earlier trees were virgin

earlier trees were virgin

20 October 2010 Last updated at 18:44

Galaxy is most distant object yet

The faintest of faint dots - a signal from the edge of the observable Universe

A tiny faint dot in a Hubble picture has been confirmed as the most distant galaxy ever detected in the Universe.

“Start Quote

If you look at the object in the Hubble image, it really isn't much”

End Quote Matt Lehnert Observatoire de Paris

This collection of stars is so far away its light has taken more than 13 billion years to arrive at Earth.

Astronomers used the Very Large Telescope in Chile to follow up the Hubble observation and make the necessary detailed measurements.
They tell the journal Nature that we are seeing the galaxy as it was just 600 million years after the Big Bang.
"If you look at the object in the Hubble image, it really isn't much," said Dr Matt Lehnert of the Observatoire de Paris, France, and lead author on the Nature paper
"We really don't know much about it, but it looks like it is quite small - much, much smaller than our own Milky Way Galaxy. It's probably got only a tenth to a hundredth of the stars in the Milky Way. And that's part of the difficulty in observing it - if it's not big, it's not bright," he told BBC News.

The Wide Field Camera 3 was fitted to Hubble during its last servicing mission

Scientists are very keen to probe these great distances because they will learn how the early Universe evolved, and that will help them explain why the cosmos looks the way it does now.
In particular, they want to see more evidence for the very first populations of stars. These hot, blue giants would have grown out of the cold neutral gas that pervaded the young cosmos.
These behemoths would have burnt brilliant but brief lives, producing the very first heavy elements.
They would also have "fried" the neutral gas around them - ripping electrons off atoms - to produce the diffuse intergalactic plasma we still detect between nearby stars today.
So, apart from its status as a record-breaker, the newly discovered Hubble galaxy, classified as UDFy-38135539, is of keen interest because it is embedded directly in this time period - the "epoch of re-ionisation", as astronomers call it.
The galaxy was one of several interesting candidates identified in the Hubble Ultra Deep Field (UDF) image of the Fornax Constellation acquired with the telescope's new Wide Field Camera 3 last year.
As a source of light, it barely registers on the Hubble picture which was made from an exposure lasting 48 hours.

The four 8.2m telescopes of the VLT. Yepun is the far-right unit. Sinfoni is circled at its base in the inset

Astronomers knew from the UDF data that the galaxy must be very far away, but it took some exquisite measurements using the Yepun Very Large Telescope unit on Mount Paranal in the Atacama Desert to determine the precise distance.
This was done using the Sinfoni instrument attached to Yepun. The spectrograph was able to pick apart the weak infrared light and establish the degree to which it had been stretched on its long journey through space and time by the expansion of the Universe.
Using this measure, known as redshift, the astronomers could confirm that UDFy-38135539 was more than 13 billion light-years distant (a redshift of 8.55).
Dr Andy Bunker from Oxford University, UK, worked with one of the Hubble teams that first spotted the galaxy. He said Lehnert and colleagues had made a compelling case for the object's great distance.
"These things are incredibly faint and far away," he commented. "You're talking about an emission line that's a small fraction of the brightness of the night sky and you have to be very careful in your measurement; but this group is careful. The result looks convincing," he said.

It required the exquisite capabilities of the Sinfoni instrument to confirm the galaxy's great distance

A redshift of 8.55 puts the galaxy firmly within the epoch of re-ionisation.
At this early time, theory indicates, the Universe would not have been fully transparent. Much of it would have been filled with a hydrogen "fog" that absorbed the fierce ultraviolet light coming off the young galaxies.
Only as these galaxies ionised this neutral gas filling the space between them did their light sweep out across the cosmos.
One of the more puzzling aspects of the discovery is that the glow from UDFy-38135539 would not have been strong enough on its own to burrow a path through the opaque hydrogen fog.
This means there must be fainter, less massive galaxies - unseen in the Hubble UDF - helping to clear out the neighbourhood.
Professor Malcolm Bremer of Bristol University, UK, is a co-author on the Nature paper. He explained the importance of these distant objects to astronomy:
"They're beautiful probes of our understanding of galaxy formation because we're seeing them at their earliest stages and therefore, hopefully, at their simplest," he said.
"If we want to believe we understand galaxy formation and evolution, then we would want to be able to say that the observed properties in these early galaxies are what we've been predicting. We want to see the start of the process," he told BBC News.
These observations on both Hubble and the VLT push current technology to the limit.
Astronomers have other candidates of similar distance in the UDF they hope to confirm soon. However, the real breakthrough in observing the epoch of re-ionisation is probably going to have to wait until more powerful telescopes and techniques are established.
This next-generation astronomy will include Hubble's successor (the James Webb Space Telescope) and the Extremely Large Telescope (ELT) to be built near the VLT in Chile.
The ELT will catch the faintest starlight with a mirror some 42m across. That is five times the diameter of Yepun's primary mirror.

Jonathan.Amos-INTERNET@bbc.co.uk

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Halley's comet 'was spotted by the ancient Greeks'

Halley's comet 'was spotted by the ancient Greeks'

Halley's comet may have been visible from Earth in 466BC, say the researchers

A celestial event seen by the ancient Greeks may be the earliest sighting of Halley's comet, new evidence suggests.

According to ancient writers, a large meteorite smacked into northern Greece between 466BC and 467BC.
The writers also described a comet in the sky at the time the meteorite fell to Earth, but this detail has received little attention, say the researchers.
Comet Halley would have been visible for about 80 days in 466BC, researchers write in the Journal of Cosmology.

New Scientist magazine reports that, until now, the earliest probable sighting of the comet was an orbit in 240BC, an event recorded by Chinese astronomers.

If the new findings are confirmed, the researchers will have pushed back the date of the first observation of Comet Halley by 226 years.
The latest idea is based on accounts by ancient authors and concerns a meteorite that is said to have landed in the Hellespont region of northern Greece in 466-467BC.
The space rock fell during daylight hours and was about the size of "a wagon load", according to ancient sources.
The object, described as having a "burnt colour", became a tourist attraction for more than 500 years.
Look west
In his work Meteorology, Aristotle wrote about the event about a century after it occurred. He said that around the same time the meteorite fell, "a comet was visible in the west".
Astronomer Eric Hintz and philosopher Daniel Graham, both of Brigham Young University in Provo, Utah, reconstructed the likely path of Halley's comet, to see whether it agreed with the ancient observations.
They calculated that Halley's comet could have been visible for about 80 days between early June and late August in 466BC - depending on atmospheric conditions and the darkness of the sky.
"It's tough going back that far in time. It's not like an eclipse, which is really predictable," co-author Eric Hintz, from Brigham Young University in Provo, Utah, told BBC News.
"But we feel fairly good about this. If the [sighting] in 240BC is accepted, this has a fairly solid possibility."
He added: "If accepted, this would be three orbits earlier [than the Chinese sighting]."

In the 11th Century, Halley's Comet was depicted on the Bayeux Tapestry

The reconstruction of the comet's path agrees with the ancient reports, which say the comet was visible for about 75 days.
The researchers point out that while the Chinese and Babylonians kept meticulous records of heavenly phenomena for centuries, the ancient Greeks did not.
Nevertheless, the Greek accounts do provide important information, say Graham and Hintz, such as the comet's period of visibility from Earth.
Asked whether it was possible that the meteorite fall and the pass by Halley's Comet could be linked, Dr Hintz was doubtful.
"it would be really neat if they were connected - if it was a piece of Halley's that fell. My feeling is that it was just a really cool coincidence," said Dr Hintz.
The researchers say that there remains the possibility that other ancient sightings of comets could be uncovered from Chinese and Babylonian records.

Astronomers find evidence for unusual class of black holes

Astronomers find evidence for unusual class of black holes

An artist's impression of the source HLX-1 - the light blue object to the top left of the galactic bulge

Researchers say they may have found further evidence for the existence of an unusual type of black hole.

Using the European Southern Observatory's Very Large Telescope (VLT) in Chile, an international team of scientists studied the images of the most extreme ultra-luminous X-ray source, HLX-1.
They say the data about the distance and the brightness of the source shows that it may contain an intermediate-size mass black hole, located some 300 million light years away from Earth.
The results of the study have been published in the Astrophysical Journal.
A black hole is a region of space that has such an extremely powerful gravitational field that it absorbs all the light that passes near it and reflects none.
If confirmed, HLX-1 would be classified as an intermediate-type black hole - something astrophysicists suspected to exist, but for which there have been only tentative detections in the past.
Radiation question
The lead author Klaas Wiersema of the University of Leicester's department of Physics and Astronomy, said that after the earlier discovery of the very bright X-ray source, the astronomers "were very keen to find out just how far away it really is, so that we can work out how much radiation this black hole produces".

Understanding how super-massive black holes form... is crucial to our comprehension of the formation of galaxies”

End Quote Sean Farrell University of Leicester

"We could see on images taken with big telescopes that a faint optical source was present at the location of the X-ray source, located near the core of a large and bright galaxy," he said.

"We suspected that this faint optical source was directly associated with the X-ray source, but to be sure we had to study the light of this source in detail, using the Very Large Telescope in Chile."
He said that the VLT was able to measure the precise distance to HLX-1 and the data from the telescope allowed the scientists to separate the light of the big, bright galaxy from that of the faint optical source.
"Much to our delight we saw in the resulting measurements exactly what we were hoping for: the characteristic light of hydrogen atoms was detected allowing us to accurately measure the distance to this object.
"This provided conclusive proof that the black hole was indeed located inside the big, bright galaxy, and that HLX-1 is the brightest ultra-luminous X-ray source known."
Galactic centre
HLX-1 is located in another galaxy some 300 million light years from our planet. The study also shows that the source is not a super-massive black hole.

An artist's impression of a black hole at the centre of a galaxy

Astronomers believe that the centres of most galaxies contain such super-massive black holes, and intermediate black holes might simply turn out to be their progenitors.
"Understanding how super-massive black holes form and grow is thus crucial to our comprehension of the formation and evolution of galaxies, which in turn goes part of the way to answering one of the really big questions: how did our own galaxy form and evolve?" said astronomer Sean Farrell, also of the University of Leicester.