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Mysterious dance of dwarfs may force a cosmic rethink

THE DISCOVERY THAT many small galaxies throughout the universe do not ‘swarm’ around larger ones as bees do but ‘dance’ in orderly orbits is a challenge to our understanding of how the universe formed and evolved.

The finding, by an international team of astronomers, including Professor Geraint Lewis of the University of Sydney, was published in the prestigious science journal Nature today.

“Early in 2013 we announced our startling discovery that half of the dwarf galaxies surrounding the Andromeda Galaxy are orbiting it in an immense plane” said Professor Lewis. “This plane is more than a million light years in diameter, but is very thin, with a width of only 300,000 light years.”

The universe contains billions of galaxies. Some, such as the Milky Way, are immense, containing hundreds of billions of stars. Most galaxies, however, are dwarfs, much smaller and with only a few billion stars.

Many of the larger galaxies have dwarf galaxies circling around them. Astronomers call them satellite galaxies.

Result contradicts standard understandings

For decades astronomers have used computer models to predict how these dwarf galaxies should orbit the large galaxies, and they’d always found that the dwarfs should be scattered randomly.

“Our Andromeda discovery did not agree with expectations, and we felt compelled to explore if it was true of other galaxies throughout the universe,” said Professor Lewis.

Using the Sloan Digital Sky Survey, a remarkable resource of colour images and 3-D maps covering more than a third of the sky, the researchers dissected the properties of thousands of nearby galaxies.

An artist's impression of the orbit of dwarf galaxies about a large galaxy

An artist’s impression of the orbit of dwarf galaxies about a large galaxy. Credit Geraint Lewis. The Hubble Image Archive was used as a source of the galaxies used in this illustration.

They were surprised to find that a large proportion of pairs of satellite galaxies are travelling in opposite directions if they are on opposite sides of larger galaxy hosts, said lead author Neil Ibata of the Lycée International in Strasbourg, France. And each of the dwarfs seemed to orbiting in the same plane, or angle, around the parent galaxy.

“Everywhere we looked we saw this strangely coherent co-ordinated motion of dwarf galaxies,” said Professor Lewis. From this the astronomers have extrapolated that this phenomenon is widespread in the universe, and seen in about 50 percent of galaxies.

“This is a big problem that contradicts our standard cosmological models. It challenges our understanding of how the universe works including the nature of dark matter,” said Professor Lewis.

Keeping an open mind

The researchers think the explanation might lie in some currently unknown physical process that governs how gas flows in the universe, although, as yet, there is no obvious mechanism that can guide dwarf galaxies into narrow planes.

Some experts, however, have made more radical suggestions, including bending and twisting the laws of gravity and motion.

“Throwing out seemingly established laws of physics is unpalatable,” said Professor Lewis, “but if our observations of nature are pointing us in this direction, we have to keep an open mind. That’s what science is all about.”

Adapted from information issued by the University of Sydney.

Gallery: The ‘Fireworks Galaxy’

NGC 6946 IS A MEDIUM-SIZED, face-on spiral galaxy located about 22 million light years away from Earth. In the past century, eight supernovae have been observed to explode in the arms of this galaxy. Chandra space telescope observations (coloured purple in this iamge) have, in fact, revealed three of the oldest supernovae ever detected at X-ray wavelengths, giving more credence to its nickname of the ‘Fireworks Galaxy.’ This composite image also includes optical data from the ground-based Gemini Observatory.

NGC 6949

NGC 6949, also known as the ‘Fireworks Galaxy’. Image credit: X-ray: NASA / CXC / MSSL / R.Soria et al, Optical: AURA / Gemini Obs

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Astronomers spy on galaxies in the raw

A CSIRO RADIO TELESCOPE has detected the raw material for making the first stars in galaxies that formed when the Universe was just three billion years old – less than a quarter of its current age. This opens the way to studying how these early galaxies make their first stars.

The telescope is CSIRO’s Australia Telescope Compact Array telescope near Narrabri, NSW. “It one of very few telescopes in the world that can do such difficult work, because it is both extremely sensitive and can receive radio waves of the right wavelengths,” says CSIRO astronomer Professor Ron Ekers.

The raw material for making stars is cold molecular hydrogen gas, called H2. It can’t be detected directly but its presence is revealed by a ‘tracer’ gas, carbon monoxide (CO), which emits radio waves.

The Spiderweb

In one project, astronomer Dr Bjorn Emonts (CSIRO Astronomy and Space Science) and his colleagues used the Compact Array to study a massive, distant conglomerate of star-forming ‘clumps’ or ‘proto-galaxies’ that are in the process of coming together as a single massive galaxy. This structure, called the Spiderweb, lies more than ten thousand million light-years away (at a redshift of 2.16).

The Spiderweb, imaged by the Hubble Space Telescope

MAIN IMAGE: The Spiderweb, imaged by the Hubble Space Telescope – a central galaxy (MRC 1138-262) surrounded by hundreds of other star-forming ‘clumps’. (Credit: NASA, ESA, George Miley and Roderik Overzier, Leiden Observatory.) INSET: In blue, the carbon monoxide gas detected in and around the Spiderweb. (Credit: B. Emonts et al, CSIRO/ATCA)

Dr Emonts’ team found that the Spiderweb contains at least sixty thousand million  times the mass of the Sun in molecular hydrogen gas, spread over a distance of almost a quarter of a million light-years. This must be the fuel for the star-formation that has been seen across the Spiderweb. “Indeed, it is enough to keep stars forming for at least another 40 million years,” says Dr Emonts.

Magnifying lens

In a second set of studies, Dr Manuel Aravena (European Southern Observatory) and colleagues measured CO, and therefore H2, in two very distant galaxies (at a redshift of 2.7).

The faint radio waves from these galaxies were amplified by the gravitational fields of other galaxies – ones that lie between us and the distant galaxies. This process, called gravitational lensing, “acts like a magnifying lens and allows us to see even more distant objects than the Spiderweb,” says Dr Aravena.

Dr Aravena’s team was able to measure the amount of H2 in both galaxies they studied. For one of the galaxies (called SPT-S 053816-5030.8), they could also use the radio emission to make an estimate of how rapidly the galaxy is forming stars – an estimate independent of the other ways astronomers measure this rate.

Antennae of CSIRO's Compact Array telescope

Dishes of the CSIRO’s Australia Telescope Compact Array near Narrabri in New South Wales. Photo: David Smyth

Upgraded telescope

The Compact Array’s ability to detect CO is due to an upgrade that has boosted its bandwidth – the amount of radio spectrum it can see at any one time – sixteen-fold (from 256 MHz to 4 GHz), and made it far more sensitive.

“The Compact Array complements the new ALMA telescope in Chile, which looks for the higher-frequency transitions of CO,” says Ron Ekers.

Adapted from information issued by CSIRO.

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Andromeda, we have you surrounded

The Andromeda galaxy

The Andromeda galaxy appears to be surrounded by a circle of dwarf galaxies (not visible in this image). Credit: ESA / Hubble & Digitized Sky Survey 2 / Davide De Martin (ESA/Hubble).

JUST AS BILBO BAGGINS found himself the centre of some unwanted attention from a bunch of dwarfs, the Andromeda galaxy appears to have a bunch of smaller, dwarf galaxies circling it in a single plane, according to new research. The finding, published in the prestigious journal Nature, presents a challenge to ideas of how all galaxies form and evolve.

The surprising research result reveals that around half of Andromeda’s 30-odd known dwarf galaxy satellites are orbiting the larger Andromeda Galaxy – the closest giant cosmic neighbour to our own galaxy, the Milky Way.

The international group of astronomers who discovered the cosmic curiosity include Professor Geraint Lewis from the University of Sydney’s School of Physics, and Anthony Conn, a PhD student at Macquarie University, and Dr Dougal Mackey from the Australian National University.

“Astronomers have been observing Andromeda since Persian astronomers first noted it over a thousand years ago, but it is only in the past decade that we have truly studied it in exquisite detail with the Pan-Andromeda Archaeological Survey,” said Lewis, one of the lead authors on the Nature paper.

Completely unexpected findings

“The Pan-Andromeda Archaeological Survey – cutely called PAndAS – is a large project that ran between 2008 and 2011, using the Canada-France-Hawaii Telescope situated on the Mauna Kea volcano on the Big Island of Hawaii,” explained Lewis. “Now that we’re examining the data it collected, it is providing our first panoramic view of our closest large companion in the cosmos.”

“When we looked at the dwarf galaxies surrounding Andromeda, we expected to find them buzzing around randomly, like angry bees around a hive.

Diagram showing the position of dwarf galaxies orbiting Andromeda

Left: A close up of the Andromeda galaxy. Right: Diagram showing the position of the dwarf galaxies (red dots) detected orbiting Andromeda in a single plane, in the direction of the red arrow. Credit: R. Ibata (PAndAS team).

“Instead, we’ve found that half of Andromeda’s satellites are orbiting together in an immense plane, which is more than a million light years in diameter but only 30,000 light years thick. These dwarf galaxies have formed a ring around Andromeda.”

“This was completely unexpected – the chance of this happening randomly is next to nothing. It really is just weird,” said Professor Lewis.

Not anticipated by computer modelling

Large galaxies, like Andromeda and our own Milky Way, have long been known to be orbited by an entourage of smaller galaxies. These small galaxies, which are individually anywhere from ten to at least hundreds of thousands of times fainter than their bright hosts, were thought to trace independent paths around those galaxies.

For several decades, astronomers have used computer models to predict how dwarf galaxies should orbit large galaxies, and every time they found that dwarfs should be scattered randomly over the sky. Never, in these synthetic universes, did they see dwarfs arranged in a plane like that observed around Andromeda.

“Now that we’ve found that the majority of these dwarf galaxies orbit in a [plane] around the giant galaxy Andromeda, it looks like there must be something about how these galaxies formed or subsequently evolved that has led them to trace out this peculiar coherent structure,” said Professor Lewis.

“Dwarf galaxies are the most numerous galaxy type in the universe, so understanding why and how they form this disc around the giant galaxy is expected to shed new light on the formation of galaxies of all masses.”

PhD student, Anthony Conn, whose research proved key to this study said, “It is very exciting for my work to reveal such a strange structure. It has left us scratching our heads as to what it means.”

There have been similar claims of an extensive plane of dwarf galaxies about our own Milky Way Galaxy, with some claiming that the existence of such strange structures points to a failing in our understanding of the fundamental nature of the Universe.

Adapted from information issued by the University of Sydney.

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Hubble’s deepest view of the cosmos

The Hubble eXtreme Deep Field

This image, called the Hubble eXtreme Deep Field (XDF), combines Hubble observations taken over the past decade. With a total of over two million seconds of exposure time, it is the deepest image of the Universe ever made.

ASTRONOMERS HAVE ASSEMBLED a new, improved portrait of our deepest-ever view of the Universe. Called the eXtreme Deep Field, or XDF, the image was assembled by combining ten years of NASA/ESA Hubble Space Telescope observations taken of a patch of sky within the original Hubble Ultra Deep Field. The XDF is a small fraction of the angular diameter of the full Moon.

The Hubble Ultra Deep Field (UDF) is an image of a small area of space in the constellation of Fornax (The Furnace), created using Hubble data from 2003 and 2004. By collecting faint light over one million seconds of observation, the resulting image revealed thousands of galaxies, both nearby and very distant, making it the deepest image of the Universe ever taken at that time.

The new full-colour XDF image is even more sensitive than the original UDF image, thanks to the additional observations, and contains about 5,500 galaxies, even within its smaller field of view. The faintest galaxies are one ten-billionth the brightness that the unaided human eye can see.

The Hubble eXtreme Deep Field with interesting objects labelled

This view of the XDF image contains shows of the most distant objects ever identified. Among these are: UDFj-39546284, at a redshift of 10.3, is a candidate for the most distant galaxy yet discovered (awaiting confirmation); Supernova Primo, at a redshift of 1.55, the most distant type Ia supernova ever observed; UDFy-38135539, at a redshift of 8.6, is the most distant galaxy to have had its distance independently corroborated; UDFy-33436598, at a redshift of 8.6.

Magnificent spiral galaxies similar in shape to the Milky Way and its neighbour the Andromeda galaxy appear in this image, as do large, fuzzy red galaxies in which the formation of new stars has ceased. These red galaxies are the remnants of dramatic collisions between galaxies and are in their declining years as the stars within them age.

Peppered across the field are tiny, faint, and yet more distant galaxies that are like the seedlings from which today’s magnificent galaxies grew. The history of galaxies — from soon after the first galaxies were born to the great galaxies of today, like the Milky Way — is laid out in this one remarkable image.Diagram showing distances of galaxies in the XDF

Hubble pointed at a tiny patch of southern sky in repeat visits made over the past decade with a total exposure time of two million seconds. More than 2,000 images of the same field were taken with Hubble’s two primary cameras: the Advanced Camera for Surveys and the Wide Field Camera 3, which extends Hubble’s vision into near-infrared light. These were then combined to form the XDF.

The Universe is 13.7 billion years old, and the XDF reveals galaxies that span back 13.2 billion years in time. Most of the galaxies in the XDF are seen when they were young, small, and growing, often violently as they collided and merged together.

Graphic comparing the size of the XDF compared to the full Moon

This image from the Digitsed Sky Survey shows the area of the Hubble eXtreme Deep Field (XDF), with the full Moon shown to scale for comparison.

The early Universe was a time of dramatic birth for galaxies containing brilliant blue stars far brighter than our Sun. The light from those past events is just arriving at Earth now, and so the XDF is a time tunnel into the distant past when the Universe was just a fraction of its current age.

The youngest galaxy found in the XDF existed just 450 million years after the Universe’s birth in the Big Bang.

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Adapted from information issued by NASA/ESA. Images courtesy NASA, ESA, Z. Levay (STScI), T. Rector, I. Dell’Antonio/NOAO/AURA/NSF, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University) and the HUDF09 Team

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Galaxy at the dawn of time

Galaxy GN-108036

One of the most distant galaxies known, called GN-108036, is seen 750 million years after the Big Bang. The galaxy's light took 12.9 billion years to reach us. Infrared observations taken by NASA's Spitzer and Hubble space telescopes show it to be surprisingly bright, thought to result from an extreme burst of star formation

  • Galaxy seen as it was 750 million years after the Big Bang
  • Observations suggest it is forming stars at a furious rate

ASTRONOMERS USING NASA’S Spitzer and Hubble space telescopes have discovered that one of the most distant galaxies known is churning out stars at a shockingly high rate. The blob-shaped galaxy, called GN-108036, is the brightest galaxy found to date at such great distances.

The galaxy, which was discovered and confirmed using ground-based telescopes, is 12.9 billion light-years away.

Data from Spitzer and Hubble were used to measure the galaxy’s high star production rate, equivalent to about 100 Suns per year.

For reference, our Milky Way galaxy is about five times larger and 100 times more massive than GN-108036, but makes roughly 30 times fewer stars per year.

“The discovery is surprising because previous surveys had not found galaxies this bright so early in the history of the universe,” said Mark Dickinson of the US National Optical Astronomy Observatory in Arizona. “Perhaps those surveys were just too small to find galaxies like GN-108036.”

“It may be a special, rare object that we just happened to catch during an extreme burst of star formation.”

Seen shortly after the Big Bang

The international team of astronomers, led by Masami Ouchi of the University of Tokyo, Japan, first identified the remote galaxy after scanning a large patch of sky with the Subaru Telescope atop Mauna Kea in Hawaii.

Its great distance was then carefully confirmed with the W.M. Keck Observatory, also on Mauna Kea.

“We checked our results on three different occasions over two years, and each time confirmed the previous measurement,” said Yoshiaki Ono of the University of Tokyo, lead author of a new paper reporting the findings in the Astrophysical Journal.

Spitzer (left) and Hubble space telescopes

The Spitzer (left) and Hubble space telescopes were used to measure the galaxy's redshift, a indication of how far away it is.

GN-108036 lies near the very beginning of time itself, a mere 750 million years after our universe formed 13.7 billion years ago in an explosive “Big Bang.”

Its light has taken 12.9 billion years to reach us, so we are seeing it as it existed in the very distant past.

Remarkable redshift

Astronomers refer to an object’s distance by a number called its “redshift,” which is a measure of how much its light has been stretched to longer, redder wavelengths due to the expansion of the universe.

Objects with larger redshifts are farther away and are seen further back in time.

GN-108036 has a redshift of 7.2. Only a handful of galaxies have confirmed redshifts greater than 7, and only two of these have been reported to be more distant than GN-108036.

Infrared observations from Spitzer and Hubble were crucial for measuring the galaxy’s star-formation activity. Astronomers were surprised to see such a large burst of star formation because the galaxy is so small and from such an early cosmic era.

Back when galaxies were first forming, in the first few hundreds of millions of years after the Big Bang, they were much smaller than they are today, having yet to bulk up in mass.

During this epoch, as the universe expanded and cooled after its explosive start, hydrogen atoms permeating the cosmos formed a thick fog that was opaque to ultraviolet light. This period, before the first stars and galaxies had formed and illuminated the universe, is referred to as the “dark ages.”

The era came to an end when light from the earliest galaxies burned through, or “ionised,” the opaque gas, causing it to become transparent. Galaxies similar to GN-108036 may have played an important role in this event.

Adapted from information issued by NASA / JPL-Caltech / STScI / University of Tokyo.

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Galaxy gazing with The Eyes

Galaxies NGC 4438 and NGC 4435

A peculiar pair of galaxies, NGC 4438 and NGC 4435, nicknamed The Eyes. The larger of the two, NGC 4438 (top) is thought to have once been a spiral galaxy that was strongly deformed by collisions with other galaxies in the relatively recent past. The two galaxies belong to the Virgo Cluster and are about 50 million light-years away.

  • The Eyes are two galaxies, NGC 4435 and 4438
  • Located 50 million light-years from Earth
  • Probably involved in a collision 100 million years ago

THIS BEAUTIFUL YET PECULIAR pair of galaxies is nicknamed ‘The Eyes’ and is about 50 million light-years from Earth, with the two galaxies some 100,000 light-years apart.

Their nickname comes from the apparent similarity between their cores—two white ovals that resemble a pair of eyes glowing in the dark when seen through a moderate-sized backyard telescope.

But although the centres of these two galaxies look similar, their outskirts could not be more different.

The galaxy in the lower right, known as NGC 4435, is compact and seems to be almost devoid of gas and dust.

In contrast, the large galaxy in the upper left (NGC 4438) has a lane of obscuring dust just below its core, young stars can be seen left of its centre, and gas extends at least up to the edges of the image.

The contents of NGC 4438 have been stripped out by a violent process—a collision with another galaxy that has distorted its spiral shape.

NGC 4435 could be the culprit. Some astronomers think that the damage caused to NGC 4438 resulted from an approach between the two galaxies to within about 16,000 light-years some 100 million years ago.

But while the larger galaxy was damaged, the smaller one was significantly more affected. Gravitational ‘tides’ from the clash are probably responsible for ripping away the contents of NGC 4438, and for removing most of NGC 4435’s gas and dust.

Another possibility is that the giant elliptical galaxy Messier 86, further away from The Eyes and not visible in this image, was responsible for the damage caused to NGC 4438. Recent observations have found filaments of ionised hydrogen gas connecting the two large galaxies, indicating that they may have collided in the past.

Messier 86 and The Eyes belong to the Virgo Cluster, a very rich grouping of galaxies. In such close quarters, galaxy collisions are fairly frequent.

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Adapted from information issued by ESO / Gems project.

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Galaxies are running out of gas

A star-forming region

Compared to earlier cosmic epochs, galaxies these days are running of out of the gas raw material with which to make new stars. (Hubble Space Telescope image.)

THE UNIVERSE FORMS FEWER STARS than it used to, and a CSIRO study has now shown why—compared to the past, galaxies today have less gas from which to make stars.

Dr Robert Braun (CSIRO Astronomy and Space Science) and his colleagues used CSIRO’s Mopra radio telescope near Coonabarabran, NSW, to study far-off galaxies and compare them with nearby ones.

Light (and radio waves) from the distant galaxies takes time to travel to us, so we see the galaxies as they were between three and five billion years ago.

Galaxies at that stage of the Universe’s life appear to contain considerably more molecular hydrogen gas than comparable galaxies in today’s Universe, the research team found.

Stars form from clouds of molecular hydrogen. The less molecular hydrogen there is, the fewer stars will form.

The research team’s paper is in press in Monthly Notices of the Royal Astronomical Society.

Raw material for stars

Astronomers have known for at least 15 years that the rate of star formation peaked when the Universe was only a few billion years old and has declined steeply ever since.

“Our result helps us understand why the lights are going out,” Dr Braun said. “Star formation has used up most of the available molecular hydrogen gas.”

Mopra radio telescope

CSIRO's Mopra radio telescope near Coonabarabran in New South Wales.

After stars form, they shed gas during various stages of their lives, or in dramatic events such as explosions (supernovae). This returns some gas to space to contribute to further star formation.

“But most of the original gas—about 70%—remains locked up, having been turned into things such as white dwarfs, neutron stars and planets,” Dr Braun said.

“So the molecular gas is used up over time. We find that the decline in the molecular gas is similar to the pattern of decline in star formation, although during the time interval that we have studied, it is declining even more rapidly.”

Dark energy the demon

Ultimately, the real problem is the rate at which galaxies are “refuelled” from outside.

Gas falls into galaxies from the space between galaxies, the intergalactic medium. Two-thirds of the gas in the universe is still found in the intergalactic medium—the space between the galaxies—and only one third has already been consumed by previous star formation in galaxies, astronomers think.

“The drop-off in both gas availability and star formation seems to have started around the time that Dark Energy took control of the Universe,” Dr Braun said.

Up until that time, gravity dominated the Universe, so the gas was naturally pulled in to galaxies, but then the effect of Dark Energy took over and the Universe started expanding faster and faster.

This accelerating expansion has probably made it increasingly difficult for galaxies to capture the additional gas they need to fuel future generations of star formation, Dr Braun speculates.

Adapted from information issued by CSIRO; NASA, ESA, STScI/AURA.

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Cosmic expansion rate confirmed

Galaxy cluster

As the universe expands, galaxies move further apart from one another. The rate at which the expansion is proceeding is determined by the Hubble constant, which has been newly measured with high precision.

  • Hubble constant used to gauge size and age of the universe
  • Previous measurements had a level of uncertainty
  • New measurement method confirms earlier results

A STUDENT WITH THE with the International Centre for Radio Astronomy Research (ICRAR) at the University of Western Australia, has calculated how fast the Universe is growing by measuring the Hubble constant.

“The Hubble constant is a key number in astronomy because it’s used to calculate the size and age of the Universe,” said PhD candidate Mr Florian Beutler.

As the Universe expands, it carries other galaxies away from ours. The Hubble constant links how fast the galaxies are moving with how far they are away from us.

By analysing light coming from a distant galaxy, the speed and direction of that galaxy can be easily measured. But determining the galaxy’s distance from Earth is much more difficult.

Until now, this has been done by measuring the brightness of individual objects (such as certain kinds of stars) within a galaxy and using what we know about those objects to calculate how far away the galaxy must be.

This approach is based on some well-established assumptions but is prone to systematic errors, leading Mr Beutler to tackle the problem using a completely different method.

Plot of 6df Galaxy Survey data

In this plot of 125,000 galaxies from 6df Galaxy Survey data, each dot is a galaxy and Earth is at the centre. (The dark slices are regions blocked from view.) The amount of galaxy clustering has been used (along with other data) to measure the expansion rate of the universe.

New method uses super survey

Published in the Monthly Notices of the Royal Astronomical Society, Mr Beutler’s work draws on data from a survey of more than 125,000 galaxies carried out with the UK Schmidt Telescope in eastern Australia.

Called the 6dF Galaxy Survey, this is the biggest survey of relatively nearby galaxies, covering almost half the sky.

Galaxies are not spread evenly through space, but are clustered. Using a measurement of the clustering of the galaxies surveyed, plus other information derived from observations of the early Universe, Mr Beutler has measured the Hubble constant with an uncertainty of less than 5%.

The new measurement is 67.0 (±3.2) kilometres per second per megaparsec. A megaparsec is 1 million parsecs, or 3.26 million light-years.

Good agreement

“This way of determining the Hubble constant is as direct and precise as other methods, and provides an independent verification of them,” says Professor Matthew Colless, Director of the Australian Astronomical Observatory and one of Mr Beutler’s co-authors.

“The new measurement agrees well with previous ones, and provides a strong check on previous work.”

The measurement can be refined even further by using data from larger galaxy surveys.

“Big surveys, like the one used for this work, generate numerous scientific outcomes for astronomers internationally,” says Professor Lister Staveley-Smith, ICRAR’s Deputy Director of Science.

Adapted from information issued by ICRAR / Images courtesy ICRAR / Chris Fluke, Centre for Astrophysics & Supercomputing, Swinburne University of Technology / NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI),G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA.

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Fly through a field of galaxies

THIS IMPRESSIVE VIDEO showcases results from a gigantic survey of galaxies known as the 6dF Galaxy Survey. The Survey mapped the nearby universe over almost half the sky, measuring the redshifts of more than 125,000 galaxies. Of those, 11,000 have been specially chosen and have had their velocities measured—their motions through space are helping astronomers to understand the mass involved in each galaxy, and how galaxies move and group together in the wider universe.

The survey gets its name, 6dF, from an innovative instrument installed on the Australian Astronomical Observatory’s UK Schmidt Telescope at Siding Spring in New South Wales. 6dF has a 6-degree-wide field of view—12 times wider than the full Moon—which is very wide for a large telescope. This wide field of view, coupled with the instrument’s ability to study 150 galaxies at a time, makes it an extremely efficient tool with which to do large astronomical survey projects.

The video was produced by Paul Bourke, and was structured so it could be projected on the full dome of a planetarium…which is why it seems to be distorted on a flat screen. Every dot and fuzzy ball you can see is an entire galaxy.

Adapted from information issued by ICRAR / Anglo-Australian Observatory / Paul Bourke (visuals and animation), and Peter Morse and Glenn Rogers (music).

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