How Radio Interferometry works? What is it principle ? What's new?

2. Interferometry is a family of techniques in which waves,
usually electromagnetic waves are superimposed, causing
the phenomenon of interference, which is used to extract
information . Interferometry is an important investigative
technique in the fields of astronomy, fiber
optics, engineering metrology, optical
metrology, oceanography, seismology, spectroscopy,
quantum mechanics, nuclear and particle physics, plasma
physics, remote sensing, bimolecular interactions, surface
profiling, microfluidics, mechanical stress/strain
measurement, velocimetry, and optometry.

4. Radio interferometer is an array of separate telescopes,
mirror segments, or radio telescope antennas that work
together as a single telescope to provide higher resolution
images of astronomical objects such
as stars, nebulas and galaxies by means of interferometry.

5. The first use of a radio interferometer for an
astronomical observation was carried out by Payne-
Scott, Pawsey and Lindsay McCreadyy on 26 January
1946 using a SINGLE converted radar antenna
(broadside array) at 200 MHz near Sydney,
Australia.

6. Angular resolution for most telescopes ~ λ/D
,where D is the diameter of the telescope, λ is
wavelength of observation
For Example-Hubble Space Telescope resolution ~ 0.05”
D = 2.4m, λ ~ 500nm
We all Know higher the diameter D, better the resolution.
For 1 mm wavelength observations, one would need
a 5km diameter antenna to reach this resolution
Instead, we use arrays of smaller telescopes to
achieve high angular resolution in radio astronomy

7. Pros:
*Radio wavelengths are immune to dust, unlike visible waves. This
means that they can go straight through dust without being absorbed
or reflected. This allows us to see what is happening inside gas and
dust clouds.
*Most of the universe is made up of hydrogen, most of which is too
cold to emit in the visible spectrum but does emit in radio.
The biggest advantage is that they can operate day and night and in
nearly any type of weather.
Cons:
*Since most Earth's communications rely on radio waves, from TV to
phones to radio channels, radio satellite arrays must be built far
away from cities and towns. Deserts areas are a go-to for radio
telescope construction
*The arrays must also be made up of several to dozens of large and
precise antenna to pick up the wavelengths because they're very low
energy.

8. Two antennas only give you one point in the sky, but with dozens of
antennas you can get lots of points, one for each
paring of antennas. But even that only gets you a discrete set of
image points. If the Earth were fixed in relation to the sky, then
our radio image would look like a pointillist painting.
But the Earth rotates with respect to the sky, so as time goes by
the relative positions of the antennas shift with respect to an
astronomical signal. As you make observations over time, the gaps
between antennas are filled to create a more solid image.

17. Black Hole extreme gravity prevents light from escaping.
That means that they remain entirely invisible. However,
supermassive black holes in the centers of galaxies may
give themselves away by spewing bright jets of charged
particles. Others may be “seen” by the light of the nearby
stars that they fling away or rip apart. Up close, these
behemoths are surrounded by accretion disks — glowing
disks made from the material being sucked into them.
Scientists have now cleverly created a network of eight
radio telescopes. Working as one, they effectively make an
Earth-sized eye on the sky. And they have just imaged the
silhouette of a black hole’s event horizon — the edge inside
which nothing can be seen or escape. It can be seen against
the black hole’s accretion disk.

18. Thank You!!!