The second target was the supermassive black hole
M87*. One of the largest known supermassive black
holes, M87* is located at the center of the gargantuan
elliptical galaxy Messier 87, or M87, 53 million light-
years (318 quintillion miles) away. Substantially more
massive than Sagittarius A*, which contains 4 million
solar masses, M87* contains 6.5 billion solar masses.
One solar mass is equivalent to the mass of our Sun,
approximately 2x10^30 kilograms. In addition to its size,
M87* interested scientists because, unlike Sagittarius
A*, it is an active black hole, with matter falling into it
and spewing out in the form of jets of particles that are
accelerated to velocities near the speed of light. But its
distance made it even more of a challenge to capture
than the relatively local Sagittarius A*. As described by
Katie Bouman, a computer scientist with the EHT who
led development of one of the algorithms used to sort
telescope data during the processing of the historic
image, it’s akin to capturing an image of an orange on
the surface of the Moon.
By 2017, the EHT was a collaboration of eight sites
around the world – and more have been added since
then. Before the team could begin collecting data, they
had to find a time when the weather was likely to be
conducive to telescope viewing at every location. For
M87*, the team tried for good weather in April 2017
and, of the 10 days chosen for observation, a whopping
four days were clear at all eight sites!
Each telescope used for the EHT had to be highly
synchronized with the others to within a fraction of a
millimeter using an atomic clock locked onto a GPS
time standard. This degree of precision makes the EHT
capable of resolving objects about 4,000 times better
than the Hubble Space Telescope. As each telescope
acquired data from the target black hole, the digitized
data and time stamp were recorded on computer disk
media. Gathering data for four days around the world
gave the team a substantial amount of data to process.
The recorded media were then physically transported to
a central location because the amount of data, around 5
petabytes, exceeds what the current internet speeds can
handle. At this central location, data from all eight sites
were synchronized using the time stamps and combined
to create a composite set of images, revealing the
never-before-seen silhouette of M87*’s event horizon.
The team is also working on generating an image of
Sagittarius A* from additional observations made by the
EHT
As more telescopes are added and the rotation of Earth
is factored in, more of the image can be resolved, and
we can expect future images to be higher resolution.
To complement the EHT findings, several NASA
spacecraft were part of a large effort to observe the
black hole using different wavelengths of light. As
part of this effort, NASA’s Chandra X-ray Observatory,
Nuclear Spectroscopic Telescope Array (NuSTAR)
and Neil Gehrels Swift Observatory space telescope
missions – all designed to detect different varieties of
X-ray light – turned their gaze to the M87 black hole
around the same time as the EHT in April 2017. NASA’s
THE CLAPPER 2018 - 2019
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black hole that appears largest from Earth. But its
location in the same galaxy as Earth meant the team
would have to look through “pollution” caused by stars
and dust to image it, meaning there would be more data
to filter out when processing the image. Nevertheless,
because of the black hole’s local interest and relatively
large size, the EHT team chose Sagittarius A* as one of
its two targets