Posted on by Nancy Atkinson

Take a 3-D Tour of the International Space Station

ESA astronaut Paolo Nespoli shot some 3-D video during his 6 months on board the International Space Station (Dec 2010 to May 2011) and the footage has now been put together into a “tour” of the space station. Nespoli and the crew used ESA’s Erasmus Recording Binocular (ERB-2) stereoscopic camera, capturing “day-in-the-life” activiites on the ISS, from educational activities, to scientific experiments and physical training, also demonstrating the way astronauts move in weightlessness through the various modules. So, grab your red/blue 3-D glasses to watch the video.

ERB-2 was used on August 6, 2011 by astronaut Ron Garan to broadcast live 3-D video from space.

The ERB-2 is the about the size of a shoebox, with high-definition optics and advanced electronics.

Posted on by Jon Voisey

A Magnified Supernova

Galaxy Cluster Abell 1689

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Supernovae are among astronomers most important tools for exploring the history of the universe. Their frequency allows us to examine how active star formation was, how heavy elements have developed, and the distance to galaxies across vast distances. Yet even these titanic explosions are only so bright, and there’s an effective limit on how far we can detect them with the current generation of telescopes. However, this limit can be extended with a little help from gravity.

One of the consequences of Einstein’s theory of general relativity is that massive objects can distort space, allowing them to act as a lens. While first postulated in 1924, and proposed for galaxies by Fritz Zwicky in 1937, the effect wasn’t observed until 1979 when a distant quasar, an energetic core of a distant galaxy, was split in two by the gravitational disturbances of an intervening cluster of galaxies.

While lensing can distort images, it also provides the possibility that it may magnify a distant object, increasing the amount of light we receive. This would allow astronomers to probe even more distant regions with supernovae as their tool. But in doing so, astronomers must look for these events in a different manner than most supernova searches. These searches are generally limited to the visible portion of the spectrum, the portion we see with our eyes, but due to the expansion of the universe, the light from these objects is stretched into the near-infrared portion of the spectrum where few surveys to search for supernovae exist.

But one team, led by Rahman Amanullah at Stockholm University in Sweden, has conducted a survey using the Very Large Telescope array in Chile, to search for supernovae lensed by the massive galaxy cluster Abell 1689. This cluster is well known as a source of gravitationally lensed objects, making visible some galaxies that formed shortly after the Big Bang.

In 2009, the team discovered one supernova that was magnified by this cluster that originated 5-6 billion lightyears away. In a new paper, the team reveals details about an even more distant supernova, nearly 10 billion lightyears distant. This event was magnified by a factor of 4 from the effects of the foreground cluster. From the distribution of energy in different portions of the spectrum, the team concludes that the supernova was an implosion of a massive star leading to a core-collapse type of supernova. The distance of this event puts it among the most distant supernovae yet observed. Others at this distance have required extensive time using the Hubble telescope or other large telescopes.

Posted on by Ken Kremer

China set to ‘Leap Forward in Space’ as Tiangong 1 Rolls to Launch Pad

The integrated Tiangong? spacecraft and CZ-2F launch vehicle combination has arrived at launch tower

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China’s human spaceflight program is gearing up to take a highly significant “Leap forward in Space” after their “Tiangong 1” prototype space station was rolled out to the remote Gobi desert launch pad at the countries Jiuquan Satellite Launching Center in Gansu Province in anticipation of blastoff sometime this week.

Space officials from the Chinese Manned Space Engineering Office have now confirmed that liftoff of the 8.5 ton Tiangong 1 human rated module atop a Long March CZ-IIF booster rocket is slated to take place during a launch window that extends from Sept. 27 to Sept. 30. The launch was delayed a few days after the recent launch failure of a similar Chinese rocket, the Long March IIC.

China’s burgeoning space efforts come directly on the heels of the voluntary US shutdown of the Space Shuttle program, thereby dismantling all US capability to launch humans into space from American soil for several years until about 2014 at a minimum.

The US manned spaceflight capability gap will be stretched out even further if NASA’s budget for commercial space taxis and the newly proposed SLS launch system is cut by political leaders in Washington, DC.

The integrated Tiangong 1 spacecraft and CZ-2F launch vehicle combination is slowly rolling out of the VAB facility

On Sept. 20, the integrated Long March rocket and Tiangong module were wheeled out of China’s VAB while sitting on top of the Mobile Launch Platform and transferred to the launch gantry at Jiuguan.

The goal of the Tiangong 1 mission is to carry out China’s first human spaceflight related rendezvous and docking mission and to demonstrate that Chinese space engineers have mastered the complicated technology required for a successful outcome.

These skills are akin in complexity to NASA’s Gemini manned program of the 1960’s which paved the way for NASA’s Apollo missions and led directly to the first manned landing on the moon in 1969 by Apollo 11.

Chinas stated goal is to construct a 60 ton Skylab sized space station in earth orbit by 2020.

Check out this CCTV video for further details and imagery of the Chinese space hardware which shows the how China will expand the reach and influence of their space program.

View this Chinese video from NDTV for a glimpse at Chinas long range Space Station plans.

The 40 foot long Tiangong 1 space platform is unmanned and will serve as the docking target for China’s manned Shenzhou capsules in a series of stepping stone learning flights. It is solar powered and equipped to operate in a man-tended mode for short duration missions and in an unmanned mode over the long term.

The initial rendezvous and docking mission will be conducted by the Shenzhou 8 spacecraft, which will fly in an unmanned configuration for the first docking test. Shenzhou 8 is scheduled to soar to space before the end of 2011.

If successful, China plans to quickly follow up with the launch of two manned Shenzhou flights to dock at Tiangong 1 during 2012 – namely Shenzhou 9 & Shenzhou 10.

The multi astronaut chinese crews would float into Tiangong 1 and remain on board for a short duration period of a few days or weeks. The crew would conduct medical, space science and technology tests and experiments.

China’s first female astronaut may be selected to fly as a crew member on one of the two Shenzhou flights in 2012.

Meanwhile, all American astronauts will be completely dependent on the Russian Soyuz capsule for trips to the International Space Station. Russia is still working to correct the third stage malfunction which doomed the recent Progress cargo resupply launch and put a halt to Soyuz launches.

Engineers and technicians are in the process of checking out all Tiangong 1 systems and preliminary weather reports from Chinese media appear favorable for launch.

Shenzhou 8 has also been delivered to the Jinquan launch complex for check out of all systems

Get set for China’s attempt at a ‘Space Spectacular’

The integrated Tiangong 1 spacecraft and CZ-2F combination is transferring to the launch site
Posted on by Jon Voisey

Homeless Supernovae

NGC 1058. Image credit: Bob Ferguson and Richard Desruisseau/Adam Block/NOAO/AURA/NSF
NGC 1058. Image credit: Bob Ferguson and Richard Desruisseau/Adam Block/NOAO/AURA/NSF

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In a post earlier this month, we looked at a team of astronomers searching for stars that were on ejected from their birthplaces in clusters. These stars could receive the needed kick from a gravitational swing by the core of the cluster to achieve a velocity of a few tens of km/sec. But a similar mechanism can function in the cores of galaxies giving stars a speed of roughly 1,000 km/sec, enough to leave their parent galaxies. a new study asks whether we have ever witnessed any of these stellar cast offs explode as supernovae.

The team, led by Peter-Christian Zinn at Ruhr University in Bochum, Germany, searched through roughly 6,000 supernovae listed in the Sternbarg Astronomical Institute Supernova Catalog, for which no host galaxy was apparent, yet weren’t too distant from any known galaxy. The latter criteria was added because, even at the high velocities, stars still couldn’t get too far before they reached the end of their fuses. The team imposed a rough inner cut off of around 10 kiloparsecs (roughly 1/3 of the width of the disk of the Milky Way). They expected stars should be at least this distance from the cores of the parent galaxy.

The initial list contained five candidate stars, dating back as far as 1969. The first step the team used to determine if the supernova was truly in a galaxy or not, was to take long exposure images of the immediate area, to draw out potential low surface brightness hosts. The team also used archival data in the far ultraviolet as well as the x-ray spectrum to determine whether or not the nearby galaxies from which the supernovae could potentially be ejected had an extended disk, invisible in the visible portion of the spectrum that would have allowed the progenitor star to form in the outskirts of the galaxy. These wavelengths are tracers of ongoing star formation which are sites in which high mass stars that would lead to core-collapse supernovae, would likely be found.

The oldest candidate, SN 1969L, was located near the flocculent spiral NGC 1058. While the deep exposures did not show a host galaxy, the x-ray and UV images both showed some extended structure of the parent galaxy at the distance of the supernova. This led to the conclusion that this supernova, while far removed from its host galaxy, was still gravitationally tied to it.

With the second candidate, SN 1970L, the team again failed to find any faint host galaxy. However, the supernova was situated between two galaxies, NGC 2968 and a faint elliptical, NGC 2970. A 1994 study had revealed a faint bridge of matter connecting the two, implying that they had had an interaction in the past. This interaction would likely have pulled off gas and stars, of which SN 1970L could have been one.

SN 1997C was the third candidate and also lacked a discernible host galaxy, even with long exposures. This one also did not have an indication of an extended disk of which the supernova could have been part. Given the characteristics of the supernova, the team estimated that it had an original mass of 15 times that of the Sun. Given its projected distance and the lifetime of such stars, the team noted that this would correspond to a velocity of some 3,000 km/sec, which is several times the speed of the highest confirmed hypervelocity star. As such, the team expected that this star would have to be ejected in a similar manner to SN 1970L, using an interaction between galaxies. Given that the host galaxy is known to be one in a small cluster and the disk shows some signs of perturbation, they suggested this was likely.

The fourth candidate, SN 2005nc, the team selected because there was no nearby galaxy they could assign as a possible parent. They suggested this was due to an extremely distant host galaxy, too faint to resolve with previous studies. The basis for this assertion was that the supernova came with a gamma ray burst that indicated an origin some 5-6 billion light years distant. Due to the associated GRB, the Hubble telescope swung in to take a look. These archival pictures failed to reveal any objects that could readily be identified as host galaxies leaving the team to presume the host was simply too far away to resolve.

The last candidate was SN 2006bx located near the galaxy UGC 5434. This supernova did not appear to be in a faint background galaxy and did not have hints of being formed in an extended disk. The estimated velocity from the projected distance was ~850 km/sec which placed it in the realm of plausible speeds for stars ejected by gravitational assists from the supermassive black hole at the center of galaxies.

Posted on by Ken Kremer

Opportunity spotted Exploring vast Endeavour Crater from Mars Orbit

Opportunity captured at Endeavour Crater rim on Sept 10, 2011, Sol 2712. Opportunity is visible at the end of the white arrow, sitting atop some light toned outcrops on the rim of Endeavour Crater located at the southern tip of a rim segment named Cape York. Opportunity is ascending Endeavour at Cape York ridge and positioned to the right of the small crater named Odyssey. This image was taken by the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter (MRO), Opportunity travelled nearly three years to reach this rim because it contains rocks even more ancient than the rocks of Meridiani Planum, which the rover has been exploring since 2004, and hence may teach us something about an even more ancient era in Martian history. Click to enlarge. Credit: NASA/JPL/University of Arizona

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Opportunity has just been imaged in high resolution at Endeavour crater by a powerful NASA camera orbiting overhead in Mars orbit. The new image (see above) was snapped while NASA’s long lived robot was climbing a hilltop offering spectacular panoramic vistas peering into the vast crater which is some 14 miles (22 km) wide.

The HiRiSE camera aboard NASA’s Mars Reconnaissance Orbiter photographed Opportunity and her wheel tracks on September 10, 2011, or Martian Sol 2712 for a mission warrentied to last only 90 Sols ! The rover is sitting to the right of another small crater known as Odyssey. Click to enlarge the image.

Look very closely and you’ll even be able to easily discern the rovers pair of tire tracks showing the path traversed by the robot as she explores the crater and the ejecta rocks and boulders excavated and strewn about by an ancient impact.

Opportunity imaged at Endeavour crater rim with wheel tracks exploring Odyssey crater, rocks and boulders climbing up Cape York ridge. Credit: NASA/JPL/University of Arizona

Opportunity is ascending up the rim of Endeavour crater at the southern tip of a low ridge dubbed Cape York – a location that has already yielded a bonanza of new science data since her recent arrival in August 2011 after a more than 20 mile (33 km) epic trek.

The intrepid rover discovered a rock unlike any other since she safely landed at the Meridiani Planum region of Mars nearly eight years ago on Jan. 24, 2004.

Opportunity is now searching Endeavour crater and Cape York for signatures of phyllosilicates – clay minerals that formed in the presence of pH neutral water flowing on Mars surface billions of years ago.

Cape York ridge at Endeavour Crater - From Orbit
This image taken from Mars orbit shows the path driven by NASA's Mars Exploration Rover Opportunity in the weeks around the rover's arrival at the rim of Endeavour crater and up to Sol 2688. Opportunity has since driven a short distance to the right. Credit: NASA/JPL-Caltech/University of Arizona

Endeavour Crater Panorama from Opportunity, Sol 2681, August 2011
Opportunity arrived at the rim of Endeavour on Sol 2681, August 9, 2011 and climbed up the ridge known as Cape York. Odyssey crater is visible at left. Opportunity has since driven a short distance beyond Odyssey crater and was photographed from Mars orbit on Sept. 10, 2011.
Mosaic Credit: NASA/JPL/Cornell/Marco Di Lorenzo/Kenneth Kremer

Read Ken’s continuing features about Curiosity and Opportunity starting here:
Opportunity spotted Exploring vast Endeavour Crater from Mars Orbit
Twin Towers 9/11 Tribute by Opportunity Mars Rover
NASA Robot arrives at ‘New’ Landing Site holding Clues to Ancient Water Flow on Mars
Opportunity Arrives at Huge Martian Crater with Superb Science and Scenic Outlook
Opportunity Snaps Gorgeous Vistas nearing the Foothills of Giant Endeavour Crater
Dramatic New NASA Animation Depicts Next Mars Rover in Action
Opportunity Rover Heads for Spirit Point to Honor Dead Martian Sister; Science Team Tributes

Posted on by Nancy Atkinson

Awesome Pic: Astronaut Ron Garan’s Window to the World

Astronaut Ron Garan in the cupola of the International Space Station off the coast of Australia. Credit: NASA

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This has become my new favorite space photo! Look closely into the windows of the Cupola on the International Space Station: That’s astronaut Ron Garan, on September 16, 2011, his last day on board the space station. “That’s me in the cupola of the International Space Station off the coast of Australia taking my last of over 25,000 pics that I still want to share with everyone,” Garan wrote on his Google+ page. Not only are the colors and view spectacular, but this has got to be one of the best destination photos ever — not to mention a priceless keepsake and memento for Garan from his expedition on the ISS.

You can see some of the thousands of images Garan took from space on his Twitpic page.

Posted on by VirtualAstro

Massive Sunspot 1302

Sun Set with the Massive Sun Spot 1302 (Upper left on the Sun) Credit: Adrian Scott

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A highly active region on the Sun threatens to deliver powerful geomagnetic storms over the week ahead. Highly energetic solar eruptions are likely heading in our direction to give Earth’s magnetic field a significant glancing blow!

Over the past few days the new sunspot AR1302 has been incredibly active, hurling massive X-class solar flares into space and it will soon face Earth.

The massive sunspot, many times larger than the Earth (see images below) is expected to increase in size and energy, and is expected to release powerful solar flares, sparking strong geomagnetic storms.

Sun Spot AR1302 through the clouds Credit: Tavi Greiner

What does this mean for the Earth and it inhabitants?

The Earth experiences material ejected from the Sun on a daily basis and we are protected by the Earth’s own magnetic field. This is normal and has been happening since the birth of the solar system. But occasionally the Sun erupts and sends vast quantities of solar material our direction in the form of Coronal Mass Ejections (CME’s).

This can trigger very powerful geomagnetic storms, which can damage satellites in orbit and cause problems for communications and power networks. One positive outcome, though, is amazing displays of aurorae at the poles (Northern and Southern Lights).

Sunspot 1302 is expected to eject material towards Earth over the next few days, so look for news of strong geomagnetic activity and displays of aurorae.

Several observers are reporting that AR1302 is easily visible on the Sun at sunset or sunrise. Never ever look at the sun with your eyes, or any other optical aid! This will damage your eyesight permanently! The Sun should only be viewed using specialist equipment.

For further updates see Spaceweather.com and NASA’ Heliophysics Science Division

Massive Sun Spot 1302 and Earth size Comparison taken with a specialist solar filter Credit: Will Gater www.willgater.com

Posted on by Jason Major

The Cassini Image Hall of Fame

 

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If you’re reading this, you’re probably very well aware of the Cassini mission. Launched in 1997, the Cassini spacecraft arrived at Saturn in June of 2004 and has been faithfully returning image after beautiful image of Saturn, its rings and its very extended family of moons ever since – not to mention all the groundbreaking scientific discoveries it’s made about the Saturnian system… and our solar system as a whole. Cassini truly is a rock star in the world of robotic space exploration, and now it has its own Hall of Fame to show off some of its best work!

The Cassini mission site put up by JPL/Caltech regularly features news and images from the mission, even including the latest downlinked raw image data from the spacecraft. In this way anyone can keep up with what Cassini is seeing and when, far before the images are included in NASA’s Planetary Data System. The new Cassini Image Hall of Fame showcases the “best of the best” from the mission, and is a great way to revisit Cassini’s past discoveries. (With so much happening at Saturn, sometimes it’s easy to forget all the amazing things Cassini has brought to our attention!)

Revisit the best of the best images of Saturn

If you’re a fan of Saturn (and really, who isn’t?) be sure to check this out. With the current mission extended into 2017 there’s sure to be lots more additions to the Hall of Fame on the way, too!

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

Click here to see the Hall of Fame images.

Also, be sure to visit the hard-working Cassini imaging team’s homepage at http://ciclops.org… they are the ones responsible for all these fantastic images in the first place!

 

Posted on by Ken Kremer

Dramatic 3 D Imagery Showcases Vesta’s Pockmarked, Mountainous and Groovy Terrain

3 D Anaglyph of Craters at Rheasilvia - the South Polar Region of Vesta. This 3-D image shows the topography, craters and grooves of Vesta’s south polar region obtained by the framing camera instrument aboard NASA’s Dawn spacecraft on Aug. 23 and 28, 2011. The image has a resolution of about 260 meters per pixel.

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Try not to plummet off a steep crater cliff or be buried under a landslide while gazing at the irresistibly alluring curves of beautiful Rheasilvia – the mythical mother of Romulus and Remus – whose found a new home at the South Pole of the giant Asteroid Vesta.

3 D is undoubtedly the best way to maximize your pleasure. So whip out your cool red-cyan anaglyph glasses to enhance your viewing experience of Rheasilvia, the Snowman and more – and maximize your enjoyment of this new 3 D collection showcasing the heavily cratered, pockmarked, mountainous and groovy terrain replete at Vesta.

3D Details of Wave-Like Terrain in the South Pole of Vesta
This image was obtained by NASA’s Dawn spacecraft from an orbit of about 1,700 miles (2,700 kilometers) above the surface of the giant asteroid Vesta. Topography in the area surrounding Vesta's south pole area shows impact craters, ridges and grooves. These images in 3D provide scientists with a realistic impression of the solid surface of the celestial body.
Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Can you find the location of the 3 D image above in the 2 D South Pole image below?

Scientists and mortals have been fascinated by the enormous impact crater Rheasilvia and central mountain unveiled in detail by NASA’s Dawn Asteroid Orbiter recently arrived at Vesta, the 2nd most massive object in the main asteroid belt. Ceres is the largest object and will be Dawn’s next orbital target in 2015 after departing Vesta in 2012.

3D - A Big Mountain at Asteroid Vesta’s South Pole
Scientists were fascinated by this enormous mound inside a big circular depression at the south pole- dubbed Rheasilvia. This stereo image was recorded from an altitude of about 1,700 miles (2,700 kilometers) above the surface and shows the structure of the mountain, displayed in the right half of this 3D image. The base of the mountain has a diameter of about 125 miles (200 kilometers), and its altitude above the surroundings is about 9 miles (15 kilometers). The vicinity of the peak of the mountain shows landslides that occurred when material from the flanks of the mountain were slipping down. Also visible are tectonic structures from tension in Vesta's crust. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

“Vesta is the smallest terrestrial planet in our Solar System”, said Chris Russell in an interview with Universe Today. “We do not have a good analog to Vesta anywhere else in the Solar System.”

And the best is yet to come. In a few days, Dawn begins snapping images from a much lower altitude at the HAMO mapping orbit of ca. 685 km vs the initial survey orbit of ca, 2700 km. where most of these images were taken.

Can you find the location of the 3 D South Pole images above in the 2 D South Pole image below?

Topography of Densely Cratered Deformed Terrain
This 3 D anaglyph image shows the topography of Vesta's densely cratered terrain obtained by the framing camera instrument aboard NASA's Dawn spacecraft on August 6, 2011. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Anaglyph of the ‘Snowman' Crater. This anaglyph image shows the topography of Vesta's three craters, informally named the "Snowman," obtained by the framing camera instrument aboard Dawn on August 6, 2011. The camera has a resolution of about 260 meters per pixel. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Vesta's Ancient, Cratered Surface in 3D
This image of the giant asteroid Vesta obtained by NASA's Dawn spacecraft shows the surface of the asteroid from an orbit of about 1,700 miles (2,700 kilometers) above the surface. Numerous impact craters illustrate the asteroid's violent youth. By counting craters on distinct geological surfaces scientists can deduce relative ages of the asteroid's surface. This 3D view provides scientists the opportunity to learn more about the morphology of craters on asteroids and physical properties of the material at Vesta's surface.. Image resolution is about 260 meters per pixel. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Viewing the South Pole of Vesta and Rheasilvia Impact Basin
This image obtained by Dawns framing camera shows the south pole of the giant asteroid Vesta. Scientists are discussing whether the Rheasilvia circular structure that covers most of this image originated by a collision with another asteroid, or by internal processes early in the asteroid's history. Images in higher resolution from Dawn's next lowered orbit might help answer that question. The image was recorded from a distance of about 1,700 miles (2,700 kilometers). The image resolution is about 260 meters per pixel. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Rhea Silvia, torso from the amphitheatre at Cartagena in Spain that was rediscovered in 1988. Rhea Silvia was the mother of Romulus and Remus, the mythical founders of Rome. Source: Wikipedia

Read Ken’s continuing features about Dawn and Vesta

Rheasilvia – Super Mysterious South Pole Basin at Vesta
Space Spectacular — Rotation Movies of Vesta
3 D Alien Snowman Graces Vesta
NASA Unveils Thrilling First Full Frame Images of Vesta from Dawn
Dawn Spirals Down Closer to Vesta’s South Pole Impact Basin
First Ever Vesta Vistas from Orbit – in 2D and 3D
Dawn Exceeds Wildest Expectations as First Ever Spacecraft to Orbit a Protoplanet – Vesta
Dawn Closing in on Asteroid Vesta as Views Exceed Hubble
Dawn Begins Approach to Asteroid Vesta and Snaps First Images
Revolutionary Dawn Closing in on Asteroid Vesta with Opened Eyes

Posted on by Steve Nerlich

Astronomy Without A Telescope – Star Formation Laws

NGC 1569 - a relatively close (11 million light years) starburst galaxy - presumably a result of fairly efficient star formation Credit: NASA/HST

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Take a cloud of molecular hydrogen add some turbulence and you get star formation – that’s the law. The efficiency of star formation (how big and how populous they get) is largely a function of the density of the initial cloud.

At a galactic or star cluster level, a low gas density will deliver a sparse population of generally small, dim stars – while a high gas density should result in a dense population of big, bright stars. However, overlying all this is the key issue of metallicity – which acts to reduce star formation efficiency.

So firstly, the strong relationship between the density of molecular hydrogen (H2) and star formation efficiency is known as the Kennicutt-Schmidt Law. Atomic hydrogen is not considered to be able to support star formation, because it is too hot. Only when it cools to form molecular hydrogen can it start to clump together – after which we can expect star formation to become possible. Of course, this creates some mystery about how the first stars might have formed within a denser and hotter primeval universe. Perhaps dark matter played a key role there.

Nonetheless, in the modern universe, unbound gas can more readily cool down to molecular hydrogen due the presence of metals, which have been added to the interstellar medium by previous populations of stars. Metals, which are any elements heavier than hydrogen and helium, are able to absorb a wider range of radiation energy levels, leaving hydrogen less exposed to heating. Hence, a metal-rich gas cloud is more likely to form molecular hydrogen, which is then more likely to support star formation.

But this does not mean that star formation is more efficient in the modern universe – and again this is because of metals. A recent paper about the dependence of star formation on metallicity proposes that a cluster of stars develops from H2 clumping within a gas cloud, first forming prestellar cores which draw in more matter via gravity, until they become stars and then begin producing stellar wind.

Relationship between the power of stellar winds and stellar mass (i.e. big star has big wind) - with the effect of metallicity overlaid. The solid line is the metallicity of the Sun (Z=Zsol). High metallicity produces more powerful winds for the same stellar mass. Credit: Dib et al.

Before long, the stellar wind begins to generate ‘feedback’, countering the infall of further material. Once the outward push of stellar wind achieves unity with the inward gravitational pull, further star growth ceases – and bigger O and B class stars clear out any remaining gas from the cluster region, so that all star formation is quenched.

The dependence of star formation efficiency on metallicity arises from the effect of metallicity on stellar wind. High metal stars always have more powerful winds than any equivalent mass, but lower metal, stars. Thus, a star cluster – or even a galaxy – formed from a gas cloud with high metallicity, will have lower efficiency star formation. This is because all stars’ growth is inhibited by their own stellar wind feedback in late stages of growth and any large O or B class stars will clear out any remaining unbound gas more quickly than their low metal equivalents.

This metallicity effect is likely to be the product of ‘radiative line acceleration’, arising from the ability of metals to absorb radiation across a wide range of radiation energy levels – that is, metals present many more radiation absorption lines than hydrogen has on its own. The absorption of radiation by an ion means that some of the momentum energy of a photon is imparted to the ion, to the extent that such ions may be blown out of the star as stellar wind. The ability of metals to absorb more radiation energy than hydrogen can, means you should always get more wind (i.e. more ions blown out) from high metal stars.

Further reading:
Dib et al. The Dependence of the Galactic Star Formation Laws on Metallicity.