Milky Way’s core blazed forth furiously 6 mn years ago

Credit: Mark A. Garlick/CfA

Six million years ago, when the first human ancestors known as hominins walked the Earth, our galaxy’s core blazed forth furiously, new research shows.

The centre of the Milky Way galaxy is currently a quiet place where a supermassive black hole slumbers, only occasionally slurping small sips of hydrogen gas.

But it wasn’t always this way. New measurements show that the Milky Way galaxy weighs about 1-2 trillion times as much as our Sun.

About five-sixths of that is in the form of invisible and mysterious dark matter.
The remaining one-sixth of our galaxy’s heft, or 150-300 billion solar masses, is normal matter. However, if you count up all the stars, gas and dust we can see, you only find about 65 billion solar masses.

The rest of the normal matter – stuff made of neutrons, protons, and electrons – seems to be missing.

“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, research associate at the Harvard-Smithsonian Center for Astrophysics (CfA) and astrophysicist at the Italian National Institute of Astrophysics (INAF).

“We analysed 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,” Nicastro continued.

The astronomers found that there is a “bubble” in the centre of our galaxy that extends two-thirds of the way to Earth.

The bubble required a tremendous amount of energy. That energy, the authors say, came from the feeding black hole.

More answers may come from the proposed next-generation space mission known as X-ray Surveyor. It would be able to map out the bubble by observing fainter sources, and see finer detail to tease out more information about the elusive missing mass.

The study was published in The Astrophysical Journal.

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