Hot topics

David Bradley Science Writer

The European Southern Observatory’s Very Large Telescope (VLT) has helped an international team of astronomers to detect a stellar mass black hole that lies at a much greater distance from Earth than any observed before. The black hole is in the spiral galaxy NGC 300, about six million light years away in the constellation Sculptor.

The spiral galaxy NGC 300 lying in the constellation Sculptor (Credit: Galex/NASA)

Paul Crowther and Vik Dhillon, of the University of Sheffield, UK, Robin Barnard and Simon Clark of the The Open University, Milton Keynes, UK, and Stefania Carpano and Andy Pollock of ESAC, in Madrid, Spain report the black hole which has a mass of about twenty times that of the Sun in the Monthly Notices of the Royal Astronomical Society.

The stellar-mass black holes found in our Milky Way galaxy commonly weigh up to ten times the mass of the Sun. The newly discovered black hole is not only the most distant, but the second most massive stellar-mass black hole ever found. It is also entwined with a star that will soon become a black hole itself.

Lead author Crowther, explains: “This is the most distant stellar-mass black hole ever weighed, and it’s the first one we’ve seen outside our own galactic neighbourhood, the Local Group. The black hole’s curious partner is a Wolf-Rayet star, which also has a mass of about twenty times as much as the Sun. Wolf-Rayet stars are near the end of their lives and expel most of their outer layers into their surroundings before exploding as supernovae, with their cores imploding to form black holes.

An artist's impression of the newly discovered black hole and its stellar companion (Credit: ESO/L. Calçada)

In less than a million years, a blink of the eye cosmologically speaking, the Wolf-Rayet star will explode as a supernova and its remnants collapse into a black hole. Only one other system of this type has previously been seen, but other systems comprising a black hole and a companion star are not unknown to astronomy. The existence of such systems hints at an underlying galactic chemistry. Astronomers believe that a higher concentration of heavy chemical elements influences how a massive star evolves, increasing how much matter it sheds, resulting in a smaller black hole when the remnant finally collapses.

LINKS

Monthly Notices Royal Astronom Soc, 2010, in press
http://www.eso.org/public/archives/releases/sciencepapers/eso1004/eso1004.pdf

Paul Crowther
http://pacrowther.staff.shef.ac.uk/main.html

David Bradley Science Writer

Three billion years ago, the red planet, Mars, was warm enough to sustain lakes of liquid water, according to satellite images just published in the journal Geology. Previously, astronomers had assumed that this period was simply too cold and arid for surface water.

Researchers at Imperial College London and University College London now suggest that during the Hesperian Epoch, the Martian surface around the equator was spotted with lakes, each approximately 20 kilometres across, formed from melted ice. Earlier studies had hinted at the warm and wet early history of Mars during the period 4 billion to 3.8 billion years ago, well before the Hesperian Epoch. Detailed images from NASA’s Mars Reconnaissance Orbiter, which is currently circling the planet, suggest that there were later warm and wet periods; age is determined by meteorite crater count. The evidence lies in several flat-floored depressions located above Ares Vallis, a giant gorge that runs 2000 km across the equator of Mars.

Martian lakes

According to Nicholas Warner, of IC’s Department of Earth Science and Engineering, “Most of the research on Mars has focused on its early history and the recent past. Scientists had largely overlooked the Hesperian Epoch as it was thought that Mars was then a frozen wasteland. Excitingly, our study now shows that this middle period in Mars’ history was much more dynamic than we previously thought.”

Warner and colleagues, Sanjeev Gupta, Jung-Rack Kim, Shih-Yuan Lin, and Jan-Peter Muller, claim that there may have been increased volcanic activity, meteorite impacts or shifts in Mars’ orbit during this period, which could have warmed its atmosphere enough to melt ice. This in turn would have bolstered the greenhouse effect temporarily, trapping more heat from the sun and making the planet warm enough for liquid water to exist on its surface.

Until now, the Ares Vallis depressions have remained a mystery to scientists, although they suspected that their formation was due to sublimation of ice directly to water vapour. The loss of ice would have created cavities between the soil particles, which would have caused the ground beneath to subside.

Martian channels

The researchers have now discovered small, sinuous channels that connect the depressions, which they say could only have been formed by running water, essentially making the sublimation theory redundant. The team also compared the Mars images with images of thermokarst landscapes on Earth in places such as Siberia and Alaska. Thermokarst landscapes are areas where permafrost is melting, creating lakes that are interconnected by the same type of channels the team says exist on Mars. The team says that the melting ice created lakes that may have burst their banks allowing water to carve pathways through the frozen ground from higher lakes into lower-lying lakes.

UCL’s Muller who works at the Mullard Space Science Laboratory who carried out the 3D mapping of the Martian surface, explains how modelling with sub-metre resolution allowed the team to test their hypotheses much more rigorously than ever before.

Topographic image

One thing that the scientists do not yet know is how long the warm and wet period lasted during the Hesperian epoch or how long the lakes remained liquid. Nevertheless, the study may have implications for so-called “astrobiologists” looking for evidence of life on Mars. The team say these lake beds indicate regions on the planet that may have once been suitable for some form of microbial Martian life. As such, they represent good targets for future robotic missions seeking out ancient life on Mars.

LINKS

Geology, 2010, 38, 71-74
http://dx.doi.org/10.1130/G30579.1
Video flypast

David Bradley Science Writer

An analysis of observations from the Hinode satellite suggest that the solar wind generated by the sun is probably driven by a process involving powerful magnetic fields, according to researchers at University College London and their colleagues.

The study carried out by the UCL Mullard Space Science Laboratory, Observatoire de Paris, Konkoly Observatory in Hungary and Instituto de Astronomía y Física del Espacio in Argentina, could have implications for our understanding of our nearest star and its effects on Earth and our electronic systems including communications satellites and even devices on the ground.

Scientists have long speculated as to what gives rise to the solar wind, a constant stream of extremely high energy particles that pours out from the sun in all directions. The Extreme Ultraviolet Imaging Spectrometer (EIS), on board the Japanese-UK-US Hinode satellite has produced unprecedented data that is now enabling scientists to reveal the underlying forces that give rise to the solar wind. Data provided by the SOHO/MDI consortium, international collaboration between ESA and NASA suggest that a process referred to as “slipping reconnection” may drive the solar wind.

UCL’s Deb Baker explains: “Solar wind is an outflow of million-degree gas and magnetic field that engulfs the Earth and other planets. It fills the entire solar system and links with the magnetic fields of the Earth and other planets. Changes in the Sun’s million-mile-per-hour wind can induce disturbances within near-Earth space and our upper atmosphere and yet we still don’t know what drives these outflows.

Solar wind

“However, our latest study suggests that it is the release of energy stored in solar magnetic fields which provides the additional driver for the solar wind. This magnetic energy release is most efficient in the brightest regions of activity on the Sun’s surface, called active regions or sunspot groups, which are strong concentrations of magnetic field. We believe that this fundamental process happens everywhere on the Sun on virtually all scales.”

The team studied images taken in February 2007 from the EIS instrument, which show hot plasma outflows. At the edges of active regions where slipping reconnection might occur, according to computer models, the researchers explain that a slow, continuous restructuring of the magnetic field leads to the release of energy and acceleration of particles in the Sun’s hot outer atmosphere, its corona.

The locations proposed by the computer model correlated with gas moving outward at up to 160,000 kilometres per hour, a thousand times faster than a terrestrial hurricane.

Links:

Astrophys. J. 2009, 705, 926-935
Deb Baker homepage

David Bradley Science Writer

The media was recently drenched with the idea that water had been found on the Moon, offering speculation as to our nearest neighbour offering an oasis-like site for a lunar base from which we could launch missions to Mars and beyond. The truth, if it is ever confirmed, is a little more subtle.

Is moisture on the Moon, simply wishing on a star? (Photo by David Bradley)

The Apollo missions of the 1970s had always hinted at the presence of water on the Moon, although its presence in samples brought back to earth was thought to be nothing more than contamination. In 1998, scientists announced that the Lunar Prospector spacecraft had detected 300 million tonnes of water on the moon and hinted that there may be as much as 6 billion tonnes. In July, an analysis of tiny beads of volcanic glass collected by two Apollo missions revealed water trapped inside, suggesting that the Moon’s water had not been entirely vaporized by the violent events that led to its formation. The discovery had implications for the volcanic origin of possible water reservoirs at the Moon’s poles.

However, new evidence released at the end of September based on data from India’s Chandrayaan-1 probe and the Deep Impact and Cassini missions suggests that there may well be some degree of hydration up there. Researchers in India and the US used data from NASA’s Moon Mineralogy Mapper, the M3, aboard the Chandrayyan-1 satellite, which was launched into orbit around the moon in October 2008 to reveal the presence of water on the moon. Chandrayaan’s mission ceased in August 2009.

M3 uses reflectance spectrometry to determine the content of minerals in the thin layer of upper soil on the surface of the moon. The data revealed the presence of chemical bonds between hydrogen and oxygen atoms, like those found between the oxygen atom and its attendant hydrogen atoms in H₂O.

However, the next generation of lunar astronauts are not likely to sip from moon springs or splash their silvery boots in lunar puddles because revelations of chemical bonds between hydrogen and oxygen atoms is indicative of water molecules but is even more indicative of hydroxyl ions (OH^-). It could be that good, old-fashioned H₂O forms only when the solar wind doth blow and brings with it hydrogen atoms that can combine with the hydroxyl radicals forming “H⁺OH^-” (H₂O). It may be that less than a litre of actual water is present per tonne of rock spread across the surface to a depth of a few centimetres and present as water of hydration of the minerals from which the rock is composed.

The rocks and soils that comprise the lunar surface contain about 45 percent oxygen, mostly in the form of silicate minerals. The constant deluge of hydrogen atoms from the solar wind could readily pull oxygen and hydroxyl from the soil and form water molecules on the fly, especially given the hydrogen ions are moving at one third the speed of light when they hit.

Taylor and other M3 team members believe their findings will be of particular significance as mankind continues to plan for a return to the moon. The maps created by M3 could provide mission planners with locations prime for extraction of needed water from the lunar soil.

Following the lunar announcement, Jim Bell, President of The Planetary Society, said: “The possible presence of minor amounts of hydrated material on the Moon is intriguing, though the findings still need to be confirmed by other methods and other investigators. Chandrayaan is another great example of the power and value of international collaboration in space exploration, and The Planetary Society congratulates the entire Chandrayaan, Deep Impact and Cassini teams.”

Researchers still hope to find liquid water at the bottom of the deepest, darkest lunar craters at depths that never see sunlight nor feel the solar wind. Such, hopefully, icy depths are akin to the cold places on the planet Mars where evidence of water ice has been found.

LINKS
Science, 2009, in press
Chandrayaan-1 site

David Bradley Science Writer.

An enormous asteroid or comet smashing into the Earth 65 million years ago killed off the dinosaurs. But, according to a new study by US scientists, published in the wake of an impact event on Jupiter, cometary collisions with Earth probably didn’t cause any more than one other extinction event during life’s history.

US researchers have looked to the Oort Cloud to help them work out just how many comets may have struck the earth during the time complex life has existed. The Oort Cloud is a remnant of the nebula from which the solar system formed 4.5 billion years ago. It starts about 93 billion miles from the sun (a thousand times as far from the sun as the Earth) and stretches to an incredible three light years away. It is thought that the Oort Cloud contains billions of comets but most are so small and distant that we will never see them.

Now, Thomas Quinn, Nathan Kaib and colleagues at the University of Washington, have used computer models to simulate the evolution of comet clouds in the solar system over the last 1.2 billion years. They found that even outside the periods of comet showers, the inner Oort Cloud was a major source of long-period comets. Some of these can cross Earth’s path but the simulations show that no more than two or three comets could have struck the Earth even during the most powerful comet shower of the last 500 million years.

Astronomers have known for some time that the inner solar system of rocky planets – Earth, Mars, Venus, and Mercury – is protected from comets by the gas giants Saturn and Jupiter. The enormous gravitational fields of these planets essentially eject comets into interstellar space or act as traps for them. This latter point was reinforced on 20th July when a huge scar appeared on Jupiter’s surface, likely evidence of a cometary impact.

There are about 3,200 known long-period comets of which Hale-Bopp is perhaps the most famous as it was visible with the naked eye for much of 1996 and 1997. Some long-period comets take thousands if not millions of years to make a single orbit of the sun. Comet Halley by contrast, which reappears every 75 years, is a short-period comet, which originate in a different part of the solar system known as the Kuiper Belt and are much more predictable. The computer simulation by Quinn and colleagues assumed that the inner Oort Cloud is the only source of potentially dangerous long-period comets.

The long-period comet 2001 RX14

“For the past 25 years, the inner Oort Cloud has been considered a mysterious, unobserved region of the solar system capable of providing bursts of bodies that occasionally wipe out life on Earth,” Quinn explains, “We have shown that comets already discovered can actually be used to estimate an upper limit on the number of bodies in this reservoir.”

With three major impacts taking place almost simultaneously, researchers had suggested that the minor extinction event of 40 million years ago resulted from a comet shower. Kaib and Quinn’s research implies that if that relatively minor extinction event was caused by a comet shower, then that was probably the most-intense comet shower since the fossil record began.

Further resources

Science Express, 2009, Jul 30, online

Tom Quinn’s home page

Comet shower movie from Nathan Kaib

David Bradley Science Writer

Seemingly endless meteor storms that bombarded the Earth four billion years ago helped to create the right growing conditions from which life could first emerge. The same meteoric bombardment may also have had a similar effect on our planetary neighbour Mars.

Richard Court and Mark Sephton of the Department of Earth Science and Engineering, at Imperial College London and their colleagues publish details of a theory that could change our understanding of natural terraforming of the primordial Earth this month in the journal Geochimica et Cosmochima Acta.

Professor Mark A. Sephton

The researchers have analysed the remaining mineral and organic content of fifteen fragments of ancient meteorites to see how much water vapour and carbon dioxide they would release when subjected to very high temperatures. The experiments aimed to replicate the conditions experienced by the meteoric material as it entered the Earth’s atmosphere billions of years ago.

When a meteor enters a planet’s atmosphere, extreme heat is produced because of the retarding compression of the air due to the meteor travelling at supersonic speeds. This heat causes some of the minerals and organic matter on the meteor’s outer crust to vaporise releasing water and carbon dioxide before it breaks up or hits the ground.

A fragment of the Murchison meteorite was analysed by the IC team

This water source could have added large quantities of moisture to the atmospheres of both Earth and Mars billions of years ago. Moreover, the addition of the greenhouse gas carbon dioxide to the atmosphere would have helped trapped solar energy and so make the primordial planets warm enough for liquid oceans.

Meteoric bombardment of the early Earth may have paved the way for life to emerge

Court and Sephton used a novel analytic technique known as pyrolysis-FTIR spectroscopy to test the meteorites. The pyrolysis process involved blasting a meteorite fragment with electricity to heat it from room temperature at a rate of 20,000 degrees Celsius per second to 250 Celsius or 1000 Celsius to cause the material to break apart and vaporize. FTIR, or Fourier-transform infra-red spectroscopy, then provides a chemical fingerprint of any small molecules, such as water and carbon dioxide, produced.

For a long time, scientists have been trying to understand why Earth is so water rich compared to other planets in our solar system, Sephton explains. The team found that on average, each meteorite fragment could release 12% of its weight as water vapour and 6% as carbon dioxide gas. These figures, the researchers suggest, are not enough that a few small meteorites could have made a significant contribution to the atmosphere’s water and carbon dioxide levels.

However, the team also analysed data from an ancient meteorite shower called the Late Heavy Bombardment (LHB), which occurred 4 billion years ago, where millions of rocks crashed to Earth and Mars over a period of 20 million years. They calculated that the LHB could have added 10 billion tonnes of carbon dioxide and 10 billion tonnes of water vapour to the planets’ atmospheres every year. This rate of addition is certainly adequate to make both planets warmer and wetter enough to sustain life.

The LHB provides a missing clue. This may have been a pivotal moment in our early history where Earth’s gaseous envelope finally had enough of the right ingredients to nurture life on our planet, adds Sephton.

Because of their chemistry, ancient meteorites have been suggested as a way of furnishing the early Earth with its liquid water, says Court, Now we have data that reveals just how much water and carbon dioxide was directly injected into the atmosphere by meteorites. These gases could have got to work immediately, boosting the water cycle and warming the planet. Of course, the existence of life on Earth is obvious, but habitable conditions on Mars apparently did not last. Unlike Earth, Mars has no magnetic field to shield it from the Sun’s lethal solar wind, its atmosphere was eventually mostly stripped away, and warming volcanic activity subsided. As such any liquid water retreated to the frozen poles leaving behind the barren red planet with which we are almost familiar.

Further reading

Geochim. Cosmochim. Acta, 73 (11), 1 June 2009, 3512-3521

Professor Mark A. Sephton
http://www3.imperial.ac.uk/people/m.a.sephton

Suggested searches

meteorites

David Bradley Science Writer

Science doesn’t have a lot to say about what happened before the Big Bang, but researchers have now developed microwave detectors that will let them take a look at the first trillionth of a trillionth of a trillionth of a second after that primordial cosmic event.

A collaboration between scientists at the National Institute of Standards and Technology (NIST), Princeton University, the University of Colorado at Boulder, and the University of Chicago has yielded super-sensitive microwave detectors that were revealed at the American Physical Society (APS) April meeting held in Denver during May.

Cosmic microwave temperature fluctuations fill the sky and are an echo of the first moment after the Big Bang (Credit: NASA/WMAP Science Team)

The cosmic microwave background (CMB) is often referred to as the afterglow of creation. This remnant, or echo of the Big Bang fills the universe and various projects have obtained snapshots of the CMB stretching back closer and closer to the Big Bang. The new project will use a large array of the sensors mounted on a telescope mounted in the Chilean desert. They will look for subtle fingerprints of the CMB from primordial gravitational waves, ripples in the fabric of the spacetime continuum. Theory has it that these waves will have left an imprint on the direction of the CMB’s electric field, called the B-mode polarization.

This is one of the great measurement challenges facing the scientific community over the next twenty years, and one of the most exciting ones as well, says Kent Irwin, the NIST physicist leading the project.

Prototype NIST detector that will be used to spot signature of rapid inflation immediately after the Big Bang. (Credit: NIST)

If found, these waves would be the clearest evidence yet in support of the inflation theory, which suggests that all of the currently observable universe expanded rapidly (within the first tiny fraction of a second) from a subatomic volume, leaving in its wake the telltale cosmic background of gravitational waves.

The B-mode polarization is the most significant piece of evidence related to inflation that has yet to be observed, explained NIST’s Ki Won Yoon, at the APS meeting. A detection of primordial gravitational waves through CMB polarization would go a long way toward putting the inflation theory on firm ground.

These types of experiments can only be done by treating the universe as a whole as a cosmic laboratory. The particles and electromagnetic fields that exist immediately after the Big Bang are billions of times more energetic than those available even with the most powerful particle colliders on Earth today. On this energy scale, three of the fundamental forces of nature but excluding gravity, are predicted to merge into a single unified force.

At the energy scale at which inflation occurred, which is the GUT or Grand Unified Theory energy scale, only 3 out of the 4 fundamental forces are predicted to merge into a single unified force – electromagnetism, the strong nuclear force, and the weak nuclear force, Irwin told Spotlight.

The final force of nature, gravity, is not predicted to merge with the other three until a much higher energy scale referred to as the Planck scale, which would have occurred before inflation, and would not have been related to the primordial gravity waves. A theory that correctly incorporates gravity into a unified field is humorously referred to as a TOE or Theory of Everything, he adds.

Further reading

APS April 2009 Meeting
http://www.aps.org/meetings/april/

National Institute of Standards and Technology homepage
http://www.nist.gov/index.html

Suggested searches

Big Bang
cosmology
cosmic microwave background

David Bradley Science Writer

New observations from a collection of powerful telescopes have allowed astronomers from Germany and the US to settle a paradox regarding the behaviour of merging elliptical galaxies. The team has revealed evidence that the largest, most massive galaxies in the universe and the supermassive black holes at their cores grow together rather than one leading to the other, which explains the fluffy nature of their central regions.

Astronomers have known for many years that galaxies, containing billions of stars can grow as they absorb and merge with their neighbours. What was unclear though was the relationship between the supermassive black hole at the core of elliptical galaxies, and the growth of such a galaxy.

The elliptical galaxy NGC 4621 (Credit: WikiSky/SDSS)

Initially, astronomers assumed that the huge gravitational fields of such black holes would greedily pull all galactic matter in towards them creating a relatively small, dense cluster at the centre. In the 1980s observations revealed the opposite. The biggest galaxies have huge fluffy, low-density centres.

The best theory to explain this contrary behaviour of supermassive binary black holes was the slingshot effect now observed by Kormendy and Bender. The popular theory of such galactic mergers and acquisitions has it that as two supermassive galaxies collide, their central black holes begin orbiting each other, whisking up the cores of the merged galaxy and flinging stars out of the central region. As the black hole pair sinks to the centre of the merger to form an even more supermassive black hole, the local region should appear depleted of stars.

John Kormendy

Now, Ralf Bender of Germany’s Max-Planck-Institute for Extraterrestrial Physics and Ludwig Maximilians University Observatory together with John Kormendy of the University of Texas at Austin, have published details of their findings in the latest issue of Astrophysical Journal Letters. The team analysed data from Austin’s McDonald Observatory, the Hubble Space Telescope and many other telescopes around the world for 11 supermassive elliptical galaxies in the Virgo Cluster. They measured the dimming of the galactic core due to the stellar depletion, the so-called light deficit.

Ralf Bender

Finding evidence for light deficits in galactic cores is quite surprising, despite being founded on recent decades of new theory and observation by many astronomers, including Kormendy and Bender. The biggest elliptical galaxies contain enormous black holes with masses a billion or more times the mass of our Sun.

Our new observations are a strong and direct link between black holes and galaxy central properties, Kormendy explains, They are a ’smoking gun’ that connects black holes with the formation of the surprisingly fluffy centres of giant elliptical galaxies.

The fluffiness also increases in lockstep with another galaxy property that is known to be tied directly to black holes, namely the speeds at which stars move far out in the galaxy where they cannot feel the black hole’s gravity.

Astronomers love tight correlations, Bender says. They tell us what is connected with what. The new observations give us much stronger evidence that black holes control galaxy formation, at least at their centres.

Further reading

Astrophys. J. Lett., 2009, in press
http://dx.doi.org/10.1088/0004-637X/691/2/L142

John Kormendy homepage
http://chandra.as.utexas.edu/~kormendy/kormendy.html

McDonald Observatory
http://mcdonaldobservatory.org/

Suggested searches

black holes
galaxies

David Bradley Science Writer

Tiny particles of crystalline carbon found in sediments at six sites in North America dating back almost 13000 years, suggest that a swarm of carbon-and-water-rich comets smashed into the Earth triggering extinctions of large mammals, including the woolly mammoth, across the globe.

The nanodiamonds from these carbonaceous chondrites are formed under high-temperature and high-pressure conditions created at impact and have been found in meteorites in similarly aged sediments at Murray Springs, Arizona, Bull Creek, Oklahoma., Gainey, Michigan, and Topper, South Carolina, as well as at Lake Hind, Manitoba, and Chobot, Alberta, in Canada. Their existence represents evidence for the cause of a severe cold snap that last 1300 years known as the Younger Dryas period.

Douglas J. Kennett

The Clovis culture of hunters and gatherers was named after hunting tools referred to as Clovis points, first discovered in a mammoth’s skeleton in 1926 near Clovis, New Mexico. Researchers later identified Clovis sites later across the American continent. The Clovis people presumably reach the Americas via a land bridge from Siberia and their culture is thought to have peaked around 10,900 years to 12,500 years ago. The Younger Dryas period is thought to have fragmented the prehistoric Clovis culture and led to mass extinctions of many animals across North America.

In 2007, a 26-strong research team from sixteen institutions proposed that a cosmic impact event, possibly due to multiple airbursts of comets was the trigger for the Younger Dryas. Now, a team led by the University of Oregon’s Douglas Kennett, a member of the original research team, report the discovery of billions of nanometre-sized diamonds concentrated in sediments in the same six locations. One of the diamond-rich sediment layers reported sits directly on top of Clovis materials at the Murray Springs site.

The nanodiamonds that we found at all six locations exist only in sediments associated with the Younger Dryas Boundary layers, not above it or below it, explains Kennett. These discoveries provide strong evidence for a cosmic impact event at approximately 12,900 years ago that would have had enormous environmental consequences for plants, animals and humans across North America.

Further reading

Science, 2009, 323, 94
http://dx.doi.org/10.1126/science.1162819

Douglas J. Kennett homepage
http://www.uoregon.edu/~dkennett/Welcome.html

UO researchers involved in Clovis impact theory
http://pmr.uoregon.edu/science-and-innovation/uo-research-news/research-news-2007/september-2007/uo-researchers-involved-in-clovis-age-impact-theory

David Bradley Science Writer

Astrophysicists are using a novel 3D computer visualization technique to help them understand the role of gravity in the formation of vast, stellar nurseries, also known as molecular clouds.

Computer simulations are critical tools in understanding the behaviour of these clouds and of star formation, explains Alyssa Goodman of Harvard’s Faculty of Arts and Sciences. They are the only method by which astronomers can watch what happens over the millions of years it takes to form a star.

Alyssa Goodman

Earlier models of star formation assumed that because gravity is a relatively weak force over large distances that its effects would be negligible in these clouds until the particles are very close together. These earlier models thus explain accretion of particles prior to star formation based on turbulence rather than gravity. Once denser groupings of molecules are formed and gravity becomes a factor, they attract more and more particles until either something disrupts them or they have enough mass to collapse and form a star.

However, Goodman and colleagues have examined the process up to the point where the dense groupings form. Their analysis shows that, rather than turbulence being the only significant force pushing these gas molecules around, their gravitational influence on each other is also significant. That finding means that existing models, which leave gravity out until very dense clumps have formed, would over-predict the rate of star formation in these clouds.

This image shows a very long-exposure view of a 1-degree-square area within the Perseus star-forming region. (Credit: Jaime Pineda & Jonathan Foster, Harvard University)

The team developed imaging technology borrowed from medicine to visualize the molecular cloud in three dimensions and applied a new computer algorithm that creates a dendrogram, This branching representation of the astronomical data from COMPLETE (COordinated Molecular Probe Line Extinction Thermal Emission) Survey of Star Forming Regions, allowed the researchers to build a sophisticated 3D display of the data, which they could then rotate and examine from many different angles.

Goodman explains that the earlier modelling technology ignores hierarchical structure, regions within regions, and so obscures specific details of the molecular clouds, such as nested areas of varying density and physical breaks from one area to another. There’s no way of noticing this without being able to see this in 3-D, she says.

Further reading

Nature, 2009, 457, 63-66
http://dx.doi.org/10.1038/nature07609

Alyssa Goodman homepage
http://www.cfa.harvard.edu/~agoodman/

Suggested searches

stars formation