Six million years ago, Milky Way exploded and it was the time when first human ancestors walked the Earth
While the center of our galaxy is relatively quiet at present with black hole lying in the core of the Milky Way occasionally going into a feeding frenzy, the situation was not always like this. A new study shows that Milky Way underwent a burst of activity some six million years ago.
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The Milky Way weighs about 1-2 trillion times the mass of the Sun, according to an estimate. The mass of the Milky Way that is visible accounts for only 10 percent or 150-300 billion of solar masses while the matter that cannot be detected makes up for 80 to 90 percent of its total mass. But if we count up all the stars, gas and dust we can see, we find Milky Ways’ mass just 65 billion times that of the sun. The remaining detectable mass or mass made up of normal matter seems to be missing. Researchers believe this missing matter exists as a thin cloak of mist that is spreading throughout the galaxy as a result of a bang taking place million of years ago.
“We played a cosmic game of hide-and-seek. And we asked ourselves, where could the missing mass be hiding?" said lead author Fabrizio Nicastro from Harvard-Smithsonian Center for Astrophysics (CfA).
“We analyzed archival X-ray observations from the XMM-Newton spacecraft and found that the missing mass is in the form of a million-degree gaseous fog permeating our galaxy. That fog absorbs X-rays from more distant background sources.”
By measuring the background X-rays absorbed by the fog, researchers were able to estimate how much normal matter was there and how it was distributed in the Milky Way. Computer models showed that distribution was not smooth or uniform. Instead, it was in the form of a ‘bubble’ sitting in the center of Milky Way and an explosion in the galaxy 6 million years ago let go most of the matter. Meanwhile, the black hole gone into hibernation as it was ran out of nearby gas that it used to feed on.
The shockwaves created by this phase of activity can still be seen today while the timeline has been determined by the presence of 6-million-year-old stars near the galactic center. Those stars were formed from some of the same material that once eaten by the black hole.
“The different lines of evidence all tie together very well,” said co-author Martin Elvis. “This active phase lasted for 4 to 8 million years, which is reasonable for a quasar.”