Milky Way Humming with Microwave Mystery
A European space observatory has discovered something peculiar about our galaxy: it’s humming in microwaves and, for the moment, the source of the radiation is a complete mystery. Also, the Milky Way is home to previously unknown “islands” of cold carbon monoxide gas, helping astronomers uncover the distribution of star-forming regions.
The Planck space observatory was launched in 2009 to analyze small fluctuations in the ubiquitous cosmic microwave background (CMB) — complementing data gathered by NASA’s Wilkinson Microwave Anisotropy Probe. To understand the structure of the CMB is to open a window on the conditions immediately after the Big Bang. This extremely faint radiation is the ancient “echo” of the creation of the Universe over 14 billion years ago.
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However, Planck’s toolkit isn’t restricted to measuring ancient microwaves from the dawn of time, it is also building an all-sky map of our own galaxy. To remove the microwave radiation being emitted from the Milky Way, a very accurate survey of microwave sources within our cosmic backyard needs to be carried out.
And it is this survey that’s turning up some surprises.
On Monday, at an international conference in Bologna, Italy, Planck scientists have presented the intermediate results from the mission ahead of its first cosmological dataset expected to be released in 2013.
“The images reveal two exciting aspects of the galaxy in which we live,” said Planck scientist Krzysztof M. Gorski from NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and Warsaw University Observatory in Poland. “They show a haze around the center of the galaxy, and cold gas where we never saw it before.”
This microwave “haze” is being emitted from a region surrounding the Milky Way’s core. Usually, this kind of emission would be expected from regions that have experienced supernova activity. However, the microwaves detected have a “harder” spectrum, basically meaning the microwave emission is unusually energetic. When compared with the microwave radiation elsewhere in our galaxy, the galactic core’s emission is a real oddity.
What could possibly be generating this emission?
“Theories include higher numbers of supernovae, galactic winds and even the annihilation of dark-matter particles,” said Greg Dobler, Planck collaborator from the University of California in Santa Barbara, Calif.
The microwave emission appears to have the characteristics of synchrotron radiation, when particles emit energy as they interact with powerful magnetic fields. However, dark matter — the stuff that is thought to make up 83 percent of all the mass in our universe — could be the culprit.
Although dark matter often seems to be the “go-to” explanation for weird cosmic behavior, the annihilation of clouds of dark matter accumulating around the galactic core may generate the energy needed to explain this microwave phenomenon.
In addition to the microwave anomaly, Planck’s ability to survey the entire sky has resulted in a map of cold interstellar clouds of carbon monoxide (CO), shown above. Astronomers seek out the microwave emission associated with CO so that vast clouds of invisible hydrogen molecules may be revealed.
As molecular hydrogen is very difficult to detect (due to its low rate of emission), and CO undergoes similar formation processes (often found in the presence of molecular hydrogen), CO can be the ideal “tracer” to detect vast clouds of hydrogen. Molecular hydrogen is the fuel behind star formation processes, so the discovery of previously unknown clouds of carbon monoxide will undoubtedly improve our understanding of star birth in the Milky Way.
Probably the most fascinating thing about this research is that Planck was designed to look into the furthest reached of the Universe. To achieve this, radiation from our own galaxy needs to be removed. But far from this being an annoyance, the information gathered by looking at galactic microwave emissions may help us to understand the nature of our own galaxy on the way to revealing the true nature of the birth of our Universe.
Images: Top: All-sky image shows the distribution of the Galactic Haze seen by ESA’s Planck mission at microwave frequencies superimposed over the high-energy sky as seen by NASA’s Fermi Gamma-ray Space Telescope. Bottom: All-sky image shows the distribution of carbon monoxide (CO), a molecule used by astronomers to trace molecular clouds across the sky, as seen by Planck. Credits: ESA/Planck Collaboration