Three Satellites Needed To Bring Out 'Shy Star'
Lead author of the results, NASA GSFC
issued by the European Space Agency
July 13, 2005 Greenbelt, MD -- An international team of scientists has uncovered a rare type of neutron
star so elusive that it took three satellites to identify it.
The findings, made with ESA's Integral satellite and two NASA satellites,
reveals new insights about star birth and death in our Galaxy. We report
this discovery, highlighting the complementary nature of European and
US spacecraft, on the day in which ESA's Integral celebrates 1000 days in
The neutron star, called IGR J16283-4838, is an ultra-dense 'ember' of
an exploded star and was first seen by Integral on 7 April 2005. This
neutron star is about 20,000 light years away, in a 'double hiding place'.
This means it is deep inside the spiral arm Norma of our Milky Way galaxy,
obscured by dust, and then buried in a two-star system enshrouded by dense
'We are always hunting for new sources,' said Simona Soldi, the scientist
at the Integral Science Data Centre in Geneva (Switzerland) who first saw
the neutron star. 'It is exciting to find something so elusive. How many
more sources like this are out there?'
Neutron stars are the core remains of 'supernovae', exploded stars once
about ten times as massive as our Sun. They contain about a Sun's worth of
mass compacted into a sphere about 20 kilometres across.
'Our Galaxy's spiral arms are loaded with neutron stars, black holes and
other exotic objects, but the problem is that the spiral arms are too
dusty to see through', said Dr. Volker Beckmann at NASA Goddard Space
Flight Center, lead author of the combined results. 'The right combination
of X-ray and gamma-ray telescopes could reveal what is hiding there, and
provide new clues about the true star formation rate in our Galaxy'.
Because the Integral scientists could not immediately decipher the nature
of the object, they enlisted the help of NASA's Rossi X-ray Timing
Explorer and the newly launched Swift satellite to observe it in different
Because gamma rays are hard to focus into sharp images, the science team
then used the X-ray telescope on Swift to determine a precise location. In
mid April 2005, Swift confirmed that the light was 'highly absorbed',
which means the binary system was filled with dense gas from the stellar
wind of the companion star. Later the scientists used the Rossi Explorer
to observe the source as it faded away. This observation revealed a
familiar light signature clinching the case for a fading high-mass X-ray
binary with a neutron star.
IGR J16283-4838 is the seventh so-called 'highly absorbed', or hidden
neutron star to be identified. Neutron stars, created from fast-burning
massive stars, are intrinsically tied to star formation rates. They are
also energetic 'beacons' in regions too dusty to study in detail
otherwise. As more and more are discovered, new insights about what is
happening in the Galaxy's spiral arms begin to emerge.
IGR J16283-4838 revealed itself with an 'outburst' on or near its surface.
Neutron stars such as IGR J16283-4838 are often part of binary systems,
orbiting a normal star. Occasionally, gas from the normal star, lured by
gravity, crashes onto the surface of the neutron star and releases a great
amount of energy. These outbursts can last for weeks before the system
returns to dormancy for months or years.
Integral, the Rossi Explorer and Swift all detect X-rays and gamma rays,
which are far more energetic than the visible light that our eyes detect.
Yet each satellite has different capabilities. Integral has a large field
of view, enabling it to scan our Milky Way galaxy for neutron stars and
black hole activity.
Swift contains a high-resolution X-ray telescope, which allowed scientists
to zoom in on IGR J16283-4838. The Rossi Explorer has a timing
spectrometer, a device used to uncover properties of the light source,
such as speed and rapid variations in the order of milliseconds.