RSSArchive for November, 2010

Atom smasher in deep space

Atoms-for-Peace galaxy

The oddly shaped and oddly named Atoms-for-Peace galaxy is actually a pair of galaxies experience a long, drawn-out merger.

  • Oddly named Atoms-for-Peace galaxy
  • It’s actually two galaxies colliding
  • Named after a speech by former US President Eisenhower

A spectacular new image of the famous Atoms-for-Peace galaxy (NGC 7252) has been released by the European Southern Observatory (ESO).

This galactic pile-up, formed by the collision of two galaxies, provides an excellent opportunity for astronomers to study how galaxy mergers affect the evolution of the Universe.

Atoms-for-Peace is the curious name given to a pair of interacting and merging galaxies that lie around 220 million light-years away. It is also known as NGC 7252 and Arp 226 and is just bright enough to be seen by amateur telescopes as a very faint small fuzzy blob.

This new, deep image was produced by ESO’s Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile.

Galaxy collisions are long drawn-out events that last hundreds of millions of years.

The picture of Atoms-for-Peace represents a snapshot of its collision, with the chaos in full flow. The results of the intricate interplay of gravitational forces can be seen in the tails made from streams of stars, gas and dust.

The image also shows incredible shells that formed as gas and stars were ripped out of the colliding galaxies and wrapped around their merged, single core.

While a lot of material was ejected into deep space, other regions were compressed, sparking bursts of star formation. The result was the formation of hundreds of very young star clusters, which are now around 50 to 500 million years old. They’re also speculated to be the forerunners of what astronomers call “globular star clusters”…vast collections of hundreds of thousands or millions of stars, formed into a spherical grouping.

Close-up of the Atoms-for-Peace galaxy's core

A Hubble close-up of the Atoms-for-Peace galaxy's core. The bluish points swirling around the core are huge clusters of hot, young stars.

Atoms-for-Peace may be a harbinger of our own galaxy’s fate. Astronomers predict that in three or four billion years the Milky Way and the Andromeda Galaxy will collide, much as has happened with Atoms-for-Peace.

But there’s no need to panic—the distance between stars within a galaxy is vast, so it is unlikely that our Sun will end up in a head-on collision with another star during the merger.

See the full-size, high-resolution version here (new window or tab)

And how did the Atoms-for-Peace galaxy pairing get its unusual name?

In December 1953, US President Eisenhower gave a speech that was dubbed Atoms for Peace. The theme was promoting nuclear power for peaceful purposes—a particularly hot topic at the time.

This speech and the associated conference made waves in the scientific community and beyond to such an extent that NGC 7252 was named the Atoms-for-Peace galaxy.

In many ways, this is oddly appropriate—the curious shape that we can see is the result of two galaxies merging to produce something new and grand, a little like what occurs in nuclear fusion. Furthermore, the giant loops resemble a textbook diagram of electrons orbiting an atomic nucleus.

Adapted from information issued by ESO / NASA /  ESA.

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Aussie astronomy supercomputer in Top 100

Photo of POD in-situ at iVEC@Murdoch.

The POD supercomputer at the iVEC computing centre at Murdoch University. It has been ranked at number 87 in the world league table of supercomputers.

  • First stage of supercomputer ranks number 87 in the world
  • When finished it will be 15 times faster still
  • Will support advanced research using the Square Kilometre Array telescope

Western Australia has entered the prestigious ranks of the top 100 supercomputers on the planet, thanks to the installation of a Performance Optimised Data Centre (POD) at iVEC’s Murdoch facility.

iVEC is an advanced computer centre in Perth. It is a joint venture between CSIRO, Curtin University of Technology, Edith Cowan University, Murdoch University and The University of Western Australia and is supported by the Western Australian Government.

A global gauge of the world’s most powerful supercomputers, the prestigious Top 500 List has embraced the Hewlett- Packard (HP)-developed POD, which takes its place at number 87 following its delivery to iVEC@Murdoch.

Only one other Australian supercomputer ranks above the POD in the Top 500 list, with the National Computational Infrastructure facility in Canberra coming in at #51.

The POD is Stage 1A of the $80M Pawsey Centre project, commissioned under the Commonwealth government’s $1.1 billion Super Science Initiative to establish a petascale supercomputing facility.

Artist's impression of the SKA

Artist's impression of the core of the Square Kilometre Array (SKA) telescope network. It will be one the largest scientific facilities ever made.

The Pawsey Centre was established with the primary role of hosting new high performance computing facilities and expertise to support SKA (Square Kilometre Array) research and other high-end science.

The SKA will be a huge network of radio telescope antennae, and will be one of the world’s largest scientific facilities. Two regions are bidding for the rights to host the facility: a joint Australia-New Zealand big, and a consortium of countries in southern Africa.

The secondary goal of the Pawsey Centre is to demonstrate Australia’s ability to deliver and support world-class advanced ICT infrastructure and therefore strengthen Australia’s bid to host the SKA, which is critically dependant on advanced ICT.

When complete in early 2013, the final Pawsey Centre’s facilities are expected to operate up to 15 times faster than the POD, and will eventually see it climb to the top echelon of the world’s supercomputing centres and establish Australia’s commitment to supercomputing.

“Australian scientists are now generating massive amounts of experimental data in computationally demanding areas such as radioastronomy, nanoscience, geoscience and life science,” says iVEC@Murdoch Associate Director, Professor Matthew Bellgard.

Adapted from information issued by iVEC / ICRAR / CSIRO.

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Australia back in the space race

Australia from space

Australia from space. A new space centre at the University of NSW aims to get the nation back into the space race.

Australia’s space capabilities have received a significant boost with the opening of the country’s first centre for satellite and space engineering at the University of NSW (UNSW).

The new Australian Centre for Space Engineering Research (ACSER) will develop technologies for satellite navigation; Earth observation applications such as monitoring of disasters, climate change and mine subsidence; national security; and space vehicle engineering.

NASA space shuttle astronaut Jan Davis was the guest of honour at the centre’s launch.

ACSER Director, Associate Professor Andrew Dempster of the School of Surveying and Spatial Information Systems, said Australia lacks its own satellites at a time when the global space industry was expanding rapidly.

UNSW A/Prof Andrew Dempster with astronaut Jan Davis

UNSW A/Prof Andrew Dempster with astronaut Jan Davis

In an article published on the opinion website The National Times, Associate Professor Dempster has outlined the role ACSER can play in building up Australia’s space technology capabilities.

“Interest in space is booming as the number of satellites being launched escalates, and that increase will affect everything from smartphones and cars to innovations in industry, mining, agriculture, communication and security,” he said.

“At ACSER we are developing systems to enable real-time, highly accurate mapping of the Earth’s surface, and technologies to allow new satellite navigation systems to communicate with each other, improving service accuracy and availability.

“Australia was the fourth country in the world to launch a satellite—we did that in the 1960s—but we’ve lagged ever since. We will be working to establish an Australian presence in the space industry,” he said.

ACSER combines the expertise of researchers in the UNSW faculties of Engineering and Science, and UNSW@ADFA (Australian Defence Force Academy).

Adapted from information issued by UNSW / NASA.

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Tasman link boosts “superscope” bid

AUT dishes at Warkworth

Nestled among the green hills of Warkworth, the Auckland University of Technology now operates a 12m dish (left) and a 30m dish (right) for radio astronomy.

  • Radio astronomy data sent from NZ to Australia over new link
  • Data transfer will be vital to the Square Kilometre Array telescope
  • New Zealand astronomers also get new, large radio astronomy dish

In a taste of things to come, data from a radio telescope dish in New Zealand has been transmitted at high speed to an Australian astronomy computer centre in Perth.

Australia and New Zealand are collaborating in a bid to host the Square Kilometre Array (SKA), a vast network of radio telescope antennae that will give astronomers unprecedented data on the earliest evolution of the Universe.

The two countries’ bid is up against one from southern Africa. A decision on whether the SKA will be hosted in the Australia-New Zealand region or in southern Africa will be made in 2012. Construction will begin in the second half of this decade.

Artist's impression of the SKA

Artist's impression of the central part of the Square Kilometre Array, which will be a vast network of antennae for radio astronomy.

In this week’s test, data from the Auckland University of Technology (AUT) Institute for Radio Astronomy and Space Research (IRASR) 12-metre-diameter radio telescope was sent at a speed of 1 gigabit per second to the International Centre for Radio Astronomy Research (ICRAR) at Curtin University in Perth.

It took less than one hour to transfer the 0.5 TeraBytes of data—observations of a “radio galaxy” called Centaurus A—from AUT to Curtin, a distance of 5,500 kilometres.

This was made possible by the recent upgrade of KAREN’s (Kiwi Advanced Research and Education Network) international connectivity between New Zealand and Australia from 155 Mb/s to 1 Gb/s.

KAREN’s new international network went live on 15 November and provides the only research link between New Zealand and Australia.

The new, upgraded service provides 1 Gb/s capacity to both Sydney and Los Angeles, greatly enhancing the opportunity for KAREN members to communicate and collaborate with the global research and education community.

“For us New Zealand radio astronomers it opens up the opportunity for real-time operations and allows us to move from the technique of VLBI (very long baseline interferometry) to its real-time version, e-VLBI, the basic technique for future SKA,” says Professor Sergei Gulyaev from AUT University.

“This is a very important milestone towards Australian-New Zealand SKA development,” adds Professor Steven Tingay from Curtin University.

AUT 12m dish

The 12-metre-diameter radio telescope dish operated by the Auckland University of Technology.

“Electronic data transfer for the large data volumes generated in radio astronomy is an important technique that enables the maximum science to be extracted from our observations.”

“This milestone will allow a wide range of science to be jointly undertaken by Australian and New Zealand radio astronomers”.

New dish for New Zealand

Meanwhile, a former Telecom New Zealand 30-metre-diameter radio dish is getting a new lease of life after being handed over to AUT for use as a radio telescope—the largest in New Zealand.

Telecom has given AUT University the licence to operate the Warkworth 2 dish, based at Telecom’s Warkworth Satellite Earth Station north of Auckland, which until now has been used for used for satellite communications.

The majority of New Zealand’s voice and data traffic is now transmitted under the ground via fibre, and internationally through the Southern Cross cable, and advances in satellite technology over the years have resulted in improved transmission performance allowing dishes to be smaller.

As a result, Warkworth 2 has now been replaced by a newer antenna system, so Telecom was able to consider other uses for the antenna.

“This partnership will create a world-class national and international resource for radio astronomy research and will enable AUT’s Institute for Radio Astronomy and Space Research to significantly increase and develop the scope of their research programmes,” says Telecom chief technology officer, Dave Havercroft.

“And, importantly for New Zealand, will also build capability across other disciplines including ICT, physics, mathematics, and engineering.”

The dish, once converted into a radio telescope, will be used by AUT’s Institute for Radio Astronomy and Space Research (IRASR) to study star formation, the Milky Way’s centre and gaseous components of our Galaxy.

Professor Gulyaev says the 30-metre dish will have a collecting area six times greater than its 12-metre counterpart, which will mean much greater sensitivity and resolution.

Other uses for the new facility include the study of galactic nuclei other than the Milky Way, quasars, mega-masers, and cosmic molecules including organic molecules that may be indicators of extraterrestrial life.

The new radio telescope will be networked to its 12-metre counterpart and eventually will be linked to telescopes around the globe particularly in Asia and Australia. The IRASR already collaborates with NASA (National Aeronautics and Space Administration) in the USA, ESA (European Space Agency), the Russian Space Agency and JAXA (Japan Aerospace Exploration Agency).

Adapted from information issued by Telecom NZ / AUT / ICRAR. Images by Sergei Gulyaev / ICRAR / CSIRO.

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Cosmic eyes staring back at us

Eskimo Nebula

The Eskimo Nebula, so-called for its resemblance to a face inside a hooded parka.

Do stars live forever? No they don’t. Like everything else, they are born, go through middle age, get old and finally expire.

The manner of a star’s passing is determined by how big it was to begin with, with stars of different masses having wildly different destinies.

For very large stars—ones more than 8 times the mass of our Sun—the end comes in a violent supernova explosion, during which the remnant of the star can be squashed to form a neutron star or a black hole.

But for your average star, such as our Sun, a different fate awaits.

All stars go through their lives doing battle between two forces—the force of their own weight, which makes them want to squash in on themselves, and the force of their own heat (produced by nuclear fusion reactions in the core) which makes them want to expand.

Stars like these spend most of their lives in an uneasy equilibrium. But when their normal nuclear fuel—hydrogen—runs out, the heat drops and gravity makes the star’s outer layers squeeze in. But ironically, this squeezing in increases the pressure in the core and makes it heat up again, now fusing helium instead of hydrogen.

As the heat becomes too much, the star’s outer gas layers are blasted off, producing a huge expanding cloud. The exposed core of the star continues to radiate out enormous energy, which is absorbed up by the cloud, causing it to glow.

The result is a stunningly pretty nebula.

When astronomers first started spotting these nebulae, their early telescopes were not good enough to show them for what they really are. It was reasonably clear that they were stars surrounded by some sort of nebulosity, but through those early telescopes they looked quite tiny. In fact, they looked just like a distant planet might look—roundish and pale, rather than point-like and bright like a star.

So they were given the name “planetary nebulae“.

Here, we present our selection of the Top 10 prettiest and most spectacular planetary nebulae. All of the images were taken with the Hubble Space Telescope. In many cases the colours are not “real”; rather, they reflect the fact that the imagery was done with special filters to emphasise the light given off at particular wavelengths by certain gases.

The Eskimo Nebula

With some astronomical objects, you wonder how they ever got their names. But not this one. The picture at the top of the page shows the Eskimo Nebula, and it really does look like a face surrounded by a big, fleecy parka hood, doesn’t it? (It has also been called the Clownface Nebula.) Located almost 2,900 light-years away, it was discovered by English astronomer William Herschel in 1787 (although he didn’t quite realise what it was at the time).

The Spirograph Nebula

Two thousand light-years away and 0.3 light-years in width, the Spirograph Nebula (also known as IC 418) is so-named for its geometric patterns, which resemble those produced by the Spirograph toy. Once a red giant star, its outer layers have been puffed off and are now being illuminated by the hot radiation from the remnant white dwarf star, visible at the heart of the nebula.

The Spirograph Nebula

The Spirograph Nebula

The Boomerang Nebula

The Boomerang isn’t the most spectacular planetary nebula, but it does have a major claim to fame—it is the coldest natural body found so far in the entire universe! That’s right, the coldest natural body (colder conditions have been produced in the laboratory) at a whopping minus 272 degrees…that’s just one degree above absolute zero. An incredibly strong stellar wind is blowing from the central star, pushing gas out at a speed of 500,000 kilometres per hour. As the gas expands, it cools, leading to the frigid temperature.

The Boomerang Nebula

The Boomerang Nebula

The Butterfly Nebula

Also known as the Bug Nebula and NGC 6302, the Butterfly’s delicate appearance belies its real nature. The wings are actually clouds of gas sizzling at nearly 20,000 degrees Celsius, rushing outwards at almost one million kilometres per hour! At its heart is a star with a surface temperature of 220,000 degrees Celsius, one of the hottest known. (By comparison, our Sun’s surface temperature is a measly 5,500 degrees C.) The Butterfly is about 3,800 light-years away and is two light-years wide—that’s enough to stretch from Earth to the next nearest star system, Proxima Centauri, four light-years away.

The Butterfly Nebula

The Butterfly Nebula

The Ring Nebula

Long a favourite of amateur astronomers, the Ring Nebula (also known as M57) is 2,000 light-years from Earth and is about one light-year wide. The clouds of gas were sloughed off by the central star thousands of years ago; that star, now a white dwarf, can still be seen in the centre.

The Ring Nebula

The Ring Nebula

NGC 6751

Located about 6,500 light-years from Earth, NGC 6751 is a little less than one light-year wide. Its central white dwarf star has a scorching surface temperature of around 140,000 degrees Celsius.

NGC 6751

Planetary nebula NGC 6751

NGC 3132

Also known as the Eight-Burst or Southern Ring nebula, NGC 3132 is located about 2,000 light-years from Earth. Unlike some of the other planetary nebulae shown here, this one’s gas cloud is expanding at a very sedate 24 kilometres per second. If you look closely, at its heart you’ll see two stars. The smaller of the two is the white dwarf; earlier in its life it was a much bigger star, and was the one responsible for puffing off its outer gas layers to produce the nebula.

NGC 3132

Planetary nebula NGC 3132

The Engraved Hourglass Nebula

Not to be confused with another nebula called the Hourglass Nebula, this one—also known as MyCn 18—is 8,000 light-years from Earth. When it was discovered in 1940, its striking shape was not apparent, although it was clearly identified as a planetary nebula. It was only with the advent of modern telescopes that its arresting geometry became obvious. It is thought that the star’s equator is surrounded by a donut or torus of thick, gassy material. A stellar wind blowing from the star finds it hard to get through that torus, and instead “blows” out the top and bottom, expanding into the two halves of the hourglass shape.

The Engraved Hourglass Nebula

The Engraved Hourglass Nebula

The Cat’s Eye Nebula

The Cat’s Eye was the very first planetary nebula to be discovered, and it also turns out to be one of the most interesting and complex. Unlike some planetaries, which have a symmetrical and even appearance, the Cat’s Eye has loops and twists and knots. The faint concentric rings are thought to be shells of gas emitted by the star in the distant past. It is possible that the twisted shape of the rest of the nebula is the result of it having two central stars rather than just one. But so far, the putative second star has not been found. The Cat’s Eye is around 3,300 light-years from Earth.

The Cat's Eye Nebula

The Cat's Eye Nebula

The Helix Nebula

The Helix is one of the closest planetary nebulae to Earth, at just 700 light-years away. It’s also what our Sun might look like a few billion years from now. The Helix is the remains of a Sun-like star that sloughed off its outer gas layers thousands of years ago, just as our Sun will do one day.

The Helix Nebula

The Helix Nebula

Image credits:

Helix Nebula: NASA / ESA / C.R. O’Dell (Vanderbilt University) / M. Meixner, P. McCullough, and G. Bacon (STScI)

Eskimo Nebula: NASA / ESA / Andrew Fruchter (STScI) / ERO team (STScI + ST-ECF)

Cat’s Eye Nebula: ESA / NASA / HEIC / The Hubble Heritage Team (STScI / AURA)

Hourglass Nebula: Raghvendra Sahai, John Trauger (JPL) / WFPC2 science team / NASA / ESA

NGC 3132: Hubble Heritage Team (STScI / AURA / NASA / ESA)

NGC 6751: NASA / ESA / The Hubble Heritage Team (STScI / AURA)

Ring Nebula: Hubble Heritage Team (AURA / STScI / NASA / ESA)

NGC 6302: NASA / ESA / The Hubble SM4 ERO Team

Boomerang Nebula: ESA / NASA

IC 418: NASA / ESA / The Hubble Heritage Team (STScI / AURA)

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Jupiter gets its stripe back

Jupiter's South Equatorial Belt

This November 18 Gemini North Telescope image of Jupiter combines blue, red and yellow images into a false-colour composite that clearly shows the storm in the South Equatorial Belt. The belt is now turning dark after a brief fade to white.

One of Jupiter’s dark brown cloud bands that faded out earlier this year is regaining its colour, providing an unprecedented opportunity for astronomers to observe a rare and mysterious phenomenon caused by the planet’s winds and cloud chemistry.

Earlier this year, amateur astronomers noticed that the long-standing band, known as the South Equatorial Belt (SEB), just south of Jupiter’s equator, had turned white.

But just weeks ago, amateur astronomer Christopher Go of Cebu City in the Philippines saw a prominent bright spot in the unusually whitened belt, piquing the interest of professional and amateur astronomers around the world.

After follow-up observations with NASA’s Infrared Telescope Facility (IRTF), the 10-metre Keck telescope and the 8-meter Gemini telescope, all atop Mauna Kea in Hawaii, scientists at the University of California, Berkeley, and elsewhere now believe the stripe is making a comeback.

“The reason Jupiter seemed to ‘lose’ this band—camouflaging itself among the surrounding white bands—is that the usual downwelling winds that are dry and keep the region clear of clouds died down,” said Glenn Orton, a research scientist at NASA’s Jet Propulsion Laboratory (JPL).

One of the things the astronomers were looking for—using telescopes that see infrared wavelengths—was evidence that the darker material appearing in visible light was actually the start of clearing in the cloud deck. And that’s what they saw.

Jupiter's South Equatorial Belt

This false-colour image, taken November 11 by the Keck telescope, shows sunlight reflected off Jupiter's upper cloud deck. The bright spot in the South Equatorial Belt is the outbreak where winds are lofting particles to high altitudes.

This white cloud deck is made up of white ammonia ice particles. When the white clouds float at a higher altitude, they obscure the view of the lower brown clouds.

Every few decades or so, the South Equatorial Belt turns completely white for perhaps one to three years, an event that has puzzled scientists for decades. This extreme change in appearance has only been seen with the South Equatorial Belt.

The bright storm that Go saw in the faded belt was quite unusual, said Imke de Pater, UC Berkeley professor of astronomy.

“At infrared wavelengths, images in reflected sunlight show that the spot is a tremendously energetic ‘outburst,’ a vigorous storm that reaches extreme high altitudes,” de Pater said. “The storms are surrounded by darker areas, bluish-grey in the visible, indicative of ‘clearings’ in the cloud deck.”

The white band wasn’t the only change on the big, gaseous planet. At the same time, Jupiter’s Great Red Spot became a darker red colour. Orton said the colour of the spot—a giant storm on Jupiter that is three times the size of Earth and a century or more old—will likely brighten a bit again as the South Equatorial Belt makes its comeback.

Adapted from information issued by JPL, University of Oxford, UC Berkeley, Gemini Observatory, University of San Carlos, Philippines / NASA / ESA / H. Hammel (STScI) / JIT.

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Pulsating star mystery solved

Artist's impression of OGLE-LMC-CEP0227

Artist's impression of the binary star OGLE-LMC-CEP0227. The smaller of the two stars is a pulsating Cepheid variable and the orientation of the system is such that the stars eclipse each other during their orbits.

A lucky alignment of orbits has enabled astronomers measure the mass of a specific kind of star, and in the process solve a decades-old mystery.

The star in question is of a type known as a ‘Cepheid variable’, or just Cepheid. Cepheids are unstable stars that are larger and much brighter than the Sun. They expand and contract in a regular way, taking anything from a few days to months to complete the cycle.

The time taken to brighten and fade again is longer for stars that are more luminous and shorter for the dimmer ones. This is known as the period-luminosity relation.

Astronomers can use this to their advantage when estimating the distances to galaxies. By timing the rise and fall in light of a Cepheid in a distant galaxy, they can work out how intrinsically bright the star must be.

By comparing that inherent brightness with the actual brightness measured, they can work out how far away the star must be.

The Cepheid period-luminosity relation, discovered by Henrietta Leavitt in 1908, was used by Edwin Hubble to make the first estimates of the distance to what we now know to be galaxies.

More recently Cepheids have been studied with the Hubble Space Telescope and with ground-based telescopes to make highly accurate distance estimates to many nearby galaxies.

The period-luminosity relation makes the study of Cepheids one of the most effective ways to measure the distances to nearby galaxies and from there to map out the scale of the whole Universe.

Large Magellanic Cloud

The Large Magellanic Cloud galaxy, in which the Cepheid star was discovered. Further Cepheid discoveries in this galaxy could help astronomers pin down its distance to better than 1% precision.

Competing theories

Unfortunately, despite their importance, Cepheids are not fully understood. In particular, predictions of their masses derived from the theory of pulsating stars are 20% less than predictions from the theory of the evolution of stars. This embarrassing discrepancy has been known since the 1960s.

To resolve this mystery, astronomers needed to find a binary star containing a Cepheid where the orbit happened to be seen edge-on from Earth. In these cases, known as eclipsing binaries, the brightness of the two stars dims as one passes in front of the other, and again when it passes behind the other star.

In pairs such as these, astronomers can determine the masses of the stars to high accuracy using well-known physical laws.

Unfortunately, neither Cepheids nor eclipsing binaries are common, so the chance of finding such an unusual pair seemed very low. None are known in the Milky Way.

“Very recently we actually found the double star system we had hoped for among the stars of the Large Magellanic Cloud,” says Wolfgang Gieren, a member of the team. The Large Magellanic Cloud is a small galaxy that orbits our Milky Way galaxy at a distance of around 160,000 light-years.

The system “contains a Cepheid variable star pulsating every 3.8 days,” adds Gieren. “The other star is slightly bigger and cooler, and the two stars orbit each other in 310 days.”

The observers carefully measured the brightness variations of this rare object, known as OGLE-LMC-CEP0227, as the two stars orbited and passed in front of one another. They also used spectrographs to measure the motions of the stars towards and away from the Earth—both the orbital motion of both stars and the in-and-out motion of the surface of the Cepheid as it swelled and contracted.

This very complete and detailed data allowed the observers to determine the orbital motion, sizes and masses of the two stars with very high accuracy—far surpassing what had been done before for a Cepheid.

The mass of the Cepheid is now known to about 1% and agrees exactly with predictions from the theory of stellar pulsation. The larger mass predicted by stellar evolution theory was shown to be significantly in error.

The team hopes to find other examples of these remarkably useful pairs of stars to exploit the method further. They think that from such binary systems they will eventually be able to pin down the distance to the Large Magellanic Cloud to 1%, which would mean an extremely important improvement of the cosmic distance scale.

Adapted from information issued by ESO / L. Calçada.

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Intergalactic pile-up, but no witnesses

The Andromeda Galaxy

The Andromeda Galaxy is the largest member of our Local Group of about 40 galaxies. Simulations suggest it formed during a merger of two galaxies.

  • Local Group of galaxies has around 40 members
  • Milky Way and Andromeda are biggest are the biggest of them
  • Andromeda and two smaller galaxies could have come from a cosmic collision

Did a major collision between two massive galaxies occur in the ‘Local Group’ of galaxies six billion years ago? Computer simulations suggest it could have.

The study—by a team of six researchers from Paris Observatory, the French National Centre for Scientific Research (CNRS), and the National Astronomical Observatories of Chinese Academy of Science (NAOC)—found that our biggest neighbour, the Andromeda Galaxy, as well as the smaller Magellanic Cloud galaxies, may well have been formed during a gigantic collision between galaxies.

The Magellanic Clouds are small, ‘irregular’ galaxies close to our Milky Way. They can be seen with the unaided eye under dark skies.

The Local Group includes nearly 40 galaxies and is dominated by two giant spiral galaxies—Andromeda (Messier 31) and our own galaxy, the Milky Way.

Many astronomers think Andromeda might have been formed through the merger of two galaxies of smaller mass. When could such a major event have occurred, and how would it have affected our neighbourhood?

The team, led by Francois Hammer from Paris Observatory, used computer simulations to model for the first time the detailed structural evolution of the Andromeda Galaxy.

They concluded that Andromeda might well have been the result of a collision between two galaxies, one slightly more massive than the Milky Way, and the other about one third as massive.

The first stage of the collision would have been about 9 billion years ago, with the final fusion slightly less than 5.5 billion years ago.

The following video shows how it might have happened.

Origin of the Magellanic Clouds

The simulations also predict that an amount of mass equivalent to one third of that of the Milky Way could have been expelled during the interaction, through the formation of gigantic tidal ‘tails’.

The Large Magellanic Cloud

The Large Magellanic Cloud, a small, irregular galaxy that orbits the Milky Way. Did it form from the wreckage of the Andromeda galaxy's birth?

Most of this matter would have been gas, and a large part of this matter would have been ejected in a particular direction…towards the Milky Way.

The researchers propose that the Magellanic Cloud galaxies formed within one of the tidal tails. They would have been ejected towards the Milky Way, at a very large velocity that has been recently re-evaluated to be one million kilometres per hour (350 km/s)!

This scenario could explain why the Magellanic Clouds are the only gas-rich and irregular galaxy companions of the Milky Way.

The researchers used the measured velocities of these galaxies to trace their positions back several billion years, and they found many solutions for which they could have originated from the Andromeda Galaxy.

If confirmed, these results may support both the hypothesis that most spiral galaxies have been formed by galactic mergers, and the prediction that many dwarf galaxies may originate from tidal tails during such events.

Adapted from information issued by the Observatoire de Paris / ESA / Hubble / NASA / R. Gendler.

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Old galaxies get their second wind

NGC 4150

Images taken with the Hubble Space Telescope reveal fresh star birth in galaxy NGC 4150, 44 million light-years away. The inset shows the core of the galaxy in ultraviolet light, revealing the glow (blue) of young stars.

  • Elliptical galaxies were thought to comprise only very old stars
  • Evidence is now mounting that new stars being born within them
  • Rebirth is due to galactic cannibalism—big galaxies eating little ones

Evidence is mounting that some galaxies that were thought to be in their twilight years, are actually going through a rebirth process by forming lots of new stars.

Galaxies come in many different shapes and sizes, one of the most common being the elliptical type. Elliptical galaxies are generally very large and, unlike our Milky Way galaxy, they don’t have spiral arms.

Ellipticals were once thought to be aging star cities whose star-making heyday was billions of years ago.

But new observations with NASA’s Hubble Space Telescope are helping to show that elliptical galaxies still have some youthful vigour left, thanks to close encounters with smaller galaxies.

Images of the core of the galaxy NGC 4150, taken in near-ultraviolet light with Hubble’s sharp-eyed Wide Field Camera 3 (WFC3), reveal streamers of dust and gas and clumps of young, blue stars that are significantly less than a billion years old.

And evidence shows that the spurt of star birth was sparked when NGC 4150 merged with a dwarf galaxy.

The new study helps bolster the emerging view that most elliptical galaxies have young stars, bringing new life to old galaxies.

“Elliptical galaxies were thought to have made all of their stars billions of years ago,” says astronomer Mark Crockett of the University of Oxford, leader of the Hubble observations. “They had consumed all their gas to make new stars.”

Hubble Space Telescope in orbit

Hubble's Wide Field Camera 3 can pick out the ultraviolet light of young stars in distant galaxies.

“Now we are finding evidence of star birth in many elliptical galaxies, fuelled mostly by cannibalising smaller galaxies.

“These observations support the theory that galaxies built themselves up over billions of years by collisions with dwarf galaxies,” Crockett continues. “NGC 4150 is a dramatic example in our galactic back yard of a common occurrence in the early universe.”

Adding fuel to the cosmic fire

The Hubble images reveal turbulent activity deep inside the galaxy’s core. Clusters of young, blue stars form a ring around the centre that is rotating with the galaxy. The stellar breeding ground is about 1,300 light-years across. Long strands of dust are silhouetted against the yellowish core, which is composed of populations of older stars.

From an analysis of the stars’ colours, Crockett and his team calculated that the star-formation boom started about a billion years ago, a comparatively recent event in cosmological history. The galaxy’s star-making factory has slowed down since then.

“We are seeing this galaxy after the major starburst has occurred,” explains team member Joseph Silk of the University of Oxford. “The most massive stars are already gone. The youngest stars are between 50 million and 300 to 400 million years old. By comparison, most of the [rest of the] stars in the galaxy are around 10 billion years old.”

“We believe that a merger with a small, gas-rich galaxy around one billion years ago supplied NGC 4150 with the ‘fuel’ necessary to form new stars,” says team member Sugata Kaviraj of the Imperial College London and the University of Oxford.

The abundance of elements heavier than hydrogen and helium in the young stars is very low, suggesting the galaxy that merged with NGC 4150 was also poor in heavy elements.

This points towards a small, dwarf galaxy, around one-twentieth the mass of NGC 4150.

Magnified view of NGC 4150's core

A magnified view of NGC 4150's core. The blue areas indicate a flurry of 'recent' (less than a billion years) star birth. Most of the rest of the stars in the galaxy are about 10 billion years old.

Hubble’s vision reveals new stars

Minor mergers such as this one are more ubiquitous than interactions between hefty galaxies, the astronomers say. For every major encounter, there are probably up to 10 times more frequent clashes between a large and a small galaxy.

Major collisions are easier to see because they create incredible fireworks—distorted galaxies, long streamers of gas, and dozens of young star clusters. Smaller interactions are harder to detect because they leave relatively little trace.

Over the past five years, however, ground- and space-based telescopes have offered hints of fresh star formation in elliptical galaxies.

Ground-based observatories captured the blue glow of stars in elliptical galaxies, and satellites such as the Galaxy Evolution Explorer (GALEX), which looks in far- and near-ultraviolet light, confirmed that the blue glow came from fledgling stars much less than a billion years old. Ultraviolet light picks out the glow of hot, young stars.

Crockett and his team selected NGC 4150 for their Hubble study because a ground-based telescope analysis gave tantalising hints that the galaxy’s core was not a quiet place. The survey, called the Spectrographic Areal Unit for Research on Optical Nebulae (SAURON), revealed the presence of young stars and dynamic activity that was out of sync with the galaxy.

“In visible light, elliptical galaxies such as NGC 4150 look like normal elliptical galaxies,” Silk says. “But the picture changes when we look in ultraviolet light. At least a third of all elliptical galaxies glow with the blue light of young stars.”

Adds Crockett: “Ellipticals are the perfect laboratory for studying minor mergers in ultraviolet light because they are dominated by old red stars, allowing astronomers to see the faint blue glow of young stars.”

The astronomers hope to study other elliptical galaxies in the SAURON survey to look for the signposts of new star birth. The team’s results have been accepted for publication in The Astrophysical Journal.

Adapted from information issued by STScI / NASA / ESA / R.M. Crockett (University of Oxford, U.K.), S. Kaviraj (Imperial College London and University of Oxford, U.K.), J. Silk (University of Oxford), M. Mutchler (Space Telescope Science Institute, Baltimore), R. O’Connell (University of Virginia, Charlottesville), and the WFC3 Scientific Oversight Committee.

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Cosmic jellyfish afloat in starry sea

NGC 1514

It looks like a deep-sea creature, but it's actually a dying star, or planetary nebula, known as NGC 1514.

  • Object is known as the ‘Crystal Ball’ nebula
  • Comprises a pair of stars surrounded by gas rings
  • Indicates the dying stage of a stars’ life

A new image from NASA’s Wide-field Infrared Survey Explorer shows what looks like a glowing jellyfish floating at the bottom of a dark, speckled sea.

In reality, this critter belongs to the cosmos—it’s a dying star surrounded by fluorescing gas and two very unusual rings.

“I am reminded of the jellyfish exhibition at the Monterey Bay Aquarium—beautiful things floating in water, except this one is in space,” said Edward (Ned) Wright, the principal investigator of the WISE mission at UCLA, and a co-author of a paper on the findings, reported in the Astronomical Journal.

The object, known as NGC 1514 and sometimes the ‘Crystal Ball’ nebula, belongs to a class of objects called planetary nebulae, which form when dying stars toss off their outer layers of material.

NGC 1514 is located 800 light-years away, in the direction of the constellation Taurus.

Ultraviolet light from a central star, or in this case a pair of stars, causes the gas to fluoresce with colourful light. The result is often beautiful—these objects have been referred to as the butterflies of space.

NGC 1514 was discovered in 1790 by Sir William Herschel, who noted that its “shining fluid” meant that it could not be a faint cluster of stars, as originally suspected.

Herschel had previously coined the term planetary nebulae to describe similar objects with circular, planet-like shapes. In reality they have nothing to do with planets.

Visible light and infrared views of NGC 1514

Two views of NGC 1514. On the left is the view from a ground-based, visible-light telescope; the view on the right shows the object in infrared light, as seen by NASA's Wide-field Infrared Survey Explorer, or WISE, satellite.

Dying star’s last gasp

Planetary nebulae with asymmetrical wings of nebulosity are common. But nothing like the newfound rings around NGC 1514 had been seen before. Astronomers say the rings are made of dust ejected by the dying pair of stars at the centre of NGC 1514. This burst of dust collided with the walls of a cavity that was already cleared out by stellar winds, forming the rings.

“I just happened to look up one of my favourite objects in our WISE catalogue and was shocked to see these odd rings,” said Michael Ressler, a member of the WISE science team at NASA’s Jet Propulsion Laboratory, and lead author of the paper.

Ressler first became acquainted with the object years ago while playing around with his amateur telescope on a desert camping trip. “It’s funny how things come around full circle like this.”

WISE was able to spot the rings for the first time because their dust is being heated and glows with the infrared light that WISE can detect. In visible-light images, the rings are hidden from view, overwhelmed by the brightly fluorescing clouds of gas.

Artist's impression of the WISE space telescope

Artist's impression of the WISE space telescope, which studies the cosmos at infrared wavelengths.

“This object has been studied for more than 200 years, but WISE shows us it still has surprises,” said Ressler.

Unexpected finding

Serendipitous findings like this one are common in survey missions like WISE, which comb through the whole sky. WISE has been surveying the sky in infrared light since January 2010, cataloguing hundreds of millions of asteroids, stars and galaxies.

In late September 2010, after covering the sky about one-and-a-half times, as planned it ran out of the frozen coolant needed to chill its longest-wavelength detectors.

The mission, now called NEOWISE, is still scanning the skies with two other of its infrared detectors, focusing primarily on comets and asteroids, including near-Earth objects, which are bodies whose orbits pass relatively close to Earth’s orbit around the sun.

The WISE science team says that more oddballs like NGC 1514 are sure to turn up in the plethora of WISE data—the first batch of which will be released to the astronomical community in spring 2011.

Adapted from information issued by NASA / JPL-Caltech / UCLA / DigitiSed Sky Survey / STScI.

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