nited Kingdom Infrared Telescope (UKIRT): Mysteries Of Massive Star Formation

A false colour image of a massive star forming region shows outflows associated with IRAS 05137+3919. The image is constructed from J (1.25 micron, blue), H (1.65 micron, green) and H2 (2.122 micron, red). The shocked regions of the outflows rich in line emission appear red here. The blue objects are mostly foreground stars. IRAS 05137+3919 is a luminous Young Stellor Object (YSO) of late-O spectral type. We detect two bipolar outflows here, emanating from the central double star. Credit: JAC/UKIRT.

Using the United Kingdom Infrared Telescope (UKIRT) astronomers have found the leading mechanism by which most of the massive stars form in our Galaxy.

The largest near-infrared survey of massive star forming regions to date has revealed that a major fraction of these massive stars form by collecting matter onto disks around their equatorial regions.

This was revealed by the detection of gas outflows and shocked regions associated with massive young stars in formation, located in clouds of gas and dust in our Galaxy.

The survey was carried out by a team lead by Dr. Watson Varricatt from the Joint Astronomy Centre and included Dr. Chris Davis (Joint Astronomy Centre), Dr. Suzanne Ramsay (ESO, Germany) and Dr. Stephen Todd (UKATC, Edinburgh, UK).

We know that lower-mass stars like our Sun form by gravitational collapse of material inside clouds of gas and dust in space.

The gas and dust spiral down onto the equatorial regions of the young star via a process known as accretion.

At the same time these accreting young stars drive high velocity jets of gas outwards at thousands of miles per hour.

These "outflows" radiate at infrared wavelengths (this emission is actually produced by hydrogen molecules heated to thousands of degrees). Consequently, observations in the infrared can be used to search for not only the youngest stars, but also evidence of the accretion process.

The big question is, do the massive stars form the same way, or do they form using a different process?

For massive stars, with masses larger than 10 times the mass of our Sun, it has been proposed that the extreme energy output of these young stars, which start nuclear burning in their cores even before they complete their growth through accretion, will prevent further growth by blowing away the accretion disks.

Hence, alternate scenarios like mergers of lower mass stars have been suggested as the main mechanism for massive star formation.

The presence or absence of outflows from massive young stars will tell us whether accretion or some other methods lead to their formation.