The Milky Way Blows Bubbles

I think seeing our Milky Way galaxy in a dark sky is a most moving experience.  Knowing its immense proportions and our place in it gives me pause, it’s humbling.

Then I find out the Milky Way blows bubbles!  Just try to visualize that!  I can’t help seeing the image of an insolent teenager blowing a big one…whateverrr!

That doesn’t take away the respect I have for our home galaxy, but it is a curious phenomenon.

And the reality is we cannot see them without special instruments because they do not emit radiation in visible wavelengths.  Fortunately, we have instruments able to see other wavelengths such as radio, microwave, x-ray, and gamma.

Now termed Fermi bubbles, these enigmatic structures were first detected in the early 2000s and at that time were controversial.  We now know they exist and have mapped their extent; their enormous size is astounding!  Fermi bubbles extend for approximately 30,000 light years above and below the plane of our galaxy. In x-ray vision they look like bubbles with well-defined edges and smooth interiors.  Less defined In radio wave vision they still show signs of magnetic field order.  Microwave eyes produce an image of fog that gets less dense the farther out we look.  Gamma ray images show very sharp edges and consistent brightness.

What causes these structures?  Astronomers and astrophysicists speculate but their origin is not certain. Here is what we know:

They appear to originate about 300 light years above and below our galaxy’s center.  The bubbles are filled with energetic particles that appear to careen around within, following magnetic fields.  Whether they are electrons or protons is not known yet.  Something very powerful got these bubbles going!

One contender is good old Sagittarius A* (Sgr A*), the supermassive black hole at our galaxy’s center.  The suggested scenario is that part of a massive molecular cloud near Sgr A* got pulled into the black hole, causing an extreme outburst of energetic particles.  The subsequent broad jets of plasma smashed into surrounding gasses and dust, producing shock boundaries and the enormous bubbles. It would also help explain the very young (millions of years old) stars circling Sgr A*.

The young Fermi bubbles, maybe 6-9 million years old, coincides with the oldest hominid fossils found, dating back to about 6 million years ago.  I wonder if the black hole outburst was witnessed by our early ancestors.

In an attempt to get more evidence, astronomers have looked at nearby galaxies for similar bubbles.  No convincing sign of bubbles has been detected to date so our Milky Way bubbles appear to be unique.  Is there a significance for us?  Their distance (about 20,000 light years away) and direction make that unlikely.

What’s in the Sky?

February 1; 30 minutes after sunset; west-southwest:  Mercury is bright and low near the horizon.

February 6; before sunrise; south-southeast:  a waning crescent Moon is near Antares in Scorpius.