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.

NASA Chandra: Inside the Flame Nebula - NGC 2024

Image credit: X-ray: NASA /CXC /PSU /K.Getman, E.Feigelson, M.Kuhn & the MYStIX team; Infrared:NASA /JPL-Caltech

Stars are often born in clusters, in giant clouds of gas and dust.

Astronomers have studied two star clusters using NASA's Chandra X-ray Observatory and infrared telescopes and the results show that the simplest ideas for the birth of these clusters cannot work, as described in our latest press release.

This composite image shows one of the clusters, NGC 2024, which is found in the center of the so-called Flame Nebula about 1,400 light years from Earth.

In this image, X-rays from Chandra are seen as purple, while infrared data from NASA's Spitzer Space Telescope are coloured red, green, and blue.

A study of NGC 2024 and the Orion Nebula Cluster, another region where many stars are forming, suggest that the stars on the outskirts of these clusters are older than those in the central regions.

This is different from what the simplest idea of star formation predicts, where stars are born first in the center of a collapsing cloud of gas and dust when the density is large enough.

The research team developed a two-step process to make this discovery. First, they used Chandra data on the brightness of the stars in X-rays to determine their masses.

Next, they found out how bright these stars were in infrared light using data from Spitzer, the 2MASS telescope, and the UK Infrared Telescope (UKIRT).

By combining this information with theoretical models, the ages of the stars throughout the two clusters could be estimated.

According to the new results, the stars at the center of NGC 2024 were about 200,000 years old while those on the outskirts were about 1.5 million years in age.

In Orion, the age spread went from 1.2 million years in the middle of the cluster to nearly 2 million years for the stars toward the edges.

UKIRT Discovers Unusual Binary Stars with Close Orbit

Scientists have discovered four unusual pairs of stars that orbit each other in less than four hours, according to a new study.

Scientists claim that the orbital period is quite strange because till now they have never found a binary star with such close orbital period.

According to the scientists, more than half of the stars in our milky way are part of a binary system and orbit each other at a certain period, which is more than 5 hours.

They believe that if binary stars orbit very close to each other, they will quickly emerge into one huge star.

The unusual binary stars were discovered while monitoring the brightness of thousands of stars, including red dwarfs by using the United Kingdom Infrared Telescope (UKIRT) in Hawaii.

"To our complete surprise, we found several red dwarf binaries with orbital periods significantly shorter than the 5 hour cut-off found for Sun-like stars, something previously thought to be impossible", said Bas Nefs, scientist at the Leiden Observatory, Netherlands, in a statement.

"It means that we have to rethink how these close-in binaries form and evolve," Nefs added.

The study suggested several reasons behind the short orbital period of these stars. One of the reasons is that since stars shrink in size in their lifetime, there is a possibility that their period could also have shrunk; otherwise the stars would have emerged quite long ago.

However, scientists are not sure as to how these orbits could have shrunk so much.

Another possibility is that the magnetic field lines radiating from the cool star companions get twisted and deformed as they orbit each other, generating the extra activity through stellar wind, explosive flaring and star spots.

Powerful magnetic activity could apply the brakes to these spinning stars, slowing them down so that they move closer together.

"Without UKIRT's superb sensitivity, it wouldn't have been possible to find these extraordinary pairs of red dwarfs", said David Pinfield, researcher at the University of Hertfordshire.

"The active nature of these stars and their apparently powerful magnetic fields has profound implications for the environments around red dwarfs throughout our Galaxy," he added.

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.