Herschel reveals stellar surprises and galaxies galore

The first scientific results from ESA's Herschel infrared space observatory are revealing previously unseen star formation. New images show thousands of distant galaxies furiously building stars, and beautiful star-forming clouds draped across the Milky Way. One picture even catches an ‘impossible’ star in the act of formation.

Presented on 6th May during a major scientific symposium held at the European Space Agency (ESA), the results challenge old ideas of star birth, and open new roads for future research.

Herschel is the largest astronomical telescope ever to be placed into space. The diameter of its main mirror is four times larger than any previous infrared space telescope and one and a half times larger than Hubble. As stars begin to form, the surrounding dust and gas is warmed up to a few tens of degrees above absolute zero and starts to emit at far-infrared wavelengths. The Earth's atmosphere completely blocks the majority of these wavelengths and thus observations from space are necessary.

Stellar Behemoth

Image of RCW 120 as seen by  Herschel
Image of a cloud of gas and dust called “RCW120” as seen by Herschel.  The large blue bubble is being blown out by a massive star in the centre. The young star is seen as the bright white region on the bottom edge of the bubble. Click here for versions at different resolutions. Image credit: ESA / SPIRE, PACS and HOBYS Consortia

Herschel’s observation of a cloud of gas and dust, called “RCW120” has revealed an embryonic star which looks set to turn into one of the biggest and brightest stars in our Galaxy within the next few hundred thousand years. The very young star already weighs in at around ten times the mass of the Sun, and can continue to grow by feeding on the surrounding cloud, which still contains about 200 times as much material as the star.

In this image, the blue cavity is a bubble being blown in the cloud by a massive star in the centre.  The massive young star currently forming is seen as a white blob on the bottom edge of the bubble.

Current theories suggest that the fierce light emitted by such large stars should blast away their birth clouds before they grow any larger than around ten times the mass of the Sun. Despite this, many of these ‘impossible’ stars are already known, some up to 150 times the mass of the Sun.

“The fact that stars like this exist at all is one of the biggest mysteries in astronomy, and this star is probably going to be huge”, said Professor Derek Ward-Thompson of Cardiff University.  “Now that we’ve seen such a young example, we can start to investigate why our theories can’t explain its existence”.

Surveying the Galactic Nursery

Herschel image  of part of the Galactic Plane
Part of the Galactic Plane towards the contellation of Vulpecula. As well as bright regions where hot stars are warming up the dust, filaments of colder dust are seen. Young stars are currently forming in chains along these filaments. Click here for versions at different resolutions. Image credit: ESA / SPIRE, PACS and Hi-GAL Consortia

The image shows a part of the plane of our Galaxy in the constellation of Vulpecula, as seen at infrared wavelengths by the Herschel Space Telescope.

It is just one small part of a project, called “HiGal”, to survey the entire inner part of the plane of the Milky Way, conducting a complete census of the on-going star formation in our Galaxy.  Herschel can see through the clouds of gas and dust that surround newly-formed stars, and observe the hidden processes of their formation in unprecedented detail.

The preliminary results based on these first images already show us how stars are formed inside filaments of glowing gas and dust, draped across the Galaxy, forming chains of stellar nurseries, tens of light-years long.

Dr Toby Moore, of Liverpool John Moores University, said “the complete results from the HiGal survey will revolutionise our understanding of the physical process of star formation.  It will give us the first clear picture of the development of clouds of gas and dust clouds into the familiar bright stars of the night sky.”

Atlas of the Universe

Herschel ATLAS map
Herschel ATLAS image of a region of the sky about 60 times the size of the full moon, as seen by Herschel's SPIRE instrument. Almost every pinprick of light is a whole galaxy containing billions of stars. Click here for a hgiher resolution version of the image. Image credit: ESA / SPIRE and ATLAS Consortia

Herschel has also been measuring the infrared light from thousands of other galaxies, spread across billions of light-years. Each galaxy appears as just a pinprick but its brightness allows astronomers to determine how quickly it is forming stars.  Roughly speaking, the brighter the galaxy the more stars it is forming.  There are thousands of galaxies in this image, and the first thought of Dr Dave Clements, Imperial College, on seeing the image was “My God, it’s full of galaxies!”

Until now, astronomers believed that galaxies have been forming stars at about the same rate for the last three billion years. Herschel shows this is not true, finding that galaxies have been changing over cosmic time much faster than previously thought.

These images show that in the past there were many more galaxies forming stars much faster than our own Galaxy.  But what triggered this frantic activity is not completely understood. The largest Herschel project, called “Herschel ATLAS” will let astronomers investigate the reasons for this behaviour.

But investigating the evolution of galaxies is just one of the science projects that the Herschel ATLAS will carry out. This survey will cover one eightieth of the sky, four times larger than all the other Herschel surveys combined.  “The Herschel ATLAS is able to see the infrared light from newly forming stars in our own Galaxy, and even dusty disks from which planets will form”, said Dr Loretta Dunne of the University of Nottingham.  “All this, combined with finding the hidden action in galaxies over the past 10 billion years of cosmic history, makes Herschel ATLAS a truly diverse project.”

Professor Steve Eales, of Cardiff University, said “every time astronomers have observed the universe in a new waveband, they have discovered something new.  So as well as our regular science programmes, I am hoping for the unexpected.”

Interstellar Water

Herschel has made a discovery of water in space, but in a different form to those we see on Earth.  We are used to solid ice, liquid water, and gaseous steam, but this new form of water doesn’t occur naturally on Earth.  Water vapour is known to exist in stellar nurseries, but the intense ultraviolet light from hot young stars has caused it to become electrically charged.

“This detection of electrically charged water vapour came as a surprise,” says Arnold Benz, ETH Zurich, Switzerland. “It tells us that there are violent processes taking place during the early birth stages which lead to intense radiation throughout the cloud.”

A glimpse of things to come

From the biggest galaxies to the smallest molecules, these and many other Herschel results are being presented to the scientific community at the Herschel First Results Symposium, taking place this week at ESA’s ESTEC space research and technology centre, in Noordwijk in the Netherlands.  For those interested, the presentations are available on the Herschel Science Centre website.

“These are still early days for Herschel and this is just the beginning of all the science that we will get from this mission in the years to come,” says Göran Pilbratt, ESA Herschel Project Scientist.

Prof. Matt Griffin, Cardiff University, who leads the international team responsible for the Herschel-SPIRE instrument, said “at this meeting we are seeing how Herschel is making now discoveries across the whole range of astronomy, from the solar system to the most distant galaxies.  That’s very satisfying for those who worked for so long to build the observatory and its instruments.”

The video of the ESA press conference is shown below (give it a little time to load if using a slower connection: