A trio of supermassive black holes

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Astronomers have discovered a trinary of supermassive black holes at the center of a distant collision of multiple galaxies.

Astronomer Roger Deane of the University of Cape Town in South Africa and his colleagues have been watching a particular quasar, known as SDSS J1502+1115, in the constellation Boötes. Other astronomers had found that the object, located 4.3 billion light-years from Earth, possessed two supermassive black holes, each the center of a large galaxy smashing into another. The black holes are at least 24,000 light-years apart.

Deane wanted to confirm their existence, so he used an intercontinental array of radio dishes that yields even sharper views than the Hubble Space Telescope. Lo and behold, one of the black holes turned out to be two. “We were incredibly surprised,” says Deane, whose team reports its findings online today in Nature.

While the discovery of this system is incredibly cool, this article in the journal Science is surprisingly incorrect on some points, while also missing the main story.

First of all, there are no “radio dishes” that can yield “sharper views” than Hubble. That statement is ridiculous. Not only is the resolution of all radio telescopes far less than Hubble, this is still like comparing apples to oranges. I am surprised Science’s editors allowed that statement to get through.

Secondly, the real story here is the paucity of known supermassive black hole binaries or trinaries. Scientists believe that galaxies form by a slow merging process, almost like the formation of planets. Small galaxies merge to create larger galaxies, which then eat other galaxies. Often, two large galaxies also merge. In the last case, it is assumed that the supermassive black holes at the center of these large galaxies should form a binary system before merging themselves.

Under this scenario, astronomers should be finding many galaxies with multiple supermassive black holes at their center. So far, however, they have found only a handful, far fewer than the models predict. It is possible these giant black holes are simply hard to spot (they are black holes after all), but nonetheless the lack so far has puzzled scientists. This is the real story, which is why the astronomer near the end of the article seems so happy about it. “It’s very good to see another object,” he says. They haven’t been seeing them, and this discovery suggests that they might still be out there and that present models for galaxy formation might still be right.



  • Edward


    I spoke with my father, who reads a lot about radio astronomy and still likes to visit dishes, and it seems that with the concept of Very Long Baseline Interferometry they are getting some pretty good resolution, these days. They use radio telescopes on different continents to get the long baselines for the resolution.


    He showed me a paragraph in one of his books that says that the sensitivity is so good that they detect tidal action, both oceanic and solid land, and even detect continental drift.

  • Your father is correct, and everything you write is true, but that doesn’t change my point, that this article is very incorrect in comparing the resolution of radio telescopes with an optical telescope like Hubble.

    For one thing, the wavelengths themselves are so different. Radio wavelengths can be anywhere in size from one meter to a hundred kilometers in length. Even at the smallest, this limits the absolute smallest object or detail that you can see. Hubble, looking in the optical, observes in wavelengths ranging from 400 to 700 nanometers, which equals 0.0004 to 0.0007 millimeters in size. To put it mildly, Hubble can see details that are far smaller.

    Second, to even reach these limits you need a telescope with a big enough dish or mirror. Even with an array of radio dishes spanning the globe, such as the VLBA, the resolution will still not be sharp enough to match Hubble. This is why when you look at radio images of distant space objects they usually show those objects as a series of rough contour lines, while the same object imaged in the optical by Hubble will show the actual object with many small details visible.

    As I said, the comparison is apples to oranges, and the editors of Science should never have allowed it.

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