Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

From the Big Bang to the Cosmic Renaissance

21.08.2003


The photo shows a sky region imaged with the multi-mode FORS2 instrument on the 8.2-m VLT YEPUN telescope, in which a number of galaxies in the redshift range from 4.8 to 5.8 were discovered. They are accordingly located at a distance of about 12,600 million light-years from the Earth.


Nowadays, the Universe is pervaded by energetic ultraviolet radiation, produced by quasars and hot stars. The short-wavelength photons liberate electrons from the hydrogen atoms that make up the diffuse intergalactic medium and the latter is therefore almost completely ionised. There was, however, an early epoch in the history of the Universe when this was not so.

The Universe emanated from a hot and extremely dense initial state, the so-called Big Bang. Astronomers now believe that it took place about 13,700 million years ago.

During the first few minutes, enormous quantities of protons, neutrons and electrons were produced. The Universe was so hot that protons and electrons were floating freely: the Universe was fully ionised.



After some 100,000 years, the Universe had cooled down to a few thousand degrees and the nuclei and electrons now combined to form atoms. Cosmologists refer to this moment as the "recombination epoch". The microwave background radiation we now observe from all directions depicts the state of great uniformity in the Universe at that distant epoch.

However, this was also the time when the Universe plunged into darkness. On one side, the relic radiation from the primordial fireball had been stretched by the cosmic expansion towards longer wavelengths and was therefore no more able to ionise the hydrogen. On the contrary, it was trapped by the hydrogen atoms just formed. On the other side, no stars nor quasars had yet been formed which could illuminate the vast space. This sombre era is therefore quite reasonably dubbed the "Dark Ages". Observations have not yet been able to penetrate into this remote age - our knowledge is still rudimentary and is all based on theoretical calculations.

A few hundred million years later, or at least so astronomers believe, some very first massive objects had formed out of the huge clouds of gas that had moved together. The first generation of stars and, somewhat later, the first galaxies and quasars, produced intensive ultraviolet radiation. That radiation could not travel very far, however, as it would be immediately absorbed by the hydrogen atoms which were again ionised in this process.

The intergalactic gas thus again became ionised in steadily growing spheres around the ionising sources. At some moment, these spheres had become so big that they overlapped completely: the fog over the Universe had lifted !

This was the end of the Dark Ages and, with a term again taken over from human history, is sometimes referred as the "Cosmic Renaissance". Describing the most significant feature of this period, astronomers also call it the "epoch of reionisation".

Finding the Most Distant Galaxies with the VLT

To cast some light on the state of the Universe at the end of the Dark Ages, it is necessary to discover and study extremely distant (i.e. high-redshift [2]) galaxies. Various observational methods may be used - for instance, distant galaxies have been found by means of narrow-band imaging (e.g., ESO PR 12/03), by use of images that have been gravitationally enhanced by massive clusters, and also serendipitously.

Matthew Lehnert from the MPE in Garching, Germany, and Malcolm Bremer from the University of Bristol, UK, used a special technique that takes advantage of the change of the observed colours of a distant galaxy that is caused by absorption in the intervening intergalactic medium. Galaxies at redshifts of 4.8 to 5.8 [2] can be found by looking for galaxies which appear comparatively bright in red optical light and which are faint or undetected in the green light. Such "breaks" in the light distribution of individual galaxies provide strong evidence that the galaxy might be located at high redshift and that its light started on its long journey towards us, only some 1,000 million years after the Big Bang.

For this, they first used the FORS2 multi-mode instrument on the 8.2-m VLT YEPUN telescope to take extremely "deep" pictures through three optical filters (green, red and very-red) of a small area of sky (40 square arcmin, or approx. 5 percent the size of the full moon). These images revealed about 20 galaxies with large breaks between the green and red filters, suggesting that they were located at high redshift. Spectra of these galaxies were then obtained with the same instrument, in order to measure their true redshifts.

"The key to the success of these observations was the use of the great new red-enhanced detector available on FORS2", says Malcolm Bremer.

The spectra indicated that six galaxies are located at distances corresponding to redshifts between 4.8 and 5.8; other galaxies were closer. Surprisingly, and to the delight of the astronomers, one emission line was seen in another faint galaxy that was observed by chance (it happened to be located in one of the FORS2 slitlets) that may possibly be located even further away, at a redshift of 6.6. If this would be confirmed by subsequent more detailed observations, that galaxy would be a contender for the gold medal as the most distant one known!

The Earliest Known Galaxies

The spectra revealed that these galaxies are actively forming stars and are probably no older than 100 million years, perhaps even younger. However, their numbers and observed brightness suggest that luminous galaxies at these redshifts are fewer and less luminous than similarly selected galaxies nearer to us.

"Our findings show that the combined ultraviolet light from the discovered galaxies is insufficient to fully ionise the surrounding gas", explains Malcom Bremer. "This leads us to the conclusion that there must be many more smaller and less luminous galaxies in the region of space that we studied, too faint to be detected in this way. It must be these still unseen galaxies that emit the majority of the energetic photons necessary to ionise the hydrogen in the Universe."

"The next step will be to use the VLT to find more and fainter galaxies at even higher redshifts", adds Matthew Lehnert. "With a larger sample of such distant objects, we can then obtain insight into their nature and the variation of their density in the sky."

A British Premiere

The observations presented here are among the first major discoveries by British scientists since the UK became a member of ESO in July 2002. Richard Wade from the Particle Physics and Astronomy Research Council (PPARC), which funds the UK subscription to ESO, is very pleased: "In joining the European Southern Observatory, UK astronomers have been granted access to world-leading facilities, such as the VLT. These exciting new results, of which I am sure there will be many more to come, illustrate how UK astronomers are contributing with cutting-edge discoveries."

Richard West | alfa
Further information:
http://www.eso.org/outreach/press-rel/pr-2003/pr-24-03.html

More articles from Physics and Astronomy:

nachricht Space radiation won't stop NASA's human exploration
18.10.2017 | NASA/Johnson Space Center

nachricht Study shows how water could have flowed on 'cold and icy' ancient Mars
18.10.2017 | Brown University

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Osaka university researchers make the slipperiest surfaces adhesive

18.10.2017 | Materials Sciences

Space radiation won't stop NASA's human exploration

18.10.2017 | Physics and Astronomy

Los Alamos researchers and supercomputers help interpret the latest LIGO findings

18.10.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>