Planck steps closer to the cosmic blueprint

New images from the mission show previously undiscovered islands of star formation and a mysterious haze of microwave emissions in the Milky Way.
By | Published: February 13, 2012 | Last updated on May 18, 2023
This all-sky image shows the distribution of carbon monoxide, a molecule used by astronomers to trace molecular clouds across the sky, as seen by Planck.
ESA/Planck Collaboration

The European Space Agency’s (ESA) Planck mission has revealed that our galaxy contains previously undiscovered islands of cold gas and a mysterious haze of microwaves. These results give scientists new treasure to mine and take them closer to revealing the blueprint of cosmic structure.

These results include the first map of carbon monoxide to cover the entire sky. Carbon monoxide is a constituent of the cold clouds that populate the Milky Way and other galaxies. Predominantly made of hydrogen molecules, these clouds provide the reservoirs from which stars are born.

However, hydrogen molecules are difficult to detect because they do not readily emit radiation. Carbon monoxide forms under similar conditions, and, even though it is much rarer, it emits light more readily and is therefore more easily detectable. So, astronomers use it to trace the clouds of hydrogen.

“Planck turns out to be an excellent detector of carbon monoxide across the entire sky,” said Planck collaborator Jonathan Aumont from the Institut d’Astrophysique Spatiale, Universite Paris XI, Orsay, France.

Surveys of carbon monoxide undertaken with radio telescopes on the ground are extremely time-consuming, so they are limited to portions of the sky where molecular clouds are already known or expected to exist.

“The great advantage of Planck is that it scans the whole sky, allowing us to detect concentrations of molecular gas where we didn’t expect to find them,” said Aumont.

This all-sky image shows the spatial distribution over the whole sky of the galactic haze at 30 and 44 GHz, extracted from the Planck observations. In addition to this component, other foreground components such as charged particles accelerated radially, known as synchrotron radiation, thermal dust, spinning dust, and extragalactic point sources contribute to the total emission detected by Planck at these frequencies. The galactic haze is the infinity-like symbol seen around the galactic center.
ESA/Planck Collaboration

Planck also has detected a mysterious haze of microwaves that presently defies explanation.

It comes from the region surrounding the galactic center and looks like a form of energy called synchrotron emission. This is produced when electrons pass through magnetic fields after having been accelerated by supernova explosions.

The curiosity is that the synchrotron emission associated with the galactic haze exhibits different characteristics from the synchrotron emission seen elsewhere in the Milky Way.

The galactic haze shows what astronomers call a “harder” spectrum: Its emission does not decline as rapidly with increasing energies.

Several explanations have been proposed for this unusual behavior, including higher supernova rates, galactic winds, and even the annihilation of dark matter particles.

So far, none of them has been confirmed.

“The results achieved thus far by Planck on the galactic haze and on the carbon monoxide distribution provide us with a fresh view on some interesting processes taking place in our galaxy,” said Jan Tauber, ESA’s project scientist for Planck.

Planck’s primary goal is to observe the cosmic microwave background (CMB), the relic radiation from the Big Bang, and to measure its encoded information about the constituents of the universe and the origin of cosmic structure.

But the CMB can only be reached once all sources of foreground emission, such as the galactic haze and the carbon monoxide signals, have been identified and removed.

“The lengthy and delicate task of foreground removal provides us with prime datasets that are shedding new light on hot topics in galactic and extragalactic astronomy alike,” said Tauber. “We look forward to characterizing all foregrounds and then being able to reveal the CMB in unprecedented detail.”

Planck’s first cosmological dataset is expected to be released in 2013.