What Lies at the Center of the Milky Way?

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Image: Hubble, Spitzer, Chandra / NASA

Milky Way GC / infrared, gamma ray, X-ray

This photo caused tremendous excitement when released by NASA on November 10, 2009. The Galactic Center we cannot ‘see’ with our eyes has been made visible as never before by the genius of the digital image, technician-artists at NASA. Pink and blue represent low- and high-energy X-rays, respectively. Regions of hundreds of tiny dots reveal the uncountable numbers of black holes that live just outside the event horizon of the supermassive black hole (Sgr A*) at the Galactic Center (GC). Sagittarius A* is the most energetic object in the Milky Way and one of the major astronomy discoveries of recent years.


Image: Hubble, NASA

Milky Way GC / Sagittarius star cloud

Energy Beasties at the Galactic Center

The challenge to identify who lives at the center of our galaxy is formidable. Should you ever visit, here are some of the entities you’ll likely encounter.

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Image: NASA / CXC / MIT / Frederick K. Baganoff et al.

Milky Way GC / Sagittarius A* awakes 300 mya

Verification of the massive black hole at the GC began in 1974 when very strong radio emission from its location was confirmed. The first hard X-ray emissions from the GC were detected in 1987; then Chandra found soft X-ray emissions in 1999. It is now understood that gas near the black hole brightens and then quickly fades in the X-ray spectrum, presumably in response to X-ray pulses emanating from just outside the black hole. When gas spirals inward towards the black hole, it heats up to millions of degrees and then emits X-rays. Sgr A* now appears to be in a quiet, resting phase. Although it contains ~ 4X million Sun’s mass, the energy radiating from its immediate surroundings is billions of times weaker than that from comparable black holes in other galaxies.

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