A New Look at an Old Friend
Just weeks after NASA’s Chandra X-ray Observatory began operations in 1999,
the telescope pointed at Centaurus A (Cen A, for short). This galaxy, at a
distance of about 12 million light years from Earth, contains a gargantuan jet
blasting away from a central supermassive black hole.
Since then, Chandra has returned its attention to this galaxy, each time
gathering more data. And, like an old family photo that has been digitally
restored, new processing techniques are providing astronomers with a new look at
this old galactic friend.
This new image of Cen A contains data from observations, equivalent to over
nine and a half days worth of time, taken between 1999 and 2012. In this image,
the lowest-energy X-rays Chandra detects are in red, while the medium-energy
X-rays are green, and the highest-energy ones are blue.
As in all of Chandra’s images of Cen A, this one shows the spectacular jet of
outflowing material – seen pointing from the middle to the upper left – that is
generated by the giant black hole at the galaxy’s center. This new high-energy
snapshot of Cen A also highlights a dust lane that wraps around the waist of the
galaxy. Astronomers think this feature is a remnant of a collision that Cen A
experienced with a smaller galaxy millions of years ago.
The data housed in Chandra’s extensive archive on Cen A provide a rich
resource for a wide range of scientific investigations. For example, researchers
published findings in 2013 on the point-like X-ray sources in Cen A. Most of
these sources are systems where a compact object – either a black hole or a
neutron star – is pulling gas from an orbiting companion star. These compact
objects form by the collapse of massive stars, with black holes resulting from
heavier stars than neutron stars.
The results suggested that nearly all of the compact objects had masses that
fell into two categories: either less than twice that of the sun, or more than
five times as massive as the sun. These two groups correspond to neutron stars
and black holes.
This mass gap may tell us about the way massive stars explode. Scientists
expect an upper limit on the most massive neutron stars, up to twice the mass of
the sun. What is puzzling is that the smallest black holes appear to weigh in at
about five times the mass of the sun. Stars are observed to have a continual
range of masses, and so in terms of their progeny’s weight we would expect black
holes to carry on where neutron stars left off.
Although this mass gap between neutron stars and black holes has been seen in
our galaxy, the Milky Way, this new Cen A result provides the first hints that
the gap occurs in more distant galaxies. If it turns out to be ubiquitous, it
may mean that a special, rapid type of stellar collapse is required in some
supernova explosions.
The results described here were published in the April 1st, 2013 issue of The
Astrophysical Journal and are available online. Mark Burke led the work when he
was at the University of Birmingham in the UK and he is now at L'Institut de
Recherche en Astrophysique et Planetologie in Toulouse, France. NASA's Marshall
Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's
Science Mission Directorate in Washington. The Smithsonian Astrophysical
Observatory in Cambridge, Mass., controls Chandra's science and flight
operations
Image credit: X-ray: NASA/CXC/U. Birmingham/M. Burke et al.
NASA
Guillermo Gonzalo Sánchez Achutegui
No hay comentarios:
Publicar un comentario