Journey to the Center of the Galaxy

November 10, 2009

Because of increasing light pollution, the most spectacular structure in the sky is seen by fewer and fewer people these days – the Milky Way. During the summer months you are in fact peering in the direction of the downtown hub of our pinwheel galaxy.  The central region straddles the constellations Scorpius and Sagittarius that are low on the southern horizon when viewed from northern latitudes.

But even on the most pitch-black night you still can’t see much of the real core because foreground spiral lanes of stars and black dust obscure it. In visible light , we really see a just few percent of all the stars in the galaxy. It is definitely a backyard-only view.

Nothing less than the penetrating power of all three operating NASA Great Observatories was brought to bear on the mysterious galactic core that lies 27,000 light-years away. Their stunning panoramic image released today by NASA combines views taken in mid and near infrared light by the Hubble and Spitzer space telescopes, and seething X-rays captured by the Chandra X-ray Observatory.

The Spitzer (red) and Hubble (yellow) views reveal a firestorm of star birth throughout the region.  Three known clusters of massive stars dominate it: the Central cluster, the Arches cluster, and the Quintuplet cluster. Large arcs of glowing gas form linear filaments that might follow strong magnetic fields.

A smattering of lone superhot stars may have formed in isolation, or they may have originated in clusters but then tossed out due to strong gravitational tidal forces. The brightest of these stellar loners, weighing in at 150 solar masses, is 10 million times the brilliance of our sun.

X-ray observations from Chandra complement this view by showing the super-hot massive stars as brilliant point-like X-ray sources. The X-rays reveal that the core is also peppered with the hot remains of supernovae exploding like hot buttered popcorn. The energy in turn heats the material between the stars.

The location of the exact center of the galaxy is just off the tip of  Sagittarius’ “teapot spout.” Infrared observations with ground-based telescopes, painstaking collected over the past two decades, have gathered incontrovertible evidence for the presence of a 3 million solar mass black hole at the core of the galaxy.

The black hole has been “weighed” by measuring the slingshot motions of stars caught in the black hole’s gravitational pull. In one stunning observation a star whipped within 17 light-hours of the black hole and traveled the distance between the Earth and Pluto in less that a day!

Planets and stars actually form in the disk encircling the black hole. But their fate is terribly uncertain. Gravitational “pinball game” interactions among the stars might plunge entire planetary systems into the black hole pit. Alternatively, stars could get a slingshot kick out of the disk of the galaxy altogether.

The super-telescope trio unveils the most torturous neighborhood in the galaxy. Life as we know it would have a very tough time originating, much less surviving in this cosmic version of Vice City that is bathed in deadly radiation.