There is an unusual paradox of obstruction of the investigation into parts of the Milky way. Dense gas blocks of observations of the galactic nucleus, and may be difficult to observe in visible light from our point of view.
But distant galaxies are not always present the same obstacles. In a certain way, we can observe distant galaxies better than we can observe our own.
In order to obtain a better understanding of the galactic Center (GC) and the Interstellar Medium (ISM), a team of astronomers used a telescope called the Wisconsin H-Alpha Mapper (WHAM) to look at the core of the Milky way in the part of the optical spectrum of light.
The team of researchers focused their efforts on two features of the Milky way, called Bubble Fermi. The Bubbles from Fermi are enormous outbursts of high-energy gases that emanate from the galactic core.
They are called Bubbles from Fermi, because they were discovered in 2010 by the Fermi Gamma-Ray Space Telescope. These bubbles are huge, the extension of a total of around 50,000 light years from the disk of the Milky way, and traveling millions of miles per hour.
A document of the presentation of their observations is entitled “the Discovery of the High-Speed H-Alpha Above the Galactic Center: Testing Models of Fermi Bubble.” The main author of the work is Dhanesh Krishnarao, a graduate student in astronomy at the university of WISCONSIN, Wisconsin. The findings were presented at the 236th meeting of the American Astronomical Society, and have been presented to The Astrophysical Journal Letters.
Previous to this work, some observations of the Bubbles from Fermi were made in the UV, examining the light of distant quasars as it passed through the gas. While the observations extended to the scientists to the understanding of the bubbles, they had their limitations.
Could only be made in specific lines of vision, while WHAM is an all-sky telescope. The above observations cannot measure the speed, the temperature and the density of the gas.
But WHAM takes a different approach. As the name says, you can observe the Hydrogen-Alpha atoms. In H-Alpha atom, an electron has jumped from the third energy level to the second energy level. The leaves of a spectral line is the brightest spectral line of hydrogen in the optical light.
ABOVE: When an electron (green) jumps down an energy level from n=3 to n=2, it produces a photon with a bright spectral line in the visible light.
Matt Haffner is a Professor of Astronomy and Physics at Embry-Riddle Aeronautical University, and one of this document, the co-authors. In a press release, Haffner pointed out how the WHAM telescope is helping astronomers make progress in understanding the Milky way’s central region. Gas blocks our view of the region in a way that distant galaxies do not.
“There are regions of the galaxy in which we can target with sensitive instruments like WHAM to get this type of information to the center that previously we were only able to do in the infrared and radio,” says Haffner.
“We can make comparisons with other galaxies doing the same type of measures toward the center of the Milky way”.
The scientists behind this research also observed nitrogen emission lines in the Bubbles from Fermi. They stopped their observations and recent Hubble observations of the UV light in the same position, and combined.
In a press release, the main author Krishnarao said, “We have combined the two measurements of emission and absorption to estimate the density, the pressure and temperature of the ionized gas, and that allows us to better understand where this gas is coming from.”
In their study, the authors write “the Wisconsin H-Alpha Mapper (WHAM) observations reveal high-velocity H-alpha and [N II] λ6584 emission lines in the same direction and speed of absorption of uv of the line features that have previously been associated with the biconical gamma-ray lobes known as the Bubbles from Fermi.”
Astronomers think that what happened in the Milky way, essential to the creation of the Bubbles of Fermi, that happened several million years ago. Some researchers believe that the Sgr A*, the supermassive black hole at the center of the galaxy, drew a huge cloud of hydrogen within its accretion disk, causing a massive explosion of energy. But this study was not trying to determine the cause.
Now that researchers have data for the density, velocity and temperature of the gas of Fermi Bubbles, you can prove that the data with respect to the different models.
“The other important thing is that we now have the possibility of measuring the density and the pressure and velocity of the structure in many places,” with the all-sky WHAM telescope, says Bob Benjamin, a professor of astronomy at the university of WISCONSIN–Whitewater and co-author of the study.
“We can do an extensive mapping effort through the Bubbles of Fermi above and below the plane of the galaxy, to see if the models that have been developed are holding up. Because, unlike the ultraviolet data, we are not only limited to specific lines of sight.”
In their article, the authors explain that “These optical spectra to provide a new pathway to limit both the physical conditions of the ionized gas that has been associated with the Bubbles from Fermi, as well as the radiation field emerging from the Galactic Center of the region and within the Bubbles of Fermi.”
At the conclusion of their study, the authors describe some of their findings. They say that their findings indicate a gas temperature of 8900 ± 2700 K. it Is also pointed out that the high thermal pressure that was found is “comparable, but still higher than those predicted by the models of a halo of hot gas in the inner Galaxy or of a Fermi Bubble shell”.
But in spite of these findings are very detailed, they do not conclusively show what caused the Bubbles from Fermi. The team says that WHAM has more to give when it comes to study of them, however. And as in this study, future observations can also be combined with the Hubble observations to broaden our understanding.
“With the future of the observations, WHAM can make the monitoring of emission associated with the Bubbles from Fermi, both spatially and kinematically to the large scales. In addition, other pointed observations towards distant UV-bright sources in existing HST spectra can provide sensitive columndensity profiles of several species across different regions of the south and north Bubbles from Fermi.”
Well, maybe one day they’ll finally know what happened a few million years ago in the center of the Milky way to form these giant bubbles.
This article was originally published by Universe Today. Read the original article.