‘Blobs’ Flag Early Galaxy Formation

Look back far enough in time (and hence far enough in distance) and you see things that don’t correspond to nearby cosmic objects. The so-called ‘Lyman-alpha blobs’ that astronomers have found associated with young, distant galaxies are a case in point. Huge collections of hydrogen gas (some of them the largest single objects yet found in the universe), they’re bright at optical wavelengths, raising the question of what powers the glow and how they factored into the galaxy formation process.


New research may be offering an answer. The key is something called ‘feedback,’ a stage in galaxy formation that shows the interplay between galaxies and the intergalactic medium. Here, the cooling of gas within the dark matter halos enshrouding a young galaxy is countered by heating from active galactic nuclei (think supermassive black holes), which helps to enrich intergalactic space and also slow down star formation.

Image: An artist’s representation showing what one of the galaxies inside a blob might look like if viewed at a relatively close distance. The spiral arms of the galaxy are seen in yellow and white. A two-sided outflow powered by the supermassive black hole buried inside the middle of the galaxy is shown in bright yellow, above and below the galaxy. This outflow illuminates and heats gas surrounding the galaxy, enabling this blob to be seen across billions of light years. Credit: CXC/M. Weiss.

The instrument at work here is the Chandra X-ray Observatory, which has pinpointed the effects of supermassive black holes that, even as they grow, are obscured by the dense layers of gas and dust around them. Also implicated as a power source is the contribution of intense star formation found in these regions. The Lyman-alpha blobs found in an area of sky known as SSA22 are produced by galaxies that are ending their era of rapid growth, and now offer us an insight into how galaxies form.

Bret Lehmer (Durham University, UK), a co-author of the paper on this work, explains the process:

“We’re seeing signs that the galaxies and black holes inside these blobs are coming of age and are now pushing back on the infalling gas to prevent further growth. Massive galaxies must go through a stage like this or they would form too many stars and so end up ridiculously large by the present day.”

Thus the radiation and outflows from black holes and bursts of star formation are powerful enough to illuminate the hydrogen gas of the blobs in which they reside. That’s no small feat, considering that these blobs of gas are several hundred thousand light years across. We’re looking at them at a time when the universe was roughly two billion years old. Rather than galaxies in their infancy, we are evidently seeing galaxy formation as it begins to move away from the period of early rapid growth.

Galaxies in their adolescence? SSA22 offers powerful evidence for that belief. That points to a future where, rather than forming stars, the gaseous blobs will contribute to the gas found between the galaxies. This striking stage of galaxy formation, so unlike the mature galaxies we see in later eras, offers clues to the still earlier era when the flow of gas is inwards and the infant galaxy cools as it emits radiation.

The paper is Geach et al., “The Chandra Deep Protocluster Survey: Ly-alpha Blobs are powered by heating, not cooling,” accepted by the Astrophysical Journal and available online. A Chandra X-ray Observatory news release is also available.

Finding Life in the Ice

As we contemplate using long-range tools like spectroscopy to examine distant exoplanets for life, we’re also developing the hands-on equipment we’ll need for seeking it out in our own Solar System. Project SLIce (Signatures of Life in Ice) is a case in point, an attempt to study how organic material behaves in ice on other worlds by using Earth settings as an analogy. On that score, the archipelago of Svalbard has proven to be a helpful testbed.

Located in the Arctic Ocean between Norway and the North Pole, Svalbard is icy and spectacular. The image below conjures up memories of a nautical journey I took around Iceland in the 1970s, with white-capped seas pushing up against snow-clad peaks. The SLIce team sees Svalbard as a laboratory for looking for extant or extinct life, and a place to develop the protocols for working with rovers in operating environments like Mars.


Image: I love Iceland, but pushing as far north as Svalbard would really bring out the adventurer in me. Here we see rough seas in the Arctic Ocean with mountains and glaciers in the distance. Credit: NASA/AMASE/Kirsten Fristad.

Here’s Liane Benning (University of Leeds) discussing the procedures under examination:

“For SLIce, we applied the protocol we had developed to take ice cores, process them and analyze them in the field just as would happen on a rover on Mars, and then of course we took them back to the lab and did a much wider range of tests, so we really knew what we had found. There could be microbes living in the ice, but there could also be the dead bodies of microbes that used to live there, and there could be biological molecules that blew in from dust and micrometeorites. We need to identify what we’ve got, so that we know what it’s telling us.”

And if that earlier image didn’t make you think of Mars, at least the non-aqueous part of the image below should. Here’s we’re looking at the Redbeds in Bockfjorden. These are layered sediments in northern Svalbard that may be similar to layered sedimentary deposits on Mars (credit: Kjell Ove Storvick/AMASE).


An early SLIce result, described at the Goldschmidt2009 geochemistry meeting in Davos last week: The best place to look for microorganisms in ice is in the layers close to the surface. That’s good to know, because a planetary rover is going to be able to sample such environments much more readily than those several meters beneath. Also helpful is the team’s discovery that cleaning the rover’s sample scoop is harder than it looks, leaving dead micro-organisms on it even after it had apparently been sterilized. New procedures have resolved the problem, ensuring we don’t inadvertently ‘discover’ Earth organisms that have found their way along for the ride.

What happens as we move further out in the Solar System? It’s interesting to speculate on the status of microorganisms near the surface in a radiation-withered environment like that of Europa. But as Richard Greenberg has convincingly demonstrated in his book Unmasking Europa (Springer, 2008), the movement of ice on that world should bring material to the surface — search in the right place and life’s remnants may be close at hand. Now all we have to do is find the funding for a Europa lander (which may be harder to do than flying the mission itself), while developing sufficient radiation shielding to make it feasible. Astrobiology offers no shortage of challenges.

A Cometary Closeup for NExT

By Larry Klaes

Apropos of yesterday’s story on the possible cometary origin of the Tunguska Event in 1908, Tau Zero journalist Larry Klaes looks at the NExT (New Exploration of Tempel) mission, which gives us a second crack at observing comet Tempel 1. Ancient artifacts of the early Solar System, comets can tell us much about its earliest days, but as Larry points out, getting data out of the Deep Impact mission proved to be unexpectedly complicated. NExT is a useful re-purposing of an earlier mission that may unlock further cometary secrets when it returns to Tempel 1 in 2011. If a comet did cause Tunguska, here’s hoping such events continue to be rare, but in the meantime, garnering all the information we can about how comets are made is as important for planetary security as it is for the study of Solar System origins.

An Impact to Remember

Late on the Fourth of July in 2005, while fireworks brightened the sky across the United States, another group of American citizens were making another type of explosion millions of miles away on a small alien world, a form of fireworks being done in the name of science. A robotic space probe, aptly named Deep Impact, lobbed a heavy copper ball at an ancient comet called Tempel 1, smashing into its surface and creating a crater over 300 feet across and almost 100 feet deep in the icy crust.

Mission members had hoped to peer into the crater they made with Deep Impact’s camera eyes to study the deeper and therefore older layers of Tempel 1’s surface. However, they were surprised to discover that the debris kicked up from the impact made a very fine dust cloud that hovered over the crater long after Deep Impact had left the vicinity of the comet, heading back into interplanetary space.


Image: Deep Impact’s impactor collides with Tempel 1. Credit: NASA/JPL-Caltech.

Inventing a New Mission

Meanwhile, another comet probe named Stardust was winding its way back home after successfully collecting particles from an ice ball named Wild 2 over one year earlier. Stardust would return those priceless samples of an alien world to Earth in early 2006 using a small capsule craft. Then Stardust, its primary mission complete, would swing back out into the void, presumably forever.

Thus the dilemma: Deep Impact had not been able to image the crater it made on Tempel 1 as originally planned and could not return to that comet, while Stardust became a still-functioning spacecraft with plenty of onboard fuel, but with nowhere to go. So some clever folks with the US space agency proposed to reroute Stardust to see what its sister vessel had actually done to Tempel 1 and achieve some other important science goals. NASA approved this mission on July 3, 2007 and Stardust was rechristened NExT, which stood for New Exploration of Tempel 1.

Though NExT will not encounter its cometary target until Valentine’s Day in 2011, mission scientists are already hard at work planning every little detail of the space probe’s one shot at Tempel 1 less than two years from now. Scientists from all over the country met at Cornell University on June 8 and 9 to discuss NExT with the astronomy department’s Joe Veverka, who is the Principal Investigator, or PI, for the mission and a veteran of space expeditions throughout the Solar System.

A New View of a Cometary Crater


One of those who traveled far to be at this meeting was H. Jay Melosh, a professor of planetary science at the University of Arizona at Tucson. A former member of the Deep Impact team, Melosh is a renowned expert on impact cratering and is naturally quite interested to see what that probe did create on the surface of Tempel 1 almost four years ago.

“We want to get there when the crater made by Deep Impact is in view of NExT’s cameras,” says Melosh, who also emphasizes the importance of precisely timing when the robot explorer would fly by the comet. NExT will be moving so fast on its arrival day that the space probe will zip past Tempel 1 in just 20 minutes.

Image: Comet Tempel 1 just ninety seconds before the 2005 impact. The image was taken by the targeting sensor on Deep Impact’s impactor. Credit: NASA/JPL-Caltech/UMD.

Melosh and his team members also want to see how the comet’s surface may have changed both from the Deep Impact probe crash and natural cosmic effects during its five year orbit around the Sun. Although Tempel 1 is a fairly quiet comet compared to some of its more geologically active brethren, professional astronomers from around the globe monitoring Tempel 1 have noted that its 42-hour rotation rate has changed since humans first visited that little world in 2005. Melosh wants to know exactly how fast the comet is spinning on its axis now and when NExT arrives in 2011.

“Comets vent gas all the time,” explains Melosh, “so they have changing rotation rates as a result. Tempel 1 is a low activity comet, but its rotation rate still changed.”

On to Another Battered World

Though Melosh is now a geophysicist at his university’s Lunar and Planetary Lab (LPL), his first college degree from Princeton was in physics. When he attended Caltech in the early 1970s as a graduate student, Melosh became interested in glaciology and Earth science. He also got a chance to participate in the Mariner 10 space mission, the first vessel to encounter the planet Mercury. Melosh became fascinated with impact craters, which are widely found on this smallest of our system’s terrestrial worlds, during that time.

The scientist plans on exploring another battered celestial object in the near future with a mission labeled GRAIL, which stands for Gravity Recovery and Interior Laboratory. Launching the same year that NExT encounters comet Tempel 1, GRAIL consists of two identical craft that will study our Moon’s gravity field in detail both for science and to assist future lunar spacecraft navigating our neighboring world.

Comet Implicated in Tunguska Blast

Back in my flying days, I found myself becoming absorbed with meteorology, enough to wind up teaching the subject in various flight school settings. I was no expert, but looking for clues on flying conditions in the next few hours by studying cloud formation and movement was fascinating. In all that time, the one cloud phenomenon I always wanted to see but never did was the noctilucent cloud, an unusual, lovely formation made up of ice particles that occurs at extremely high altitudes.

‘Noctilucent’ means ‘night-shining,’ and that’s just what these clouds do when they’re illuminated by sunlight from below the horizon. Space Shuttle launches have been found to generate them as the vehicle pumps about 300 metric tons of water vapor into the thermosphere, the layer of atmosphere beginning at about ninety kilometers above the surface, just above the mesosphere. Photographs of such clouds show a unique beauty, though it’s one that might also seem eerie, at least in certain settings.


For just after the huge explosion that occurred in Siberia in 1908 night skies shone brightly for several days across Europe, particularly Britain, fully three thousand miles away. The Tunguska Event leveled 830 square miles of forest land and has been ascribed to various causes, but a new study concludes that the bright skies following the explosion are a clue to the true culprit, a comet. Those Shuttle-induced noctilucent clouds are the key.

Image: Noctilucent clouds over Lake Saimaa in Finland. Credit: Mika Yrjölä.

Michael Kelley (Cornell University), who led this work, likens it to figuring out a 100-year-old murder mystery. Kelley thinks the evidence strongly supports the comet theory. Such a comet would have started to break up at roughly the same altitude as the release of the exhaust plume from the Space Shuttle. Moreover, water particles from launches have been found to travel as far as the polar regions, where they form noctilucent clouds after settling into the mesosphere.

The Shuttle plume, in other words, parallels what we would expect from a comet, but the wild card has been how water vapor could travel large distances without diffusing. We’re talking about moving this material thousands of kilometers, and quickly. Noting that there is no model that would predict this movement, Kelley calls the result “totally new and unexpected physics.”

Such new physics would involve, the researchers believe, so-called ‘two dimensional turbulence’ — counter-rotating atmospheric eddies packed with extreme energy, powerful enough that when the water vapor becomes involved with them, it travels at more than 90 meters per second. The problem is that the structure of winds in the boundary areas between the mesosphere and the thermosphere is not well understood. Noctilucent clouds may be giving us clues to the nature of this tricky region.

The paper is Kelley et al., “Two-dimensional turbulence, space shuttle plume transport in the thermosphere, and a possible relation to the Great Siberian Impact Event,” in press at Geophysical Research Letters. More in this Cornell University news release.

Enceladus: Riddle of the Plumes

Is there really an underground ocean on Enceladus? The Cassini spacecraft’s striking images have created a cottage industry in speculation, with spectacular glimpses of erupting plumes composed of ice and water vapor. This week, however, we get two contrasting views on what all this means. In one, a paper in Nature by a European team led by Frank Postberg (Universität Heidelberg), studies of sodium salts in dust ejected by the Enceladus plumes reveal telltale signs of a salty ocean deep below the surface.

Postberg was working with data from the Cosmic Dust Analyzer (CDA) instrument aboard Cassini, and the results imply a level of sodium chloride that may be as high as that found in Earth’s oceans. The data come from ice grains in Saturn’s E-ring, which is thought to consist largely of material from Enceladus. Thus we seem to be gathering direct evidence for the presence of the hypothesized ocean, which should be salty from long contact with the rocky core.


But not so fast. The same issue of Nature delivers a report from Nicholas Schneider (University of Colorado at Boulder), whose own team examined sodium emission in the plumes erupting from Enceladus. Using the 10-meter Keck 1 telescope and the 4-meter Anglo-Australian telescope, the researchers found no sign of sodium emission, a result that suggests alternative solutions to the riddle of the plumes. One possibility is the presence of deep caverns from which water evaporation is slow, or warm ice vaporising into space. “It could even,” says Schneider, “be places where the crust rubs against itself from tidal motions and the friction creates liquid water that would then evaporate into space.”

Image: Geysers near the south pole of Enceladus. Are we seeing evidence of a subsurface ocean, or are there other explanations? Credit: NASA/JPL/Space Science Institute.

Enceladus comes out of this as enigmatic as ever, the existence of its ocean still debated. If there is a reservoir of salty water on the moon, what are the mechanisms regulating the escape of sodium, and how do we account for the sodium salts of the E-ring? More to come, but for now, the CDA paper is Postberg et al., “Sodium salts in E-ring ice grains from an ocean below the surface of Enceladus,” Nature 459 (25 June 2009), pp. 1098-1101 (abstract). The Schneider paper is “No sodium in the vapour plumes of Enceladus,” in the same issue of Nature, pp. 1102-1104 (abstract).