How Scientists Captured the First Image of a Black Hole
In the News
Accomplishing what was previously thought to be
impossible, a team of international astronomers has
captured an image of a black hole’s silhouette. Evidence
of the existence of black holes – mysterious places in
space where nothing, not even light, can escape – has
existed for quite some time, and astronomers have
long observed the effects on the surroundings of these
phenomena. In the popular imagination, it was thought
that capturing an image of a black hole was impossible
because an image of something from which no light can
escape would appear completely black. For scientists,
the challenge was how, from thousands or even millions
of light-years away, to capture an image of the hot,
glowing gas falling into a black hole. An ambitious team
of international astronomers and computer scientists
has managed to accomplish both. Working for well over
a decade to achieve the feat, the team improved upon an
existing radio astronomy technique for high-resolution
imaging and used it to detect the silhouette of a black
hole – outlined by the glowing gas that surrounds its
event horizon, the precipice beyond which light cannot
escape. Learning about these mysterious structures
can help students understand gravity and the dynamic
nature of our universe, all while sharpening their math
skills.
Telescopes of all types are used to see distant objects.
The larger the diameter, or aperture, of the telescope,
the greater its ability to gather more light and the higher
its resolution (or ability to image fine details). To see
details in objects that are far away and appear small
and dim from Earth, we need to gather as much light as
possible with very high resolution, so we need to use a
telescope with a large aperture.
That’s why the VLBI technique was essential to capturing
the black hole image. VLBI works by creating an array
of smaller telescopes that can be synchronized to focus
on the same object at the same time and act as a giant
virtual telescope. In some cases, the smaller telescopes
are also an array of multiple telescopes. This technique
has been used to track spacecraft and to image distant
cosmic radio sources, such as quasars.
The aperture of a giant virtual telescope such as the
Event Horizon Telescope is as large as the distance
between the two farthest-apart telescope stations – for
the EHT, those two stations are at the South Pole and in
Spain, creating an aperture that’s nearly the same as the
diameter of Earth. Each telescope in the array focuses
on the target, in this case the black hole, and collects
data from its location on Earth, providing a portion of
the EHT’s full view. The more telescopes in the array that
are widely spaced, the better the image resolution.
How They Did It
Though scientists had theorized they could image black
holes by capturing their silhouettes against their glowing
surroundings, the ability to image an object so distant still
eluded them. A team formed to take on the challenge,
creating a network of telescopes known as the Event
Horizon Telescope, or the EHT. They set out to capture
an image of a black hole by improving upon a technique
that allows for the imaging of far-away objects, known
as Very Long Baseline Interferometry, or VLBI.
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THE CLAPPER 2018 - 2019
To test VLBI for imaging a black hole and a number of
computer algorithms for sorting and synchronizing
data, the Event Horizon Telescope team decided on two
targets, each offering unique challenges.
The closest supermassive black hole to Earth, Sagittarius
A*, interested the team because it is in our galactic
backyard – at the center of our Milky Way galaxy, 26,000
light-years (156 quadrillion miles) away. (An asterisk is
the astronomical standard for denoting a black hole.)
Though not the only black hole in our galaxy, it is the