Archive for star formation

Young stars and dusty nebulae in Taurus

Posted in astronomy with tags , , on April 22, 2017 by Tim Kendall

Image and text credit: APOD: Lloyd L. Smith, Deep Sky West. This complex of dusty nebulae lingers along the edge of the Taurus molecular cloud, a mere 450 light-years distant. Stars are forming on the cosmic scene. Composed from almost 40 hours of image data, the 2 degree wide telescopic field of view includes some youthful T-Tauri class stars embedded in the remnants of their natal clouds at the top. Millions of years old and still going through stellar adolescence, the stars are variable in brightness and in the late phases of their gravitational collapse. Their core temperatures will rise to sustain nuclear fusion as they grow into stable, low mass, main sequence stars, a stage of stellar evolution achieved by our middle-aged Sun about 4.5 billion years ago. Another youthful variable star, V1023 Tauri, can be spotted in the lower part of the image. Within its yellowish dust cloud, it lies next to the striking blue reflection nebula Cederblad 30, also known as LBN 782. Above the bright bluish reflection nebula is dusty dark nebula Barnard 7.

T Tauri and Hind’s variable nebula

Posted in astronomy with tags , on December 31, 2016 by Tim Kendall

hindsvariable_goldmanT Tauri stars exist often in association with OB stars, whose short lifetimes mean the lower-mass T Tauri stars must also be young. The history of how this came to be known is recounted in a 2008 paper by Scott J. Kenyon et al., here, and an excerpt is below. Image: Optical image of T Tauri and surroundings (courtesy D. Goldman, APOD). T Tau is the bright yellow star near the centre. Barnard’s nebula is visible as faint nebulosity immediately surrounding T Tau. Hind’s nebula is the bright, arc-shaped cloud that covers some of the lower-right pair of diffraction spikes from the T Tau image. Fainter nebulosity, mostly ionized gas powered by a weak ultraviolet radiation field, covers the rest of the image. Burnham (1894) and Barnard (1895) discuss the relationship between Burnham’s nebula and the more distant Hind’s and Struve’s nebulae.

In October 1852, J. R. Hind ‘noticed a very small nebulous looking object’ roughly 18′′ west of a tenth magnitude star in Taurus. Over the next 15 years, the nebula slowly faded in brightness and in 1868 vanished completely from the view of the largest telescopes. O. Struve then found a new, smaller and fainter, nebulosity roughly 4′ west of Hind’s nebula. While trying to recover these nebulae, Burnham (1890, 1894) discovered a small elliptical nebula surrounding T Tau (above image). In the 1940’s, A. Joy compiled the first lists of ‘T Tauri stars,’ irregular variable stars associated with dark or bright nebulosity, with F5-G5 spectral types and low luminosity (Joy 1945, 1949; Herbig 1962). Intense searches for other T Tauri stars revealed many stars associated with dark clouds and bright nebulae, including a class with A- type spectra (e.g. Herbig 1950a, 1960). Most of these stars were in loose groups, the T associations, or in dense clusters, the O associations (e.g., Herbig 1950b, 1957; Kholopov 1958; Dolidze & Arakelyan 1959). Because O stars have short lifetimes, both types of associations have to be composed of young stars, with ages of 10 Myr or less (Ambartsumian 1957). This realization – now 50 years old – initiated the study of star formation in dark [molecular] clouds.

Earliest stages of star formation in Perseus

Posted in astronomy with tags , on November 13, 2016 by Tim Kendall

perseuscloud_hilborn2048Stardust in Perseus: image APOD, credit & copyright: Lynn Hilborn. The Perseus star-forming clouds contain objects which are candidates to be a first hydrostatic core (FHSC), theorized by Larson (1969) to be the very first stage of star formation, consisting mostly of molecular hydrogen and intermediate in evolutionary status between dense molecular cores known as “starless” and “pre-stellar”. Its lifetime is short, less than 30,000 yr. The subject was treated by Scientific American in 2010, the year one such object was found, Per-Bolo 58 (see abstract below). The region is the subject of much ongoing work with new surveys at (sub)-mm and longer wavelengths: see new work by Storm et al. (2016) for a very recent example.

The first hydrostatic core (FHSC) represents a very early phase in the low-mass star formation process, after collapse of the parent core has begun but before a true protostar has formed. This large (few AU), cool (100 K), pressure-supported core of molecular hydrogen is expected from theory, but has yet to be observationally verified. Here, we present observations of an excellent candidate for the FHSC phase: Per-Bolo 58, a dense core in Perseus that was previously believed to be starless. The 70 μm flux of 65 mJy, from new deep Spitzer MIPS observations, is consistent with that expected for the FHSC. A low signal-to-noise detection at 24 μm leaves open the possibility that Per-Bolo 58 could be a very low luminosity protostar, however. We utilize radiative transfer models to determine the best-fitting FHSC and protostar models to the spectral energy distribution and 2.9 mm visibilities of Per-Bolo 58. The source is consistent with an FHSC with some source of lower opacity through the envelope allowing 24 μm emission to escape; a small outflow cavity and a cavity in the envelope are both possible. While we are unable to rule out the presence of a protostar, if present it would be one of the lowest luminosity protostellar objects yet observed, with an internal luminosity of ~0.01 L .

Gemini adaptive optics imaging of shocked star formation in the Large Magellanic Cloud

Posted in astronomy with tags , on July 5, 2016 by Tim Kendall


( Gemini South GeMS/GSAOI near-infrared image of the N159W field in the Large Magellanic Cloud. The image spans 1.5 arcminutes across, resolves stars to about 0.09 arcseconds, and is a composite of three filters (J, H, and Ks). Integration (exposure) time for each filter was 25 minutes. Color composite image by Travis Rector, University of Alaska Anchorage. Image credit: Gemini Observatory/AURA

An unprecedented view from the Gemini South telescope in Chile probes a swarm of young and forming stars that appear to have been shocked into existence. The group, known as N159W, is located some 158,000 light years away in the Large Magellanic Cloud (LMC), a satellite to our Milky Way Galaxy. Despite the group’s distance beyond our galaxy the extreme resolution of the image presents researchers with a fresh perspective on how prior generations of stars can trigger, or shock, the formation of a new generation of stars. “Because of the remarkable amount of detail, sensitivity, and depth in this image we identified about 100 new Young Stellar Objects, our YSOs, in this region,” says Benoit Neichel of the Laboratoire d’Astrophysique de Marseille, who worked with PhD student Anais Bernard on the research. Bernard expects to complete her PhD based upon this work in 2017.

Bernard adds that YSO’s are very red objects, often still enshrouded in a cocoon of the natal material from which they were born. “What we are seeing appears to be groups of YSOs forming at the edge of a bubble containing ionized gas expanding from an older generation of stars within the bubble.” Astronomers refer to these areas of expanding gas as HII regions due to the abundance of ionized (energized) hydrogen gas. “In a very real sense these young stars are being shocked into existence by the expanding gas from these more mature stars,” said Bernard. “Without this advanced adaptive optics technology on Gemini we wouldn’t be able push our observations out to the distance of the LMC,” said Neichel. “This gives us a unique chance to explore star formation in a different environment.” He adds that part of the challenge is differentiating between “boring field stars” and the YSOs, which, he describes as “…the gems that make this research possible.”

The research team, led by Neichel and Bernard, published their work in the journal Astronomy and Astrophysics. The team used the Gemini South telescope with the Gemini Multi-conjugate adaptive optics System (GeMS) combined with the Gemini South Adaptive Optics Imager (GSAOI). The Gemini South adaptive optics system uses a multi-conjugated configuration that samples turbulence in several layers in our atmosphere using a “constellation” of five laser guide stars. This system provides exceptionally large adaptive optics fields of view and high levels of correction to minimize the blurring effect of atmospheric distortions uniformly across the image (essentially to the theoretical, or “diffraction limit”).

Complex structure at sub-arcsecond resolution in the gas-rich debris disk HD 141569A

Posted in astronomy with tags , , , on June 6, 2016 by Tim Kendall

28396PerrotHD 141569A is a transition disk that is still gas-rich but contains significant amounts of dust. In a new paper using the SPHERE coronagraph on the ESO VLT, Perrot et al. reveal that the inner 100 astronomical units (au) contains a series of concentric ringlets at physical separation of 47 au, 64 au, and 93 au. The paper is “Discovery of concentric broken rings at sub-arcsec separations in the HD 141569A gas-rich, debris disk with VLT/SPHERE”, 2016, A&A 590, L7. From the abstract:

Transition disks correspond to a short stage between the young protoplanetary phase and older debris phase. Along this evolutionary sequence, the gas component disappears leaving room for a dust-dominated environment where already-formed planets signpost their gravitational perturbations. We endeavor to study the very inner region of the well-known and complex debris, but still gas-rich disk, around HD 141569A using the exquisite high-contrast capability of SPHERE at the VLT. Recent near-infrared (IR) images suggest a relatively depleted cavity within ~200 au, while former mid-IR data indicate the presence of dust at separations shorter than ~100 au. We obtained multi-wavelength images in the near-IR in J, H2, H3 and Ks-bands with the IRDIS camera and a 0.95–1.35 μm spectral data cube with the IFS. Data were acquired in pupil-tracking mode, thus allowing for angular differential imaging. We discovered several new structures inside 1′′, of which the most prominent is a bright ring with sharp edges (semi-major axis: 0.4′′) featuring a strong north-south brightness asymmetry. Other faint structures are also detected from 0.4′′ to 1′′ in the form of concentric ringlets and at least one spiral arm. Finally, the VISIR data at 8.6 μm suggests the presence of an additional dust population closer in. Besides, we do not detect companions more massive than 1–3 mass of Jupiter. The performance of SPHERE allows us to resolve the extended dust component, which was previously detected at thermal and visible wavelengths, into very complex patterns with strong asymmetries; the nature of these asymmetries remains to be understood. Scenarios involving shepherding by planets or dust-gas interactions will have to be tested against these observations.

ESO/ALMA imaging of planet formation in an Earth-like orbit

Posted in astronomy with tags , , , on April 2, 2016 by Tim Kendall
( ALMA‘s best image of a protoplanetary disc to date. This picture of the nearby young star TW Hydrae reveals the classic rings and gaps that signify planets are in formation in this system. Credit: S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO). The star TW Hydrae is a popular target of study for astronomers because of its proximity to Earth and its status as an infant (or T Tauri) star about 10 million years old. Its distance has been recently re-calculated to be as close as 38 pc. The star itself is slightly less massive than the Sun, spectral type K8IVe (as given in an excellent recent review of young stars in nearby stellar associations here). It also has a face-on orientation as seen from Earth, giving astronomers a rare view of the complete protoplanetary disc around the star.

ALMA TW Hya central regions

This is the inner region of the TW Hydrae protoplanetary disk as imaged by ALMA. The image has a resolution of 1 AU (Astronomical Unit, the distance from the Earth to the Sun in our own Solar System). This new ALMA image reveals a gap in the disk at 1 AU, suggesting that a planet with the same orbit as Earth is forming there. Credit: S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO). The paper “Ringed Substructure and a Gap at 1 AU in the Nearest Protoplanetary Disk”, by S.M. Andrews et al., appearing in the Astrophysical Journal Letters (pdf copy via ESO). These recent observations represent a huge breakthrough in direct imaging at the resolutions required and are very suggestive evidence for the existence of Earth-like planets in nearby interstellar space. From the abstract:
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 870 μm continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that trace millimeter-sized particles down to spatial scales as small as 1 AU (20 milliarcseconds). These data reveal a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli (1-6 AU) with modest contrasts (5-30%). We associate these features with concentrations of solids that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima. No significant non-axisymmetric structures are detected. Some of the observed features occur near temperatures that may be associated with the condensation fronts of major volatile species, but the relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the so-called zonal flows). Other features, particularly a narrow dark annulus located only 1 AU from the star, could indicate interactions between the disk and young planets. These data signal that ordered substructures on ~AU scales can be common, fundamental factors in disk evolution, and that high resolution microwave imaging can help characterize them during the epoch of planet formation.

Update on the ongoing search for the proposed “Planet Nine”, from Scientific American: The article highlights the research of Fienga et al., (2016) using the Cassini spacecraft data to pinpoint the planet. The planet is likely sub-Jovian, ten Earth masses, eccentric, e ~ 0.6, distant but not that distant, ~ 700 AU, and possibly located in the region of the sky in the direction of the southern constellation of Cetus, with true anomaly 117.8°±11°. I predict that it will be found soon, and there is as good a chance of finding it by its own internal heat, in millimeter data, as by reflected light in the visible part of the spectrum.

Combined VLA/ALMA view of the forming planetary system HL Tauri

Posted in astronomy with tags , on March 26, 2016 by Tim Kendall


Image: Combined ALMA (red) and VLA image of HL Tau. Credit: Carrasco-Gonzalez, et al.; Bill Saxton, NRAO/AUI/NSF. The paper is Carrasco-Gonzalez et al., “The VLA view of the HL Tau Disk – Disk Mass, Grain Evolution, and Early Planet Formation,” accepted by Astrophysical Journal Letters (preprint). The image above is certainly ground-breaking, and has been noted extensively elsewhere. The age of the system is thought to be less than 100,000 (105) years and HL Tau itself is quite Sun-like, spectral type K5. It was already known to host a protoplanet (the bright clump in the yellow VLA data above) about 14 times as massive as Jupiter and about twice as far from HL Tau as Neptune is from our Sun. From the abstract:

The first long-baseline ALMA campaign resolved the disk around the young star HL Tau into a number of axisymmetric bright and dark rings. Despite the very young age of HL Tau these structures have been interpreted as signatures for the presence of (proto)planets. The ALMA images triggered numerous theoretical studies based on disk-planet interactions, magnetically driven disk structures, and grain evolution. Of special interest are the inner parts of disks, where terrestrial planets are expected to form. However, the emission from these regions in HL Tau turned out to be optically thick at all ALMA wavelengths, preventing the derivation of surface density profiles and grain size distributions. Here, we present the most sensitive images of HL Tau obtained to date with the Karl G. Jansky Very Large Array at 7.0 mm wavelength with a spatial resolution comparable to the ALMA images. At this long wavelength the dust emission from HL Tau is optically thin, allowing a comprehensive study of the inner disk. We obtain a total disk dust mass of 0.001 – 0.003 Msun, depending on the assumed opacity and disk temperature. Our optically thin data also indicate fast grain growth, fragmentation, and formation of dense clumps in the inner densest parts of the disk. Our results suggest that the HL Tau disk may be actually in a very early stage of planetary formation, with planets not already formed in the gaps but in the process of future formation in the bright rings.

A new observational basis for star formation studies in Orion

Posted in astronomy with tags , , on March 8, 2016 by Tim Kendall


A new paper entitled “VISION – Vienna Survey in Orion. I. VISTA Orion A Survey” is the first looking at the closest region of massive star formation – Orion. At the moment the complete paper by S. Meingast, J. Alves, D. Mardones, et al. (2016) is available here:

The Orion nebula cluster (ONC), the nearest region of massive star formation, is embedded in the much larger Orion A molecular cloud. The ONC has been studied much more extensively than other parts of Orion A, in spite of the opportunity that this region offers to understand the processes connected with the formation of both low- and high-mass stars. Using the ESO Visible and Infrared Survey Telescope for Astronomy (VISTA), the authors have surveyed the entire Orion A molecular cloud in the J, H, and K (short) near-infrared bands, covering a total of around 18.3 square degrees, and present the most detailed and sensitive near-infrared (NIR) observations of the entire molecular cloud to date. They find about 2500 embedded objects in Orion A and confirm the existence of a recently discovered foreground population above the Galactic field. The Orion A VISTA catalog contains 799 995 sources, which increases the source counts by about an order of magnitude compared to the 2MASS survey. It provides a basis for future studies of star formation processes toward Orion.

Young multiple system DI Chamaeleontis observed by Hubble/ACS

Posted in astronomy with tags , , on November 6, 2015 by Tim Kendall

Smoke ring for a halo

Credit: ESA/Hubble & NASA, Acknowledgement: Judy Schmidt

( Two stars shine through the centre of a ring of cascading dust in this image taken by the NASA/ESA Hubble Space Telescope. The star system is named DI Cha, and while only two stars are apparent, it is actually a quadruple system containing two sets of binary stars. As this is a relatively young star system it is surrounded by dust. The young stars are molding the dust into a wispy wrap. The host of this alluring interaction between dust and star is the Chamaeleon I dark cloud—one of three such clouds that comprise a large star-forming region known as the Chamaeleon Complex. DI Cha’s juvenility is not remarkable within this region. In fact, the entire system is among not only the youngest but also the closest collections of newly formed stars to be found and so provides an ideal target for studies of star formation.

Iron droplet clouds and hot silicates in the atmosphere of lone planetary mass object PSO J318.5-22

Posted in astronomy with tags , , , on November 2, 2015 by Tim Kendall

ps1-lonely_planet-3x3in300dpiRGBimageOnly Deep multi-colour image from the Pan-STARRS1 telescope of the free-floating planet PSO J318.5-22, in the constellation of Capricornus. The exoplanet, or low mass brown dwarf, is extremely cold and faint, about 100 billion times fainter in optical light than the planet Venus. Most of its energy is emitted at infrared wavelengths, hence the very red colour. The image is 125 arcseconds on a side. An update on this object from New Scientist: the paper by Beth A. Biller et al., (2015) “Variability in a Young, L/T Transition Planetary-Mass Object” is accepted to the Astrophysical Journal Letters [preprint]. From the abstract:

As part of our ongoing NTT SoFI survey for variability in young free-floating planets and low mass brown dwarfs, we detect significant variability in the young, free-floating planetary mass object PSO J318.5-22, likely due to rotational modulation of inhomogeneous cloud cover. A member of the 23±3 Myr β Pic moving group, PSO J318.5-22 has Teff = 1160+3040 K and a mass estimate of 8.3±0.5 MJup for a 23±3 Myr age. PSO J318.5-22 is intermediate in mass between 51 Eri b and β Pic b, the two known exoplanet companions in the β Pic moving group. With variability amplitudes from 7-10% in JS at two separate epochs over 3-5 hour observations, we constrain the rotational period of this object to >5 hours. In KS, we marginally detect a variability trend of up to 3% over a 3 hour observation. This is the first detection of weather on an extrasolar planetary mass object. Among L dwarfs surveyed at high-photometric precision (<3%) this is the highest amplitude variability detection. Given the low surface gravity of this object, the high amplitude preliminarily suggests that such objects may be more variable than their high mass counterparts, although observations of a larger sample is necessary to confirm this. Measuring similar variability for directly imaged planetary companions is possible with instruments such as SPHERE and GPI and will provide important constraints on formation.

New Scientist gives a glimpse as to the hellish nature of the atmosphere of this bizarre object:

The starless planet, PSO J318.5-22, was discovered in the Pan-STARRS survey in 2013. At about eight times the mass of Jupiter, it’s much more like the giant planets we see orbiting other stars than the small, failed stars called brown dwarfs. That means it probably formed around a star and was somehow shot out of its orbit into lonely deep space. That also makes this planet much easier to study than those that are almost lost in the dazzle from the stars they circle. “You have to work really hard to even see them, whereas this object is just by itself,” says Beth Biller at the University of Edinburgh, UK. Biller’s team measured the planet’s brightness and found that it could vary by up to 10 per cent in just a few hours. The explanation, they say, could lie in its weather systems. “If you think about the Great Red Spot on Jupiter, it would be stormy spots like that,” Biller says. Both worlds have similar rotation periods: 10 hours for Jupiter, and between 5 and 10 hours for the lone planet. But unlike Jupiter, which has cooled from a hot start over the long life of our solar system, this planet retains a scorching surface temperature of about 1100 kelvin – maintained by internal heat since it has no star. Those conditions mean that any clouds it has should be molten, containing liquid metals where on Earth we would have water. “These are likely hot silicates and iron droplet clouds,” Biller says. “This makes Venus look like a nice place.” Caroline Morley, who models exoplanet atmospheres at the University of California, Santa Cruz, thinks the finding may mean that similar planets – whether orbiting stars or not – might show the same behaviour. “It strongly suggests that these objects should be variable [in brightness],” Morley says. “We really want to be able to look at this variability and then connect it to storm systems.” Biller’s team is already trying to tease out a similar analysis from observations of a star called HR 8799, which has planets closely resembling this lone world.

VLT/SPHERE imaging of the circumbinary disk and massive exoplanet around HD 106906

Posted in astronomy with tags , , , , on October 28, 2015 by Tim Kendall

Planet-hunting SPHERE Images First Circumbinary Planet System wi

Image and text credit: ESO, A. M. Lagrange (Université Grenoble Alpes) Observations by ESO’s planet-finding instrument, SPHERE, a high-contrast adaptive optics system installed on the third Unit Telescope of ESO’s Very Large Telescope, have revealed the edge-on disc of gas and dust present around the binary star system HD 106906AB.

HD 106906AB is a double star located in the constellation of Crux (The Southern Cross). Astronomers had long suspected that this 13 million-year-old stellar duo was encircled by a debris disc, due to the system’s youth and characteristic radiation. However, this disc had remained unseen — until now. The system’s spectacular debris disc can be seen towards the lower left area of this image. It is surrounding both stars, hence its name of circumbinary disc. The stars themselves are hidden behind a mask which prevent their glare from blinding the instrument.These stars and the disc are also accompanied by an exoplanet, visible in the upper right, named HD 106906 b, which orbits around the binary star and its disc at a distance greater than any other exoplanet discovered to date — 650 times the average Earth–Sun distance, or nearly 97 billion kilometres. HD 106906 b has a mammoth mass of up to 11 times that of Jupiter, and a scorching surface temperature of 1500 degrees Celsius. Thanks to SPHERE, HD 106906AB has become the first binary star system to have both an exoplanet and a debris disc successfully imaged, providing astronomers with a unique opportunity to study the complex process of circumbinary planet formation.

HD_106906_b_imageImage: This is a discovery image of planet HD 106906 b in thermal infrared light from MagAO/Clio2, processed to remove the bright light from its host star, HD 106906 AB. The planet is more than 20 times farther away from its star than Neptune is from our Sun. This is one of the most extreme separations known and it may be more appropriate to consider HD 106906 b a low mass brown dwarf companion. (Image: Vanessa Bailey).

Gemini views star formation in the Herbig-Haro object HH24

Posted in astronomy with tags , on October 2, 2015 by Tim Kendall

Gemini HH24Image and text credits: The HH 24 jet complex emanates from a dense cloud core that hosts a small multiple protostellar system known as SSV63. The nebulous star to the south is the visible T Tauri star SSV59. Color image based on the following filters with composite image color assignments in parenthesis: g (blue), r (cyan), I (orange), hydrogen-alpha (red), sulphur II (blue) images obtained with GMOS on Gemini North in 0.5 arcsecond seeing, and NIRI. Field of view is 4.2×5.1 arcminutes, orientation: north up, east left. Credit: Gemini Observatory/AURA/B. Reipurth, C. Aspin, T. Rector

A new Gemini Observatory image reveals the remarkable “fireworks” that accompany the birth of stars. The image captures in unprecedented clarity the fascinating structures of a gas jet complex emanating from a stellar nursery at supersonic speeds. The striking new image hints at the dynamic (and messy) process of star birth. Researchers believe they have also found a collection of runaway (orphan) stars that result from all this activity. Gemini Observatory has released one of the most detailed images ever obtained of emerging gas jets streaming from a region of newborn stars. The region, known as the Herbig-Haro 24 (HH 24) Complex, contains no less than six jets streaming from a small cluster of embedded in a molecular cloud in the direction of the constellation of Orion.

“This is the highest concentration of jets known anywhere,” says Principal Investigator Bo Reipurth of the University of Hawaii’s Institute for Astronomy (IfA), who adds, “We also think the very dynamic environment causes some of the lowest mass stars in the area to be expelled, and our Gemini data are supporting that idea.” Reipurth along with co-researcher, Colin Aspin, also at the IfA, are using the Gemini North data from the Gemini Multi-Object Spectrograph (GMOS), as well as the Gemini Near-Infrared Imager, to study the region which was discovered in 1963 by George Herbig and Len Kuhi. Located in the Orion B cloud, at a distance of about 400 parsecs, or about 1,300 light-years from our Solar System, this region is rich in young stars and has been extensively studied in all types of light, from radio waves to X-rays.

“The Gemini data are the best ever obtained from the ground of this remarkable jet complex and are showing us striking new detail,” says Aspin. Reipurth and Aspin add that they are particularly interested in the fine structure and “excitation distribution” of these jets. “One jet is highly disturbed, suggesting that the source may be a close binary whose orbit perturbs the jet body,” says Reipurth. The researchers report that the jet complex emanates from what is called a Class I protostar, SSV63, which high-resolution infrared imaging reveals to have at least five components. More sources are found in this region, but only at longer, submillimeter wavelengths of light, suggesting that there are even younger, and more deeply embedded sources in the region. All of these embedded sources are located within the dense molecular cloud core.

A search for dim optical and infrared young stars has revealed several faint optical stars located well outside the star-forming core. In particular, a halo of five faint Hydrogen-alpha emission stars (which emit large amounts of red light) has been found with GMOS surrounding the HH 24 Complex well outside the dense cloud core. Gemini spectroscopy of the hydrogen alpha emission stars show that they are early or mid-M dwarfs (very low-mass stars), with at least one of which being a borderline brown dwarf. The presence of these five very low-mass stars well outside the star-forming cloud core is puzzling, because in their present location the gas is far too tenuous for the stars to have formed there. Instead they are likely orphaned protostars ejected shortly after birth from the nearby star-forming core. Such ejections occur when many stars are formed closely together within the same cloud core. The crowded stars start moving around each other in a chaotic dance, ultimately leading to the ejection of the smallest ones. A consequence of such ejections is that pairs of the remaining stars bind together gravitationally. The dense gas that surrounds the newly formed pairs brakes their motion, so they gradually spiral together to form tight binary systems with highly eccentric orbits. Each time the two components are closest in their orbits they disturb each other, leading to accretion of gas, and an outflow event that we see as supersonic jets. The many knots in the jets thus represent a series of such perturbations.

Formation of brown dwarfs like stars

Posted in astronomy with tags , on August 3, 2015 by Tim Kendall

brown_dwarf_jetAn impression of a young brown dwarf. Evidence appears to be mounting that the star formation process also produces brown dwarfs by the same mechanism, i.e. disk accretion accompanied by energetic, sometimes episodic, outflows.  Even though there is almost certainly an overlap in mass distribution with giant planets, the two classes of bodies are fundamentally different. Article from Scientific American.

If the universe were a fairy tale, the celestial objects called brown dwarfs would be the ugly ducklings. Small and dim as they are, brown dwarfs are informally known as “failed stars.” But some scientists have proposed that brown dwarfs possess unrecognized majesty—that they are in fact gargantuan planets. Alas, a new study suggests that the story is not destined for a happy ending. Astronomers have detected the first direct evidence that these cosmic misfits are forged in a miniature version of star formation. The study was published in The Astrophysical Journal on July 1.

Brown dwarfs have, at most, 8 percent of the mass of our sun, so their interiors lack the high heat and pressure necessary to fuse hydrogen into helium—the thermonuclear process that powers regular stars. But brown dwarfs do not fit comfortably in the planet category, either. They are tens of times more massive than even heavyweights such as Jupiter, and keep much hotter cores by contracting in on themselves and fusing deuterium, explains James Di Francesco, an astrophysicist at the National Research Council Canada who was not involved with the study.

Because brown dwarfs seem to reside in this no-man’s-land between planets and stars, astronomers have long wondered about their origins. On the one hand, brown dwarfs could form like stars, through the collapse of vast clouds of gas and dust. The protostar born in such a condensation wraps itself in a disk of material, and interactions between this accretion disk and the baby star’s magnetic field launch two jets of material from opposite sides of the disk. On the other hand, planets form when bits of material in a disk around a star glom onto one another. Some astronomers even proposed that if a big enough chunk of material broke off the disk, it could seed a brown dwarf.

Over the last 15 years astronomers have found that young brown dwarfs share similar properties with young normal stars, particularly the jets and accretion disks, says Emma Whelan, an astrophysicist at University of Tübingen in Germany. But these surveys primarily examined brown dwarfs whose surrounding envelope of gas and dust had already begun to disperse. In the new study an international team of scientists led by Oscar Morata, an astronomer at the Academia Sinica in Taiwan, examined even younger proto–brown dwarfs to see if they found the jets of material that could only be explained by a process akin to that of normal star formation. “Basically we thought, you know, ‘if it walks like a duck, talks like a duck,’ maybe stars and brown dwarfs are the same kind of thing,” Morata says.

Glimpsing brown dwarfs at such an early stage of formation had previously proved difficult because brown dwarfs are so dim. But Morata’s team scoured data from the Spitzer and Herschel space telescopes for young, faint objects. They eventually settled on 10 proto–brown dwarf candidates and examined them using the Very Large Array (VLA) of radio telescopes in Socorro, New Mexico.

Among their sample, the astronomers spotted four proto–brown dwarfs spitting out the jets characteristic of regular star formation. Moreover, Morata’s team found that the brightness of these jets depended on the brightness of the proto–brown dwarf itself. There is a similar relationship between the brightness of protostars and their associated jets. These results lend the first direct observational evidence to the idea that brown dwarfs are produced by a scaled-down version of the process that forms stars. “I think that this team has done a terrific job of advancing our understanding of how brown dwarfs form,” Di Francesco says.

But what about the other six objects—the majority? According to Morata, the accretion process that drives jets on young stars and brown dwarfs is not continuous, so jets spurt on and off and may have been missed on the other six objects. Or the jets of these objects are simply too faint to see. Morata also allows for the possibility that these objects were not proto–brown dwarfs at all, but rather background galaxies. He says that the team’s next steps will be analyzing data on their proto–brown dwarf candidates that they have collected with the Atacama Large Millimeter/submillimeter Array (ALMA) of radio telescopes and requesting more VLA observation time to reexamine the candidates in better detail. Morata and his colleagues also hope to find other newborn brown dwarfs to study. “Four—well, it’s not that much,” Morata says. “It would be nice to have something more robust.”

Whelan says that many interesting questions arise from the conclusion that brown dwarfs form like stars, particularly regarding whether these objects could host their own planetary systems—and what those systems might be like. If so, the ugly ducklings might be home to great beauty after all.

Note: an updated abstract for the V1309 Sco paper (see sidebar) can be found here.

A multiple-star system in the first stages of formation

Posted in astronomy with tags , , on February 12, 2015 by Tim Kendall

54db86cdb5c4aCourtesy Large scale Herschel image of the dust in the region in blue, with the dense gas low resolution image in green, and the dense gas high-resolution image displaying filaments in red. Credit: B. Saxton (NRAO/AUI/NSF)

For the first time, astronomers have caught a multiple-star system in the beginning stages of its formation, and their direct observations of this process give strong support to one of several suggested pathways to producing such systems. The scientists looked at a cloud of gas some 800 light-years from Earth, homing in on a core of gas that contains one young protostar and three dense condensations that they say will collapse into stars in the astronomically-short period of 40,000 years. Of the eventual four stars, the astronomers predict that three may become a stable triple-star system. “Seeing such a multiple star system in its early stages of formation has been a longstanding challenge, but the combination of the Very Large Array (VLA) and the Green Bank Telescope (GBT) has given us the first look at such a young system,” said Jaime Pineda, of the Institute for Astronomy, ETH Zurich, in Switzerland. The scientists used the VLA and GBT, along with the James Clerk Maxwell Telescope (JCMT) in Hawaii, to study a dense core of gas called Barnard 5 (B5) in a region where young stars are forming in the constellation Perseus. This object was known to contain one young forming star. When the research team led by Pineda used the VLA to map radio emission from methane molecules, they discovered that filaments of gas in B5 are fragmenting, and the fragments are beginning to form into additional stars that will become a multiple-star system. “We know that these stars eventually will form a multi-star system because our observations show that these gas condensations are gravitationally bound,” Pineda said. “This is the first time we’ve been able to show that such a young system is gravitationally bound,” he added.

54db86db44d2bLeft: Close up of above to focus in the region forming the stars. Credit: B. Saxton (NRAO/AUI/NSF)

“This provides fantastic evidence that fragmentation of gas filaments is a process that can produce multiple-star systems,” Pineda said. Other proposed mechanisms include fragmentation of the main gas core, fragmentation within a disk of material orbiting a young star, and gravitational capture. “We’ve now convincingly added fragmentation of gas filaments to this list,” Pineda added. The condensations in B5 that will produce stars now range from one-tenth to more than one-third the mass of the Sun, the scientists said. Their separations will range from 3,000 to 11,000 times the Earth-Sun distance. The astronomers analyzed the dynamics of the gas condensations and predict that, when they form into stars, they will form a stable system of an inner binary, orbited by a more-distant third star. The fourth star, they suggest, will not long remain part of the system. inafirstastr

Above: A triple star system forming within a dense gas filament in a numerical simulation modeling a group of forming stars. The color indicates the gas density, where lighter colors are higher densities. Rhe image is about 10,000 astronomical units across where the projected separations between the three objects is about 2,000 and 4,000 AU. Credit: UMass Amherst

“Nearly half of all stars are in multiple systems, but catching such systems at the very early stages of formation has been challenging. Thanks to the combination of the VLA and the GBT, we now have some important new insight into how multiple systems form. Our next step will be to look at other star-forming regions using the new capabilities of the VLA and of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile,” Pineda said. In addition to Pineda, the international research team included members from the U.S., the UK, Germany, and Chile. The astronomers reported their findings in the 12 February edition of the scientific journal Nature.

The paper is Pineda J.E., Offner S.S.R., Parker R.J., Arce H.G., Goodman A.A., Caselli P., Fuller G.A., Bourke T.L., Corder S.A. “The formation of a quadruple star system with wide separation”, Nature, published online 11 February 2015,

Early stages of massive star formation: “Yellow balls” in W33

Posted in astronomy with tags , , on February 7, 2015 by Tim Kendall

Volunteers using the web-based Milky Way Project brought star-forming features nicknamed "yellowballs" to the attention of researchers, who later showed that they are a phase of massive star formation.Image Credit: NASA/JPL-Caltech

Citizen scientists have helped identify a particular stage in the still poorly understood process of massive star formation:

Infrared wavelengths of 3.6, 8.0, and 24.0 microns observed by the Spitzer Space Telescope are mapped into visible colors red, green, and blue in this striking image. The cosmic cloud of gas and dust is W33, a massive starforming complex some 13,000 light-years distant, near the plane of our Milky Way Galaxy. So what are all those yellow balls? Citizen scientists of the web-based Milky Way Project found the features they called yellow balls as they scanned many Spitzer images and persistently asked that question of researchers. Now there is an answer. The yellow balls in Spitzer images are identified as an early stage of massive star formation. They appear yellow because they are overlapping regions of red and green, the assigned colors that correspond to dust and organic molecules known as PAHs at Spitzer wavelengths. Yellow balls represent the stage before newborn massive stars clear out cavities in their surrounding gas and dust and appear as green-rimmed bubbles with red centers in the Spitzer image. Of course, the astronomical crowdsourcing success story is only part of the Zooniverse. The Spitzer image spans 0.5 degrees or about 100 light-years at the estimated distance of W33.

Text and image: APOD. Update: Here’s a great article from Scientific American about the future of exoplanet research and in particular the difficulties of studying different types of exoplanet with the same instrument. It is well worth a read.

Cloud-sculpting star cluster NGC 6823

Posted in astronomy with tags , on October 15, 2014 by Tim Kendall

Image credit and copyright: Donald P. Waid (Waid Observatory) courtesy Astronomy Picture of the Day

Star cluster NGC 6823 is slowly turning gas clouds into stars. The center of the open cluster, visible on the upper left, formed only about two million years ago and is dominated in brightness by a host of bright young blue stars. Some outer parts of the cluster, visible in the featured image’s center as the stars and pillars of emission nebula NGC 6820, contain even younger stars. The huge pillars of gas and dust likely get their elongated shape by erosion from hot radiation emitted from the brightest cluster stars. Striking dark globules of gas and dust are also visible across the lower left of the featured image. Open star cluster NGC 6823 spans about 50 light years and lies about 6000 light years away toward the constellation of the Fox (Vulpecula).

Wide-field view from ESO of part of the Taurus star-forming region

Posted in astronomy with tags , on September 6, 2014 by Tim Kendall

Wide-field view of part of the Taurus star formation region
Credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin

This wide field image shows extensive dust and small clumps of star formation in part of the Taurus star formation region. A faint star at the centre of this picture is the young binary star system HK Tauri. ALMA observations of this system have provided the clearest picture ever of protoplanetary discs in a double star. The new result demonstrates one possible way to explain why so many exoplanets — unlike the planets in the Solar System — came to have strange, eccentric or inclined orbits. This picture was created from images from the Digitized Sky Survey 2.

Artist’s impression of the discs around the young stars HK Tau

Artist’s impression of the misaligned protoplanetary disks HK Tauri A and B (courtesy ESO). Update: The most massive star in the Milky Way’s largest star-forming region, W49, has been reckoned at between 100 and 180 solar masses:

Astronomers led by Shiwei Wu of the Max Planck Institute for Astronomy have identified the most massive star in our home galaxy’s largest stellar nursery, the star-forming region W49. The star, named W49nr1, has a mass between 100 and 180 times the mass of the Sun. Only a few dozen of these very massive stars have been identified so far. As seen from Earth, W49 is obscured by dense clouds of dust, and the astronomers had to rely on near-infrared images from ESO’s New Technology Telescope and the Large Binocular Telescope to obtain suitable data. The discovery is hoped to shed light on the formation of massive stars, and on the role they play in the biggest star clusters.


Credit: S.-W. Wu, A. Bik, Th. Henning, A. Pasquali, W. Brandner, A. Stolte and MPIA Heidelberg press release. J and H-band data originally published in Alves and Homeier 2003.

The Omega nebula M17 from ISAAC on the VLT

Posted in astronomy with tags , , on February 4, 2014 by Tim Kendall

Image credit: ESO Three-colour composite of the sky region of M 17, a H II region excited by a cluster of young, hot stars. A large silhouette disc has been found to the south-west of the cluster centre. The present image was obtained with the ISAAC near-infrared instrument at the 8.2-m VLT ANTU telescope at Paranal.

Star-Forming Region LH 95 in the Large Magellanic Cloud

Posted in astronomy with tags , on January 16, 2014 by Tim Kendall

hs-2006-55-a-xlarge_webImage credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA) –ESA Hubble Collaboration

Swirls of gas and dust reside in this ethereal-looking region of star formation imaged by NASA’s Hubble Space Telescope. This majestic view, located in the Large Magellanic Cloud (LMC), reveals a region where low-mass, infant stars and their much more massive stellar neighbors reside. A shroud of blue haze gently lingers amid the stars.

Known as LH 95, this is just one of the hundreds of star-forming systems, called associations, located in the LMC some 160,000 light-years distant. Earlier ground-based observations of such systems had only allowed astronomers to study the bright blue giant stars present in these regions. With Hubble’s resolution, the low-mass stars can now be analyzed, which will allow for a more accurate calculation of their ages and masses.

This detailed view of the star-forming association LH 95 was taken with Hubble’s Advanced Camera for Surveys and provides an extraordinarily rich sample of newly formed low-mass stars. The LMC is a galaxy with relatively small amounts of elements heavier than hydrogen, giving astronomers an insight into star formation in environments different than our Milky Way.

Of spiral galaxies, star formation and supernovae

Posted in astronomy with tags , , on October 22, 2013 by Tim Kendall

Image: APOD NGC 2841 is a type of galaxy called a flocculent spiral, which features short spiral arms rather than prominent and well-defined galactic limbs. Credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration Acknowledgment: M. Crockett and S. Kaviraj (Oxford University, UK), R. O’Connell (University of Virginia), B. Whitmore (STScI) and the WFC3 Scientific Oversight Committee. The details of star formation in rare spirals such as NGC 2841 are difficult:

There is still much that astronomers don’t understand, such as how do the properties of stellar nurseries vary according to the composition and density of the gas present, and what triggers star formation in the first place? The driving force behind star formation is particularly unclear for a type of galaxy called a flocculent spiral, such as NGC 2841.

Because of the short-lived nature of massive stars, supernovae and star formation are inextricably linked, with the effects of shock waves either triggering or inhibiting star formation, as the shocks interact with the gas. Two recent papers have investigated supernovae in distant galaxies which appear unexpectedly luminous. The first gives an alternative to the pair instability route for the most massive stars, postulating supernovae driven in part at least by draining energy from the magnetar remnant. The second points to the origin of type Ib supernovae in the helium-rich, stripped cores of Wolf-Rayet stars.


Dust in the edge-on spiral galaxy NGC 891, courtesy APOD

The Cat’s Paw Nebula NGC 6334 from the ArTeMiS camera on APEX

Posted in astronomy with tags , , , on October 3, 2013 by Tim Kendall


ArTeMiS is a new wide-field submillimetre-wavelength camera that will be a major addition to APEX’s suite of instruments and further increase the depth and detail that can be observed. The new generation detector array of ArTeMIS acts more like a CCD camera than the previous generation of detectors. This will let wide-field maps of the sky be made faster and with many more pixels.

Image and credit: ESO show the wide field structure of the submillimeter sky, revealing the glow of dust in regions of ongoing star formation and how the regions are linked with inflowing material, glowing at a few tens and up to around a hundred degrees Kelvin. While similar observations have been made as early as 1975 (for the reflection nebula NGC 2023), only now is the wide-field detector capability reaching this level of imaging. The optical view of the obscuring dust and stars of various degrees of reddening is overlain. The usual optical view of the dust, not showing it glowing but only obscuring starlight, is on display in this view of the Corona Australis region (below). Credit to an alternative site today. I would also like to clarify my previous post to point out that the Hipparcos parallax for R CrA itself is not reliably measured. The accepted distance for it and the whole cloud complex is 130 pc. The very much more distant globular cluster NGC 6723 is prominent at the top of this image. For another view of the Cat’s Paw Nebula, see here. For a comprehensive look at the Corona Australis star forming region, go here.


A review by Philippe André of the new paradigm of star formation in the light of Herschel is here (arXiv):

Recent studies of the nearest star-forming clouds of the Galaxy at submillimeter wavelengths with the Herschel Space Observatory have provided us with unprecedented images of the initial conditions and early phases of the star formation process. The Herschel images reveal an intricate network of filamentary structure in every interstellar cloud. These filaments all exhibit remarkably similar widths – about a tenth of a parsec – but only the densest ones contain prestellar cores, the seeds of future stars.

On a related topic, the earlier Spitzer infrared space telescope has now been refitted for exoplanet observations. In another microlensing find, a sub-Neptune mass planet has been found ~ 1 AU from a late M dwarf. The paper (arXiv, accepted to ApJ) rounds up the interesting concepts at the frontiers of astrometry. Finally, this great picture of Phobos and Deimos, a raw frame from Curiosity, is exceeded only by this video.


Update: arXiv/astro-ph today latest on the heavy concentrations of protostars in NGC 6334, which has been likened to a “mini-starburst” event.

The Herschel view of the heart of Orion

Posted in astronomy with tags , , , on August 27, 2013 by Tim Kendall


Image: ESA/Herschel/ Ph. André, V. Könyves, N. Schneider (CEA Saclay, France) for the Gould Belt survey Key Program. The image is a composite of the wavelengths of 70 microns (blue), 160 microns (green) and 250 microns (red) and spans about 1.3 x 2.4 degrees. North is up and east is to the left. In this view, the nebula corresponds to the brightest region in the center of the image, where it is lit up by the Trapezium group of stars at its heart. Embedded within the red and yellow filaments are a handful of point-like sources: these are protostars, the seeds of new stars that will soon ignite and begin to flood their surrounds with intense radiation.


This colour-composite image of IC 5146 shows the extended filamentary structure of this star-forming cloud. A detailed study of this complex has shown a total of 27 filaments that all appear to have very similar widths, with a value of about 0.3 light years. The glowing cavity at the top of the image, also known as the Cocoon Nebula, is an HII region, where a young and bright B0 star illuminates the ionised hydrogen gas, causing it to shine. Some young stellar objects are visible as bright spots along the main filaments; many other young stellar objects are located in the Cocoon Nebula but are not visible in this image.

Global collapse of a dark molecular cloud sees hundred solar mass star caught at formation

Posted in astronomy with tags , on July 14, 2013 by Tim Kendall


Images: (top) This wide-field optical view shows a region of sky in the southern constellation of Norma. At the centre lies the massive star-forming region SDC 335.579-0.292, but this is too obscured by dust to be visible. The very hot blue star HD 147937 and its surrounding ejected clouds can be seen at upper right. Credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin (below) Observations of the dark cloud SDC 335.579-0.292 using the Atacama Large Millimeter/submillimeter array (ALMA) have given astronomers the best view yet of a monster star in the process of forming. A stellar womb with over 500 times the mass than the Sun has been found and appears as the yellow blob near the centre of this picture. This is the largest ever seen in the Milky Way — and it is still growing. Credit: ALMA (ESO/NRAJ/NRAO)/NASA/Spitzer/JPL-Caltech/GLIMPSE

eso1331a There are two theories on the formation of the most massive stars. One suggests that the parental dark cloud fragments, creating several small cores that collapse on their own and eventually form stars. The other is more dramatic: the entire cloud begins to collapse inwards, with material racing towards the cloud’s centre to form one or more massive behemoths there. A team led by Nicolas Peretto of CEA/AIM Paris-Saclay, France, and Cardiff University, UK, realised that ALMA was the perfect tool to help find out what was really happening. SDC335.579-0.292 was first revealed as a dramatic environment of dark, dense filaments of gas and dust through observations with NASA’s Spitzer Space Telescope and ESA’s Herschel Space Observatory. Now the team has used the unique sensitivity of ALMA to look in detail at both the amount of dust and the motion of the gas moving around within the dark cloud — and they have found a true monster. This core — the womb of the embryonic star — has over 500 times the mass of our Sun swirling around within it. The ALMA observations show that much more material is still flowing inwards and increasing the mass still further. This material will eventually collapse to form a young star up to 100 times as massive as our home star — a very rare beast.

The paper is N. Peretto et al., “Global collapse of molecular clouds as a formation mechanism for the most massive stars”, A&A, 555, A112 (2013). The data imply a huge mass infall rate of around 0.0025 solar masses per year.

Stars forming in the Rosette Nebula

Posted in astronomy with tags , , on May 18, 2013 by Tim Kendall

Original image download(11 Mb jpeg). I think this is probably the best image from Herschel where the forming stars are truly pinpointed:

The Rosette Nebula resides some 5000 light-years from Earth and is associated with a larger cloud that contains enough dust and gas to make the equivalent of 10 000 Sun-like stars. The Herschel image shows half of the nebula and most of the Rosette cloud. The massive stars powering the nebula lie to the right of the image but are invisible at these wavelengths. Each colour represents a different temperature of dust, from –263ºC (only 10ºC above absolute zero) in the red emission to –233ºC in the blue. The bright smudges are dusty cocoons hiding massive protostars. These will eventually become stars containing around ten times the mass of the Sun. The small spots near the centre and in the redder regions of the image are lower mass protostars, similar in mass to the Sun.

A new paper today by Gahm et al. ( pdf) addresses the question of brown dwarf formation in the region. From the abstract:

We conclude that the entire complex of shells, elephant trunks, and globulettes in the northern part of the nebula is expanding with nearly the same velocity of ~22 km/s, and with a very small spread in velocity among the globulettes. Some globulettes are in the process of detaching from elephant trunks and shells, while other more isolated objects must have detached long ago and are lagging behind in the general expansion of the molecular shell. The suggestion that some globulettes might collapse to form planetary-mass objects or brown dwarfs is strengthened by our finding of dense cores in several objects.

“Baby stars in the Rosette Cloud” (ESA)

Update: The results from the Herschel mission have shown us a pre-picture of star formation, as material flows under the influence of magnetic fields into and along streams, or filaments, which lead to condensation under self-gravitation and all the accretion phenomena of star formation – disks – which have been observed in the near-infrared. Now, in a new paper by P. Hennebelle, “On the origin of non-self-gravitating filaments in the ISM”, Astronomy & Astrophysics 556, A153, the physical origins of the filaments themselves, as they exist in the interstellar medium before any onset of self-gravitation and star formation, have been investigated thoroughly by supercomputer simulations of the underlying magnetohydrodynamic processes within the material. The formation of the filaments themselves is thought to be simply driven by energy dissipation.

Filaments are ubiquitous in the interstellar medium, as recently emphasized by Herschel observations, but their physical origin remains elusive. In this paper, the author uses ideal MHD simulations to study the formation of non-gravitating clumps in various conditions, including different setups, magnetization, and Mach numbers. On average, clumps in MHD simulations are more filamentary than clumps in hydrodynamic simulations. Detailed analyses reveal that the filaments are in general preferentially aligned with the strain, indicating that they simply result from the stretch induced by turbulence. Moreover, filaments tend to be confined by the Lorentz forces, which therefore lead them to survive longer in magnetized flows. The author concludes that filaments are ubiquitous because they are the results of the very generic turbulent strain, and because the magnetic field helps to keep them coherent. Energy dissipation appears to play a fundamental role in filament formation.