UWISH-2 Survey: Numerous unknown jets from young stars and planetary nebulae

The area shown here was part of the very first image taken for the UWISH2 survey. 

It shows on the top a region of massive star formation (called G35.2N) with two spectacular jets. 

On the bottom an intermediate mass young stellar cluster (Mercer14) can be seen. 

Several jets are visible in its vicinity, as well as a region of photo-ionized material surrounding a young massive star. 

Credit: University of Kent

For many years astronomers have known that young 'protostars' drive supersonic jets of gas from their north and south poles. However, this is the first time that so many of them have been detected at once.

The results come from a five year survey undertaken with the UK Infra-Red Telescope (UKIRT) and are expected to prompt significant changes in the understanding of the planetary nebulae population in the Galaxy, as well as the properties of jets ejected from young forming stars.

By examining images of excited hydrogen molecules at infrared wavelengths, scientists have been able to see through the gas and dust in the Milky Way to observe more distant targets.

These targets are normally hidden from view and many of them have never been seen before.

The entire survey area covers approximately 1450 times the size of the full moon, or the equivalent of a 95 GigaPixel image.

The survey reveals jets from protostars and planetary nebulae, as well as supernova remnants, the illuminated edges of vast clouds of gas and dust, and the warm regions that envelope massive stars and their associated clusters of smaller stars.

Based on current estimates using these data, the project expects to identify about 1000 unique jets from young stars, at least 90% of these are new discoveries, as well as 300 planetary nebulae, with almost half of them unknown.

This is a text-book example of triggered star formation. 

There is the outline of a molecular cloud, which is illuminated by ionizing radiation of massive stars situated off the bottom of the image. 

The radiation pressure has compressed the cloud and started the process of star formation.

The forming stars can be identified by reflection nebulae surrounding them, or by their jets. 

Models of the process of triggered star formation predict an age gradient of the forming stars with younger objects further inside, away from the source of the ionizing radiation.

The object shown here is a prime example that confirms this scenario with reflection nebulae ranging in colours from blue, near the tip of the molecular cloud, to green and yellow further inside.

The colour change towards red indicates the objects are further embedded in their parental cloud core and thus younger. 

The youngest object is completely invisible even at these infrared wavelengths, and can only by identified by the jet it is launching (top of image). 

Credit: University of Kent

Dr Dirk Froebrich of the University of Kent's Centre for Planetary Science said: "These discoveries are very exciting."

"We will ultimately have much better statistics, meaning we will be able to investigate the physical mechanisms that determine the jet lengths, as well as their power."

"This will bring us much closer to answering some of the fundamental questions of star formation: How are these jets launched and how much energy, mass and momentum do they feed back into the surrounding interstellar medium."

To mark the 5th anniversary of the start of the observations of the survey on 27 August, the project has released a number of images taken with the UK Infra-Red Telescope (UKIRT), based in Hawaii and used for the research.

This image shows a field that contains a newly discovered photogenic planetary nebulae. 

Internally dubbed by the research team as the "Jelly-Fish PN" it shows an almost circular ring of emission from molecular hydrogen with a variety of structure in the ring itself and inside. 

The central ionizing source responsible for the radiation is a white dwarf, which is too faint at the near infrared wavelengths to be visible in the image. 

Credit: University of Kent

The project has been led by Dr Dirk Froebrich from the Centre for Planetary Sciences at the University of Kent, in collaboration with Dr Chris J. Davis from the Astrophysics Research Institute at Liverpool John Moores University.

Hubble Image: Bizarre alignment of planetary nebulae

This image shows an example of a bipolar planetary nebula known as PN Hb 12 -- popularly known as Hubble 12 -- in the constellation of Cassiopeia. 

The striking shape of this nebula, reminiscent of a butterfly or an hourglass, was formed as a Sun-like star approached the end of its life and puffed its outer layers into the surrounding space. 

For bipolar nebulae, this material is funnelled towards the poles of the ageing star, creating the distinctive double-lobed structure. 

Credit: NASA, ESA Acknowledgement: Josh Barrington

Astronomers have used the NASA/ESA Hubble Space Telescope and ESO's New Technology Telescope to explore more than 100 planetary nebulae in the central bulge of our galaxy.

They have found that butterfly-shaped members of this cosmic family tend to be mysteriously aligned—a surprising result given their different histories and varied properties.

The final stages of life for a star like our Sun result in the star puffing its outer layers out into the surrounding space, forming objects known as planetary nebulae in a wide range of beautiful and striking shapes.

One type of such nebulae, known as bipolar planetary nebulae, create ghostly hourglass or butterfly shapes around their parent stars.

All these nebulae formed in different places and have different characteristics. Neither the individual nebulae, nor the stars that formed them, interact with other planetary nebulae.

However, a new study by astronomers from the University of Manchester, UK, now shows surprising similarities between some of these nebulae: many of them line up in the sky in the same way.

"This really is a surprising find and, if it holds true, a very important one," explains Bryan Rees of the University of Manchester, one of the paper's two authors.

"Many of these ghostly butterflies appear to have their long axes aligned along the plane of our galaxy. By using images from both Hubble and the NTT we could get a really good view of these objects, so we could study them in great detail."

The astronomers looked at 130 planetary nebulae in the Milky Way's central bulge. They identified three different types, and peered closely at their characteristics and appearance.

"While two of these populations were completely randomly aligned in the sky, as expected, we found that the third—the bipolar nebulae—showed a surprising preference for a particular alignment," says the paper's second author Albert Zijlstra, also of the University of Manchester.

"While any alignment at all is a surprise, to have it in the crowded central region of the galaxy is even more unexpected."

Planetary nebulae are thought to be sculpted by the rotation of the star system from which they form.

This is dependent on the properties of this system—for example, whether it is a binary, or has a number of planets orbiting it, both of which may greatly influence the form of the blown bubble.

The shapes of bipolar nebulae are some of the most extreme, and are thought to be caused by jets blowing mass outwards from the star system perpendicular to its orbit.

"The alignment we're seeing for these bipolar nebulae indicates something bizarre about star systems within the central bulge," explains Rees.

"For them to line up in the way we see, the star systems that formed these nebulae would have to be rotating perpendicular to the interstellar clouds from which they formed, which is very strange."

While the properties of their progenitor stars do shape these nebulae, this new finding hints at another more mysterious factor.

Along with these complex stellar characteristics are those of our Milky Way; the whole central bulge rotates around the galactic centre.

This bulge may have a greater influence than previously thought over our entire galaxy—via its magnetic fields.

The astronomers suggest that the orderly behaviour of the planetary nebulae could have been caused by the presence of strong magnetic fields as the bulge formed.

As such nebulae closer to home do not line up in the same orderly way, these fields would have to have been many times stronger than they are in our present-day neighbourhood.

"We can learn a lot from studying these objects," concludes Zijlstra. "If they really behave in this unexpected way, it has consequences for not just the past of individual stars, but for the past of our whole galaxy."

More information: 
Research paper: www.spacetelescope.org/static/archives/releases/science_papers/heic1315a.pdf