our galaxy.
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The position of the function – known to scientists as the “tilted disc” because it appears tilted relative to the rest of the Milky Way – could not be explained by known physical phenomena such as galactic rotation. The team had a rare opportunity to study the protruding tilted disc, a part 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 hidden by dust. In the image below, the region around the bright globular cluster, NGC6522 (center), is surrounded by dark bands of obscuring dust.
Freed from its usual uneven dust cover, using optical light, the tilted disc can be studied with infrared or radio light techniques, which allow researchers to make observations through the dust, but limit their ability to know more on ionized gas.
“Being able to take these measurements in optical light made it much easier to compare the nucleus of the Milky Way with other galaxies,” said Haffner. “Many previous studies have measured the quantity and quality of ionized gas from the centers of thousands of spiral galaxies across the universe. For the first time, we were able to directly compare the measurements of our galaxy to this large population. ”
Optical image of the milky way with an Hα emission line ratio associated with the inclined disc. (Axel Mellinger)
Krishnarao used an existing model to try to predict the amount of ionized gas that should be in the emitting region that had caught Benjamin’s attention. The raw data from the WHAM telescope allowed it to refine its forecasts until the team had an accurate 3D image of the structure. Comparison of other visible light colors from hydrogen, nitrogen and oxygen in the structure gave researchers new clues to its composition and properties.
The team reported that at least 48% of the hydrogen gas contained in the tilted disc in the center of the Milky Way was ionized by an unknown source. “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, researchers have reported. Previously, scientists only knew the neutral gas (non-ionized) located in this region.
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“Near the nucleus of the Milky Way,” said astronomer “DK” Krishnarao, “the gas is ionized by the newly formed stars, but when you move away from the center, things get more extreme and the gas becomes similar to a class of galaxies called LINER, or regions with low ionic emission (nuclear). ”
Researchers discovered that the structure appeared to be moving 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 represent about a third of all galaxies. They have centers with more radiation than galaxies which form only new stars, but less radiation than those whose supermassive black holes actively consume an enormous amount of matter.
“Before this discovery by WHAM, the Andromeda galaxy was the closest LINER spiral to us,” said Haffner. “But there are still millions of light years left. 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. The study of this extended ionized gas should help us to know more about the current and past environment in the center of our galaxy. ”
Next, the researchers will need to determine the energy source at the center of the Milky Way. Being able to classify the galaxy according to its radiation level was an important first step towards this goal.
Now that Haffner has joined Embry-Riddle’s growing program in Astronomy and Astrophysics, he and his colleague Edwin Mierkiewicz, associate professor of physics, have big plans. “Over the next few years, we hope to build the successor to WHAM, which would give us a more precise view of the gas we are studying,” said Haffner. “Right now, our map“ pixels ”are twice the size of the full moon. The WHAM was an excellent tool for producing the first aerial study of this gas, but we now need more details. ”
In separate research, Haffner and colleagues reported earlier this month the very first visible light measurements of “Fermi Bubbles” – mysterious plumes of light that protrude from the center of the Milky Way. This work has been presented to the American Astronomical Society.
More information: D. Krishnarao el al., “Discovery of diffuse optical emission lines of the interior galaxy: proofs of gas LI (N) ER”, Science Advances (2020). avances.sciencemag.org/lookup
Le Daily Galaxy, Sam Cabot, via Embry-Riddle Aeronautical University et Harvard University
Image credit: Image Optical Milky Way. Credit: Axel Mellinger