To earn my place at the University of Leeds I have been asked to complete an assignment on the science and importance of a Nobel Prize discovery. It was daunting at first trying to attempt this piece of work (the three page project brief was enough to make me eyes water) and yet I soon enjoyed picking out my articles, reading them then turning my shorthand attempts into this essay. Happy reading!
Black holes
have captured the public’s imagination and inspired a wave of Sci-fi science:
from Interstellar to Doctor Who, the black hole is deemed as key to human time
travel through the warping of space time. Despite seeming fantastical, the 2020
Physics Nobel Prize winners Reinhard Genzel and Andrea Ghez could bring us a
step closer to this improbable reality and provides further evidence for
Einstein’s Theory of General Relativity. As a science geek myself, I’m
fascinated by the future of space and having the opportunity to further delve
into its discoveries was not one to be missed.
The 2020
Nobel Prize for Physics was jointly awarded to Genzel and Ghez ‘for the
discovery of a supermassive compact object at the centre of our galaxy’. Our
fascination with black holes started, however, in the 18th century
with Pierre-Simon Laplace and John Michell. Using Newtonian physics, Laplace derived
1/2mv2 – (GMm)/r = 0 where the test particle’s total rest energy
equals 0 which forms r < (2GM)/c2 when
light is unable to reach infinity. Michell commented “from the motions of these
revolving bodies infer the existence of the central ones”. Guided by these
principles, Genzel and Ghez proved Laplace’s equation and found what could only
be a black hole in the Milky Way. 
Figure 1: Dusk at the Very Large Telescope operated by the European Southern Observatory on Cerro Paranal.
Genzel, from
the Max Plank Institute started work in the early 1990s and was soon followed
by Ghez from the University of California. Previously, quasar Q503C273 (a large
radiation source) had been detected from Sagittarius A* at the centre of our
galaxy by Maarten Schmidt in 1963 and became the focus of Genzel and Ghez’s
research. Genzel used the telescopes NTT and VLT (which has the world’s largest
monolithic mirrors) in Chile while Ghez used Keck Observatory, Hawaii with its
36 hexagonal segments – each segment controlled separately.
However, in
order to create accurate observations, atmospheric air bubbles and gas clouds
of varying densities and temperatures must be overcome. The variation of
density and temperature results in blurring and reduces the telescope’s
diffraction limit as they cause distortion on the light waves. The teams used
Speckle Imaging techniques by taking many short images with a sensitive
detector and aligning them, hence reducing the blur. Active and Adaptive Optics
were also used by measuring the light’s wavelength, calculating the amount of
shift and therefore the level distortion for which a correction can be applied
by adjusting the telescope’s mirrors. At the Keck Observatory, this correction
could be applied individually to each mirror segment – improving the overall
image.
In using Adaptive Optics, Genzel and Ghez were able to determine radial velocity as well as projected velocity of individual stars which allowed them to track the celestial bodies’ orbits. From their observations, it was noticed that stars within a radius of one light month didn’t have orderly orbits but stars outside this radius had uniform orbits. Stars closer to the centre also had faster velocities hence following Kepler’s Law and alluding to the presence of a high mass object at Sagittarius A*’s centre.
Star
SO2 displayed a disorderly orbit and with its short 16-year orbit, it became
the focus of teams’ observations. Einstein’s Theory of General Relativity
states gravity is the curvature due to objects with mass in space-time and so the
rate of change of an object’s orbit is different to that predicted by Newtonian
physics. Though already proven in weaker
gravitational fields by Mercury and the Sun, SO2 proved Einstein’s Theory held
in stronger gravitational fields – providing further 
Figure 2: a) Orbit of SO2. b) Graph showing velocity of SO2 during orbit.
SO2’s radial
velocity was also used to calculate the mass of the central body as suggested
by Laplace and Michell which was found to equal to 4 million solar masses. All
this evidence further supports the possibility of a black hole at the centre of
our galaxy.
The
interferometric techniques developed by Genzel and Ghez have been further
utilised by Roberto Abuter and his team in tracing the inner structure of
wind-wind interaction of η Car. η Car is a stellar system with at least two
stars but any other structural details of this system had remained
undiscovered. By using spectro-interferometric observations with the K-band (radio
wavelengths with frequencies between 18–27 GHz) beam combiner GRAVITY at VLTI,
He I emissions (producing Helium ion spectrums) could be tracked therefore
showing the cloud movement. The results were consistent with previous
hydrodynamical models and can be used to predict the formation of η Car. This
research was highlighted in the Scientific Background for the 2020 Nobel Physics
prize and I used the author’s name to search for the research on the University
of Leeds’ library catalogue. 
Figure 3: η
Car’s u−v coverages
References:
·
Press Release:
The Nobel Prize in Physics Press
release: The Nobel Prize in Physics 2020
Published: 06/10/2020
Date
Accessed: 26/05/2021
·
Popular science
background: Black holes and the Milky Way’s darkest secret The
Nobel Prize in Physics 2020: Popular science background
Published: 06/10/2020
Date
Accessed: 26/05/2021
·
Scientific
Background: Theoretical foundation for black holes and the supermassive compact
object at the galactic centre Scientific
Background on the Nobel Prize in Physics 2020
Published: 06/10/2020
Date
Accessed: 26/05/2021
·
Imaging Black
Holes Imaging
black holes: Physics Today: Vol 71, No 4 (scitation.org)
Published: 01/04/2018
Date Accessed:
29/05/2021
·
Nobel Prize in
Physics honors the discovery of a supermassive compact object at the heart of
the Milky Way Nobel
Prize in Physics honors the discovery of a supermassive compact object at the
heart of the Milky Way: Physics Today: Vol 73, No 12 (scitation.org)
Published: 01/12/2020
Date Accessed:
29/05/2021
·
Compact Objects
and Black Holes; 2020 Nobel Prize in Physics Compact
Objects and Black Holes | SpringerLink
Published: 30/12/2020
Date
Accessed: 07/06/2021
·
Milky Way’s black
hole provides long-sought test of Einstein’s general relativity Milky Way’s black
hole provides long-sought test of Einstein’s general relativity (nature.com)
Published: 26/07/2018
Date
Accessed: 28/06/2021
Research:
·
GRAVITY chromatic
imaging of η Car’s core GRAVITY
chromatic imaging of η Car’s core - Milliarcsecond resolution imaging of the
wind-wind collision zone (Brγ, He I) | Astronomy & Astrophysics (A&A)
(openathens.net)
Published: 23/10/2018
Date
Accessed: 11/06/2021
·
K-Band - Handbook of Terahertz Technology for Imaging,
Sensing and Communications (6.2 Motivation for terahertz wireless
communications) K-Band - an
overview | ScienceDirect Topics
Published: 2013
Date
Accessed: 21/06/2021
Images:
·
Figure 1: Dusk at
the Very Large Telescope operated by the European Southern Observatory on Cerro
Paranal (photo) Bridgeman
Education (openathens.net)
Date
Accessed: 17/06/2021
·
Figure 2: Nobel
Prize in Physics honors the discovery of a supermassive compact object at the
heart of the Milky Way. Figure 2. The star S2 follows an elliptical orbit
around Sagittarius A*. Nobel
Prize in Physics honors the discovery of a supermassive compact object at the
heart of the Milky Way: Physics Today: Vol 73, No 12 (scitation.org)
Date
Accessed: 17/06/2021
·
Figure 3: η Car’s
u−v coverages obtained during the GRAVITY runs in February 2016 (top panel) and
May-June 2017 (bottom panel). GRAVITY
chromatic imaging of η Car’s core - Milliarcsecond resolution imaging of the
wind-wind collision zone (Brγ, He I) | Astronomy & Astrophysics (A&A)
(openathens.net)
Date
Accessed: 17/06/2021
That was a great read! Very well researched with a clear understanding and passion for science and space!
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