------------------------------------------------------------------
ISO confirms that the normal matter in the Universe is not enough
------------------------------------------------------------------
The fate of the Universe depends on the total amount of existing matter.
New clues on this value have been obtained by an international team of
astronomers using ESA's infrared space telescope, ISO, by measuring for
the first time the abundance of a particular chemical element,
deuterium, in a very active star forming region in the Orion nebula.
Their result confirms that the total amount of normal matter is not
enough to stop the expansion of the Universe and cause it to collapse
into a 'Big Crunch' in the future.
Deuterium, an isotope of hydrogen, is a key element for astronomers
studying the origin of the Universe. All the deuterium that can be
detected today was produced a few minutes after the Big Bang, during a
process called primordial nucleosynthesis --in which a few other
elements, like hydrogen and helium,were also made. Apart from the Big
Bang, there are no other known sources of deuterium in the Universe.
Thus, astronomers regard deuterium as a 'fossil element' that holds a
lot of cosmological information.
Specifically, the abundance of deuterium in the new-born Universe is
directly related to the total amount of existing normal matter -the
so-called 'baryonic' matter--, the value upon which depends the ultimate
fate of our Universe. According to the most accepted theories, if the
total amount of matter exceeds a certain number, known as the critical
density, in the far future the Universe will stop expanding and will
collapse into a 'Big Crunch'; otherwise, the expansion will continue
forever.
But measuring the abundance of primordial deuterium is not easy. It
started off at one value at the time of the Big Bang -10 to 15 billion
years ago-, but has since diminished significantly because it is
destroyed by nuclear reactions in the interior of the stars.
Astronomers, therefore, have measured different values for deuterium in
different places and are trying to extrapolate back in time to the
deuterium abundance at the Big Bang.
The new result obtained by the international team led by Chris Wright
(School of Physics, University College, Canberra, Australia) and Ewine
van Dishoeck (Leiden University Observatory, The Netherlands), using the
Long Wavelength Spectrometer (LWS) on board ISO, allows for the first
time to infer the deuterium abundance in an actively star forming
region, the Orion Bar in the Orion nebula, about 1,500 light-years
away.
The deuterium they measured was locked up in the primary deuterium
bearing molecule in the Universe, hydrogen deuteride (HD). They found in
the Orion Bar one deuterium atom for every 100,000 hydrogen atoms, which
is consistent with other measurements in other places indicating that
the amount of normal matter in the Universe is not enough to cause a
'Big Crunch'.
"This is one step along the road to determine the deuterium abundance at
the time of the Big Bang, the value that everybody is trying to zoom in
on!", says Wright. "And it confirms that the density of normal (or
baryonic) matter is less than that required to close the Universe".
The new result demonstrates also the feasibility of a new technique for
measuring the deuterium abundance in active star forming regions, a
useful legacy for future infrared space telescopes such as ESA's FIRST,
due for launch in 2007.
The team will explain their work in a future issue of Astrophysical
Journal Letters.
The scientific community is now expecting a stream of new discoveries
from ISO, since the ISO Archive, a "goldmine" filled with nearly 30,000
scientific ISO observations, has recently been opened to astronomers all
over the world. The ISO Archive is located at the ISO Data Center, at
Villafranca, Spain, and can be accessed for free via the Internet from :
FOOTNOTE ON ISO
ISO was put into orbit in November 1995, by an Ariane 44P launcher from
the European Spaceport in Kourou, French Guiana. As an unprecedented
observatory for infrared astronomy, the spacecraft was able to examine
cool and hidden places in the Universe.
For more information and ISO pictures : ESA Public Relations Division:
Tel: +33(0)1.53.69.71.55 Fax: +33(0)1.53.69.76.90
Martin Kessler, ISO Project Scientist and co-discoverer: ESA's Satellite
Tracking Station in Villafranca (Spain). mkessler@iso.vilspa.esa.es
Visit the ISO web-site (Hi-Res Images available) at:
http://www.iso.vilspa.esa.es http://sci.esa.int/iso
---Marcelo Puhlmark@plug-in.com.br