Ghostly planetary nebula Abell 39

Image credit: Adam Block, Mt. Lemmon Sky Center

This unusually spherical planetary nebula resides roughly 7000 light years distant within the constellation Hercules. The shell spans five light years.

Magnetic Sun

Magnetohydrodynamics (MHD) in action as solar plasma is confined, constrained and twisted by a changing magnetic field.

Gradients are, in fact, a mathematical description that highlights the places of greatest physical change in space. A gradient filter, in turn, enhances places of contrast, making them all the more obviously different, a useful tool when adjusting photos. Scientists, too, use gradient filters to enhance contrast, using them to accentuate fine structures that might otherwise be lost in the background noise. On the sun, for example, scientists wish to study a phenomenon known as coronal loops, which are giant arcs of solar material constrained to travel along that particular path by the magnetic fields in the sun’s atmosphere. Observations of the loops, which can be more or less tangled and complex during different phases of the sun’s 11-year activity cycle, can help researchers understand what’s happening with the sun’s complex magnetic fields, fields that can also power great eruptions on the sun such as solar flares or coronal mass ejections.

This video is public domain and can be downloaded at: http://svs.gsfc.nasa.gov/goto?11112

A gibbous Saturn from Cassini

Courtesy NASA. The small moon Mimas is seen at top. Another view from the a similar Sun-planet-spacecraft, or phase, angle is here, again showing the side of the rings which is not illuminated.

Closest yet habitable planet candidate around a Sun-like star

HD 40307g is a super-Earth at least seven times more massive than Earth orbiting the star at the right distance to support liquid water. The planet could have a size between 1.9 and 2.5 Earth radii depending on composition, either rocky or water-rich, respectively. HD 40307g receives on average about 67% of the light Earth receives from the Sun.

There is no information about the type and composition of the atmosphere of HD 40307g. Average temperatures might be near 9°C (48°F) assuming a similar scaled-up terrestrial atmosphere. It might also experience strong seasonal surface temperature shifts between -17° to 52°C due to its orbital eccentricity. Nevertheless, these extremes are tolerable by most complex life, as we know it.

Planetary Habitability Laboratory press release. The quoted bounds on radii scale respectively to 1.93 and 1.12 Earth gravities. The system is 42 light years (13 parsecs) away. This is further than the exoplanet candidate Gliese 667Cc which orbits an M dwarf (22 light years; see sidebar) but much closer than Kepler-22b, the first exo-Earth candidate in the habitable zone of a Sun-like star.

Two young stars and the reflection nebula vdB1

Image credit Adam Block, Mt Lemmon SkyCenter

This is the first object in the van den Bergh Catalog (vdB, 1966) of stars surrounded by reflection nebulae. Two intriguing nebulae at top left show loops and outflow features associated with the energetic process of star formation. Within are extremely young variable stars V633 Cas (left) and V376 Cas.

Rare emission nebula driven by O star

Image credit: Don Goldman

The halo of NGC 6164 imaged here is likely a result of a previous episode of mass loss in the lifetime of the central O star, HD 148937. The nebula itself is bioplar and, as seen in bipolar planetary nebulae, its shape may arise because of interaction between the central star and a companion. In this case, the star is thought to be a triple system.

NGC 6164-5 is a bipolar nebula surrounding the peculiar O 7f star HD 148937. Although the nebula was believed initially to represent a planetary nebula, it is now understood to represent a shell-like ejected nebula, formed by the winds of its young central star. Wind blown nebulae are usually considered the outcome of Wolf-Rayet type stars (WR), evolved O-type stars that have left the main sequence, molding their surroundings by way of fierce stellar winds. In the case of the S-shaped bipolar nebula NGC 6164-5, the central star is not a WR star, but a young O-type supergiant of 40 solar masses. Relatively few examples of such objects are known to exist, making NGC 6164-5 particularly unique. The true age of the star is not known although estimates of its age vary from a pre-main sequence age of 350,000 years to a more evolved age of one to two million years. HD 148937 is a peculiar type of Of star with exotic emission lines (carbon emission lines (CIII) equal in strength to Nitrogen (NIII)) and other peculiar spectra indicative of significant mass loss. Only five such stars are known to exist, three in our galaxy and two in Small Magellanic Cloud.

(Source)

A short period O star binary in the Large Magellanic Cloud

The period of this binary, LH54-425, is 2.25 days. The stars have around 62 and 37 solar masses and the mean orbital velocity is 1.1 million mph, making it one of the most extreme main sequence binaries so far identified.

NGC 3603 A1 is a galactic example of a pair whose masses have been measured dynamically, as it is a double-lined eclipsing binary. The masses are 116 and 89 solar masses and the period 3.77 days. These are Wolf-Rayet stars, a classification which includes the most massive stars, and is defined by the exclusive presence of emission lines in their spectra. They originate as O stars on the zero age main sequence (ZAMS) but are evolving so quickly and undergoing such extreme mass loss that they cannot be thought of or classified even as O stars more massive than 03V. Near-infrared spectra of point 2MASS sources with IRAS counterparts but no optical detection can also show emission lines due to dense circumstellar material.

Update: A hierarchical triple consisting only of O stars is known, HD 150136, which has been studied interferometrically using the PIONIER combiner at VLT. The dynamical masses are 63, 40 and 33 solar masses.

Eta Carinae and pair instability supernovae

The progenitors of pair instability supernovae are thought to be the most massive stars, and may have been more common in the early Universe. An Australian team, using Keck, has recently searched for such events at high redshift and discovered the most distant example, at z = 3.9. From A. Gal-Yam et al., a paper concerning SN2007bi published in Nature in 2009:

Stars with initial masses between ten and one hundred solar masses fuse progressively heavier elements in their centres, up to inert iron. The core then gravitationally collapses to a neutron star or a black hole, leading to an explosion — an iron-core-collapse supernova (SN). In contrast, extremely massive stars with initial masses greater than 140 solar masses, if such exist, have oxygen cores which exceed fifty solar masses. There, high temperatures are reached at relatively low densities. Conversion of energetic, pressure-supporting photons into electron-positron pairs occurs prior to oxygen ignition, and leads to a violent contraction that triggers a catastrophic nuclear explosion. Tremendous energies (>10⁵² erg) are released, completely unbinding the star in a pair-instability SN (PISN), with no compact remnant.

Eta Carinae, around 2.5 kpc distant, was famously observed to erupt in the mid-nineteenth century to outshine Canopus in the southern sky. The occurrence gave rise to the remarkable bipolar nebula imaged above. The star itself is a luminous blue variable with 100 – 120 solar masses, and might also become a pair instability supernova, leaving behind no black hole but a huge abundance of heavy elements, possibly within a 10⁴ year timescale. If the eta Carinae event were comparable to the most instrinsically luminous supernova yet observed, SN2006gy, its apparent magnitude would exceed -10.

High galactic latitude clouds in Pegasus

Image copyright and credit: John Davis

Spanning around 5 degrees on the sky, this view contains the bright star Markab in Pegasus. The dust clouds are high latitude galactic cirrus.

What is happening around Fomalhaut?

Image credit: NASA/ESA

The circumstellar debris disk at Fomalhaut (α PsA, 7.7 pc, A3V) was among the first to be detected way back in 1984 by the IRAS satellite. Such debris disks are analogous to the  Solar System’s Kuiper belt and can be seen among the closest stars via their infrared excesses. Given what we know about the diversity of planetary systems, there is no reason to suspect these disks should be similar to the Solar System case. They might be more extensive or rarefied, or for that matter denser and compact. If the disk is acted upon gravitationally by large planets it may become a ring, with well-defined inner and outer edges, which might be continually replenished by loss from the inner gaseous planet. The material giving rise to the infrared excess at Fomalhaut is known to arise from collisional processes and sublimation of large bodies. Such a ring might persist around a young  (~ 400 Myr) star like Fomalhaut, not having had time to dissipate via further accretion.

Could a star rather more massive than the Sun really harbour a large planet shepherding, and perhaps replenishing, a huge disk? This is what seems to be observed in visible light by Hubble (above), using techniques to subtract the image of the central star. The finding has been recently confirmed, and the absence of a near-infrared detection limits is mass to less than ~ 2M_Jup , demonstrably sufficient to at least sculpt the disk. It is worth noting that Fomalhaut has a very distant (57000 AU) common proper motion companion, Gliese 879 (TW PsA), and possible that the offset of the disk from Fomalhaut arises dynamically via binary interaction. The system is imaged (left) by Herschel at 70 μm in the far-infrared, showing the smooth disk, which arises from cometary collisions occurring at a very high rate. The enormous number of collisions required (the equivalent of 2000 1 km size comets every day) seem more reasonable if we postulate disk replenishment from the planet. At even longer wavelengths, 850 μm, purely thermal emission by dust is traced, resulting in the toroidal pattern shown (right), where the highest intensities are seen where the line of sight intercepts the largest amounts of disk dust.

The observed spectral energy distribution of the planet from optical through mid-infrared can not be explained by direct or scattered radiation alone. Two models have very recently been proposed: either a large circumplanetary disk around a massive, but unseen, planet or the aftermath of a collision during the past 100 years of two Kuiper Belt-like objects of radii about 50 km. The former scenario would be supported if there indeed is some mechanism whereby the planet is still losing mass to the disk. Speculatively, Fomalhaut b could be a super-Earth sized molten lava body, continually pummelled by collisions. Further observations will be needed to elucidate the connection between the giant body dynamically inferred by the existence of the disk and the visible light source clearly seen in the HST data.

Update: Fomalhaut b has been confirmed and appears to be on a rogue, disk crossing orbit.

Cosmic dust clouds in Messier 78

Image credit: ESO/APEX (MPIfR/ESO/OSO)/T. Stanke et al./Igor Chekalin/Digitized Sky Survey 2

This image of the region surrounding the reflection nebula Messier 78, just to the north of Orion’s belt, shows clouds of cosmic dust threaded through the nebula like a string of pearls. The submillimetre-wavelength observations, made with the Atacama Pathfinder Experiment (APEX) telescope and shown here in orange, use the heat glow of interstellar dust grains to show astronomers where new stars are being formed. They are overlaid on a view of the region in visible light.

http://www.eso.org/public/images/eso1219a/

Carbon-rich exoplanets real and hypothetical

Artist’s impression of a carbonaceous exoplanet, taken from http://www.novacelestia.com. From the website:

A hypothetical extrasolar carbon planet. You are seeing the south pole of the planet to the left, where methane has condensed into ice. The white dots on the surface are reflections from layers of diamonds on the surface. The seas found at the center of the image are made of oil of various hydrocarbons. The dark areas on the planet are marks of tar-like precipitation. The clouds are also made of various hydrocarbons.

Carbon and oxygen are of roughly equal abundance in the Universe. However in most stars oxygen predominates: for example the solar C:O ratio is 0.57. Observationally, a great deal can depend on whether the ratio of carbon to oxygen is large (C:O > 1) or small in a given system. Most evolved red giants are richer in oxygen, with spectra very different – showing bands of oxygen-rich molecules and possibly silicate-rich dust – to those in which carbon is predominant. The latter are the rarer carbon stars, whose optical spectra are dominated by bands of C₂ and which may also show infrared features arising from polycyclic aromatic hydrocarbons (PAHs). Systems richer in carbon may host carbon-rich planets. Where the C:O ratio is solar carbon and oxygen combine to form the CO molecule, but if C:O > 1 CH₄ is formed instead, and it is this which has been observed in the planet WASP-12b.

Similarly, for the recently announced carbon-rich exoplanet 55 Cancri e, the C:O ratio as measured in the stellar spectrum is 1.12 ± 0.19. With this in mind, modelling of the possible carbon-rich interior, complete with diamond layer, is discussed here.

Update: High C:O ratios in planet-hosting stars called into question

Dust, nebulae and a globular in Corona Australis

Image credit & copyright: Marco Lorenzi (Glittering Lights)

The dust cloud, around 150 pc distant, blocks light from more distant stars in this view towards the northern part of the constellation Corona Australis. The blue reflection nebulae are catalogued as NGC 6726 and NGC 6727, while the smaller yellowish nebula NGC 6729 surrounds the young star R CrA. The globular cluster NGC 6723, top right, is of course much more distant.

Colliding galaxies gallery

http://hubblesite.org/newscenter/archive/releases/2008/16/image/a/

Dark nebulae in the Aquila Rift

I like this image so much I’m reblogging it. See this paper for information on the embedded young stars in the image.

Curiosity panorama from inside Gale crater

Web templates

Credit:NASA/JPL/MSSS/Stuart Atkinson & NASA/JPL/MSSS/Emily Lakdawalla via io9.com

Pinwheel outflow of extreme carbon star AFGL 3068

This amazing discovery is a few years old now and had escaped my attention. I remember there was some discussion in the literature some years ago as to whether the central star of another protoplanetary nebula, the Red Rectangle (HD 44179) was also binary* and whether this could give rise to its unique structure. The origin of the structures seen in planetary nebulae is an emerging field of study.

This remarkable picture from the Advanced Camera for Surveys on the NASA/ESA Hubble Space Telescope shows one of the most perfect geometrical forms created in space. It captures the formation of an unusual pre-planetary nebula, known as IRAS 23166+1655, around the star LL Pegasi (also known as AFGL 3068) in the constellation of Pegasus (the Winged Horse).

The striking picture shows what appears to be a thin spiral pattern of astonishingly regularity winding around the star, which is itself hidden behind thick dust. The spiral pattern suggests a regular periodic origin for the nebula’s shape. The material forming the spiral is moving outwards a speed of about 50 000 km/hour and, by combining this speed with the distance between layers, astronomers calculate that the shells are each separated by about 800 years.

The spiral is thought to arise because LL Pegasi is a binary system, with the star that is losing material and a companion star orbiting each other. The spacing between layers in the spiral is expected to directly reflect the orbital period of the binary, which is indeed estimated to be also about 800 years.

Image source

Full 2006 paper ‘A binary-induced pinwheel outflow from the extreme carbon star AFGL 3068’

* A recent paper discusses the geometry of binary, accretion disk, jet and outflow of HD 44179.

Earthrise, 1968

http://keithlaney.net/ApolloOrbitalimages/apollo_8_orbital_images.htm

UKIRT Announcement of Opportunity

The United Kindgom Infrared Telescope was the first dedicated telescope for infrared observations, and started operations in the early 1980s. Sadly, UK funding has been pulled for this unique 3.8 metre telescope so an invitation has been sent to the global astronomy community in the hope that it may continue to produce science of the highest quality.

“This is the first time that a productive, world-leading observatory in the 4-m class has been offered to the global community. We invite you to consider this unprecedented opportunity.”

http://www.jach.hawaii.edu/UKIRT/news/UKIRT_AO/

Using UKIRT to find LSPM 1459+0857 AB a “Rosetta Stone” T dwarf in orbit around a white dwarf, allowing for the first time to age a brown dwarf precisely:

UKIRT instrumental in finding first methane dwarf around a dying star

Image of the WFCAM camera used for the ground breaking UKIDSS survey:

First planet discovered by the WFCAM transit survey (see sidebar)

Dwarf galaxy DDO 190

DDO 190 lies around nine million light-years away from our solar system. It is considered part of the loosely associated Messier 94 group of galaxies, not far from the Local Group of galaxies that includes the Milky Way. Canadian astronomer Sidney van der Bergh was the first to record DDO 190 in 1959 as part of the DDO catalog of dwarf galaxies.

http://www.nasa.gov/mission_pages/hubble/science/ddo190.html

Sloan Digital Sky Survey

The Sloan Digital Sky Survey III (SDSS-III) has released the largest-ever three-dimensional map of massive galaxies and distant black holes, which will help astronomers explain the mysterious “dark matter” and “dark energy” that scientists know makes up 96 percent of the Universe.

Early last year, the SDSS-III released the largest-ever image of the sky. With the new release of data, SDSS-III has begun to expand this image into a full three-dimensional map. A “fly-through” video is available below:

http://www.sdss3.org/press/dr9.php

Shown above is the open cluster, Messier 37. Located about 4,000 light years away, this group of stars is in the constellation Auriga. It is also among the older known open clusters known, and some of the brighter red stars in this image are evolved stars known as red giants. The numerous bluer stars are less massive stars that are still on the main sequence. Check out the SDSS image of the week gallery.

Dust and emission in the Rho Ophiuchi cloud complex

Image credit: Tom O’Donoghue

Among all the other things to notice in this image, which represents a total of 60 hours exposure time, is how easy it is to see the background star field reddened and extincted by the intervening dust.

http://apod.nasa.gov/apod/ap120828.html

V 838 Monocerotis: the prototypical “red nova”?

V 838 Mon is a unique object whose precise nature is still uncertain. Once thought to be a normal nova – originating in a close binary, with a white dwarf companion – it is known to be a different kind of binary which may have merged:

For the first time, astronomers have watched the spiralling dance performed by two stars merging into a single star. The observations, taken between 2001 and 2008, suggest a solution to the vexed problem of how rare ‘red novae’ form. Most novae are blue and occur when material on a white dwarf star explodes. But what causes red novae has been a mystery. The best-known red nova was spotted in January 2002 toward the edge of our Galaxy’s disk. Named V838 Monocerotis, it was more luminous than normal novae — at peak brightness, it briefly rivalled the most powerful stars in the Galaxy.

The so-called red novae originate in contact binary stars. An example is the case of V1309 Scorpii :

A contact binary consists of two stars that circle each other so closely that they touch. If viewed from an orbiting planet, the stuck-together suns would resemble a glowing peanut-shaped object. Exotic though they seem, contact binaries are common: the nearest, named 44 Boötis B, is just 41 light years (13 parsecs) from Earth.

Because they are so close together, the two stars continually eclipse each other, causing the brightness we see to vary. This allowed Tylenda and his team to deduce the nature of V1309 Scorpii, which is roughly 10,000 light years (3,000 parsecs) from Earth.

Before the explosion, the two stars danced around each other every 1.4 days. As they spiralled together, this period shortened until the stars merged and exploded, upping their brightness by 10,000 times. Tylenda and his colleagues estimate that the larger star had about as much mass as the Sun. Current observations indicate that the system is now single.

Source: “Dancing stars turn on the red light”

Update: Ivanova et al. (2013) new paper in Science with theoretical treatment of common-envelope events.

“The natural range of time scales and energies from this model, as well as the expected colors, light-curve shapes, ejection velocities, and event rate, match those of a recently recognized class of red transient outbursts…”

The new Hubble Extreme Deep Field

This image, called the Hubble eXtreme Deep Field (XDF), combines Hubble observations taken over the past decade of a small patch of sky in the constellation of Fornax. With a total of over two million seconds of exposure time, it is the deepest image of the Universe ever made, combining data from previous images including the Hubble Ultra Deep Field (taken in 2002 and 2003) and Hubble Ultra Deep Field Infrared (2009). The image covers an area less than a tenth of the width of the full Moon, making it just a 30 millionth of the whole sky. Yet even in this tiny fraction of the sky, the long exposure reveals about 5500 galaxies, some of them so distant that we see them when the Universe was less than 5% of its current age. The Hubble eXtreme Deep Field image contains several of the most distant objects ever identified.

http://www.nasa.gov/mission_pages/hubble/science/xdf.html

Massive star formation in Cygnus OB2

Bright white filaments and clumps show chains and regions of massive star formation. These shapes are sculpted by strong stellar winds. From Herschel.

Rosette Nebula in hydrogen alpha

Image courtesy Nick Wright and the IPHAS survey

Neptune

Fusion propulsion to the outer Solar System

Today’s bold claim in Scientific American is for nuclear propulsion methods for human exploration of the Solar System within timescales of a century:

Nuclear fusion reactions sparked by beams of antimatter could be propelling ultra-fast spaceships on long journeys before the end of the century, researchers say. A fusion-powered spacecraft could reach Jupiter within four months, potentially opening up parts of the outer solar system to manned exploration, according to a 2010 NASA report.

I was surprised to hear of the use of uranium in deuterium/tritium-rich fuel pellets:

Inside each pellet, this fuel would be surrounded by another material, perhaps uranium.

The US patent page describes further, filling in the missing detail:

In connection with a fusion process which can be initiated by a high energy input such as a laser beam, the use of a layer of uranium surrounding the fusion fuel such as deuterium-tritium or a non-cryogenic fuel such as lithium deuterium-lithium tritium. The uranium serves as a tamper layer to contain the fusion fuel and supplement the heating by a fission reaction which not only increases the fusion yield but increases the time of disassembly, thus materially increasing the efficiency of the fusion system.

Image courtesy Space.com

Nebulosity in eta Carinae region

Hubble Space Telescope (HST) image of NGC 3372, 50 light-years wide and a composite of 48 frames. The false colour image was created using the following formula: red for sulphur, green for hydrogen, and blue for oxygen emissions.

Curiosity makes tracks

Tracks from the first drives of Nasa’s Curiosity rover, from a camera on Nasa’s Mars Reconnaissance Orbiter. Colour has been enhanced to show the surface details better. Dark marks reveal deeper dust when the surface was blown away on landing. Image courtesy: AP/Nasa/University of Arizona.

Episodic mass loss from the Cat’s Eye nebula

Image credit: NASA, ESA, HEIC, and The Hubble Heritage Team (STScI/AURA)

Deep HST image reveals episodes of mass loss separated by ~ 1500 years occurring during the proto-planetary nebula evolutionary phase of this well-known object.

New Horizons to Pluto and beyond

The New Horizons probe is well on its way to the furthest reaches of the solar system and you can follow the countdown to the Pluto/Charon encounter here. Subsequently New Horizons will further explore the Kuiper belt. The first new discovery there was 1992 QB1. Images taken at ESO shortly after the discovery are shown here (top panel). The apparent motion of about 75 arcseconds per day places the object further than Pluto. Other more recent dicoveries include the strange object Haumea, the very distant object Sedna, the dwarf planet Eris with its moon Dysnomia and of course the recent discovery of a fifth moon of Pluto.