Galactic cores

Nov 29, 2007 07:59 GMT  ·  By

The object in question is a neutron star, known as RX J0822-4300, in close proximity to the center of the Milky Way, traveling at about 4.8 million kilometers per hour, and is thought to have been accelerated by the gravitational interaction with the supermassive black hole, present in the core of the galaxy, that might have altered its trajectory in such a way that it will most probably be ejected out of the Milky Way, in the next few million years.

Previously, similar stars that were traveling at speeds as high as 1.6 million kilometers per hour have been discovered in the vicinity of the galactic core, and were also ejected from the galaxy.

A neutron star represents one of the many final stages a star can go through, at the end of its life. They usually have masses between 1 and 2 time that of the Sun, compacted in a sphere with a diameter of 20 to 40 kilometers, with densities slightly higher than that of an atomic nuclei. That's why astronomers believe that these stars might be composed of a core of heavy liquid, formed of mostly neutrons and other sub-atomic particles, covered by a solid crust that could be as thick as 1.6 kilometers.

The observations made by the Chandra X-ray Space Telescope, during a five year period, revealed in three separate situations that the neutron star was moving away from the center of a remnant supernovae, named Puppis A, that exploded about 3700 years ago, showing that it traveled about 20 light years from its original position.

The study of the remnant debris of the Puppis A supernovae suggests that the neutron star was put in motion by the blast of the explosion in a direction, while the debris were pushed in the contrary direction, as a result of a lop-sided explosion. The supernovae was created by the collapse of the core of the original star, which imploded and created a neutron star, while the outer shells of the star exploded outward and were ejected, to release the enormous amounts of remnant energy, at speeds exceeding a few million kilometers per hour. Due to the complexity of the flow of the ejected material, the explosion was asymmetric and led to the creation of a propelling effect that pushed the neutron star in the opposite direction.

The calculation, regarding how fast the neutron star was moving, was made on the basis of the distance at which the star was from the Earth, and of its apparent movement on the sky. According to Frank Winkler, from the Middlebury College in Vermont, the difference in position observed on a five year period is comparable to the height of the numbers on a penny coin; seen from the distance, the equivalent of a football field.

However, the Puppis A neutron star presents some deviation from even the most sophisticated supernovae explosion models, by showing an apparent lack of pulsation and a phenomenal speed at which it is traveling.

The present models, regarding the outcome of these energetic supernovae explosions, are extremely complicated and hard to apply to real situations. The first report of the discovery of this fast traveling neutron star was made in 2006 by astronomers, at the Max Planck Institute for Extraterrestrial Physics in Munich, based on the analysis of two observations, made by the Chandra X-ray Space Telescope, which revealed the fact that it was moving two thirds as fast, but within certain margins of error.

Nevertheless, the source of the hypervelocity observed in the RX J0822-4300 neutron star, is somehow a mystery, but usually, these stars present in the vicinity of the supermassive black holes, are ejected out of the galaxy during the interaction.