Astronomers uncover mystery at galactic core

How did it get so hot?

A group of astronomers has come up with a new theory to explain the X-ray glow in the centre of our galaxy. The only problem is that in their search for answers, they've stumbled on a bigger mystery.

After gathering data on the region for 170 days with the Chandra X-ray telescope, the researchers eliminated all of the 2,357 known X-ray sources from a 100-light-year-wide section of the galactic centre. These sources have been attributed to white dwarfs, neutron stars and black holes.

Michael Muno, who led the team at UCLA, found that the remaining 'light' from other X-ray sources was not easily explained. To fully explain the remaining X-ray glow, researchers say you would need around 200,000 more X-ray sources, approximately 10 times more than current theories predict.

The scientists say their analysis, which will appear in the 20 September issue of Astrophysical Journal suggests the majority of the X-rays come from two distinct sources, huge clouds of plasma, or ionised gas.

One seems to be perfectly normal, with an average temperature of 10 million degrees. It is probably the residue of the death of massive stars, blown off during their explosive endings. The other is more of an enigma.

The second cloud of plasma is roughly the same size as the first, but it is around 10 times hotter, at 100 million degrees. This is so hot that its own gravity is not sufficient to keep the cloud together, and it should boil away into space.

According to a report on Scientific American, stellar winds and supernovae could replenish the cloud, but cannot account for the extraordinary temperature. The UCLA team cannot fully explain how it got so hot, although they note that heat can be generated by a number of phenomena, including excess supernovae, cosmic rays and magnetic fields.

The team may get more of the answers it seeks following the launch of the Japanese Astro E2 satellite, which is able to resolve the X-ray spectrum very finely. ®

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