Close-up of the drama of star formation

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This very detailed enhanced-colour image from ESO’s Very Large Telescope shows the dramatic effects of very young stars on the dust and gas from which they were born in the star-forming region NGC 6729. The baby stars are invisible in this picture, being hidden behind dust clouds at the upper left of the picture, but material they are ejecting is crashing into the surroundings at speeds of that can be as high as one million kilometres per hour. This picture was taken by the FORS1 instrument and records the scene in the light of glowing hydrogen and sulphur.

T Pyxidis Finally Blows Again

T Pyx on April 15, 2011

The recurrent nova T Pyxidis, which had its last outburst in December 1966 and has been very overdue for its next, has shot up from magnitude 15.4 to at least 8.5. In 1966–67 it reached 6.5.

It's in the dim constellation Pyxis east of Puppis and Canis Major. Pyxis is currently fairly high in the south-southwest right after dark, in good view for observers at north temperate latitudes and points south. The star is at declination –32°.

Here are finder and comparison-star charts from Sky & Telescope, and larger-scale comparison-star charts 15° wide, 5° wide, and
2° wide courtesy of the American Association of Variable Star Observers (AAVSO). On all charts north is up and east is to the left. The numbers next to stars are comparison-star magnitudes to the nearest tenth with the decimal points omitted.

A Very Cool Pair of Brown Dwarfs

Brown dwarfs are essentially failed stars: they lack enough mass for gravity to trigger the nuclear reactions that make stars shine. The newly discovered brown dwarf, identified as CFBDSIR 1458+10B, is the dimmer member of a binary brown dwarf system located just 75 light-years from Earth [1].

The powerful X-shooter spectrograph on ESO’s Very Large Telescope (VLT) was used to show that the composite object was very cool by brown dwarf standards. "We were very excited to see that this object had such a low temperature, but we couldn’t have guessed that it would turn out to be a double system and have an even more interesting, even colder component," said Philippe Delorme of the Institut de planétologie et d’astrophysique de Grenoble (CNRS/Université Joseph Fourier), a co-author of the paper. CFBDSIR 1458+10 is the coolest brown dwarf binary found to date.

The dimmer of the two dwarfs has now been found to have a temperature of about 100 degrees Celsius — the boiling point of water, and not much different from the temperature inside a sauna [2]. “At such temperatures we expect the brown dwarf to have properties that are different from previously known brown dwarfs and much closer to those of giant exoplanets — it could even have water clouds in its atmosphere," said Michael Liu of the University of Hawaii’s Institute for Astronomy, who is lead author of the paper describing this new work. "In fact, once we start taking images of gas-giant planets around Sun-like stars in the near future, I expect that many of them will look like CFBDSIR 1458+10B."

Unravelling the secrets of this unique object involved exploiting the power of three different telescopes. CFBDSIR 1458+10 was first found to be a binary using the Laser Guide Star (LGS) Adaptive Optics system on the Keck II Telescope in Hawaii [3]. Liu and his colleagues then employed the Canada–France–Hawaii Telescope, also in Hawaii, to determine the distance to the brown dwarf duo using an infrared camera [4]. Finally the ESO VLT was used to study the object’s infrared spectrum and measure its temperature.

The hunt for cool objects is a very active astronomical hot topic. The Spitzer Space Telescope has recently identified two other very faint objects as other possible contenders for the coolest known brown dwarfs, although their temperatures have not been measured so precisely. Future observations will better determine how these objects compare to CFBDSIR 1458+10B. Liu and his colleagues are planning to observe CFBDSIR 1458+10B again to better determine its properties and to begin mapping the binary's orbit, which, after about a decade of monitoring, should allow astronomers to determine the binary’s mass.

The Drama of Starbirth

The star-forming region NGC 6729 is part of one of the closest stellar nurseries to the Earth and hence one of the best studied. This new image from ESO’s Very Large Telescope gives a close-up view of a section of this strange and fascinating region (a wide-field view is available here: eso1027). The data were selected from the ESO archive by Sergey Stepanenko as part of the Hidden Treasures competition [1]. Sergey’s picture of NGC 6729 was ranked third in the competition.

Stars form deep within molecular clouds and the earliest stages of their development cannot be seen in visible-light telescopes because of obscuration by dust. In this image there are very young stars at the upper left of the picture. Although they cannot be seen directly, the havoc that they have wreaked on their surroundings dominates the picture. High-speed jets of material that travel away from the baby stars at velocities as high as one million kilometres per hour are slamming into the surrounding gas and creating shock waves. These shocks cause the gas to shine and create the strangely coloured glowing arcs and blobs known as Herbig–Haro objects [2].

In this view the Herbig–Haro objects form two lines marking out the probable directions of ejected material. One stretches from the upper left to the lower centre, ending in the bright, circular group of glowing blobs and arcs at the lower centre. The other starts near the left upper edge of the picture and extends towards the centre right. The peculiar scimitar-shaped bright feature at the upper left is probably mostly due to starlight being reflected from dust and is not a Herbig–Haro object.

This enhanced-colour picture [3] was created from images taken using the FORS1 instrument on ESO’s Very Large Telescope. Images were taken through two different filters that isolate the light coming from glowing hydrogen (shown as orange) and glowing ionised sulphur (shown as blue). The different colours in different parts of this violent star formation region reflect different conditions — for example where ionised sulphur is glowing brightly (blue features) the velocities of the colliding material are relatively low — and help astronomers to unravel what is going on in this dramatic scene.

QUASAR’S BELCH SOLVES LONGSTANDING MYSTERY

For the first time, observations with the Gemini Observatory clearly reveal an extreme, large-scale galactic outflow that brings the cosmic dinner to a halt. The outflow is effectively blowing the galaxy apart in a negative feedback loop, depriving the galaxy’s monstrous black hole of the gas and dust it needs to sustain its frenetic growth. It also limits the material available for the galaxy to make new generations of stars.

The groundbreaking work is a collaboration between David Rupke of Rhodes College in Tennessee and the University of Maryland’s Sylvain Veilleux. The results are to be published in the March 10 issue of The Astrophysical Journal Letters and were completed with support from the U.S. National Science Foundation.

According to Veilleux, Markarian 231 (Mrk 231), the galaxy observed with Gemini, is an ideal laboratory for studying outflows caused by feedback from supermassive black holes. “This object is arguably the closest and best example that we know of a big galaxy in the final stages of a violent merger and in the process of shedding its cocoon and revealing a very energetic central quasar. This is really a last gasp of this galaxy; the black hole is belching its next meals into oblivion!” As extreme as Mrk 231’s eating habits appear, Veilleux adds that they are probably not unique, “When we look deep into space and back in time, quasars like this one are seen in large numbers and all of them may have gone through shedding events like the one we are witnessing in Mrk 231.”

Although Mrk 231 is extremely well studied, and known for its collimated jets, the Gemini observations exposed a broad outflow extending in all directions for at least 8,000 light years around the galaxy’s core. The resulting data reveal gas (characterized by sodium, which absorbs yellow light) streaming away from the galaxy center at speeds of over 1,000 kilometers per second. At this speed, the gas could go from New York to Los Angeles in about 4 seconds. This outflow is removing gas from the nucleus at a prodigious rate – more than 2.5 times the star formation rate. The speeds observed eliminate stars as the possible “engine” fueling the outflow. This leaves the black hole itself as the most likely culprit, and it can easily account for the tremendous energy required.

The energy involved is sufficient to sweep away matter from the galaxy. However, "when we say the galaxy is being blown apart, we are only referring to the gas and dust in the galaxy,” notes Rupke. “The galaxy is mostly stars at this stage in its life, and the outflow has no effect on them. The crucial thing is that the fireworks of new star formation and black hole feeding are coming to an end, most likely as a result of this outflow.”

The environment around such a black hole is commonly known as an active galactic nucleus (AGN), and the extreme influx of material into these black holes is the power source for quasi-stellar objects or quasars. Merging galaxies help to feed the central black hole and also shroud it in gas. Mrk 231 is in transition, now clearing its surroundings. Eventually, running out of fuel, the AGN will become extinct. Without gas to form new stars, the host galaxy also starves to death, turning into a collection of old aging stars with few young stars to regenerate the stellar population. Ultimately, these old stars will make the galaxy appear redder giving these galaxies the moniker “red and dead.”

Numerical astrophysicist Philip Hopkins, a Miller Fellow at the University of California at Berkeley, explains that many physical processes unique to rapidly growing black holes are likely to play a role in propelling the winds observed by Gemini. “At its peak, the quasar shines with such intensity that the light itself is ‘trapped’ by a cocoon of gas and dust pushing on material with a force that can easily overcome the gravitational pull of the black hole.” Hopkins adds that the bath of X-rays and gamma rays known to be generated by quasars could also heat up the gas in the galaxy’s center until it reaches a temperature where it "boils over" and causes a bomb-like explosion. “But until now, we haven’t been able to catch a system ‘in the act.’” Part of the problem, according to Hopkins, has been that the most visible outflows are those ‘collimated jets’ already known in Mrk 231. These jets are trapped (probably by magnetic fields) in an extremely narrow beam, whereas material is falling into the black hole from all directions. The previously known jets therefore only cause very localized damage – drilling a tiny hole in the cocoon, rather than sweeping it away more broadly as seen in these new, more all-encompassing, outflows.

The observations for this study were obtained with the Gemini Multi-Object Spectrograph (GMOS) on Gemini North, on Mauna Kea, Hawai‘i. The study used a powerful technique known as integral field spectroscopy. The integral field unit (IFU) in GMOS obtains a spectrum at several hundred points around the galaxy’s core. Each spectrum is then, in turn, used to determine the velocity of the gas at that point and represents the third dimension in what is called a data cube.

Markarian 231 is located about 600 million light years away in the direction of the constellation of Ursa Major. Although its mass is uncertain, some estimates indicate that Mrk 231 has a mass in stars about three times that of our Milky Way galaxy and its central black hole is estimated to have a mass of at least ten million solar masses or also about three times that of the supermassive black hole in the Milky Way.

Reflected Glory

The nebula Messier 78 takes centre stage in this image taken with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile, while the stars powering the bright display take a backseat. The brilliant starlight ricochets off dust particles in the nebula, illuminating it with scattered blue light. Igor Chekalin was the overall winner of ESO’s Hidden Treasures 2010 astrophotography competition with his image of this stunning object.

Messier 78 is a fine example of a reflection nebula. The ultraviolet radiation from the stars that illuminate it is not intense enough to ionise the gas to make it glow — its dust particles simply reflect the starlight that falls on them. Despite this, Messier 78 can easily be observed with a small telescope, being one of the brightest reflection nebulae in the sky. It lies about 1350 light-years away in the constellation of Orion (The Hunter) and can be found northeast of the easternmost star of Orion’s belt.

This new image of Messier 78 from the MPG/ESO 2.2-metre telescope at the La Silla Observatory is based on data selected by Igor Chekalin in his winning entry to the Hidden Treasures competition [1].

The pale blue tint seen in the nebula in this picture is an accurate representation of its dominant colour. Blue hues are commonly seen in reflection nebulae because of the way the starlight is scattered by the tiny dust particles that they contain: the shorter wavelength of blue light is scattered more efficiently than the longer wavelength red light.

This image contains many other striking features apart from the glowing nebula. A thick band of obscuring dust stretches across the image from the upper left to the lower right, blocking the light from background stars. In the bottom right corner, many curious pink structures are also visible, which are created by jets of material being ejected from stars that have recently formed and are still buried deep in dust clouds.

Two bright stars, HD 38563A and HD 38563B, are the main powerhouses behind Messier 78. However, the nebula is home to many more stars, including a collection of about 45 low mass, young stars (less than 10 million years old) in which the cores are still too cool for hydrogen fusion to start, known as T Tauri stars. Studying T Tauri stars is important for understanding the early stages of star formation and how planetary systems are created.

Remarkably, this complex of nebulae has also changed significantly in the last ten years. In February 2004 the experienced amateur observer Jay McNeil took an image of this region with a 75 mm telescope and was surprised to see a bright nebula — the prominent fan shaped feature near the bottom of this picture — where nothing was seen on most earlier images. This object is now known as McNeil’s Nebula and it appears to be a highly variable reflection nebula around a young star.

This colour picture was created from many monochrome exposures taken through blue, yellow/green and red filters, supplemented by exposures through an H-alpha filter that shows light from glowing hydrogen gas. The total exposure times were 9, 9, 17.5 and 15.5 minutes per filter, respectively.
Notes

[1] Igor Chekalin from Russia uncovered the raw data for this image of Messier 78 in ESO’s archives in the competition Hidden Treasures (eso1102). He processed the raw data with great skill, claiming first prize in the contest for his final image (Flickr link). ESO’s team of in-house image processing experts then independently processed the raw data at full resolution to produce the image shown here.

Get Ready for a Solar-System Bonanza

Don't get me wrong: I would never suggest that NASA throttle back its efforts to explore the worlds around us. But I have to admit that, even for folks like me who follow space activities closely, things are getting a little crazy. Over the next several months, interplanetary exploration will rev up to a dizzying pace.

The first event occurred just a few days ago, when the twin STEREO spacecraft finally took up positions on opposite sides of the Sun. (We space junkies sometimes forget that the Sun is part of our solar system.) For the first time, solar scientists can monitor all of the Sun's disk at once — and that'll pay big dividends as solar activity ramps up in the months ahead.

An artist's portrayal of the Stardust spacecraft approaching Comet Tempel 1 on February 14, 2011.

Coming up fast is a return visit to Comet 9P/Tempel 1. You'll recall that this 5-by-3-mile iceberg was the target of NASA's Deep Impact mission on July 4, 2005. When a 815-pound (370-kg) projectile slammed into the comet's nucleus, it unleashed an unexpected fireworks display of gas and dust.

Since then Tempel 1 has made one complete trip around the Sun, and on February 14th it'll again be in the crosshairs (this time just with instruments) of the Stardust
spacecraft. This is a great example of how old spacecraft can do new tricks: Stardust completed its primary mission five years ago after zipping through the coma of Comet Wild 2 in early 2004 and dropping off a sample capsule when it swung past Earth. But the main spacecraft remained in solar orbit, and now it's posed to reconnoiter a second
comet.

(Officially, the mission's name is now Stardust-NeXT — that latter bit standing for "New Exploration of Tempel 1" — but it's just too much of a stretch for my taste.)

In the best of all worlds, Stardust's camera would record the crater made by Deep Impact's copper-cored cannonball. But even if the nucleus has rotated it from view, there's still plenty to look at. The nucleus of Tempel 1 appears to have multiple layers and bizarre flows. Can a mountain-size blob of ice and dirt be geologically active? We'll have more answers to that question very soon.

There's no letup in the pace of solar-system exploration once Stardust has its hi-and-bye. In fact, NASA officials
have dubbed 2011 the "Year of the Solar System." Well, truth be told, in their minds YSS began last October, when Deep Impact visited its second comet, 103P/Hartley 2, and it won't end until August 2012, when the not-even-launched-yet rover Curiosity (a.k.a. Mars Science Laboratory) reaches Mars.

Whatever. Here's a rundown of the other interplanetary headlines you can expect to see in the coming months:

March 18: After three warm-up flybys, NASA's Messenger
spacecraft will fire its braking rocket and slip into a looping polar
orbit around Mercury that comes within 125 miles (200 km) of its
surface. Equipped with seven very capable cameras, spectrometers, and
other instruments, Messenger has already made a trove of new
discoveries about the innermost planet. But the real science
breakthroughs (such as its interior structure) will come after the
orbiter has made long-term observations. Messenger is a contraction of
"Mercury Surface, Space Environment, Geochemistry, and Ranging."

July 16:
The Dawn spacecraft will reach 4 Vesta, which is hands down the
asteroid belt's most amazing chunk of rock: it's thought to have an
iron–nickel core, a rocky olivine mantle, a crust, lava flows, and a
giant crater. The spacecraft has been almost gliding toward Vesta using
ion-fueled thrusters, and it will remain in orbit for a year before
easing away and setting course for 1 Ceres. (Remarkably, Dawn isn't an
acronym and doesn't stand for anything.) This mission's website is here, and I highly recommend the "Dawn Journal" written by chief engineer Marc Rayman.

August 5: The launch date for NASA's ambitious Juno
spacecraft. This is the first outer-planet-bound spacecraft to use
solar-cell arrays, rather than plutonium power packs, to generate
electricity. When it reaches Jupiter in 2016, Juno is to slip into a
looping polar orbit that will both subject it to dangerously high
radiation levels and, its science team hopes, answer key questions
about the planet's composition, its interior structure, and from those
how our solar system formed. Also not an acronym, Juno is named for the
jealous god-sister-wife of Jupiter in Roman mythology.

September 8: Lunar scientists will look on expectantly as the twin GRAIL
spacecraft rocket skyward from Cape Canaveral, Florida. The Gravity
Recovery and Interior Laboratory mission intends to fly these craft in
tandem just 30 miles (50 km) above the lunar surface. By carefully
tracking how the Moon's gravity alters the crafts' orbital motion,
scientists hope to map the Moon's gravity field with unprecedented
detail and, using that, derive the detailed structure of the lunar
interior from crust to core.

November 8: If everything comes together in time, the Russian Space Agency plans to launch its problematic Phobos-Grunt mission. (Grunt is Russian for "ground".) Talk about a checkered history!
Conceived in 1996 to land on the larger of Mars's two satellites and
return a sample to Earth, this spacecraft has had more transformations
than Cher at the Academy Awards! In its latest configuration, the
spacecraft will carry a passenger, the Chinese-built spacecraft Yinghou
1, which will detach from Phobos-Grunt and orbit Mars for up to a year.
Plans still call for the main spacecraft to land on Phobos, scoop up
several samples totaling a total of 3 to 5½ ounces (85 to 160 g), and
return them to Earth by early 2013.

November 25: Another troubled mission, Mars Science Laboratory,
will begin its flight to Mars. The primary scientific objective is
straightforward: assess whether the Red Planet ever had an environment
conducive to life — or still does. But MSL, renamed Curiosity after a Disney-inspired contest in 2009, has had a world of trouble getting to the launch pad. The beefy 1-ton lander should have already reached Mars, but development problems caused a two-year launch delay and ballooned its price tag to $2½ billion.

All these dates are subject to change, so to keep up to date I recommend that you check Ron Baalke's comprehensive Space Calendar for the latest schedules.