RSSArchive for September, 2011

Galaxy caught blowing bubbles

Hubble Space Telescope image of Holmberg II

The Hubble Space Telescope captured this image of dwarf irregular galaxy Holmberg II. The main part of the galaxy is the spread of stars in the lower left half of the image. Huge bubbles of glowing gas produced by stellar explosions dominate the galaxy; they are now sites of ongoing star formation.

HUBBLE’S FAMOUS IMAGES OF GALAXIES typically show them to be elegant spirals or soft-edged elliptical shapes.

But these neat forms are only representative of large galaxies. Smaller galaxies like the dwarf irregular galaxy Holmberg II come in many shapes and types that are harder to classify.

Holmberg II’s indistinct shape is punctuated by huge glowing bubbles of gas, captured in this image from the Hubble Space Telescope.

The intricate glowing shells of gas were formed by the energetic life cycles of many generations of stars. High-mass stars form in dense regions of gas, and later in life expel strong stellar winds that blow away the surrounding material.

At the very end of their lives, they explode in as a supernova. Shock waves rip through these less dense regions blowing out and heating the gas, forming the delicate shells we see today.

Holmberg II is a patchwork of dense star-forming regionsand extensive barren areas with less material, which can stretch across thousands of light-years.

Keck Observatory view of Holmberg II

A wider view of Holmberg II. Courtesy B. Mendez / Keck Observatory.

As a dwarf galaxy, it has neither the spiral arms typical of galaxies like the Milky Way nor the dense nucleus of an elliptical galaxy.

This makes Holmberg II, gravitationally speaking, a gentle haven where fragile structures such as these bubbles can hold their shape.

A hidden black hole?

While the galaxy is unremarkable in size, Holmberg II does have some intriguing features. As well as its unusual appearance—which earned it a place in Halton Arp’s Atlas of Peculiar Galaxies, a treasure trove of weird and wonderful objects—the galaxy hosts an ultraluminous X-ray source in the middle of the three gas bubbles in the top right of the image.

There are competing ideas as to what causes this powerful radiation—one intriguing possibility is that an intermediate-mass black hole is pulling in material from its surroundings, with the material giving off energy as it nears the black hole.

The colourful image is a composite of visible and near-infrared exposures taken using the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Hubble is a project of international cooperation between the European Space Agency and NASA.

Download the Hubble wallpapers:

Holmberg II (1024×768, 588.2 KB)

Holmberg II (1280×1024, 1.0 MB)

Holmberg II (1600×1200, 1.5 MB)

Holmberg II (1920×1200, 1.8 MB)

Adapted from information issued by HEIC / NASA / ESA.

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Astronaut’s view of Earth’s aurora

THIS VIDEO OF THE AURORA AUSTRALIS was created from a sequence of still shots taken by astronauts on board the International Space Station (ISS). The images were acquired on September 11, 2011 as the ISS orbit pass descended over eastern Australia.

The Aurora Australis is the glow produced by air molecules as charged particles from the Sun are deflected into the upper reaches of the atmosphere by Earth’s magnetic field.

Adapted from information issued by NASA.

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Earth from Space – Sand dunes

Dunes in the Burqin-Haba River-Jimunai Desert

Huge dunes dot the Burqin-Haba River-Jimunai Desert near the borders of China, Mongolia, Russia and Kazakhstan.

A SAND DUNE FIELD within the Burqin-Haba River-Jimunai Desert near the borders of China, Mongolia, Russia and Kazakhstan, is seen in this photograph taken by an astronaut on the International Space Station.

The dune field (approximately 32 kilometres long) is located immediately west-northwest of the city of Burqin (not shown), and is part of the Junggar Basin, a region of active petroleum production in northwestern China.

The Irtysh River—with associated wetlands and riparian vegetation (appearing grey-green in the image) —flows from its headwaters in the Altay Mountains towards Siberia (right to left across the image).

Tan, linear dunes at image centre (on the south side of the Irtysh River) dominate the view. The dunes are formed from mobile barchan (crescent-shaped) dunes moving from left to right in this view. The barchans eventually merge to form the large, linear dunes, which can reach 50 to 100 metres in height.

Sand moving along the southern edge of the field appears to be feeding a southeastern lobe with a separate population of linear dunes (image lower right).

The Burqin-Haba River-Jimunai Desert area also includes darker gravel-covered surfaces that form pavements known locally as gobi. At the resolution of an astronaut photograph, these are somewhat indistinguishable from the vegetated areas arresting some of the dunes. But gobi tend to be located on the flat regions between the dunes.

See the full-size image of the Burqin-Haba River-Jimunai Desert dunes.

Astronaut photograph provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Centre. Text adapted from information issued by William L. Stefanov and M. Justin Wilkinson, Jacobs/ESCG at NASA-JSC.

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Hubble’s replacement put to the test

THE MANY COMPONENTS of the James Webb Space Telescope undergo testing at their place of construction, as well as at the locations where the individual pieces are assembled into larger parts.

But closer to launch, engineers need to put the fully assembled telescope through environmental testing.

NASA will be using its largest thermal vacuum chamber to accomplish this task. The chamber at Houston’s Johnson Space Centre was used to test Apollo vehicles back in the ’60s and ’70s, and has been used sporadically throughout the following years for other space vehicles.

Changes are being made to the chamber so the James Webb Space Telescope can be tested even more rigorously than the Apollo spacecraft.

Adapted from information issued by Space Telescope Science Institute.

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Earth from Space – Åland Islands

Landsat 7 image of the Åland Islands

The Åland Islands lie between Sweden and Finland.

THE ÅLAND ISLANDS (also known as the Aaland Islands) lie at the southern end of the Gulf of Bothnia, between Sweden and Finland. The archipelago consists of several large islands and roughly 6,500 small isles, many of them too small for human habitation.

Åland vegetation is a combination of pine and deciduous forest, meadows, and farmed fields. On nearly every island, however, the region’s characteristic red rapakivi granite appears.

Modern residents of Åland cut and use the granite in buildings and pavement, but much earlier, ice sculpted these rocks. About 20,000 years ago, a massive ice sheet stretched over Scandinavia and the Gulf of Bothnia, and glacial action gradually wore the granite smooth.

The granite in this region is actually far older than the glaciers that smoothed its surface, having formed in the Proterozoic Era. The rapakivi was deposited tens of millions of years before the first amphibians crawled out of water and onto land, and hundreds of millions of years before the first dinosaurs evolved.

NASA Earth Observatory Landsat 7 image created by Jesse Allen and Robert Simmon, using Landsat data provided by the United States Geological Survey. Text adapted from information issued by Michon Scott.

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Satellite re-entry poses no danger

UARS graphic

The Upper Atmospheric Research Satellite is due to re-enter Earth's atmosphere in the next 24 hours.

SPACE JUNK COMES IN different shapes and sizes, and can pose two main kinds of threats—a threat to other spacecraft (unmanned and manned) through collisions, and threats to us down here on Earth.

The satellite making news at the moment—the former Upper Atmospheric Research Satellite, better characterised as a decommissioned or defunct satellite rather than space junk—falls into the second category.

In 2005, NASA decommissioned UARS and intentionally placed it into an orbit a couple of hundred kilometres lower than its operational orbit. This was done to accelerate is eventual demise, and means it is re-entering the atmosphere 20 years earlier than it otherwise would have done.

This was a very responsible thing to do. The longer a spacecraft stays in orbit, the more chance it has of being hit by other orbital debris, leading to a destructive breakup and therefore many more bits of debris.

UARS poses a negligible threat to life and property on Earth. Most of the satellite will burn up during re-entry, with perhaps as many as 26 of the stronger or harder small pieces surviving to reach the surface.

But with the majority of Earth comprising oceans or uninhabited (or very sparsely inhabited) remote regions, the chances are overwhelming that any pieces of UARSthat survive re-entry will fall harmlessly and never be seen again.

UARS re-entry map

This map shows the orbital path of the Upper Atmospheric Research Satellite, and it's predicted impact located (yellow symbol within the orange circle at left) in the southern Pacific Ocean.

Because the spacecraft is no longer powered, NASA has no control over where it comes down.

It is thought to be tumbling gently as it makes its final orbits. Friction with the thin upper atmosphere is slowly lowering its orbit, bit by bit. Sometime in the next 24 hours it will reach a low enough point and sufficient air friction such that it will no longer be able to maintain orbital velocity.

At this point it will begin to burn up and streak across the sky like a huge fireball. It would be quite something to see, but chances are that no one will witness it.

The other kind of space junk—bits of orbital debris that range from less than a millimetre wide up to entire spacecraft—is more of a worry. Space junk can damage or destroy an operational spacecraft, leading to loss of the asset and the service it provides.

More information:

NASA UARS re-entry page

Re-entry prediction map

UARS mission

Text by Jonathan Nally, SpaceInfo.com.au. Images courtesy NASA and aerospace.org

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Moon sinks into the gloom

ISS image of the Moon

An astronaut's view of the Moon, seen through the upper layers of Earth's atmosphere.

PHOTOGRAPHED BY an Expedition 28 crewmember aboard the International Space Station, this image shows the Moon at centre, with the limb (edge of the atmosphere) of Earth near the bottom transitioning into the orange-coloured troposphere, the lowest and most dense portion of our planet’s atmosphere.

The troposphere ends abruptly at the tropopause, which appears in the image as the sharp boundary between the orange- and blue-coloured parts of the atmosphere.

Adapted from information issued by NASA.

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New way of looking at the sky

THE SKY IS NO LONGER THE LIMIT for Australian astronomy, with CAASTRO—the new ARC (Australian Research Council) Centre of Excellence for All-sky Astrophysics—launching recently.

CAASTRO is taking a revolutionary new approach to astronomy by using an all-sky perspective to answer the big questions about our universe, bringing together unique expertise across six Australian universities, along with local and international partners.

“CAASTRO is a major new initiative that is revolutionising the way we see the universe,” says Professor Bryan Gaensler, director of CAASTRO and based in the School of Physics at the University of Sydney.

“The traditional approach to astronomy has had a lot of success, but we’re now running up against a whole range of questions these old approaches can’t answer,” he adds.

Australia in the vanguard

“The big unsolved questions in astronomy demand entirely new approaches, requiring us to look at the whole sky at once, rather than studying single objects in the sky in isolation,” says Professor Gaensler.

“You really need to look at how everything works together to truly understand what is going on out there and that’s what CAASTRO will do with our all-sky approach to astronomy.”

“CAASTRO research will use wider fields of view, with bigger data sets, processed more deeply and more subtly, than anyone has attempted before,” he adds.

CAASTRO team members

(L-R) CAASTRO team members Associate Professor Scott Croom, Professor Elaine Sadler, Professor Bryan Gaensler and PhD student Kitty Lo.

“In the last few years, Australia has invested more than $400 million in new wide-field telescopes and the high-performance computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to be at the vanguard of the upcoming information revolution in all-sky astronomy.”

Tackling the big questions

CAASTRO brings together expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation to investigate three interlinked themes: the evolving universe, the dynamic universe, and the dark universe.

CAASTRO’s three interlinked research themes are:

  • The evolving universe: when did the first galaxies form, and how have they evolved?
  • The dynamic universe: what is the high-energy physics that drives rapid change in the universe?
  • The dark universe: what are the dark energy and dark matter that dominate the cosmos?

Professor Gaensler says CAASTRO’s strength is that it will be a collaborative structure that for the first time combines the relevant expertise and resources into a single coherent unit.

“In addition to our revolutionary science, we’ve decided right from the outset that CAASTRO should also put a high priority on training the next generation of scientists, on providing a family friendly environment for all our staff, and engaging with schools and the public with outreach activities,” he adds.

The new centre is led by the University of Sydney, in collaboration with the Australian National University, the University of Melbourne, the University of Western Australia, Curtin University and Swinburne University of Technology.

Adapted from information issued by CAASTRO. Images courtesy CAASTRO, ESO and CASS / Swinburne.

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Australia from Space – The Blue Mountains

Landsat image of the Blue Mountains

The dramatic and dense Blue Mountains are located to the west of Sydney, Australia. This image was taken by the Landsat 7 satellite.

THE BLUE MOUNTAINS RISE to a broad plateau not far west of Sydney, Australia. In the heart of the mountains lies the Grose Valley, bounded by sheer 300-metre-high cliffs.

This dramatic landscape was sculpted by forces of erosion acting on the underlying geology; that is, characteristics of each rock type helped determine the topography.

This natural-colour satellite image was acquired by the Enhanced Thematic Mapper Plus (ETM+) instrument on the Landsat 7 satellite.

Deep green forests, dominated by eucalyptus trees, cover the landscape. The light grey buildings of Blackheath lie just to the west of the valley (lower left), and the light green orchards and pastures surrounding Berambing are visible to the northeast (upper right).

Two main types of rocks make up the Grose Valley and the immediate surroundings: a young, thin layer of volcanic rock, and a thick sequence of sedimentary rocks, laid down by wind and water several hundred million years ago. Several distinct types of shale, sandstone, and siltstone appear in the sedimentary sequence, which comprises the bedrock in most of this image.

Artist's impression of the Landsat 7 satellite

Artist's impression of the Landsat 7 satellite

The topmost layer is comprised of basalt erupted 15 to 18 million years ago from an unknown source. Most of this basalt has eroded away, but some can still be found at high points like Mount Tomah. Soils in these areas support a unique ecosystem called Tableland Basalt Forest, which appears bright green in this image.

Directly beneath the basalt are Wianamatta Group shales, followed by the Hawkesbury Sandstone—which forms the cliffs along the Sydney coast, 100 kilometres to the east. These two rock layers are softer than the basalt above and the sandstone below, so they have mostly eroded away except where protected by a cap of basalt.

Beneath the Wianamatta Group and Hawkesbury Sandstone are layers of very hard sandstone called the Narrabeen Group. These 240 million-year-old sandstones resist erosion and form the sheer cliffs that surround Grose Valley.

Softer shales and sandstones, the “Coal Measures,” underlie the Narrabeen sandstones and make up the slopes visible beneath the cliffs. Coal and oil shales in these formations have been mined extensively.

At the base of the valley is Berry Siltstone, originally deposited on an ocean floor over 260 million years ago. The Grose River flows atop this siltstone, carrying freshly eroded sand grains eastwards to the ocean.

See the full-size image of the Blue Mountains from space.

Text adapted from information issued by Robert Simmon. NASA Earth Observatory image by Jesse Allen and Robert Simmon, with Landsat data from the USGS Global Visualization Viewer. Landsat graphic courtesy NASA.

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Rare view of Earth and Moon

Juno spacecraft image of Earth and Moon

Earth and Moon, as seen by the Juno spacecraft from a distance of around 10 million kilometres

LOOKING HOMEWARD in its long journey to Jupiter, NASA’s Juno spacecraft offered up this rare view of our home planet with its moon. The spacecraft was nearly 10 million kilometres from Earth when it took this photo on August 26, 2011.

From that distance, oceans, land, clouds, and ice blend into a blur of light, a mere dot against the vastness of space. Even fainter and smaller, the Moon provides an additional sense of scale—the Earth and Moon are about 402,000 kilometres apart. (Juno travelled the Earth–Moon distance in less than a day.)

The spacecraft launched on August 5, and will reach Jupiter, another 2,800 million kilometres away, in about five years. The mission team took the photo as part of the first detailed check of the spacecraft’s instruments and subsystems.

“This is a remarkable sight people get to see all too rarely,” said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio, in a NASA release.

“This view of our planet shows how Earth looks from the outside, illustrating a special perspective of our role and place in the universe. We see a humbling yet beautiful view of ourselves.”

Adapted from information issued by NASA/JPL-Caltech and Holli Riebeek / NASA Earth Observatory.

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