Highly energetic cosmic object hides its identity

Dec 27, 2007 09:08 GMT  ·  By

We used to think that Quasi Stellar Objects or quasars are the most energetic structures in the Universe, but this doesn't seem to be the case with the Milky Way, and why would our galaxy be more special than the others? The quasar is a special type of black hole, which goes through a 'feeding' process as it swallows massive amounts of gas and dust, spinning around it in an accretion disk. The friction between the gas and dust particles raises the temperature of the cloud to a point at which it emits high amounts of light in most of the visible spectrum, X-ray and gamma-ray. In addition, the part of the accelerated gas that is not drawn towards the singularity escapes to the object's pole at relativistic speed, and can create jet particles millions of light years long.

Albeit as earlier said, it seems that the most energetic particles emitted in our galaxy come from objects which are mostly covered in mystery. Relatively recently discovered by the European telescope High Energy Stereoscopic System or H.E.S.S., these cosmic objects emit particles and accelerate them to speeds close to that of light. In order to solve the astronomical problem, a collaboration between the Japanese Aerospace Exploration Agency and NASA has been employed to study the elusive objects.

The ground based telescope H.E.S.S., located in Africa, Namibia, detected the cosmic objects during gamma-ray scans of the sky that revealed extremely high energy gamma-ray busts, representing the highest energy form of light emitted by a cosmic body beyond the orbit of Earth. Interestingly enough, these radiation emissions are so mysterious that they have determined the creation of a new branch in astronomy.

Not only the bodies which emit these radiations are elusive, but even the effects produced on Earth's atmosphere have been subject of debate until recently. Cherenkov radiation represents the resulting blue light bursts created by extremely energetic sub-atomic particles colliding with the atoms in the atmosphere. However, there seemed to be a problem regarding the particles themselves. Measurements revealed that they were traveling at speeds greater than that of light, which, as we know today, is impossible, at least in a relativistic sense. Later on, it has been shown that, in fact, the Cherenkov radiation is produced by gamma-ray photons, a form of light, and the particle speed measurements have been distorted by comparison with the speed of light in Earth's atmosphere which is slightly smaller than that of photons in void.

Although H.E.S.S. was able to determine the location of the cosmic objects emitting high energy particles, its resolution prevents it from making a precise image of the exact location from which and of how the particles are being accelerated to such high energies. Thus, the Suzaku X-ray telescope was put to solve this problem with the help of its high sensitivity X-ray instruments. Some might say, yes... but what does the X-ray have to do with the gamma-ray? It seems that any object that has the capability of producing gamma-ray bursts will also emit X-ray radiation automatically.

Preliminary results of the observations made by Suzaku show that the X-ray signature of the unknown radiation source closely resembles that of a pulsar star known as neutron star which is created in the late stages of a star's life, as its massive core, being unable to sustain the enormous pressure created by gravity, collapses on itself when the nuclear forces cannot balance it.

Aside the pulsar-like structure, it looks like the additional material ejected by the star during the supernova phase, which has currently formed a nebula around the dead stars, radiates more particles than previously predicted.

Hironori Matsumoto, from the University of Kyoto, suggests that HESS J1614-518, the cosmic body studied by Suzaku, Chandra and XMM Newton, belongs to a class of objects known as 'dark particle accelerators', but what kind of particles are being accelerated in these object remains a subject of debate.

Previously, astrophysicists have suggested that they might be protons, sub-atomic particles that have 2000 the mass of the electron, and could be accelerated to energies as high as that contained by a fast baseball, theory seemingly confirmed by observations made by the Suzaku Telescope which revealed that, similarly to proton sub-atomic particles, the HESS J1614-518 object emits low amounts of X-ray.