Heart of the Milky Way

Heart of the Milky Way[1]

At one time, astronomers believed the Milky Way was the entire universe. We soon learned different. And we learned how little we really know about our own galaxy, just one of 2000 billion (at least) galaxies in the universe.

That makes us somewhat insignificant in one respect. So maybe we should understand the Milky Way better. Well, we know it’s a spiral galaxy (actually a barred spiral). But what is at the center. From what we can observe it seems there is a central bulge. But why can’t we see it better?

Dust normally obscures the Milky Way’s galactic center. But from overlaying images taken in different wavelengths by different telescopes we can pierce the veil of dust. It seems evident that the crown jewel of our galaxy is a black hole packing the mass of more than 4 million Suns. What we’ve seen is that our galaxy’s supermassive black hole lets out frequent blasts of energy. Astronomers have seen the black hole outburst an average of twice a day in infrared and once per day in low-energy “soft” x rays. But they have no idea what is causing these flares.

Despite these extremes, the Milky Way’s supermassive black hole is relatively weak in comparison to the active galaxies astronomers have turned up in recent years. But its proximity makes it an ideal place to learn about all galactic cores.

“Screams” (actually particularly long emissions of x rays) are seen coming from the galactic center. High-energy astrophysicists hope these signals indicate the dusty gas cloud near the galactic center have begun interacting with the supermassive black hole. The “screams” appear to be coming from an extremely magnetized type of neutron star called a magnetar. Magnetars are the most magnetic objects in the universe. They have magnetic fields hundreds to thousands of times stronger than normal neutron stars, which are already a trillion times that of Earth. The radio pulses from the magnetar imply that there is potentially a much clearer window to the galactic center in radio waves. It reopens the hope that we can detect radio pulsars there and maybe one day to some amazing dynamical relativistic test.

The center of the Milky Way is a fabulous location to study. It is a region crammed with exciting celestial objects, all within a fields of view of today’s best instruments. It is the perfect astrophysical laboratory.

 

[1] See Liz Kruesi, “What Lurks in the Monstrous Heart of the Milky Way,” Astronomy (43, 10, October 2015).

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