X-Ray Chimneys

First astronomers discovered enormous gamma-ray-emitting bubbles above and below the galactic plane—the ‘Fermi bubbles’ I wrote about last time.

Then they found ‘X-ray chimneys’ connecting these bubbles to the center of the Milky Way!

These X-ray chimneys are about 500 light-years tall. That’s huge, but tiny compared to the Fermi bubbles, which are 25,000 light years across. They may have been produced by the black hole at the center of the Galaxy. We’re not completely sure yet.

Here’s an X-ray image taken by the satellite XMM-Newton in 2019. It clearly shows the X-ray chimneys:

Sagittarius A* is the black hole at the center of our galaxy. It’s an obvious suspect for what created these chimneys!

Puzzle. What’s the white circle?

For more, try this:

• G. Ponti, F. Hofmann, E. Churazov, M. R. Morris, F. Haberl, K. Nandra, R. Terrier, M. Clavel and A. Goldwurm, The Galactic centre chimney, Nature 567 (2019), 347–350.

Abstract. Evidence has increasingly mounted in recent decades that outflows of matter and energy from the central parsecs of our Galaxy have shaped the observed structure of the Milky Way on a variety of larger scales. On scales of ~15 pc, the Galactic centre has bipolar lobes that can be seen in both X-rays and radio, indicating broadly collimated outflows from the centre, directed perpendicular to the Galactic plane. On far larger scales approaching the size of the Galaxy itself, gamma-ray observations have identified the so-called Fermi Bubble features, implying that our Galactic centre has, or has recently had, a period of active energy release leading to a production of relativistic particles that now populate huge cavities on both sides of the Galactic plane. The X-ray maps from the ROSAT all-sky survey show that the edges of these cavities close to the Galactic plane are bright in X-rays. At intermediate scales (~150 pc), radio astronomers have found the Galactic Centre Lobe, an apparent bubble of emission seen only at positive Galactic latitudes, but again indicative of energy injection from near the Galactic centre. Here we report the discovery of prominent X-ray structures on these intermediate (hundred-parsec) scales above and below the plane, which appear to connect the Galactic centre region to the Fermi bubbles. We propose that these newly-discovered structures, which we term the Galactic Centre Chimneys, constitute a channel through which energy and mass, injected by a quasi-continuous train of episodic events at the Galactic centre, are transported from the central parsecs to the base of the Fermi bubbles.

9 Responses to X-Ray Chimneys

  1. wyager says:

    Is there enough pressure in the intergalactic medium to cause a “termination shock” type effect like at the boundary of the heliosphere? I.e. charged particles come out of the galactic core moving quickly, and once the flow drops below the speed of sound, it suddenly slows and spreads out, transitioning from chimney to bubble.

    • John Baez says:

      I don’t know the answer to your question. It’s a great question! But I don’t think the X-rays chimneys extend into intergalactic space. They are only 500 light years tall, while the so-called “bulge” at the Galactic Center has a radius of about 5000 light years. So if there’s a termination shock, it could be happening in the gas of the bulge—which makes it more plausible.

  2. Jonathan says:

    Answer: I’d bet money that the telescope has a blind spot, just like our eyes do.

  3. Simplicio says:

    Answer: seems to round to be natural, so presumably a mask placed to block an overly bright x-ray source. The sun?

    • John Baez says:

      Yes, this is right. But it’s not the Sun. As the year goes by, Sun moves relative to the Milky Way from our point of view: it does not permanently block a specific portion of the Milky way. I believe this image was created from many X-ray images created at different times. And when we look for X-ray sources in the sky, I suspect we always look far away from the Sun.

      • Jonathan says:

        I’m sure that happens, but that spot looks awfully perfectly round. I would expect there to be a much more ragged edge around that location, unless there >~50 observations that sampled near that location. (I doubt I could tell a 50-gon and a circle apart).

        I definitely lost my bet (where do I send the money?), as your point about being a mosaic of views taken with the telescope pointing different directions rules that out, but I’m still not sure we have the right explanation.

      • John Baez says:

        I think the correct explanation will be easier to guess after reading my next post on this blog:

        Scorpius X-1.

  4. Wyrd Smythe says:

    Ha! Our galaxy is blowing bubbles through straws. My first question remains whether this is a common galactic phenomenon. Secondarily whether the energy emitted might have contributed to evolution (via genetic mutation rates) on Earth.

    A very simplified version of the Drake Equation — that intelligent life requires at least five events with 1:10^4 odds (the right kind of star, the right kind of planet, the right kind of distance from the star and the galactic center, a large moon, large gas giants in the outer solar system, and others). If one agrees with the premise, the combined probability is 1:10^20, which is significantly greater than the number of stars in the galaxy (10^11) or even in the local group. It makes one wonder if, Copernican Principle aside, intelligent life is indeed rare.

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