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The best Herschel images & results

A Galactic bubble with a large surprise

It’s a Galactic bubble with a large surprise. How large? At least 8 times the mass of the Sun. Nestled in the shell around this large bubble is an embryonic star that looks set to turn into one of the brightest stars in the Galaxy.

The Galactic bubble is known as RCW 120. It lies about 4300 light-years away and has been formed by a star at its centre. The star is not visible at these infrared avelengths but pushes on the surrounding dust and gas with nothing more than the power of its starlight. In the 2.5 million years the star has existed. It has raised the density of matter in the bubble wall so much that the quantity trapped there can now collapse to form new stars.

The bright knot to the right of the base of the bubble is an unexpectedly large, embryonic star, triggered into formation by the power of the central star. Herschel’s observations have shown that it already contains between 8-10 times the mass of our Sun. The star can only get bigger because it is surrounded by a cloud containing an additional 2000 solar masses.

Not all of that will fall onto the star, even the largest stars in the Galaxy do not exceed 150 solar masses. But the question of what stops the matter falling onto the star is a puzzle for modern astronomers. According to theory, stars should stop forming at about 8 solar masses. At that mass they should become so hot that they shine powerfully at ultraviolet wavelengths.

This light should push the surrounding matter away, much as the central star did to form this bubble. But clearly sometimes this mass limit is exceeded otherwise there would be no giant stars in the Galaxy. So astronomers would like to know how some stars can seem to defy physics and grow so large. Is this newly discovered stellar embryo destined to grow into a stellar monster? At the moment, nobody knows but further analysis of this Herschel image could give us invaluable clues.

Credits: ESA / PACS & SPIRE Consortium, Dr. Annie Zavagno, LAM, HOBYS Key Programme Consortia

Text & image from the OSHI ESA Web page.


Baby stars in the Rosette Cloud

A sweeping arc of warm dust marks the boundary between stars that have formed and power the Rosette Nebula, and stars that are still forming in the surrounding Rosette cloud. This Herschel image uses infrared light to reveal embedded stars up to 10 times the mass of our Sun busily forming inside dusty cocoons.

Working from the Royal Greenwich Observatory, England, the first Astronomer Royal, John Flamsteed, discovered a cluster of stars in 1690. We know that cluster as NGC 2244. Almost 150 years later, another English astronomer, John Herschel, discovered faint wisps of gas surrounding the stars. This is what we call the Rosette Nebula. Now the Herschel space observatory, named after John Herschel’s father, William, has revealed newly forming stars – protostars – in a previously invisible portion of the surrounding cloud.

This Herschel image shows most of the Rosette cloud, which resides 5000 light-years from Earth. The original star cluster lies to the right of the image but the stars are invisible at these wavelengths. The newly discovered stars are the bright points of white light scattered across the central portion of the image.

The bright smudges are dusty cocoons containing high-mass protostars. These will eventually become stars containing around 10 times the mass of the Sun. In the redder regions of the image and near its centre, are lower mass protostars, similar in mass to the Sun.

If our eyes could see faintly enough, the Rosette cloud would dominate the night sky, close to the famous constellation of Orion, the Hunter. In area, it would appear around five times larger than the full Moon. As it is, the light given out by this ring of celestial dust and gas is too feeble to be seen by anything other than Herschel.

Herschel collected the nebula’s infrared light given out by dust and this image is a three-colour composite made of wavelengths at 70 microns (blue), 160 microns (green) and 250 microns (red). It was put together using observations from Herschel’s Photoconductor Array Camera and Spectrometer (PACS) and the Spectral and Photometric Imaging Receiver (SPIRE). Each colour represents a different temperature of dust, from 10K in the red emission to 40K in the blue. Pillars of dust point towards the star cluster.

The picture shows the dusty component of the nebula. One percent of the mass in a giant molecular cloud is dust; the rest is gas. In total, the cloud contains enough dust and gas to make 10 000 Sun-like stars.

Credits: ESA/PACS & SPIRE Consortium, Frédérique Motte, Laboratoire AIM Paris-Saclay, CEA/IRFU - CNRS/INSU - Uni. Paris Diderot, HOBYS Key Programme Consortia

Text & image from the OSHI ESA Web page.


The spine of swan

This image shows the DR21 ridge, a very massive filamentary structure oriented north-south in the extremely active star-forming region Cygnus X. It resides at a distance of about 4500 light-years from Earth in the constellation of Cygnus, the Swan.

A combination of three maps observed by ESA's Herschel space observatory, the image reveals the finely detailed structure of the cold interstellar material in red colour. This cold material is organised into filaments, many of which converge towards the main ridge.

Within the ridge, bright white compact sources trace the very young new stars that are caught in formation, including several high-mass stars. Due to its large mass reservoir, the DR21 ridge is expected to transform into the most massive young star cluster in the whole Cygnus X region.

Herschel also shows the evolution of star formation along the DR21 ridge from the southern, brightest object – the HII region DR21 itself – to the more northern, fainter, less evolved young stars.

High-mass stars are rare in number relative to stars like our Sun, but due to their much stronger radiation and their death as supernovae, they have a large influence on the evolution of the interstellar medium in our Galaxy.

These new Herschel observations strongly suggest that the convergence of filaments in areas like the DR21 ridge is a way nature forms massive star clusters containing high-mass stars. The filaments play an important role in the process as they channel material towards the DR21 ridge to build up a large reservoir of mass.

"The spine of the swan: a Herschel study of the DR21 ridge and filaments in Cygnus X" scientific paper is available at: http://dx.doi.org/10.1051/0004-6361/201219429

Credits: ESA/PACS & SPIRE consortium, HOBYS key programme, Martin Hennemann & Frédérique Motte, Laboratoire AIM Paris-Saclay, CEA/Irfu - CNRS/INSU - Univ. Paris Diderot, France

Text & image from the OSHI ESA Web page.


Cygnus X

Chaotic networks of dust and gas signpost the next generations of massive stars in this stunning new image of the Cygnus-X star-nursery captured by ESA’s Herschel space observatory.

Cygnus-X is an extremely active region of massive-star birth some 4500 light-years from Earth in the constellation of Cygnus, the Swan.
Using Herschel’s far-infrared eyes, astronomers can seek out regions where dust has been gently heated by stars, pointing them to dense clumps of gas where new generations of stars are forming.

Bright white areas highlight zones where large stars have recently formed out of turbulent clouds, especially evident in the chaotic network of filaments seen in the right-hand portion of the image.

Here, dense knots of gas and dust mark intersections where filaments meet and collapse to form new stars, and where bubble-like structures are carved by their immense radiation.

In the centre of the image, fierce radiation and powerful stellar winds from stars undetected at Herschel’s wavelengths have partly cleared and heated interstellar material, which then glows blue in this representation.

The left-hand part of the scene is dominated by a pillar of gas whose shape resembles that of the neck of a swan.

Below and to the right, a shell of gas and dust has likely been ejected from a supergiant star at its centre, but which is not seen directly in this image.

Strings of compact red objects scattered throughout the scene map the cold seeds of future generations of stars.

The image highlights the unique capabilities of Herschel to probe the birth of large stars and their influence on the surrounding interstellar material with a level of detail at far-infrared wavelengths that has never before been available.

Credits: ESA/PACS & SPIRE consortium, HOBYS key programme, Martin Hennemann & Frédérique Motte, Laboratoire AIM Paris-Saclay, CEA/Irfu - CNRS/INSU - Univ. Paris Diderot, France

Text & image from the OSHI ESA Web page.


Vela C & RCW 36

The Vela Molecular Ridge is a vast star-forming complex in the plane of our Galaxy, the Milky Way. Observing this region at far-infrared wavelengths, ESA's Herschel Space Observatory has obtained an extraordinarily detailed image of the most massive component of this molecular complex, known as Vela-C.

Located roughly 2300 light years away, Vela-C saw the onset of star formation less than a million years ago – relatively recently on astronomical timescales. Massive, as well as low- and intermediate-mass, stars are being born in this region, making it an ideal laboratory to study the birth of different populations of stars.

This image reveals previously unseen detail in the cold mixture of gas and dust that pervades the region. Cosmic dust is a minor but crucial component of the interstellar medium and, due to its low temperature, it shines brightly at the far-infrared wavelengths that Herschel is designed to observe. By detecting emission from cosmic dust, astronomers can unravel the distribution of the raw material out of which stars form.

The coldest and densest portions of the cloud complex release most of their radiation at the longest wavelengths probed by Herschel, shown in red in this image. The cloud material is organised in a highly sub-structured network, with tangled and less organised material alternating with more defined and elongated filaments. Intricate bundles of material can be seen on the left, centre and right of the image. These nest-like structures are linked to one another by dense, ridge-like filaments.

A number of white flecks dot the clouds and, in particular, the prominent ridge-like filaments in Vela-C. These flecks are in fact pre-stellar cores – compact clumps of matter that might eventually give rise to star formation – and proto-stellar cores, whose density is high enough for star formation to have already begun, eventually resulting in fully-fledged stars. As a result of Herschel's unparalleled resolution and sensitivity at these wavelengths, astronomers are able to carry out detailed studies of the properties, such as their mass and temperature, of the different cores across the nests and filaments. From the Herschel image, it appears that the majority of pre- and proto-stellar cores with large masses are found along the two densest filaments, suggesting that these sites are the most likely, in the cloud, to host the formation of massive stars.

Studies done with Herschel data seem to indicate that the ridge-like filaments in star-forming regions such as Vela-C formed from converging flows of matter in the interstellar medium. The high densities in these thick, elongated structures induce massive clumps of matter to collapse under their own gravity, giving rise to high-mass stars. The nest-like structures, on the other hand, appear to be dominated by turbulence rather than by gravity and are likely to form mainly low- and intermediate-mass stars.

Not only does Vela-C host seeds of future stellar generations, it also comprises a handful of objects that have already evolved into young, massive stars. Embedded in the central part of the image is a stellar cluster whose stars are not visible in the Herschel image, but their effects are. The butterfly-shaped structure at the centre of the image, known as RCW 36 (or Gum 20), is a result of winds and radiation released by the hot stars in this cluster. RCW 36 is an HII region – a pocket of gas that is being energised and ionised by the action of nearby young, massive stars. Due to its higher temperature relative to the colder material in the cloud, RCW 36 shines brightly at the shortest wavelengths probed by Herschel, indicated in blue in this image. In the lower right corner of the image is another HII region called RCW 34 (or Gum 19); it is unclear whether RCW 34 and the hot stars that illuminate it are part of the Vela-C molecular cloud or whether they are located farther away.

ESA/PACS& SPIRE Consortium, Tracey Hill, Frédérique Motte, Minier Vincent, Laboratoire AIM Paris-Saclay, CEA/IRFU - CNRS/INSU - Uni. Paris Diderot, HOBYS Key Programme Consortia

Text & image from the OSHI ESA Web page.


Hunting high-mass stars in W3

In this new view of a vast star-forming cloud called W3, ESA’s Herschel space observatory tells the story of how massive stars are born.

W3 is giant molecular cloud containing an enormous stellar nursery, some 6200 light-years away in the Perseus Arm, one of our Milky Way galaxy’s main spiral arms.

Spanning almost 200 light-years, W3 is one of the largest star-formation complexes in the outer Milky Way, hosting the formation of both low- and high-mass stars. The distinction is drawn at eight times the mass of our own Sun: above this limit, stars end their lives as supernovas.

Dense, bright blue knots of hot dust marking massive star formation dominate the upper left of the image in the two youngest regions in the scene. Intense radiation streaming away from the stellar infants heats up the surrounding dust and gas, making it shine brightly in Herschel’s infrared-sensitive eyes.

Older high-mass stars are also seen to be heating up dust in their environments, appearing as the blue regions in the lower left of the image and at bottom right.

Extensive networks of much colder gas and dust weave through the scene in the form of red filaments and pillar-like structures. Several of these cold cores conceal low-mass star formation, hinted at by tiny yellow knots of emission.

By studying the two regions of massive star formation in the upper left of the image, scientists have made progress in solving one of the major conundrums in the birth of massive stars. That is, even during their formation, the radiation blasting away from these stars is so powerful that they should push away the very material they are feeding from. If this is the case, how can massive stars form at all?

Observations of W3 point toward a possible solution: in these very dense regions, there appears to be a continuous process by which the raw material is moved around, compressed and confined, under the influence of clusters of young, massive protostars.

Through their strong radiation and powerful winds, populations of young high-mass stars may well be able to build and maintain localised clumps of material from which they can continue to feed during their earliest and most chaotic years, despite their incredible energy output.

Notes for Editors:

“Herschel observations of the W3 GMC: Clues to the formation of clusters of high-mass stars,” by A. Rivera-Ingraham et al., is published in The Astrophysical Journal, 766, 85; doi:10.1088/0004-637X/766/2/85.

The study was part of the Guaranteed Time Key Program HOBYS, the Herschel imaging survey of OB Young Stellar objects.

The image presented here was taken in three colour bands centred on 70 micron m (blue), 160 micron m (green) and 250 micron m (red).

Credits: ESA/PACS & SPIRE consortia, A. Rivera-Ingraham & P.G. Martin, Univ. Toronto, HOBYS Key Programme (F. Motte)

Text & image from the OSHI ESA Web page.



This image shows the broader region W48 around the supernova remnant W44 (SNR W44). It is considered as a laboratory of massive stars from their infancy (within this red filament) to HII regions (blue bubbles) and SNR.

Credits: ESA/PACS & SPIRE Consortium, Frédérique Motte, Laboratoire AIM Paris-Saclay, CEA/IRFU - CNRS/INSU - Uni. Paris Diderot, HOBYS Key Programme Consortia

Text & image from the OSHI ESA Web page.


W44 supernova remnant

This image shows the supernova remnant W44 (SNR W44), a prime example of the interaction between the remains of a supernova and the dense interstellar material around it. The image is based on data gathered with ESA's Herschel space observatory at far-infrared wavelengths.

The image shows SNR W44's asymmetric expanding shell, which can be seen as the large violet bubble with filamentary texture occupying the left half of the image. The shell is about 100 light-years across and, just above the centre of the image, it is impacting the arc-shaped bright feature to the right – an HII region known as G34.8-0.7.

Observations at X-ray wavelengths have highlighted that the remnant's expanding shell is filled with hot, X-ray emitting gas. Hence, SNR W44 is classified as a mixed-morphology supernova remnant.

Around 10 000 light-years from us, SNR W44 is located in the molecular cloud complex known as W48, a rich star-forming region where a multitude of massive stars are being born. Two HII regions stand out in violet in the image, showing the intense activity of star formation in W48: G035.1387-00.7622 in the upper part of the image to the right, and G35.0-0.5 just to the right of the image centre. The bright flecks scattered across the image are denser clumps in the turbulent cloud medium and are the seeds of future massive stars. In the lower left corner of the image, the diffuse glow corresponds to emission from warm dust in the Galactic Plane, the disc-like structure that contains most of the stars and star-forming clouds in our Galaxy, the Milky Way.

Credits: ESA/PACS/SPIRE/Quang Nguyen Luong & Frederique Motte, HOBYS Key Program consortium

Text & image from the OSHI ESA Web page.



#36 - Last update : 04/04 2013
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