Ghosts of Milky Way&rsquo;s Powerful Past Revealed
In the image:&nbsp;This artist&amp;#8217;s conception shows an edge-on view of the Milky Way galaxy. Newly discovered gamma-ray jets (pink) extend for 27,000 light-years above and below the galactic plane, and are tilted at an angle of 15 degrees. Previously known gamma-ray bubbles are shown in purple. The bubbles and jets suggest that our galactic center was much more active in the past than it is today.&nbsp;
Today the Milky Way Galaxy is a relatively quiet place. Our galaxy has grown up, and intense activity seen in other galaxies is a thing of our past. But scientists have long assumed the past was more hectic. A new study finds ghosts of past activity in the form of twin jets spat into space from the Milky Way&rsquo;s central black hole.
Unlike our quiescent galaxy, active galaxies have cores that glow brightly, powered by supermassive black holes swallowing material and exciting the gas and dust around them to grow brightly in many wavelengths, from visible light to X-rays and gamma rays. Active galaxies also often shoot twin jets in opposite directions &mdash; beams of material thought to be directed by intense magnetic energy.
The new evidence of ghostly gamma-ray beams suggests that the Milky Way&amp;#8217;s central black hole was much more active in the past.
&amp;#8220;These faint jets are a ghost or after-image of what existed a million years ago,&amp;#8221; said Meng Su, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA), and lead author of a new paper in the Astrophysical Journal. &amp;#8220;They strengthen the case for an active galactic nucleus in the Milky Way&amp;#8217;s relatively recent past.&rdquo;
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