An impossible star

The first science results from ESA's Herschel Space Observatory include an image of the birth of an 'impossible' star that is set to challenge ideas of star formation.

The protostar, embedded within a cloud of gas and dust known as RCM 120, is destined to evolve into one of the biggest and brightest stars in our Galaxy within the next few hundred thousand years. Already weighing in at ten times the mass of the Sun, it will grow by consuming the material in its surrounding cloud, which contains 200 times more material than the protostar itself.

The large blue bubble is being blown out by a massive star seen as a bright white region on the bottom edge of the bubble, located in the RCW 120 gas cloud some 4,300 light years away. Image: ESA / PACS, SPIRE and HOBYS Consortia.

“This star can only grow bigger,” says Annie Zavagno of the Laboratoire d’Astrophysique de Marseille. “According to our current understanding, you should not be able to form stars larger than eight solar masses,” says Dr. Zavagno.

Massive stars are rare and short-lived because the ferocious radiation thrown out by the forming star should blast away the surrounding material. Although a handful of 'impossibly' massive stars are already known – some containing as much as 150 solar masses – this is the first captured early on in its life, thus providing the missing link to investigate how these behemoths form and maintain their mass.

Herschel has also been seeking out star-formation rates in galaxies far beyond our own. Based on the assumption that the brighter the galaxy the more stars it is forming, Herschel has again been collecting data that challenge currently accepted theories, finding that galaxies have been evolving over time much faster than previously thought, and not at a steady rate for the last three billion years.

Although it is known that in the past there were many more star-burst galaxies – those forming stars at a frenetic rate of 10 to 15 times that we see in the Milky Way today – what triggers this flurry of activity is not completely understood. “Herschel will now let us investigate the reasons for this behavior,” says Steve Eales of Cardiff University.

Herschel is studying star birth in our Galaxy. Here, towards the galactic centre, two massive star-forming regions are seen in the centre and to the left of the image. Known as G29.9 and W43 respectively, these mini-starburst regions are forming stars of all sizes, from those just like our Sun to those several tens of times heavier. Image: ESA/Hi-GAL Consortium.

In yet another exciting announcement, Herschel has also detected a new phase of electrically charged water molecule in the birth clouds surrounding young stars. In these inhospitable birthing wards, ultraviolet radiation races through the gas, which can knock an electron out of the water molecule, leaving it with an electrical charge. “This detection of ionized water vapour came as a surprise,” comments Arnold Benz of ETH Zurich, Switzerland. “It tells us that there are violent processes taking place during the early birth stages which lead to widespread energetic radiation throughout the cloud.”

Herschel was launched a year ago and the first science results are being presented at the Herschel First Results Symposium this week at ESA’s ESTEC space research and technology centre in the Netherlands.

“At this meeting we are seeing how Herschel is making new 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,” adds Matt Griffin, principal investigator for Herschel's SPIR instrument.

For more on the current state of the Herschel mission, watch our video interview with Matt Griffin at the National Astronomy Meeting, held last month in Glasgow.