THE SOUTHWORTH PLANETARIUM
70 Falmouth Street      Portland, Maine 04103
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43.6667° N    70.2667° W  Altitude:  10 feet below sea level Founded
January 1970
2021-2022: CXXV
        "Anyone who uses the phrase “easy as taking candy from a baby” has
never tried taking candy from a baby. "  -Anonymous

THE DAILY ASTRONOMER Tuesday, May 17, 2022
Hole in the Center

[image: eso2208-eht-mwa.jpg]

Finally, incontrovertible proof of its existence. The "it," in this
instance refers to the Supermassive Black Hole occupying the Milky Way's
nucleus. Such proof seems somewhat superfluous, for most astronomers have
been confident that it was there since around 1974, the time when strong
radio signals emanating from the galactic center were first detected. At
the time, many researchers correctly assumed that these signals could only
emanate from a highly massive black hole lurking deep in the galaxy's
center. And, weighing in at a hefty 4.3 million solar masses,* while only
spanning a distance of merely 44 million kilometers -approximately the
average separation distance between the Sun and Mercury- the supermassive
Black Hole Sagittarius A* has been imaged for the very first time. The
resultant snap is seen above!

In this image, we are "seeing" the superheated maelstrom of gases
surrounding the "black hole," a space-time region so gravitationally
powerful that even light is unable to escape from it. The gaseous disk was
imaged by capturing radio waves, which are detectable here on Earth.
Unfortunately, the object is small and quite remote, about 23,000 light
years from us.** Consequently, capturing its radio signals requires a radio
telescope the size of our planet. Naturally, constructing such a large
telescope isn't feasible or, for that matter, politically tenable.
Fortunately, radio astronomers can use a series of radio telescopes placed
around the world to produce an image equal in resolution to an Earth-sized
telescope.

These radio telescopes, 11 in all, comprise a system called the Event
Horizon Telescope. This telescope system utilizes a technique known as *Long
Baseline Interferometry*, which synchronizes two radio telescopes in such a
way so that they can capture an image equal in clarity to that produced by
a single telescope with a diameter equal to the telescopes' separation
distance.

[image: event-horizon-distribution.webp]
An artistic depiction of part of the EHT

Over many hours, the telescopes focused on Sagittarius A* and with the aid
of powerful computer algorithms, developed the first photo of it. Note that
the brighter regions within that image denote those areas in which more
data was gathered and are not indicative of actual "hot spots."

The EHT first gained attention by producing the first supermassive black
hole image in 2019. That SBH is located in the center of the galaxy M87,
located 55 million light years away. Despite its far greater distance,
imaging that black hole presented less of a challenge to EHT astronomers
than capturing Sagittarius A*. Imaging our own SBH proved difficult because
of the vast quantities of intervening gas and dust and our own angle on the
nucleus. (M87's black hole was face-on to us, making it easier to snap.)
Despite these obstacles, we can now see that monstrous black hole tucked
away deep in the Milky Way's heart. Yes, it truly is frightening, but its
presence isn't that startling.


Tomorrow: Hey, just wait a nanosecond! How can we possibly know the mass of
Sagittarius A*?



*4.3 million solar masses = 4.3 million times more massive than the Sun

**The radiation captured in this image left Sagittarius A* 23,000 years
ago. To put that time frame into perspective, we're seeing Sagittarius A*
around the time that the cave bear (Ursus spelaeus) went extinct and the
first humans had migrated into the regions now known as Alaska and the
Yukon.


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