Young star-forming region NGC 2264 from Spitzer

All NASA Spitzer images of NGC 2264

The region has now been studied in detail by Sung & Bessell (2010), and 79 young brown dwarf candidates (YBDCs) are given (Sect. 5). Following my 2005 attempt to find the young brown dwarfs in NGC 2264, which Sung & Bessell discuss, I am delighted to see I found three of their 79. I think, zooming in on the Spitzer image you can pretty much see straightaway which ones are the cluster members (pinkish) and which are in the foreground (blue). Another Spitzer image, lacking the longest wavelength infrared light, is below.

Identifying primordial substructure in NGC 2264

According to the discovery’s lead author Paula Teixeira, [then] a PhD student working at the Harvard-Smithsonian Center for Astrophysics, star-forming clouds like this one are dynamic and evolving structures. She suspects that at a certain stage of their evolution, chaotic internal motions in the clouds cause strands of dusty filaments, or fragments, to form. As the filaments cool, gas and dust inside the strands clump and fragment further, eventually creating a line of evenly spaced protostars. The average distance separating the baby stars is determined by the temperature and the density of the filaments.

The line of sight toward the planetary nebula Jonckheere 900

Image credit: ESA/Hubble and NASA

The object in this image is Jonckheere 900 or J 900, a planetary nebula — glowing shells of ionized gas pushed out by a dying star. Discovered in the early 1900s by astronomer Robert Jonckheere, the dusty nebula is small but fairly bright, with a relatively evenly spread central region surrounded by soft wispy edges.

Despite the clarity of this Hubble image, the two objects in the picture above can be confusing for observers. J 900’s nearby companion, a faint star in the constellation of Gemini, often causes problems for observers because it is so close to the nebula — when observation conditions are bad, this star seems to merge into J 900, giving it an elongated appearance. Hubble’s position above the Earth’s atmosphere means that this is not an issue for the space telescope.

The nebula lies close to the galactic plane and is 4.9 kpc distant. It is coincident with a radio source. The bright star in the field is not associated, and lies in the foreground. It is angularly separated from the nebula by about 12 arcseconds. In the 2MASS point source catalogue it has designation 06255700+1747161, with J, H and K magnitudes 11.34, 11.04 and 10.96 respectively. These colours suggest it is a mid-G dwarf (see Fig. 2 of this link) with absolute J magnitude ~ +3.6 (Table 3), yielding a distance of ~ 350 pc. Even if it were a giant, with absolute magnitude ~ 0, it would be only 2 kpc distant. There is no counterpart in the WISE data, because the nebula itself becomes overwhelmingly bright in the longer WISE passbands. The Hubble imaging presented here shows that the star itself has a faint companion, although there is no proof the two are physically related. The companion may itself lie serendipitously in the line of sight, as does the extended reddish object at lower left, which is likely a galaxy.

The central star of the planetary nebula is of the 18th magnitude. The faint companion to the star looks comparable, so I roughly estimate V ~ 18. Therefore, if the faint companion does lie at 350 pc, this gives an absolute V band magnitude of +10.3, which corresponds to a spectral type ~ M2.5 dwarf.

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Thirty million year old open cluster NGC 2547

Image credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin.

The region has been studied in detail by Jeffries et al. (2004). Gorlova et al. (2007) have also searched for debris disks, concluding that by 30 Myr the inner regions of disks around solar-type stars (within 1 AU) have been comprehensively cleared of potential planet-forming material.

Another cluster of similar age is IC 4665 in Ophiuchus (above). A complete mass function down to the substellar regime has now been published, in agreement with findings from older clusters, notably the Pleiades.

The earliest stages of star formation in Orion

Image credit: Herschel Space Observatory

The Herschel Photodetector Array Camera and Spectrometer (PACS) instrument collected infrared light at 70 and 160 micrometers in wavelength, comparable to the width of a human hair. Researchers compared these observations to previous scans of the star-forming regions in Orion taken by Spitzer. Extremely young protostars identified in the Herschel views but too cold to be picked up in most of the Spitzer data were further verified with radio wave observations from the APEX ground telescope. Of the 15 newly discovered protostars, 11 possess very red colors, meaning their light output trends toward the low-energy end of the electromagnetic spectrum. This output indicates the stars are still embedded deeply in a gaseous envelope, meaning they are very young. An additional seven protostars previously seen by Spitzer share this characteristic. Together, these 18 budding stars comprise only five percent of the protostars and candidate protostars observed in Orion. That figure implies the very youngest stars spend perhaps 25,000 years in this phase of their development.

Top: the nebula Messier 78 is shown in a three-color composite from three telescopes: in green is the 160-micron, far-infrared light collected by Herschel’s Photodetector Array Camera and Spectrometer (PACS). Appearing in blue is 24-micron light from Spitzer. Finally, 870-micron radio wave light gathered by APEX glows red. Bottom: the same region appears in a separate three-color composite that shows infrared observations from two instruments aboard NASA’s Spitzer Space Telescope. Blue represents 3.6- and 4.5-micron light and green shows light of 5.8 and 8 microns, both captured by Spitzer’s Infrared Array Camera (IRAC). Red is 24-micron light detected by Spitzer’s Multiband Imaging Photometer (MIPS). Image credit: NASA/ESA/ESO/JPL-Caltech/Max-Planck Institute for Astronomy.

Image: ESO 2.2m/WFI La Silla Observatory

Pre-discovery imaging of the 2 pc brown dwarf binary WISE 1049-5319

WISE 1049-5319 is the brown dwarf binary recently discovered at a distance of only 2.0 ± 0.15 pc by Luhman (2013, now published). The above image spans 10 x 10 arcminutes and is centered on the WISE position. This is the POSS-II red imaging of the region provided by the Digitized Sky Survey, obtained in 1992. The lines indicate the detection of the brown dwarf pair in this imaging, as identified in the paper (arXiv.org pdf preprint, Fig. 1, p. 6), to which readers should compare. The red band magnitude is ~ 18.6. The box is the current position, again from inspection of the published imaging. The proper motion is roughly 3 arcseconds per year, so the object has moved approximately one arcminute in the ~ 20 years since the POSS imaging, as can be seen.

Further discussion of this object has been published today by Mamajek (arXiv pdf) who detects it in images from 1984, which also hint at its binarity. The object can be detected on the DSS IR plate from 1978, as Luhman indicates. This is the first object outside the solar system to be found so close to the Sun since the 1916 measurement of Barnard’s Star, for which the accepted distance is 1.834 ± 0.001 pc. That it has been overlooked for so long is a consequence of its location close to the galactic plane, which previous searches have largely avoided because of the difficulties of identifying faint, nearby, moving objects against the dense background star fields.

Update: Seventy-six T dwarfs from the UKIDSS Large Area Survey

Direct imaging discovery of a 12 – 14 Jupiter mass circumbinary object

The new object is 2MASS J01033563-5515561ABb, which orbits a pair of young M dwarfs at a projected separation of 84 AU. Both a common proper motion and Keplerian orbital motion have been verified. The object is of spectral type L and has a mass at the deuterium-burning limit, which is often used as an ad-hoc definition of the mass boundary which separates brown dwarfs from planets. The system is likely a member of the Tucana-Horologium association, with an age of 30 Myr. The existence of the object is a strong challenge for theories of the planet formation process. From the paper (internal references omitted):

A planetary formation scenario by core-accretion can very probably be excluded for several reasons. First, the separation is too large for a formation in situ. Second, the companion has 3.6% of the mass of its host system, which is of the order of magnitude of the maximum total mass of the proto- planetary disc from which core-accretion planets are formed. Finally, such a 12-14 M Jup companion would be a very rare occurence, according to [recent estimates of the] the core-accretion planetary mass function.

Update: I have included the imaging courtesy New Scientist/ESO. The paper is P. Delorme et al., “Direct imaging discovery of 12-14 Jupiter mass object orbiting a young binary system of very low-mass stars”, and is accepted to A&A letters. It appears today at arXiv.org (pdf).

Earth, Sun and comet PanSTARRS

Image caption: Image of the solar corona, taken by the SECCHI inner Heliospheric Imager (HI-1) on the STEREO Behind observatory on March 12, 2013 at 06:49:44 UT. Image credit: STEREO latest images and daily browse images. This remarkable image is just one of many showing comet Pan-STARRS from the vantage point of one of the STEREO spacecraft. See Where is STEREO? Dark and bright vertical lines are detector artifacts.

Update: A recent NASA video has the comet moving up along the dark line, which is itself moving across the image. The dark line may be a slit for spectroscopy of moving objects.

Multiwavelength imaging of the supernova SN 1006 remnant

Image credit: ESO Radio (red): NRAO/AUI/NSF/GBT/VLA/Dyer, Maddalena & Cornwell, X-ray (blue): Chandra X-ray Observatory; NASA/CXC/Rutgers/G. Cassam-Chenaï, J. Hughes et al., Visible light (yellow): 0.9-metre Curtis Schmidt optical telescope; NOAO/AURA/NSF/CTIO/Middlebury College/F. Winkler and Digitized Sky Survey.

Supernova SN 1006: brightest stellar event in recorded history

Different communities of astronomers all over the world observed the supernova of the year 1006. Some of them, including Chinese astronomers, highlighted the fact that the astronomical event was visible for three years. The most explicit record, made by the Egyptian doctor and astronomer Ali ibn Ridwan (988-1061), notes that the phenomenon was about three times brighter than Venus, and that it emitted light of a quantity equivalent to almost a quarter of the Moon’s brightness.

Infall of dark carbon-rich material in the Jupiter system

Sky and Telescope report on a recently accepted paper in Icarus:

Callisto’s reflectivity is only about 19% — even though its surface should be largely water ice. Something has contaminated the ice, and over the years several planetary scientists have suggested that carbon-rich debris from the irregular satellites was somehow involved. The numbers suggest that some 50 million billion tons of small particles, coffee-ground size and smaller, have been winnowed away. A subtle sunlight-induced effect called Poynting-Robertson drag causes these bits to slowly spiral toward Jupiter. The effect was first postulated in 1937.

Image credits: Ganymede (top) and Callisto, from the Galileo orbiter, 1999 and 2001.

Young brown dwarfs in IC 348, Serpens, Ophiuchus, Upper Scorpius, and Orion

Spitzer image credit: NASA, ESA, J. Muzerolle (STScI), E. Furlan (NOAO and Caltech), K. Flaherty (University of Arizona/Steward Observatory), Z. Balog (Max Planck Institute for Astronomy), and R. Gutermuth (University of Massachusetts, Amherst)

The young (3 Myr) star-forming region IC 348 has been in the news recently concerning pulsed accretion in the protostar LRLL 54361. The region has now been examined extremely thoroughly by C. Alves de Oliveria and co-workers at Grenoble, who have spectroscopically confirmed thirteen new brown dwarfs to add to the previously known thirty. The latest objects have spectral type L0 and masses at the deuterium-burning limit.

The log-normal initial mass function measured in this work is consistent with the expectation of one further T dwarf, which has indeed been observed by the Grenoble group using methane imaging, but not yet spectroscopically confirmed.

The Grenoble group is also searching in core of Serpens, where two objects have been found with masses of a few Jupiters. Together with S Ori 70, and contingent upon confirmation spectroscopy, these are among the lowest-mass brown dwarf candidates yet found in star forming regions.

The controversy surrounding S Ori 70 appears not yet resolved, with some arguments favouring membership of the star-forming region and others indicating this is a T dwarf in the foreground. H-band spectroscopy does not in this case indicate youth. However the small proper motion, along with other factors, does point towards cluster membership. Two papers from 2008, both making use of mid-infrared imaging from Spitzer, come to opposite conclusions on the matter.

Other low mass young cluster candidates have been found in the Trapezium and the rho Ophiuchi (pictured; WISE image from Wikipedia) star-forming regions. In addition to the disk brown dwarf ISO-Oph 102* and binary objects I have referred to in a previous post, the least massive candidate brown dwarf member of the latter cluster has two or three Jupiter masses, a temperature around 1400 K and, remarkably, is seen behind fifteen or sixteen magnitudes of visual extinction. However, there is doubt about the status of this object, as pointed out by Lodieu et al., who give a recent overview of the topic. Furthermore, methane imaging might not be an effective tool to find young T dwarfs. The reasons for this likely originate in cloud formation in these low-gravity atmospheres, which may be methane-poor.

*The designation comes from the original ISOCAM study of star formation in the region.

As a footnote: the astrophysics research institute at Grenoble used to be called the Laboratoire d’Astrophysique de Grenoble (LAOG), but has undergone a name change and is now IPAG, the Institut de Planétologie et Astrophysique de Grenoble.

Update: Upper Scorpius is part of the Sco-Cen OB association and now has a revised age of around 11 Myr, with implications for the model-derived masses of brown dwarfs found there. A new, complete census of the substellar population in the region has been published very recently.

The flaming star, runaway stars and ancient collisions in Orion

Image credit: APOD and copyright

AE Aurigae is a hot, blue runaway star which shares with μ Columbae an origin in a gravitational interaction between two massive binaries 2.5 Myr ago in the Orion nebula, near the present location of the Trapezium cluster. The two binaries are thought to have exchanged partners, dynamically ejecting the two runaways and leaving behind the odd eccentric spectroscopic binary ι Orionis. The two runaways are moving away from Orion with equal velocities in opposite directions. Another runaway star, 53 Arietis, was also ejected from Orion but likely in an earlier event.

Recently, a pulsar has been found which can be kinematically traced back to the Upper Scorpius OB association, to an event which also gave rise to the famous runaway star zeta Ophiuchi. This event is thought to have been precipitated by the supernova explosion itself dissociating the previously existing binary pair. The bow shock seen below is created as ζ Oph ploughs through the interstellar medium at 24 kilometers per second. Quoting Hoogerwerf et al. 2000:

These two cases provide the first specific kinematic evidence that both mechanisms proposed for the production of runaway stars, the dynamical ejection scenario and the binary-supernova scenario, operate in nature.

Image credit: APOD, NASA, JPL, Spitzer

Star-forming region NGC 602 in the Small Magellanic Cloud

Image Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA) – ESA/Hubble Collaboration

Otherwise known as N90, this is a classic region for the study of star formation, boasting a well-defined pre-main sequence. More than 5,500 cluster members have been detected with HST, down to the 28th magnitude.

The region, with Chandra X-ray (purple) and Spizter infrared (red) overlain on the Hubble optical image.

Massive star-forming region Sharpless 2-106

Image credit: HST

Sharpless 2-106, Sh2-106 or S106 for short, lies nearly 2,000 light-years from us. The nebula measures several light-years in length. It appears in a relatively isolated region of the Milky Way galaxy. A massive, young star, IRS 4 (Infrared Source 4), is responsible for the furious activity we see in the nebula. Twin lobes of super-hot gas, glowing blue in this image, stretch outward from the central star. A ring of dust and gas orbiting the star acts like a belt, cinching the expanding nebula into an “hourglass” shape. Hubble’s sharp resolution reveals ripples and ridges in the gas as it interacts with the cooler interstellar medium. Dusky red veins surround the blue emission from the nebula. The faint light emanating from the central star reflects off of tiny dust particles. This illuminates the environment around the star, showing darker filaments of dust winding beneath the blue lobes. Detailed studies of the nebula have also uncovered several hundred brown dwarfs. At purely infrared wavelengths, more than 600 of these sub-stellar objects appear. These “failed” stars weigh less than a tenth of our Sun. Because of their low mass, they cannot produce sustained energy through nuclear fusion like our Sun does. They encompass the nebula in a small cluster.

An alternative image from the Gran Telescopio Canarias (GTC) is here and a press release from the Subaru telescope concerning the brown dwarf discoveries is here, with the 2006 paper from the Astronomical Journal. At left is the infrared imaging from Subaru. The least massive and faintest brown dwarfs observed are only a few times more massive than Jupiter. Examples are highlighted in a supplementary image.

Orion Nebula ‘bullets’ with Gemini adaptive optics

Image Credit: Gemini Observatory/AURA

This image, obtained during the late commissioning phase of the GeMS adaptive optics system, with the Gemini South AO Imager (GSAOI) on the night of December 28, 2012, reveals exquisite details in the outskirts of the Orion Nebula. The large adaptive optics field-of-view (85 arcseconds across) demonstrates the system’s extreme resolution and uniform correction across the entire field. The three filters used for this composite color image include [Fe II], H2, and, K(short)-continuum (2.093 microns) for blue, orange, and white layers respectively. The natural seeing while these data were taken ranged from about 0.8 to 1.1 arcseconds, with AO corrected images ranging from 0.084 to 0.103 arcsecond. Each filter had a total integration (exposure) of 600 seconds. In this image, the blue spots are clouds of gaseous iron “bullets” being propelled at supersonic speeds from a region of massive star formation outside, and below, this image’s field-of-view. As these “bullets” pass through neutral hydrogen gas it heats up the hydrogen and produces the pillars that trace the passage of the iron clouds.

Image source and more, including an animation of this image together with a 2007 image from an earlier AO instrument, showing the movement of the bullets over a five year baseline.

Crescent Mercury from MESSENGER

Image credit and detail

It is said that the astronomer Copernicus never saw the elusive planet Mercury, so perhaps it is not so surprising that modern day astronomers had to wait a long time before the first observational confirmation of both brown dwarfs and extrasolar planets in 1995, although while planets around other stars had been postulated for centuries, the idea of a brown dwarf first hit the science stands only in 1963.

Today I want to mention two ongoing research efforts, one using the radial velocity method and the other an unusual direct imaging technique. The MARVELS survey is one of four efforts which form the third phase of the Sloan Digital Sky Survey (SDSS III). This ongoing project will monitor the radial velocities of 11,000 bright stars over six years and be able to detect giant planets in orbits with periods of two years or less. One aim of the project is to investigate the so-called ‘brown dwarf desert’, an apparent paucity of these objects in close binary orbit around main sequence stars when compared to low-mass stellar companions. One brown dwarf companion has a minimum mass around 28 Jupiter masses and orbits a slightly evolved F9 star roughly every six days. A further similar discovery was announced today, a forty Jupiter mass object in an eccentric 13 day orbit around a G0 subgiant.

The Lucky imaging technique exploits extremely short exposure times to ‘freeze’ atmospheric (seeing) disturbances to obtain resolutions near the diffraction limit from ground-based telescopes. In a recent paper new low mass companions have been found in a sample of 451 late K and M stars, constraining the binary fraction in this regime to around 20%.

Those interested in the pre-1995 history of seeking brown dwarfs should refer to this presentation by Rafael Rebolo, one of the leaders in the field, and review articles by Gibor Basri (2000), Oppenheimer et al. (2000) and Kumar (2002).

The Planets around Low Mass Stars (PALMS) collaboration has published two discoveries relevant to the ‘brown dwarf desert’ question, using high contrast adaptive optics imaging on Keck and Subaru. The second is a good candidate for a near-future dynamical mass measurement.

Update: MARVELS-6b is a newly discovered 32 Jupiter mass object in a 47 day orbit around a solar-type star with an age less than 6 Gyr.

Star forming filament Lupus 3

Image credit: ESO

An evocative new image from ESO shows a dark cloud where new stars are forming, along with a cluster of brilliant stars that have already emerged from their dusty stellar nursery. The new picture was taken with the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile and is the best image ever taken in visible light of this little-known object. In the centre of this new image there is a dark column resembling a cloud of smoke. Within this column shines a small group of brilliant stars. At first glance these two features could not be more different, but they are in fact closely linked. The cloud contains huge amounts of cool cosmic dust and is a nursery where new stars are being born. It is likely that the Sun formed in a similar star formation region more than four billion years ago. This cloud is known as Lupus 3 and it lies about 600 light-years from Earth in the constellation of Scorpius. As the denser parts of such clouds contract under the effects of gravity they heat up and start to shine. At first this radiation is blocked by the dusty clouds and can only be seen by telescopes observing at longer wavelengths than visible light, such as the infrared. But as the stars get hotter and brighter their intense radiation and stellar winds gradually clear the clouds around them until they emerge in all their glory.

Post common envelope binary WD 0137-349

Image credit: Digital Drew Space Art’s photostream as featured by Universe Today.

The WD 0137-349 system is an odd ultra close binary approximately 200 light years away. The smaller but more massive component is a small massive white dwarf, formerly the core region of a normal star. The larger component is a close low mass brown dwarf which orbits its white dwarf companion in a tight two hour orbit. It glows with dull reddish color, and largely from this angle the brown dwarf is illuminated by the white dwarf.

This binary, discovered in 2006, is proof of the survival of a brown dwarf companion through engulfment during the red giant phase. The brown dwarf has been detected in the near-infrared. The period is 116 minutes. An even shorter period binary, NLTT 5306, has been discovered very recently. Wider, spatially resolved binaries consisting of a white dwarf and a proven substellar companion are known, but rare. Unresolved L dwarf companions to white dwarfs are also few in number. Prior to the discovery of the Y dwarf companion to WD 0806-661 to which I drew attention a few days ago, one wide T dwarf companion is also in the literature, the companion to the high proper motion white dwarf LSPM 1459+0857. Lastly, one interacting white dwarf binary with a substellar secondary has been confirmed spectroscopically using the 8 meter Gemini instrument, SDSS 1212.

Cometary globule in Scorpius

Image credit and information APOD. Cometary globules, where dust grains are swept back and made to glow by ultraviolet radiation from nearby hot stars, were only recognised as a phenomenon in 1976. This image represents several hours exposure time with a 14.5 inch telescope, and can be compared to an older view from the Anglo-Australian Observatory, which I learn today has, along with everyone associated with Siding Spring, survived the bush fires. The exception is the observatory Lodge.

Co-moving Y dwarf companion to white dwarf WD 0806-661

Image credits

This image shows just how difficult it is to pick out faint brown dwarf companions against the stellar background, in this case by measurement of proper motion to confirm the association of the companion with the white dwarf, over a five year baseline. Lead author Kevin Luhman on this 2011 discovery:

“This planet-like companion is the coldest object ever directly photographed outside our solar system,” said Luhman, who led the discovery team. “Its mass is about the same as many of the known extra-solar planets — about six to nine times the mass of Jupiter — but in other ways it is more like a star. Essentially, what we have found is a very small star with an atmospheric temperature about cool as the Earth’s.”

Two further papers further clarify the nature of the companion, which is also known as GJ 3483b. It has an effective temperature in the range 300 – 345K, and a mass less than 10 – 13 Jupiter masses. It is also the reddest brown dwarf known to date.

Today a new, similar object, WISE 1828+2650, has been reported, a Y2 dwarf with an estimated temperature of 250 – 400K. The two objects are compared in the paper. Unlike the companion to WD 0806-661, where the age is known from the age of the white dwarf (about 1.5 Gyr) there is no age constraint, so the mass could lie anywhere between 0.5 and 20 Jupiter masses for ages 0.1 – 10 Gyr. Comparison with theoretical models gives a mass 3 – 6 Jupiter masses for a plausible age between 2 and 4 Gyr. This estimate is backed by the high tangential motion of the object. Whether WISE 1828+2650 sits at the low mass end of the brown dwarf population or is the first example of a large number of “free-floating” planets is not yet known. If such a population exists, it may yet be discoverable at lower signal-to-noise ratios in the WISE data. I caution that the status of these objects is still uncertain. From the new paper:

The absolute magnitude of WISE 1828+2650 is brighter by several magnitudes (depending on wavelength) than extrapolated from other Y dwarfs making the true nature of this source somewhat of a mystery. WISE 1828+2650 is similar in color and absolute magnitude to the cool object orbiting the nearby white dwarf WD 0806-661 B. The exact nature and evolutionary state, including its mass and age, of WISE 1828+2650 will require further observation and theoretical investigation.

On the subject of a population of isolated planetary mass objects, the young (3 Myr) sigma Orionis cluster was one of the first hunting grounds for such objects, which are brighter at young ages for a given mass. As reported in another new paper today, the number of planetary mass objects (4 – 12 Jupiter masses) known in the region has increased by 23 to 37, together with 69 brown dwarfs.

Compact planetary system Kepler-11

This system*, discovered in 2010 and published in Nature in 2011, contains six planets orbiting with periods between 10 and 118 days. The planets are super-Earths, with masses of 4.3, 13.5, 6.1, 8.4 and 2.3 Earth masses (the mass of the outermost planet is not well constrained) and radii between 2 and 4.5 Earth radii. The star is very Sun-like, spectral type G6V. Compared to the Solar system, the orbits would all be contained within the orbit of Venus. Lead author Jack J. Lissauer states:

By measuring the sizes and masses of the five inner planets, we have determined they are among the smallest confirmed exoplanets, or planets beyond our solar system. These planets are mixtures of rock and gases, possibly including water. The rocky material accounts for most of the planets’ mass, while the gas takes up most of their volume.

More discoveries of this nature may soon be made from the ground at Paranal with the Next Generation Transit Survey (NGTS), which is a cost-effective venture using off-the-shelf telescopes, publicized today and led by Don Pollacco at the University of Warwick. The wide-field NGTS will survey nearby stars brighter than thirteenth magnitude, concentrating on spectral types between early M and late F. This covers the types of star thought most likely to harbour habitable planets, and will naturally feed instruments like HARPS for ground-based radial velocity follow-up observations. The figure (left) shows the detection space:

Parameter space for transit detection with the yellow area indicating the prime science parameter space search of NGTS. Transit depth is indicated as a function of planet and star radius. Approximate spectral types of stars are also indicated, as well as the radii of representative Solar system planets. Known transiting systems are marked in green where they were discovered in ground-based transit surveys, blue if they were originally identified in radial velocity surveys, and red if they were discovered from space.

The special geometry of transit observations allows masses and radii of planets to be accurately constrained, which is sought after to allow statistical comparison of bulk planetary composition with theoretical models. Moreover, the transit geometry also allows to probe the atmosphere during secondary eclipse. NGTS will make available targets for high precision transmission spectroscopy of starlight passing through the planetary atmosphere, which is only possible using large telescopes, or from space.

*Note: planet masses and radii in this link are in units of Jupiter masses and radii.

White dwarf debris disks, planetary remnants

White dwarf stars can shred and vaporise any asteroids or rocky planets in their vicinity, if these small bodies are flung inward by gravitational interaction with a larger outer body. The debris disk reveals itself spectroscopically via double peaked emission lines. From the New Scientist article:

The spectra indicate that a disc containing calcium, magnesium, and iron gas is orbiting the white dwarf at a distance 100 times closer than Mercury’s orbit around the Sun (below right). At this distance, intense radiation from the white dwarf heats the gas to 5000 Kelvin. The spectra also show that the white dwarf’s atmosphere is enriched in magnesium. That indicates material from the disc is falling onto the star, since the star’s own surface gravity is so great that its own heavy elements should have already sunk towards its centre – and out of sight.

In another, early postulation of a tidally destroyed asteroid calcium was found to be abundant in the white dwarf G29-38. There is now a diversity of up to eleven different metals observed, with carbon-to-silicon ratios consistent with bulk Earth material, implying rocky material made up of iron- and magnesium- rich silicates.

Observationally, disk material is sought using wide area surveys via detection of infrared excesses. Cool DZ white dwarfs, with metal lines, have been found in the Sloan Digital Sky Survey. Rather than originating in the interstellar medium, as was thought for many years, the source of the metal lines is rocky planetesimals. Since white dwarfs are the end point of evolution of the vast majority of stars, observations of metal-rich material associated with them give a robust lower limit on the number of stars like the Sun, as well as those rather more massive, which form planetary systems.

Main image credit. Note this is a simulation of an accretion disk around a compact object, such as a white dwarf, rather than a bona-fide debris disk illustration.

Update: Detecting biomarkers via transits of white dwarfs?

Melas, Candor, Ophis and Hebes Chasmata

Image from HRSC. Seen here in new light and online for the first time, this bird’s-eye view of Valles Marineris was created from data captured during 20 individual orbits of ESA’s Mars Express. It is presented in near-true colour and with four times vertical scale exaggeration.

On 8 June, the same high-resolution stereo camera on Mars Express captured a region within the 1800 km-wide and 5 km-deep Argyre basin, which was created by a gigantic impact in the planet’s early history. After Hellas, the Argyre impact basin is the second largest on the Red Planet.

The word Chasma has been designated by the International Astronomical Union to refer to an elongate, steep-sided depression, as seen in the above image of Tithonium Chasma from HiRISE.

Complex planetary nebula NGC 5189

Image credits and detail from APOD

More soundings from the frontier of physics today, and this is the weirdest since I read John Taylor’s 1973 book “Black Holes: The End of the Universe?“, which warned us to beware the gravitational collapse of a ‘rugby-football shaped star’*, since this might give rise to a naked singularity where the end of physics would be laid bare for all to observe, without the decency of a surrounding event horizon.

There are three fundamental principles of physics under question, one of which apparently has to go, otherwise the archetypal unwary space traveller, falling through the event horizon even of a black hole large enough that tidal effects (‘spaghettification’) would not yet be noticeable, would immediately be confronted and incinerated by a ‘firewall’ of Hawking radiation invisible to those outside the horizon. The first principle is the equivalence principle, that there is no difference between free fall and inertial motion. The second is the principle that black holes are information sinks. The third principle is simply that ‘normal physics’ holds sway sufficiently far outside black hole.

Physicists don’t lightly abandon time-honored postulates. That’s why so many find the notion of a wall of fire downright noxious. “It is odious,” John Preskill of the California Institute of Technology declared earlier this month at an informal workshop organized by Stanford University’s Leonard Susskind. For two days, 50 or so physicists engaged in a spirited brainstorming session, tossing out all manner of crazy ideas to try to resolve the paradox, punctuated by the rapid-fire tap-tap-tap of equations being scrawled on a blackboard. But despite the collective angst, even the firewall’s fiercest detractors have yet to find a satisfactory solution to the conundrum.

The article was in Scientific American but first appeared here. There is also an interview with Joe Polchinski, author of the paper (abstract here) which began the controversy, here.

*It is easy to find reasons to imagine such an object would be unlikely to exist.

High-phase Saturnian imaging from Cassini

Image Credit: NASA/JPL-Caltech/SSI
A splendor seldom seen

The internet is abuzz today with this beautiful image and of course also with the news that there may be planets in the tau Ceti system (see sidebar), including at least one in the habitable zone. I want to sound a note of proper scientific caution that these tiny signals have been extracted from within noise which is notoriously hard to characterize (stellar ‘jitter’), using new and highly sophisticated techniques. The work bodes extremely well for further analyses of existing radial velocity data to uncover still smaller Doppler signals of low-mass planets as yet undetected. Indeed this dataset was chosen for the study not because tau Ceti is a nearby, sunlike star with a famous place in the annals of SETI but precisely because prior to today no planets at all had been detected, making the dataset a good one to intensively model the jitter. To quote from the paper:

Future data will be of essence in determining the nature of the signals we detect. If the five periodicities can be detected independently in different datasets, their genuine nature as signals of stellar origin will be verified. While even this will not imply that they are definitely Doppler signatures of low-mass planets, it will help ruling out spurious periodicities that insufficient modelling and instrumental instability might cause.

Excellent, scientific accounts of today’s tau Ceti news can be found here, and in particular here. Meanwhile, I note in passing that there is controversy over another recent paper, this time for the Gliese 667C system (also linked in sidebar). This paper has not yet been published in peer review and it is possible the system, as newly envisaged with additional habitable zone planets, is not dynamically stable. I emphasise though that the existence and potential habitability of Gliese 667Cc itself are not in question here.

Plumes and a Crescent

This image was captured at a phase, or Sun-Enceladus-spacecraft, angle of 157 degrees so that sunlight would reveal the backlit plumes. Terrain near the south pole is now dark as spring has come to the northern hemisphere of the moon.

Plumes and a Crescent

The Arches Cluster with adaptive optics

Image credit: ESO

The Arches cluster is the most densely packed cluster of young massive stars in the Galaxy and is thought to be a galactic analogue of the starburst phenomena observed in some distant galaxies. It lies near the central supermassive black hole of the Milky Way. Being near the galactic centre it is obscured by dust and therefore not visible at optical wavelengths, but lies towards the centre of the top quarter of the image below. The main image is taken with the NACO instrument on ESO’s Very Large Telescope, in the near-infrared.

Note the field of view above is not more than 56 x 56 arcseconds. The diffuse haloes seen around each stellar image are characteristic of images taken using adaptive optics. Compare the non-AO image (left).

Hypothetical warm planetary surface near a brown dwarf

Image

A possible warm planetary surface lit by an isolated brown dwarf. I am reminded of Megas and Erythro in Asimov’s 1989 story Nemesis.

Following the 4-7 Jupiter mass object CFBDSIR2149 in the AB Doradus moving group, here is another discovery. 2MASS J035523.37+113343.7 is more massive but also young and its kinematics show likely AB Dor membership, with age 50-120 Myr which yields a mass in the range 13-30 Jupiter masses.

Another artists impression (left) shows one of the first cool field brown dwarfs to be found, the T7.5 object Gliese 570 D. The surface temperature is around 800K, and ammonia is seen in the infrared spectrum. The rocky planet is hypothetical. The existence of cloud bands and ‘weather’ in the atmospheres of brown dwarfs is a topic of ongoing research (right).

2MASS J035523.37+113343.7 is the reddest known L dwarf, and this extreme redness is thought to be linked to youth, together with spectoscopic features such as a strongly peaked spectrum near 1.6 microns wavelength, first observed in brown dwarfs in star formation regions. Low surface gravity enhances photospheric dust, shifting radiation further into the infrared and reddening the spectral energy distribution of these young brown dwarfs, compared to cooler, older objects in the field. It is worth noting that even a field object with the same absolute infrared magnitudes would be below the hydrogen-burning limit, at seventy Jupiter masses.

The title of the new paper is Faherty, Jacqueline K., A Young, Dusty, Nearby, Isolated Brown Dwarf Resembling a Giant Exoplanet., 2013, AJ. Image: Jon Lomberg

Clouds in Cygnus

APOD image credit and description

With this beautiful image I also wanted to share a top class article by Carlo Rovelli on the subject of loop quantum gravity.

Skipping from Faraday via Feynman, the essentials of this idea are grasped through conceptual discussion, to arrive at an alternative to string theory. Loop quantum gravity predicts that spacetime is made up of elementary grains of volume at the Planck scale. Numerical simulations (left) reveal how such discrete quantum geometries “evolve” into smooth classical space. The article appeared in Physics World November 2003.

Brown dwarf rho Oph-102 in Ophiuchus

The newly investigated brown dwarf is highlighted here against a background dark, dusty region of the rho Ophiuchus star-forming region.
The observation of a dusty disc by ALMA, and inference of millimetre sized grains (left), has implications for possible rocky planet formation around brown dwarfs, and also shows the star formation process creating a body just too small (60 Jupiter masses) to ignite hydrogen fusion. The grains are similar to those found in the denser discs around very young stars. (ESO)

Cluster of galaxies in Perseus

(Photo Credit: David W. Hogg, Michael Blanton, SDSS Collaboration)

The small lenticular galaxy NGC 1277 now holds the record for the most enormous supermassive black hole; 17 billion solar masses. This is 14% of the mass of the galaxy itself. The event horizon of the SMBH is 4 light days in extent, some twenty times larger than the orbit of Neptune. The galaxy is just above right of center.

ArXiv abstract to Nature paper.

Image credits: NASA/ESA/Andrew C. Fabian / Remco C. E. van den Bosch (MPIA)

Out of proportion black hole is a rare cosmic fossil

If the result stands, the black hole may be a pristine remnant of an ancient quasar. […] NGC 1277’s stars are all old and its shape indicates it has not collided with other galaxies, so it may preserve a record of why the super-quasars grew so fast in the early universe.

A menagerie of directly imaged exoplanets

Image credit: NAOJ/Subaru/J. Carson (College of Charleston)/T. Currie (University Toronto). The light from the host star is subtracted in software.

The recent discovery of a 13 Jupiter mass companion to kappa Andromedae (above), a B9 dwarf and one of the most massive stars yet found to host a planet, together with the ‘rogue planet’ in the AB Doradus moving group with 4 to 7 Jupiter masses, brings to mind once again the linked questions of the formation processes of these kinds of objects and whether they should be thought of as low-mass brown dwarfs or planets. Thirteen Jupiter masses is an interesting figure because this is the mass below which no fusion at all, not even of deuterium, can occur during the lifetime of the body. The former discovery seems to show that objects of this mass might form as planets do, in a disc as part of the star formation process itself, and the latter one that objects of lower mass can form as stars do, perhaps in isolation. Bear in mind that it is likely that free floating planets could have been thrown out (dynamically ejected) from parent clusters very early in the star formation process.

All of this muddles the answers to simple questions such as what constitutes an image of an extrasolar planet and when was the first one obtained? The companion to the brown dwarf 2M1207 (right) in the TW Hya region, is an early candidate. It was discovered in April 2004 and is only just over 50 parsecs distant. It is not unique. But orbiting another brown dwarf as it does, can it truly be considered a planet or did the system form in a process of fragmentation in a molecular cloud, like a binary star? Being young, only 8 Myr, the object shines brightly in the infrared by the heat of its own formation. So, the spectral type (L, ~1600K, under debate) is more typically that of a more massive, older object well above the deuterium burning limit, perhaps even an ultra low-mass star. However the mass obtained by comparison with predictions of evolutionary models is not more than 5 Jupiter masses.

We do not, though, have to rely on finding examples by chance in these very young regions which are typically hard to census because of contamination by field stars and extinction by dust. Improvements in wide-field survey and detection technologies now allow the identification of objects in the field (CFBDSIR 1458+10, left), with cooler effective temperatures. These could have any age from a very few Gyr up to the age of the Galaxy. Errors on the masses are large because of uncertainties in the modelling of the emergent spectra; 6 to 15 Jupiter masses for the fainter object of the pair, still small enough to be called a planet. But bearing in mind the likely formation process, we think of these objects as cooling low-mass brown dwarfs.

What about objects of similar mass orbiting more solar-type stars? The companion to 1RXS J160929.1-210524 (right) is around 8 Jupiter masses, spectral type L4 orbiting a young K7 dwarf at 330 AU. This was imaged in 2008 and confirmed two years later. This scale is ten times the size of the solar system! This alone suggests this companion is more like a brown dwarf companion than a planet, again analogously to an unequal mass stellar binary. Since a determination of the orbital eccentricity is unlikely owing to the long period – but a circular orbit would be more planet-like – we can only note that the kappa And ‘planet’ at least is only twice as far from its star as Neptune is from the Sun.

The young, solar-type star beta Pictoris (right) is well known for its dusty debris disk which, like that of Fomalhaut, was first detected as early as 1984. I have looked at the putative planet of Fomalhaut in a previous post; its existence and nature remain controversial. The beta Pic planet on the other hand was first sought in 2003 and definitively detected in later analysis of the same dataset. The orbital motion has now been confirmed. The planet orbits at a distance of between 8 and 15 AU, comparable to the orbit of Saturn, and has around 8 Jupiter masses. It is much more likely than any of the objects discussed so far to have formed in a similar way to the gas giants of the Solar system.

The HR 8799 multiplanet system (left) was first found in 2007-8 around the star, which like beta Pic is young and somewhat more massive than the Sun. These planets are distant from the host star (25, 40 and 70 AU) but represent the first directly imaged multi-planet system. Masses between 5 and 13 Jupiters are derived. A fourth planet was subsequently detected in 2010. Orbital motion is also confirmed. The system is a testbed for distinguishing between competing planetary formation scenarios based on disk instabilities or core accretion.

Finally, I note the imaging of what might be more correctly called a protoplanet around the 2 Myr object Lk Ca 15 in the Taurus star-forming region (above). The mass of this planet, still forming and seen through a gap in the protostellar disk, is highly model dependent but likely about 6 Jupiter masses. This detection provides crucial insight into the gas giant formation process at the epoch of assembly. The protoplanet appears surrounded by dusty material and is around 11 AU from its host object. A complete list of all direct imaging detections of a wide variety of objects up to 30 Jupiter masses can be found here. As a footnote, I note also the indirect detection of a disk around the 14 Jupiter mass, 5 Myr, L0 companion to GSC06214-00210, in the Upper Sco association.

Star-forming region RCW49 from Spitzer

Guide to star formation from the University of Arizona.

Stars have formed in the core of a molecular cloud and they have blown a hole in the cloud. You can see them glowing blue inside the hole. The remains of the cloud are heated by the new stars and glow pink. The image was obtained with the IRAC instrument on Spitzer, and ranges from 3.6 microns (blue) to 8 microns (red). Because it is an infrared image, we can see through the foreground dust that blocks our view in the visible region.

Stars normally form in the well-known regions such as Orion but occasionally in an isolated manner, as illustrated by the Bok globules (left). I have discovered an interesting piece which appeared in the New York Times, reproduced here, which perfectly describes the star forming process:

The apparent inside-out collapse has been a source of confusion for theorists and observers alike. More than a decade ago, astronomers began finding that nearly all newborn stars go through a phase in which they seem to be rejecting mass at the same time they were also presumably drawing in mass from the cloud collapse. This was a common occurrence. Astronomers repeatedly observed two jets of gas shooting out at opposite sides and perpendicular to the disk of rotating matter around the protostar. The rotational forces were apparently twisting the magnetic field lines, producing winds carrying gas out in powerful jets.

The outflow phenomenon was as frustrating as it was fascinating. The jets were easily detected by radio telescopes and tended to obscure the view of other star-formation processes, like the inflow of material. So astronomers naturally devoted most of their time and thought to the jets they could see but could not explain, rather than on the inflowing material they hoped to see but could not. The new research promises to draw new attention to questions related to the intermediate stage of star formation, the time after the initial collapse of the gas sphere into a protostar and before the fall of material ceases and planetary formation becomes possible.

The source research concerns the dark cloud Barnard 335 (right). Unusually, it makes use of the capabilities of large, single radio dishes able to observe objects with relatively large angular sizes (~30 arcsec).