A black hole and its lively neighborhood

By Liz Kruesi | July 6, 2016 2:47 pm
The central region of the Milky Way is a hectic and curious place. There, a supermassive black hole steals the show. (Credit: X-ray: NASA/CXC/UMass/D. Wang et al.; Optical: NASA/ESA/STScI/D.Wang et al.; IR: NASA/JPL-Caltech/SSC/S.Stolovy)

The central region of the Milky Way is a hectic and curious place. There, a supermassive black hole steals the show. (Credit: X-ray: NASA/CXC/UMass/D. Wang et al.; Optical: NASA/ESA/STScI/D.Wang et al.; IR: NASA/JPL-Caltech/SSC/S.Stolovy)

We all have our favorites. Some stargazers prefer our rust-hued neighbor, Mars. Others instead look toward the Orion Nebula, the glowing stellar nursery. Personally, I’m quite fond of our galaxy’s center. There, the extremes of nature meet in spectacular fashion — and give us a pretty great laboratory to explore those extremes.

I know, other writers at Discover have also focused on this same target. There are reasons for that popularity.

First of all, a black hole takes center stage, and black holes are pretty rad. This one weighs in at 4 million times our sun, and all that mass is crammed into a space not even 20 times as wide as our sun. That makes for a very dense region of space. (Which certainly makes sense, because black holes are the densest objects nature makes.) Anything that comes too close to a black hole — anything that reaches beyond the point of no return — falls into the black hole’s gravitational pull. For our galaxy’s central supermassive black hole, with the unexciting name of Sagittarius A*, that tipping point is around 7.3 million miles. That sounds like a lot, but in the grand scheme of things, it’s not. Our sun’s radius is about 430,000 kilometers.

Whizzing nearby and around the black hole are dozens of stars. Tracking how those pinpricks of light move in the presence of Sagittarius A*’s immense gravitational pull is actually why astronomers even know the black hole exists and how heavy it is. But the black hole doesn’t just calmly sit at our galaxy’s center. It spins, likely dragging the fabric of space with it. The black hole munches on gas that comes too close. It throws out flashes of light. Surrounding the black hole is a tumultuous environment, laced with magnetic fields and hot plasma and who knows what else. It’s a constantly evolving, congested place.

Astronomers have trained a brigade of telescopes on the center of our galaxy. They’ve seen X-ray flashes and a diffuse X-ray glow. They’ve detected infrared flares, gamma-ray signals, and constant radio waves. The galactic center glows in every color of the radiation rainbow.

But there’s a lot they still haven’t seen, like the outline of that black hole — a shadow marking the border of no return, beyond which everything falls into Sagittarius A*’s gravitational pull. Astronomers probably won’t have to wait much longer to see it. They’ve been prepping a system of radio telescopes scattered across Earth to image that shadow, and the long-awaited photo may come next year.

We also think the black hole’s environs boost electrons and other lightweight particles to extraordinarily high energies. The power required to do this is out of reach of anything that exists on Earth, and so the center of our galaxy is the nearest laboratory to us to find out how particles with those energies can even exist.

The Milky Way’s center is a location rich in astronomy and physics and the extremes, making it a prime target for the armada of telescopes we have today. My declaration of the best place in the universe (well, aside from the comfort of our hospitable planet) makes for my introduction to the blogging world. Welcome to Astrobeat, where I’ll explore the ever-evolving rhythm of the universe — from new research, to the stories of those looking toward the cosmos, to historical perspectives, and everything in between.

  • OWilson


    Looking forward to briefly discussing some of the more puzzling questions in cosmology, as we presently understand it!

    If it takes “Dark Energy” to keep the cosmos expanding and prevents gravity from collapsing our universe back to a singularity, why does the extreme gravity of our local black hole, not manifest its intense power by sucking in nearby stars?

    Do we ever see stars blinking out on the BH horizon?

    • zlop

      Is “Dark Energy”directional?

      • OWilson

        According to the latest.

        Dark Energy is apparently what is responsible Perlmutter’s exponential expansion of space.

        Could it be called anti-gravity?

        • zlop

          With an intensity profile, we could guess the source.
          What does exponential suggest?

          “Could it be called anti-gravity?”– Interesting thought,
          gravity decreasing with distance to negative?

          • OWilson

            That’s new!

            But if it explains observation, why not keep it?

            (for the time being)

    • Liz Kruesi

      Thank you for the welcome! Every black hole affects its environment out to a certain distance, and that distance relates to its mass. It’s similar to how our sun affects the region around it. (Our sun’s gravity is felt less farther out, for example, if a rocky object was zipping through space some 3 light-years away, the gravity of the next nearest star to us would be stronger on that object than our sun’s gravity). It’s the same thing with any black hole — for stars at some distance, the gravity of other things would start pulling on those stars more than the black hole.

      And X-ray astronomers have spied flashes of light near blink out near some black holes. They think what’s happening is a star gets pulled apart as it approaches the black hole, that star’s pulled-apart gas heats up by friction and glows, and then the signal disappears. All signs point to that star falling beyond the black hole’s horizon.

  • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

    the ever-evolving rhythm of the universe” We know from assumed fact that anything entering a black hole, as viewed from an external distance, will be unlimitedly red-shifted and therefore require forever to fall in. We know from assumed fact that information conservation arguments require a firewall ( Unruh effect) on entry, thus anomalous net binding energy.

    We only know from observation, twice re LIGO, that black hole mergers go to externally viewed equilibrium in real time (fractions of a second) and proceed via classical physics (general relativity) with zero observed quantum higgledy-piggledies. Is said “ever-evolving rhythm” scored by John Cage, Jr. with libretto by Paul Jackson “Jack the Dripper” Pollock? “Enquiring minds want to know.”

    • zlop

      Interestingly confusing.
      Is entanglement ruled out?

      • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

        LIGO observed two pairs of black holes merging. The composite bodies reached external viewer equilibrium within a fractional second. Theory that predicts otherwise, as in “forever asymptotic,” is wrong.

        You say “entanglement,” I say “dissipation.” Physics’ deepest, most beautiful predictions are not observed. Quantized gravitation, dark matter detection, validated supersymmetry, and black hole event horizon anomalies are 45 years of wiffle dust.

        Physics is forever disobliging to test whether spacetime is fundamentally trace chiral, below. Baryogenesis, the excess of matter over antimatter as the Big Bang cooled, requires it. Nekuklturny! A good answer, versus intractable studies, unemploys the discipline.

        • zlop

          “You say “entanglement,” I say “dissipation.””
          Very good — I laughed at my confusion.

        • http://gabriel-laddel.github.io Gabriel Laddel
  • Mike Richardson

    Glad to see a new blog site here, particularly one dealing with one of my favorite subjects. And quite the timely post, too, since Sagittarius (the constellation and star clouds) is now in view in the Northern Hemisphere. Might be checking it out tonight, despite the mosquitoes, if the sky stays clear. While only specialized instruments can observe the regions closest to the center of the galaxy, the monstrous black hole lurking there is still amazing to ponder as one observes the closer vistas Sagittarius provides in the summer. Looking forward to more good posts on this site.

  • Paul F. Dietz

    “(Which certainly makes sense, because black holes are the densest objects nature makes.) ”

    The “density” of a black hole depends on its mass, since the “volume” is proportional to mass cubed. For the very largest black holes, their density can be less than that of liquid water.


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Astrobeat follows the rhythm of the universe and tells the stories of those who are listening in.

About Liz Kruesi

Liz Kruesi is a science writer specializing in everything astronomical. She studied physics and astrophysics in college and graduate school, before leaving behind mathematical equations to instead focus on the words that tell the stories of the universe.

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