Starbirth captured by Herschel

In mid-December, astronomers working on the Herschel Space Telescope met in Madrid to discuss the initial results from the European Space Agency's far-infrared and sub-mm space telescope. These are the first scientific results to emerge from the mission, and have demonstrated the huge range of scientific discoveries which will be possible over the next few years.

In particular, Herschel has imaged regions in which stars are being born, of which a few examples are shown in the images below. When seen in optical light, for example by the Hubble Space Telescope, these regions are masked by dark clouds of gas and dust and don't shine themselves. However when viewed in infrared light, the regions where stars are forming are seen to shine like Christmas tree lights, heating up the surrounding gas and dust and showing us these regions in more detail than we've seen before. Observations like these will help drive the theories of how our solar system came to be the way it is.

The full complement of presentations given at the meeting can now be seen online at the Herschel Science Centre Website. The end of the Science Demonstration Phase marks the transition from the calibration and testing phase of the mission to the routine science operations.

More images and results from the Science Demonstration Phase are available here.

SPIRE and PACS three-colour image of star formation region on the outskirts of the Rosette Nebula
Image of the outskirts of the Rosetta Nebula, made from SPIRE and PACS data. The tiny red dots are all dense clouds of dust which are forming new stars. Image credit: ESA/Herschel/HOBYS Key Project

This view shows the outskirts of the Rosette Nebula, a cloud of gas and dust around 5000 light-years away towards the constellation of Monoceros. The image is made from data from both the PACS and SPIRE instruments, and uses three different wavelengths: 70 microns (blue) and 160 microns (green) from PACS, and 250 microns (red) from SPIRE. Warmer gas and dust show up as blue, while colder material appears green and red. Embedded in the nebula are billowing pillars of gas and dust, with incredibly complex structures.

Some massive, very bright stars have recently formed just out of shot to the right. These have blown a hole in the gas, forming the appearance of a breaking wave in the picture. Just above the centre, and also towards the top left of the image, small collections of reddish dots can be seen, showing where the cold material has collapsed into a much denser ball due to gravity.

Each one is a pre-stellar core, about to form a star like our Sun. The gas and dust which doesn't become part of the star will form a disc around the star, from which planets will form. Star and planet formation take millions of years, so it's not possible to follow an individual object from dust cloud to solar system. However, by observing many regions like this, Herschel astronomers hope to see many young stars at different stages of formation, allowing them to build up a better picture of how our own solar system came into being.

Professor Ward-Thompson, of Cardiff University, said "This image really shows the potential of Herschel. The detail that can be seen in the image is absolutely incredible. This is only the beginning. We're going to learn more about the processes that form stars like the Sun than we could ever have previously imagined."

SPIRE image of distant galaxies, with an imposter "blob", possibly a tiny pre-stellar core
This SPIRE image primarily shows distant galaxies, but an imposter object of the left is likely to be a tiny clump of gas and dust on its way to forming a new, young star. Image credits: ESA/Herschel/ATLAS Key Project

As well as looking at regions where we know there are stars forming, Herschel can also find them by accident. Some astronomers are looking out at the distant Universe, trying to avoid the Galaxy by looking in the other direction (up out of the plane). However, since the Sun and Earth are within the disc Galaxy some objects are still seen. This image, from the SPIRE instrument at 250 microns, is around 2o across and mainly shows very distant galaxies seen in the early Universe. However, there's an imposter, easily visible on the left, which is probably much, much closer.


This “blob” is thought to be within our own Galaxy, and therefore only a few thousand light-years away. If this is the case, which should be confirmed by future observations, it is likely to be a “pre-stellar core” forming all alone in the outer reaches of the Galaxy. Professor Steve Ealse, of Cardiff University and leading member of the ATLAS survey for which this image was taken said"We always knew that because our survey would be the biggest Herschel survey, and would be operating at wavelengths that nobody has ever observed in before, there was the chance of discovering completely new types of object. I hope this tiny gas cloud, which seems to be completely isolated from other gas clouds, may be the first of these." The total amount of gas and dust is estimated to be less than the mass of the Sun, so if this small blob does go on to become a star, it will be a tiny, orphaned star all alone in the outskirts of the Galaxy.

SPIRE and PACS image of a region in the Galactic Plane, showing many star formation regions
Region of the Galactic Plane as imaged by the SPIRE and PACS instruments, showing regions where gas and dust is being heated by hot, young stars and also forming new stars. Image credit: ESA/Herschel/Italian Space Agency (ASI)/Hi-GAL Key Project

Star formation is most common within the disc of our Galaxy, which is seen from Earth edge-on, forming a diffuse line stretching across the sky called the Galactic Plane. One of the Herschel mission's key objectives is to map huge swathes of the Galactic Plane. This image shows an area around 2o on a side, as seen at wavelengths of 70 microns (blue) and 160 microns (green) by the PACS instrument, and 350 microns (red) by the SPIRE instrument. The main plane of the Galaxy is seen across the centre of the image.

The small, blue knots of material are hotter, dense clouds being heated from within by hot, young stars. Towards the top and bottom of the image the cooler, redder gas and dust are seen to form complex wispy structures. The many dense clumps seen here show stars at a range of stages through their formation process.

Sergio Molinari, leading the Hi-GAL programme which is conducting this survey, said "To be able to see the entire lifecycle of material in the galaxy in a single real image, exactly as shown in theory, from diffuse to dense clouds and on until the final phases of stellar evolution was a truly remarkable experience".