Astronomers take highest resolution radio image of black hole


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shadow of black hole

Using a network of ground-based radio telescopes astronomers today released the highest resolution radio image of black hole ever produced.

Before giving more details, I must correct every other news report, as well as all of the press releases about this image. It is not “The first image of a black hole!” as these releases are claiming breathlessly. Radio telescope arrays have taken such images in the past, but their resolution was poor, so the result was not very imagelike. Instead, it showed contour lines in a coarse manner. Moreover, the coarseness of the resolution prevented them from seeing the black hole’s shadow itself.

This image now produced has the highest resolution ever for such a radio image, but believe me, it is still coarse. Nonetheless, it represents a giant technological leap forward. The effort required upgrades to many of these telescopes, along with significantly improved computer analysis. Now for some details:

Black holes are extraordinary cosmic objects with enormous masses but extremely compact sizes. The presence of these objects affects their environment in extreme ways, warping spacetime and super-heating any surrounding material. “If immersed in a bright region, like a disc of glowing gas, we expect a black hole to create a dark region similar to a shadow — something predicted by Einstein’s general relativity that we’ve never seen before,” explained chair of the EHT Science Council Heino Falcke of Radboud University, the Netherlands. “This shadow, caused by the gravitational bending and capture of light by the event horizon, reveals a lot about the nature of these fascinating objects and allowed us to measure the enormous mass of M87’s black hole.”

The image reveals the black hole at the center of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides 55 million light-years from Earth and has a mass 6.5-billion times that of the Sun.

Multiple calibration and imaging methods have revealed a ring-like structure with a dark central region — the black hole’s shadow — that persisted over multiple independent EHT observations. “Once we were sure we had imaged the shadow, we could compare our observations to extensive computer models that include the physics of warped space, superheated matter and strong magnetic fields. Many of the features of the observed image match our theoretical understanding surprisingly well,” remarks Paul T.P. Ho, EHT Board member and Director of the East Asian Observatory. “This makes us confident about the interpretation of our observations, including our estimation of the black hole’s mass.” [emphasis mine]

Note the highlighted words. To create this image they needed to combine data from numerous radio telescopes. Such work requires extensive calibration. The resulting image is manufactured, though without doubt it is manufactured from real radio data accumulated by multiple telescopes. Because those telescopes are separated by distance, however, there will always be gaps between their images, and it is in the calibration and imaging methods that the gaps are extrapolated away.

I don’t wish to imply that this image is fake. It is not. That the features persisted over multiple observations confirms that they were actually seeing the black hole’s shadow. It also confirms that these new interferometry techniques work.

However, much of the press hyperbole today is an effort to justify the many millions in tax dollars spent on this effort. The effort was absolutely worthwhile scientifically, but government bureaucracies always feel a need to oversell their work. That is partly what is happening here.

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5 comments

  • I was expecting a highly-pixelated image with poor resolution. As you note, the image is coarse, but with more detail than I anticipated. A spectacular effort.

  • Edward

    Blair Ivey,
    When I heard the news on the radio, I expected someone had confused a recent xkcd comic for actual news. From last Friday:
    https://xkcd.com/2133/

    Robert wrote:
    To create this image they needed to combine data from numerous radio telescopes. Such work requires extensive calibration.

    And from the article:
    The EHT links telescopes around the globe to form an Earth-sized virtual telescope with unprecedented sensitivity and resolution.

    For those who have forgotten the optics topic of their physics class, the larger the eye, telescope, lens, or mirror, the more resolution that can be achieved. Building a telescope the diameter of the Earth is difficult, but since we don’t need the size and surface area for signal gathering, we can do a similar thing by connecting two (or more) telescopes on opposite sides of the Earth.

    The Very Large Array telescope works in a similar way, but it is much smaller than the Earth (21 km radius rather than 6,000 km).
    https://en.wikipedia.org/wiki/Very_Large_Array
    in essence, the array acts as a single antenna with a variable diameter. The angular resolution that can be reached is between 0.2 and 0.04 arcseconds.

  • commodude

    And a tweet from MIT is giving credit to one lone female programmer for the successful effort…..regardless of the fact that the research began before she was born.

  • Edward

    commodude wrote: “regardless of the fact that the research began before she was born.

    My takeaway from that is that they couldn’t do it without her. All those years, and they couldn’t make it happen; she joins the effort and it gets done.

    The team has known since at least June of 2016 that the algorithm for doing the task was going to be key:
    https://www.americaninno.com/boston/mit-telescope-algorithm-to-take-picture-of-black-hole/

    But now, a group of researchers at MIT believe they can piece together the first-ever image of a black hole using the powers of radio waves and algorithms. The algorithm will be aggregating and analyzing data from radio telescopes around the globe, as part of the international project called the Event Horizon Telescope. “Radio wavelengths come with a lot of advantages,” Katie Bouman, an MIT graduate student who helped develop the new algorithm, said in a press release.

  • commodude

    Note: HELPED, not singelhandedly created out of whole cloth.

    A relative posted the tweet from MIT on social media crowing about females in STEM, and the comments in the tweet responses were so full of vitriol against the patriarchy it was both humorous and unreadable.

    Projects like this are team efforts, with many individuals making valuable contributions.

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