May 02, 2015

Discovery of Milky Way’s Galactic Graveyard


A group of international scientists has discovered a vast galactic graveyard nestled in the shadow of a supermassive black hole at the heart of the Milky Way. 
The scientists discovered the site after studying X-ray emissions emanating from Sagittarius A-star, 26,000 light years away from Earth at the centre of the Milky Way. It is believed to be the location of a supermassive black hole with a mass four million times that of the Sun.
The black hole is one of the most puzzling objects known in the Milky Way, and despite its immense mass is very faint.

Before this study, outlined this morning in the journal Nature, high-energy X-ray sources had been difficult to resolve. Using the space-based NuSTAR (Nuc­lear Spectroscopic Telescope Array), the group has revealed a distinct X-ray emission near the galactic centre that has previously eluded detection.

The scientists — led by Columbia University physicist Kers­tin Perez, now with Haverford College in Pennsylvania — have been able to focus through dense clouds of gas to pick up high concentrations of X-rays that predict a puzzling population of as many as 10,000 stellar objects near the black hole.

The kaleidoscopic site of gal­actic activity is believed to host an abundance of surprisingly young, relatively massive stars bound to the central supermassive black hole, and a more extended population of burnt-out stars, or white dwarfs, as well as remnants of a supernova.

Studies had suggested that the presence of low-energy X-rays predicted a population of stellar objects dominated by white dwarf systems. But the new study, and its discovery of the galactic detritus, indicates the presence of a significantly larger population of massive star systems.

The paper says the presence of young and old stars in such close galactic proximity — and the ­differing interpretations of what the X-ray emissions could accurately represent — are expected to present significant challenges to understanding of how massive objects form and evolve in the centre of the galaxy.