Newborn Stars: Seeing Dark Filaments Inside A Molecular Cloud

Astronomers have measured the distribution of mass inside a dark filament in a molecular cloud with an amazing level of detail and to great depth. The measurement is based on a new method that looks at the scattered near-infrared light or 'cloudshine' and was made with ESO's New Technology Telescope. Associated with the forthcoming VISTA telescope, this new technique will allow astronomers to better understand the cradles of newborn stars.

Part of a filament in the Corona Australis molecular cloud. The image is a composite of J-, H-, and K-band near-infrared observations that were made with the SOFI instrument on ESO's NTT telescope in August 2006. The observations were made to test, how easily the scattered light can be observed and how good it is as a tracer of cloud structure. The J-, H-, and K-band intensities are coded with blue, green, and red colours. The gradual saturation of the near-infrared bands is visible as a change of colour. In diffuse regions the shorter wavelength J-band is strong and the colour is bluish. When the J-band saturates the colour changes first to green and finally, in the centre of the filament, the red colour corresponding to the K-band becomes the strongest. In the most saturated regions the surface brightness data can only be used to derive a lower limit for the total amount of dust on the line of sight. (Credit: Copyright ESO)

The vast expanses between stars are permeated with giant complexes of cold gas and dust opaque to visible light. Yet these are the future nurseries of stars to be.

"One would like to have a detailed knowledge of the interiors of these dark clouds to better understand where and when new stars will appear," says Mika Juvela, lead author of the paper in which these results are reported.

Because the dust in these clouds blocks the visible light, the distribution of matter within interstellar clouds can be examined only indirectly. One method is based on measurements of the light from stars that are located behind the cloud_^[1] .

"This method, albeit quite useful, is limited by the fact that the level of details one can obtain depends on the distribution of background stars," says co-author Paolo Padoan.

In 2006, astronomers Padoan, Juvela, and colleague Veli-Matti Pelkonen, proposed that maps of scattered light could be used as another tracer of the cloud's inner structure, a method that should yield more advantages. The idea is to estimate the amount of dust located along the line of sight by measuring the intensity of the scattered light.

Dark clouds are feebly illuminated by nearby stars. This light is scattered by the dust contained in the clouds, an effect dubbed 'cloudshine' by Harvard astronomers Alyssa Goodman and Jonathan Foster. This effect is well known to sky lovers, as they create in visible light wonderful pieces of art called 'reflection nebulae'. The Chameleon I complex nebula is one beautiful example.

When making observations in the near-infrared, art becomes science. Near-infrared radiation can indeed propagate much farther into the cloud than visible light and the maps of scattered light can be used to measure the mass of the material inside the cloud.

To put this method to the test and use it for the first time for a quantitative estimation of the distribution of mass within a cloud, the astronomers who made the original suggestion, together with Kalevi Mattila, made observations in the near-infrared of a filament in the Corona Australis cloud_[2] . The observations were made in August 2006 with the SOFI instrument on ESO's New Technology Telescope at La Silla, in the Chilean Atacama Desert. The filament was observed for about 21 hours.

Their observations confirm that the scattering method is providing results that are as reliable as the use of background stars while providing much more detail.

"We can now obtain very high resolution images of dark clouds and so better study their internal structure and dynamics," says Juvela. "Not only is the level of details in the resulting map no longer dependent on the distribution of background stars, but we have also shown that where the density of the cloud becomes too high to be able to see any background stars, the new method can still be applied."

"The presented method and the confirmation of its feasibility will enable a wide range of studies into the interstellar medium and star formation within the Milky Way and even other galaxies," says co-author Mattila.

"This is an important result because, with current and planned near-infrared instruments, large cloud areas can be mapped with high resolution," adds Pelkonen. "For example, the VIRCAM instrument on ESO's soon-to-come VISTA telescope has a field of view hundreds of times larger than SOFI. Using our method, it will prove amazingly powerful for the study of stellar nurseries."

Journal reference: The report appears in the journal Astronomy and Astrophysics ("A Corona Australis cloud filament seen in NIR scattered light - I. Comparison with extinction of background stars", by Mika Juvela, Veli-Matti Pelkonen, Paolo Padoan, and Kalevi Mattila). Juvela, Pelkonen and Mattila are associated with the Helsinki University Observatory (Finland), while Padoan is at the University of California, San Diego, USA.

Notes

[1]: When the light from the background stars passes through the cloud, it is absorbed and scattered, resulting in the background stars appearing redder than they really are. The effect is proportional to the amount of obscuring material and is therefore largest for stars that are situated behind the cloud's densest parts. By measuring the degree of this 'reddening' experienced by stars seen through different areas of the cloud, it is thus possible to chart the distribution of dust in the cloud. The finer the net of background stars is, the more detailed this map will be and the better the information about the internal structure of the cloud. And that is exactly the problem. Even small clouds are so opaque that very few background stars can be seen through them. Only large telescopes and extremely sensitive instruments are able to observe a sufficient number of stars in order to produce significant results.

[2]: Located in the constellation of the same name ('Southern Crown'), the Corona Australis molecular cloud is shaped like a 45 light year long cigar. Located about 500 light years away, it contains the equivalent of about 7000 Suns. On the sky, the dark cloud is surrounded by many beautiful 'reflection nebulae'.

Adapted from materials provided by ESO.

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Mankind's secrets kept in lunar ark

IF civilisation is wiped out on Earth, salvation may come from space. Plans are being drawn up for a “Doomsday ark” on the moon containing the essentials of life and civilisation, to be activated in the event of earth being devastated by a giant asteroid or nuclear war.

Construction of a lunar information bank, discussed at a conference in Strasbourg last month, would provide survivors on Earth with a remote-access toolkit to rebuild the human race.

A basic version of the ark would contain hard discs holding information such as DNA sequences and instructions for metal smelting or planting crops. It would be buried in a vault just under the lunar surface and transmitters would send the data to heavily protected receivers on earth. If no receivers survived, the ark would continue transmitting the information until new ones could be built.

The vault could later be extended to include natural material including microbes, animal embryos and plant seeds and even cultural relics such as surplus items from museum stores.

As a first step to discovering whether living organisms could survive, European Space Agency scientists are hoping to experiment with growing tulips on the moon within the next decade.

According to Bernard Foing, chief scientist at the agency’s research department, the first flowers - tulips or arabidopsis, a plant widely used in research - could be grown in 2012 or 2015.

“Eventually, it will be necessary to have a kind of Noah’s ark there, a diversity of species from the biosphere,” said Foing.

Tulips are ideal because they can be frozen, transported long distances and grown with little nourishment. Combined with algae, an enclosed artificial atmosphere and chemically enhanced lunar soil, they could form the basis of an ecosystem.

The first experiments would be carried out in transparent biospheres containing a mix of gases to mimic the earth’s atmosphere. Carbon dioxide given off by the decomposing plants would be mopped up by the algae, which would generate oxygen through photosynthesis.

The databank would initially be run by robots and linked to earth by radio transmissions. Scientists hope to put a manned station on the moon before the end of the century.

The databank would need to be buried under rock to protect it from the extreme temperatures, radiation and vacuum on the moon. It would be run partly on solar power. The scientists envisage placing the first experimental databank on the moon no later than 2020 and it could have a lifespan of 30 years. The full archive would be launched by 2035.

The information would be held in Arabic, Chinese, English, French, Russian and Spanish and would be linked by transmitter to 4,000 “Earth repositories” that would provide shelter, food, a water supply for survivors.

Nasa sees light

A Nasa satellite has detected radiation emitted trillionths of a second after the big bang, the closest humans have got to directly observing the explosion that created the universe, writes Jonathan Leake.

The pattern of radiation - at 13.7 billion years, the oldest light detected - shows how the universe expanded. The results give scientists the most detailed timeline on the evolution of the universe.

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Warming Oceans = Fish Getting Lost at Sea :(

Researchers examining Australian damselfish have found small fry with asymmetrical ear bones are less likely to make it back to their reef homes after a stint out at sea (research paper, press release). This could be because fish at sea listen for the sounds of home in order to navigate (see the BBC coverage for more on this angle).

Stress factors such as temperature and acidity will probably increase the number of fish with funny ears, they say. Increased acidity reduces the amount of calcium around for making ear bones, and having to regulate internal pH against changing water pH will also have a negative impact (Reuters, New Scientist).

As warmer and more acidic oceans are likely to result from global warming, more fish are going to be swimming around lost.

“Five years ago we used to see them [damselfish] in the thousands; now they are not so plentiful. A lot more work needs to be done, but I suspect it has something to do with the development of ears in the fish,” says paper author Monica Gagliano, of the Australian Institute of Marine Science (The Australian).

Another study out of AIMS this week finds that Porites corals’ growth has slowed by 21% over the last 16 years (press release, research paper).

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