Gaia 'billion-star surveyor' returns test image

Europe's billion-star surveyor, Gaia, is on track to begin operations in the next two or three months.

Launched in December, the satellite has now taken up its observing station some 1.5 million km from Earth.
Engineers are currently commissioning Gaia's two telescopes and its three instruments, getting them ready to begin mapping the precise positions and motions of one-thousand-million stars.
As part of that process, an image has been produced of a small star cluster.
This grouping is sited in the Large Magellanic Cloud (LMC), a companion galaxy to our own Milky Way, some 160,000 light-years in the distance.
If the picture just released by the European Space Agency looks somewhat underwhelming, that is not really surprising - taking pretty vistas of the sky is not what this mission is about.
Rather, Gaia's job when operational will be to track and characterise points of light moving across its big camera detector - be those stars, asteroids, comets or the flashes generated by exploding objects such as supernovae - to work out how far away they are and how they are moving in relation to everything else.
Prof Gerry Gilmore, the UK Gaia principal investigator from Cambridge University, told BBC News: "This image tells us that they've turned on the electronics, that they've turned on the computer, and that they've turned on Gaia's incredible British-built camera - and it's all working.

GAIA - THE DISCOVERY MACHINE

• The Gaia mission will make a very precise 3D map of our Milky Way galaxy
• It is Europe's successor to the Hipparcos satellite which mapped some 100,000 stars
• The one billion to be catalogued by Gaia is still only 1% of the Milky Way's total
• But the quality of the new survey promises a raft of discoveries beyond just the stars themselves
• Gaia will find new asteroids, failed stars, and allow tests of physical constants and theories
• Its map of the sky will be a reference frame to guide the investigations of future telescopes

• Gaia: The 'impossible mission'
• A billion pixels for a billion stars

"Gaia was not designed to take Hubble-like pictures; this is not its operating mode at all. What it will eventually do is draw little boxes around each of the stars you see in this picture and send just that information to the ground."

The satellite has been given an initial mission duration of five years to make its 3D map of the sky.
By repeatedly viewing its targets, it should get to know the brightest stars' coordinates down to an error of just seven micro-arcseconds - an angle equivalent to a euro coin on the Moon being observed from Earth.
One of the benefits of such study will be to refine the distance "ladder" used to measure scale in the Universe.
This ladder describes a number of techniques that lean on each other in a stepwise fashion to calculate the separation between Earth and some of the most far flung objects in the cosmos.
To the bottom of this ladder is the trigonometric parallax technique that Gaia will employ to measure distances.
Traditionally, this has only worked with stars inside the Milky Way. But Gaia's advanced optics will for the first time extend parallax to stars in the LMC.
In the past, the cloud's position has been determined only indirectly by studying the next rung up - the characteristic pulsations of particular stars known as Cepheids.
Having some parallax measurements in the LMC instead will allow astronomers to better calibrate the ladder and its various techniques, such as Cepheid pulsations. And that should mean researchers having more confidence in the figures calculated for even greater distances.
Prof Gilmore said: "Currently, we have precision distances - i.e. to 1% accuracy - to only one Cepheid star, which is Polaris (the North Star). So the whole distance scale to the Magellanic clouds depends on very shaky foundations. Gaia will be the 'sanity check' on the distance ladder where all of our different methods overlap.
"But Gaia will do even more because until now the accuracy to which we could work meant that we had to assume the Large Magellanic Cloud was a single point at one distance. We've had to average out properties. With Gaia, we will resolve out the LMC in three dimensions and that will tell us far more about its structure, and that will really open it up to proper scientific study."

• As the Earth goes around the Sun, relatively nearby stars appear to move against the 'fixed' stars that are even further away
• Because we know the Sun-Earth distance, we can use the parallax angle to work out the distance to the target star
• But such angles are very small - less than one arcsecond for the nearest stars, or 0.05% of the full Moon's diameter
• Gaia will make repeat observations to reduce measurement errors down to seven micro-arcseconds for the very brightest stars
• Parallaxes are used to anchor other, more indirect techniques on the 'ladder' deployed to measure the most far-flung distances

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

http://www.bbc.co.uk/news/science-environment-26073173 

Four new galaxy clusters take researchers further back in time

Four previously unknown galaxy clusters – each potentially containing thousands of individual galaxies – have been discovered some 10 billion light years from Earth.
An international team of astronomers, led by Imperial College London, used a new way of combining data from the two European Space Agency satellites, Planck and Herschel, to identify more distant galaxy clusters than has previously been possible. The researchers believe up to 2000 further clusters could be identified using this technique, helping to build a more detailed timeline of how clusters are formed. They publish their work in a paper in the journal Monthly Notices of the Royal Astronomical Society.
An artist's impression of the Herschel spacecraft. Credit: ESA/ AOES Medialab / NASA/ESA/STScI. Click for a full-resolution image.Galaxy clusters are the most massive objects in the universe, containing hundreds to thousands of galaxies, bound together by gravity. While astronomers have identified many nearby clusters, they need to go further back in time to understand how these structures are formed. This means finding clusters at greater distances from the Earth.
The light from the most distant of the four new clusters identified by the team has taken over 10 billion years to reach us. This means the researchers are seeing what the cluster looked like when the universe was just three billion years old.
Lead researcher Dr David Clements, from the Department of Physics at Imperial College London, explains: “Although we’re able to see individual galaxies that go further back in time, up to now, the most distant clusters found by astronomers date back to when the universe was 4.5 billion years old. This equates to around nine billion light years away. Our new approach has already found a cluster in existence much earlier than that, and we believe it has the potential to go even further.”
The clusters can be identified at such distances because they contain galaxies in which huge amounts of dust and gas are being formed into stars. This process emits light that can be picked up by the satellite surveys.
Galaxies are divided into two types: elliptical galaxies that have many stars, but little dust and gas; and spiral galaxies like our own, the Milky Way, which contain lots of dust and gas. Most clusters in the universe today are dominated by giant elliptical galaxies in which the dust and gas has already been formed into stars.
“What we believe we are seeing in these distant clusters are giant elliptical galaxies in the process of being formed,” says Dr Clements.
Three (false) colour Herschel images of the clumps identified by Planck. Blue, green and red represent infrared light at successively longer wavelengths, of 250μm, 350μm and 500μm respectively. The green circle indicates the size of the Planck beam at the position of the source, which Herschel was able to resolve in far greater detail. Credit: D. Clements / ESA / NASA. Click for a full-resolution image.Observations were recorded by the Spectral and Photometric Imaging Receiver (SPIRE) instrument as part of the Herschel Multi-tiered Extragalactic Survey (HerMES). Prof Seb Oliver, Head of the HerMES survey said: "The fantastic thing about Herschel-SPIRE is that we are able to scan very large areas of the sky with sufficient sensitivity and image sharpness that we can find these rare and exotic things. This result from Dr Clements is exactly the kind of thing we were hoping to find with the HerMES survey".
The researchers are among the first to combine data from two satellites that ended their operations last year: the Planck satellite, which scanned the whole sky, and the Herschel satellite, which surveyed certain sections in greater detail. The researchers used Planck data to find sources of far-infrared emission in areas covered by the Herschel satellite, then cross referenced with Herschel data to look at these sources more closely. Of sixteen sources identified by the researchers, most were confirmed as single, nearby galaxies that were already known. However, four were shown by Herschel to be formed of multiple, fainter sources, indicating previously unknown galaxy clusters.
The team then used additional existing data and new observations to estimate the distance of these clusters from Earth and to determine which of the galaxies within them were forming stars. The researchers are now looking to identify more galaxy clusters using this technique, with the aim of looking further back in time to the earliest stage of cluster formation.
The research involved scientists from the UK, Spain, USA, Canada, Italy and South Africa. It was part funded by the Science and Technology Facilities Research Council and the UK Space Agency.
 http://www.ras.org.uk/news-and-press/news-archive/254-news-2014/2396-four-new-galaxy-clusters-take-researchers-further-back-in-time

Astronomers discover oldest star: Formed shortly after the Big Bang 13. 7 billion years ago

Ateam led by astronomers at The Australian National University has discovered the oldest known star in the Universe, which formed shortly after the Big Bang 13.7 billion years ago.

The discovery has allowed astronomers for the first time to study the chemistry of the first stars, giving scientists a clearer idea of what the Universe was like in its infancy.

"This is the first time that we've been able to unambiguously say that we've found the chemical fingerprint of a first star," said lead researcher, Dr Stefan Keller of the ANU Research School of Astronomy and Astrophysics.

"This is one of the first steps in understanding what those first stars were like. What this star has enabled us to do is record the fingerprint of those first stars."

The star was discovered using the ANU SkyMapper telescope at the Siding Spring Observatory, which is searching for ancient stars as it conducts a five-year project to produce the first digital map the southern sky.

The ancient star is around 6,000 light years from Earth, which Dr Keller says is relatively close in astronomical terms. It is one of the 60 million stars photographed by SkyMapper in its first year.

"The stars we are finding number one in a million," says team member Professor Mike Bessell, who worked with Keller on the research.

"Finding such needles in a haystack is possible thanks to the ANU SkyMapper telescope that is unique in its ability to find stars with low iron from their colour."

Dr Keller and Professor Bessell confirmed the discovery using the Magellan telescope in Chile.

The composition of the newly discovered star shows it formed in the wake of a primordial star, which had a mass 60 times that of our Sun.

"To make a star like our Sun, you take the basic ingredients of hydrogen and helium from the Big Bang and add an enormous amount of iron -- the equivalent of about 1,000 times the Earth's mass," Dr Keller says.

"To make this ancient star, you need no more than an Australia-sized asteroid of iron and lots of carbon. It's a very different recipe that tells us a lot about the nature of the first stars and how they died."

Dr Keller says it was previously thought that primordial stars died in extremely violent explosions which polluted huge volumes of space with iron. But the ancient star shows signs of pollution with lighter elements such as carbon and magnesium, and no sign of pollution with iron.

"This indicates the primordial star's supernova explosion was of surprisingly low energy. Although sufficient to disintegrate the primordial star, almost all of the heavy elements such as iron, were consumed by a black hole that formed at the heart of the explosion," he says.

The result may resolve a long-standing discrepancy between observations and predictions of the Big Bang.

The discovery was published in the latest edition of the journal Nature.

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Story Source:
The above story is based on materials provided by The Australian National University. Note: Materials may be edited for content and length.
http://www.sciencedaily.com/releases/2014/02/140209200836.htm