Herschel scans hidden Milky Way

By Jonathan Amos
Science reporter, BBC News

Herschel trains two eyes, Pacs and Spire, on our Galaxy's centre Enlarge Image

A remarkable view of our Galaxy has been obtained by Europe's billion-euro Herschel Space Observatory.

The telescope was put in a special scanning mode to map a patch of sky.

The images reveal in exquisite detail the dense, contorted clouds of cold gas that are collapsing in on themselves to form new stars.

Herschel, which has the largest mirror ever put on an orbiting telescope, was launched in May as a flagship mission of the European Space Agency.

It is tuned to see far-infrared wavelengths of light and is expected to give astronomers significant insights into some of the fundamental processes that shape the cosmos.

Herschel's great advantage is that its sensitivity allows it to see things that are beyond the vision of other space telescopes, such as Hubble.

A prime goal is to understand the mechanisms that control the earliest phases of stellar evolution.

Rich data return

Herschel's special scanning mode means it has to shift its gaze back and forth across an area of sky, which in this case was about 16 times as big as the size of the Moon as viewed from Earth.

HERSCHEL SPACE TELESCOPE The observatory is tuned to see the Universe in the far-infrared Its 3.5m diameter mirror is the largest ever flown in space Herschel can probe clouds of gas and dust to see stars being born It will investigate how galaxies have evolved through time The mission will end when its helium refrigerant boils off

The telescope was looking towards the plane of our Milky Way Galaxy, in the direction of the Southern Cross constellation.

The scanning mode works with two of Herschel's three instruments operating in tandem.

The UK-led Spire camera responds to longer wavelengths of light (250-500 microns - that is about 500-1,000 times longer than the wavelengths of light we detect with our eyes).

The German-led Pacs camera covers shorter wavelengths (70-170 microns).

Their pictures reveal a chaotic scene of gas and dust, and stars in all stages of development.

The material being observed is very cold - typically less than minus 170C (100 kelvin).

Anomaly investigation

Scientists say the images are information-rich.

"Our wavelength coverage is telling us details about the physics," explained Professor Matt Griffin, of Cardiff University, who is the Spire principal investigator.

"Spire is particularly good at seeing the cold and extended material which might correspond, for instance, to the earliest stages of star formation.

"Pacs is slightly more sensitive to what we would call warmer material, although by any normal standards it is still extremely cold; and that material might be closer to regions where stars have already formed and have been heated up by the young stellar objects."

Herschel intends to study large regions of the Milky Way in its combined Spire-Pacs scanning mode. The instruments will, of course, also work independently.

The mission is due to go into routine operations in the next few weeks. However, its third instrument is currently down after experiencing a fault.

Engineers can switch to a back-up system to reactivate the Heterodyne Instrument for the Far Infrared (HiFi), but they do not intend to do that until they have satisfied themselves the cause of the anomaly is properly understood.

The Dutch-led HiFi is a spectrometer that will identify elements and molecules in the clouds of gas and dust which give rise to stars.

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