First Light For Black Hole Observatory

A newly installed instrument on the European Southern Observatory’s (ESO) Very Large Telescope (VLT) has just taken it’s first images, what we call ‘first light’ in the astronomy world.  The instrument, called GRAVITY, uses four different 8m telescopes to perform what we call ‘Baseline Interferometry.’  It is expected that tis is the instrument that will allow humanity to take the first ever direct picture of a black hole.

Trapezium cluster in Orion nebula, taken with GRAVITY. Credit: ESO/GRAVITY consortium/NASA/ESA/M. McCaughrean

Interferometry is a technique that uses multiple small telescopes all collecting light at a specific wavelength.  These telescopes form a line that we call the baseline.  The combination of these telescopes and the use of a mathematical imaging technique called a Fourier transform allows the final image to have a resolution as if it was taken by a telescope as wide as the entire baseline.  For example, the GRAVITY telescopes are all spread out along a 200 m wide array, so the final images look as if they were taken by a 200 meter telescope!

A telescope with this kind of power is necessary to peek deep within star forming regions and see how stars themselves are forming in their birth clouds.  The real gem, however, is that we finally have a telescope powerful enough to directly image the black hole in the center of the Milky Way Galaxy, Sag A*.  Now you may be thinking ‘How do we take a picture of a black hole if light can’t even escape the thing?’  The answer is that we can’t.  We can only image the event horizon, the edge of the black hole where light can just barely escape.  We don’t know exactly what it will look like, but some theorists have proposed that it will be a spherical or football-shaped black spot.

But until GRAVITY really stretches its legs, we will have to wait.


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