I found this article on the National Geographic which explored this amazing volcano...
A report from Andrew Fazekas (scientist)
For years astronomers
have been puzzled as to why our Milky Way galaxy's "volcano"—a
supermassive black hole (SMBH) at its core—is dormant today. It seems the
answer may simply be that we didn't catch the cosmic monster—weighing at least
four million times the mass of our sun—feeding at the right time, according to
a new study.
"If we had been around to see it two million years ago, the
situation would have been very different," said study co-author Philip
Maloney of the University of Colorado in Boulder. “The Milky Way's black hole
was maybe ten million times brighter [then]," he said. "I don't think
anyone really had any expectation that SMBH might vary in luminosity by such a
huge factor on such a short—relatively speaking—time scale."
Astronomers have
long suspected there was an ancient outburst from the hibernating black hole,
but it’s only now that they believe they have found an actual ‘fossil imprint’
of the cosmetic monster’s last big meal.
The international team’s new theory points to a lacy
filament of gas, mostly hydrogen, called magellanic stream, which can be seen
trailing behind our galaxies two small companion galaxies: the large and small
Magellanic Clouds. Maloney believes powerful beams of energy erupting from the
SMBH two million years ago hit the stream—causing its hydrogen gas to get
ionized and light up, much like the glow of auroras we see here on Earth. This
ionization of the Magellanic Stream has puzzled scientists since its discovery
two decades ago. “No one has been able previously to come up with a good model
to explain the ionization," said Maloney.The team now suspects that this
glowing stream of extragalactic gas may be the fossil imprint of the SMBH
eruption two million years ago.
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