ESA's new view of the Milky Way -- in gamma rays! (Forwarded)

ESA News
http://www.esa.int

11 November 2003

ESA's new view of the Milky Way -- in gamma rays!

ESA's gamma-ray observatory Integral is making excellent progress, mapping the
Galaxy at key gamma-ray wavelengths.

It is now poised to give astronomers their truest picture yet of recent changes
in the Milky Way's chemical composition. At the same time, it has confirmed an
'antimatter' mystery at the centre of the Galaxy.

Since its formation from a cloud of hydrogen and helium gas, around 12,000
million years ago, the Milky Way has gradually been enriched with heavier
chemical elements. This has allowed planets and, indeed, life on Earth to form.

Today, one of those heavier elements -- radioactive aluminium -- is spread
throughout the Galaxy and, as it decays into magnesium, gives out gamma rays
with a wavelength known as the '1809 keV line.' Integral has been mapping this
emission with the aim of understanding exactly what is producing all this aluminium.

In particular, Integral is looking at the aluminium 'hot spots' that dot the
Galaxy to determine whether these are caused by individual celestial objects or
the chance alignment of many objects.

Astronomers believe that the most likely sources of the aluminium are supernovae
(exploding high-mass stars) and, since the decay time of the aluminium is around
one million years, Integral's map shows how many stars have died in recent
celestial history. Other possible sources of the aluminium include 'red giant'
stars or hot blue stars that give out the element naturally.

To decide between these options, Integral is also mapping radioactive iron,
which is only produced in supernovae. Theories suggest that, during a supernova
blast, aluminium and iron should be produced together in the same region of the
exploding star. Thus, if the iron's distribution coincides with that of the
aluminium, it will prove that the overwhelming majority of aluminium comes
indeed from supernovae.

These measurements are difficult and have not been possible so far, since the
gamma-ray signature of radioactive iron is about six times fainter than that of
the aluminium. However, as ESA's powerful Integral observatory accumulates more
data in the course of the next year, it will finally be possible to reveal the
signature of radioactive iron. This test will tell astronomers whether their
theories of how elements form are correct.

In addition to these maps, Integral is also looking deeply into the centre of
the Galaxy, to make the most detailed map ever of 'antimatter' there.

Antimatter is like a mirror image to normal matter and is produced during
extremely energetic atomic processes: for example, the radioactive decay of
aluminium. Its signature is known as the '511 keV line.' Even though Integral's
observations are not yet complete, they show that there is too much antimatter
in the centre of the Galaxy to be coming from aluminium decay alone. They also
show clearly that there must be many sources of antimatter because it is not
concentrated around a single point.

There are many possible sources for this antimatter. As well as supernovae, old
red stars and hot blue stars, there are jets from neutron stars and black holes,
stellar flares, gamma-ray bursts and interaction between cosmic rays and the
dusty gas clouds of interstellar space.

Chris Winkler, Integral's Project Scientist, says: "We have collected excellent
data in the first few months of activity but we can and will do much more in the
next year. Integral's accuracy and sensitivity have already exceeded our
expectations and, in the months to come, we could get the answers to some of
astronomy's most intriguing questions."

Note to editors:

These and other preliminary results, plus a thorough description of the Integral
spacecraft and mission are published this month in a dedicated issue of the
journal Astronomy and Astrophysics.

At its 105th meeting on 6 October 2003, ESA's Science Programme Committee
unanimously decided to extend the Integral mission until December 2008.

The International Gamma Ray Astrophysics Laboratory (Integral) is the first
space observatory that can simultaneously observe celestial objects in gamma
rays, X-rays and visible light. Integral was launched on a Russian Proton rocket
on 17 October 2002 into a highly elliptical orbit around Earth. Its principal
targets include regions of the galaxy where chemical elements are being produced
and compact objects, such as black holes.

SPI measures the energy of incoming gamma rays with extraordinary accuracy. It
is more sensitive to faint radiation than any previous gamma ray instrument and
allows the precise nature of gamma ray sources to be determined. SPI's Principal
Investigators a J.-P. Roques, (CESR Toulouse, France), V. Schönfelder (MPE
Garching, Germany).

For further information, please contact:

ESA Media Relations Service
Tel: +33 (0)1.53.69.71.55
Fax: +33 (0)1.53.69.76.90

More information

* Integral
http://www.esa.int/SPECIALS/Integral/index.html

Related articles

* ESA's Integral discovers hidden black holes
http://www.esa.int/esaCP/SEMPHV1P4HD_Expanding_0.html
* A gamma-ray burst bonanza
http://www.esa.int/esaCP/SEMIVX8YFDD_FeatureWeek_0.html

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/esaCP/SEMF9YWLDMD_Expanding_1.html]
A portion of Integral's gamma-ray map of the galaxy. This false colour picture
was taken by the spectrometer on board Integral (SPI) between December 2002 and
March 2003. The yellow dots correspond to bright known gamma-rays sources,
whilst blue areas indicate regions of low emission. Data similar to these, but
in a higher energy range, have been used to study where aluminium and iron are
produced in the Galaxy.

Credits: ESA/SPI team

[Image 2:
http://www.esa.int/esaCP/SEMF9YWLDMD...html#subhead1]
Artist's view of Integral

The task of Integral, ESA's International Gamma-Ray Astrophysics Laboratory, is
to gather the most energetic radiation that comes from space. The spacecraft was
launched October 2002 and will help to solve some of the biggest mysteries in
astronomy. Gamma rays are even more powerful than the X-rays used in medical
examinations. Fortunately, the Earth's atmosphere acts as a shield to protect us
from this dangerous cosmic radiation. However this means that gamma rays from
space can only be detected by satellites. Integral is currently the most
sensitive gamma-ray observatory ever launched. It detects radiation from the
most violent events far away and from processes that made the Universe habitable.

Credits: ESA. Illustration by D. Ducros

[Image 3:
http://www.esa.int/esaCP/SEMF9YWLDMD...html#subhead2]
Integral launched at 06:41 CEST 17 October 2002 from Baikonur in Kazakhstan.

Credits: ESA - S.Corvaja