RIPPLES IN SPACE TIME
Gravitational Wave
Introduction:
Gravitational waves are propagating
fluctuations of gravitational fields, that is, “ripples” in space-time
generated mainly by moving massive bodies. This distortion of space-time travel
with the speed of light. Gravitational waves can be detected by devices which
measure the induced length changes. The frequencies and the amplitudes of the
waves are related to the motion of the masses involved. Thus the analysis of
the gravitational waveforms allows us to learn about their source and, if there
are more than two detectors involved in observation, to estimate the distance
and position of their source and the sky.
Here space-time is any mathematical model that
fuses the 3-dimensions of space and the one dimension of time in to a single
four dimensional continuum. Space-time diagram is useful in visualizing and
understanding relativistic effects such as how different observes perceive
where and when events occur.
The idea of space-time continuum comes from the ground-breaking work of ‘Albert-Einstein’. One way of envisioning the space-time continuum is to think of a large piece of fabric, such as a sheet. Einstein realized that objects with mass, such as a person or planet earth, create wrinkles in space-time, which creates a dimple in a sheet. Einstein identified the curves in a space-time as ‘Gravity’ but he thought they would be too small to detect.
In February 2016 the direct measurement of gravitational waves are announced. This provides us with a new method for exploring the universe.
From Prediction to Reality: A history of the search
for gravitational waves
1915 -Albert Einstein publishes general theory of
relativity, explains gravity as the warping of space-time by mass or energy.
1916 -Einstein predicts massive objects whirling in certain
ways will cause space-time ripples—gravitational waves.
1936 -Einstein has second thoughts and argues in a
manuscript that the waves don't exist—until reviewer points out a mistake.
1962 -Russian physicists M. E. Gertsenshtein and V. I.
Pustovoit publish paper sketch optical method for detecting gravitational
waves—to no notice.
1969 -Physicist Joseph Weber claims gravitational wave detection
using massive aluminum cylinders—replication efforts fail.
1972 -Rainer Weiss of the Massachusetts Institute of
Technology (MIT) in Cambridge independently proposes optical method for
detecting waves.
1974-Astronomers discover pulsar orbiting a neutron star
that appears to be slowing down due to gravitational radiation—work that later
earns them a Nobel Prize.
1979 -National Science Foundation (NSF) funds California
Institute of Technology in Pasadena and MIT to develop design for LIGO.
1990 -NSF agrees to fund $250 million LIGO experiment.
1992 -Sites in Washington and Louisiana selected for LIGO
facilities; construction starts 2 years later.
1995 -Construction starts on GEO600 gravitational wave
detector in Germany, which partners with LIGO and starts taking data in 2002.
1996 -Construction starts on VIRGO gravitational wave
detector in Italy, which starts taking data in 2007.
2002–2010 -Runs of initial LIGO—no detection of gravitational
waves.
2007 -LIGO and VIRGO teams agree to share data, forming a
single global network of gravitational wave detectors.
2010–2015 -$205 million upgrade of LIGO detectors.
2015 -Advanced LIGO begins initial detection runs in
September
2016 -On 11 February, NSF and LIGO team announce successful
detection of gravitational waves.
Who has received the 2017
Nobel Prize for Physics?
The prize is shared by Rainer Weiss,
Barry Barish and Kip Thorne “for decisive contribution to the LIGO detector and
discovery of gravitational waves.”
Dr. Weiss- has born in Berlin and now
a U.S. citizen- receives half the prize. The remaining half is shared equally
by two Caltech scientists- Dr. Barish, Prof. of Physics and Dr. Thorne, Prof., Theoretical Physics.
WHAT DID THEY DISCOVER?
They are receiving the prize for the
discovery of the gravitational waves released by violent events in the universe
such as the mergers of black holes. First time this was detected on September 14th,
2015, by the LIGO-VIRGO collaboration. Since then three more detections have
been made, the last one on September 28th, 2017.
WHY DO GRAVITATIONAL WAVES MATTER TO
US?
The discovery is due to an extremely
delicate experiment. Gravitational waves were predicted by Einstein almost
hundred years ago. After about 50 years of experimentation the waves were
detected for the first time on September 2015.
The discovery and the repeated
detection have made the possibility of gravitational wave astronomy very real.
Gravitational wave astronomy is a way of mapping out some of the most violent
processes in the universe such as black hole or neutron star mergers that
cannot be detected with light or the conventional methods.
The discovery can prove the way of
proving the general theory of relativity, so that we can look deeper and deeper
in to the universe. It also throws up the possibility of detectors that can
look at the begging of the universe.
Gravity is the weakest of the four
fundamental forces so only the most extreme events Black holes colliding,
Neutron star twirling and Supernova erupting produce detectable waves.
BLACK HOLE COLLIDING:
It is possible for two black holes to
collide. Once they come so close that they cannot escape each other’s gravity,
they will merger to become one bigger black hole. Such an event would be
extremely violent. Black hole merger would produce tremendous energy and send
massive ripples through the space time fabric of the universe. The ripples are
called gravitational waves.
Neutron star twirling:
Neutron stars, the densest objects
in the universe, can rotate up to several hundred times per second. If the star
has properly spherical shape then it won’t emit gravitational waves as it
spins. Only if the surface is bumpy, the spinning asymmetry would generate
gravitational waves.
Supernova erupting:
The
gravitational waves are emitted from deep inside the core of the star where no
electromagnetic radiation can escape. This allows a gravitational wave
detection to tell us information about the explosion mechanism that cannot be
determined with other methods.
The
gravitational waves that are detectible by LIGO will be caused by some of the
most energetic events in the universe-colliding black holes, exploding stars,
and even the birth of the universe itself. Detecting and analyzing the
information carried by gravitational waves will allow us to observe the
universe in a way never before possible. It will open up a new window of study
on the universe.
LIGO:
LIGO is the world's largest
gravitational wave observatory and a cutting edge physics experiment.
Comprising two enormous laser interferometers located thousands of kilometers
apart, LIGO exploits the physical properties of light and of space itself to
detect and understand the origins of gravitational waves.
Although LIGO will search for
gravitational waves from space, and it is called an "Observatory",
LIGO is not, strictly speaking, intended to be solely an astronomical facility.
LIGO is truly a physics experiment on the scale and complexity of some of the
world's giant particle accelerators and nuclear physics laboratories. Though
its mission is to detect gravitational waves from some of the most violent and
energetic processes in the Universe, the data it will collect will have
far-reaching effects on many areas of physics including gravitation,
relativity, astrophysics, cosmology, particle physics, and nuclear physics.
Three things truly distinguish LIGO
from an astronomical observatory:
First, LIGO is blind. Unlike optical or radio
telescopes, LIGO cannot see electromagnetic radiation (e.g., visible light,
radio waves, and microwaves) nor does it have to because gravitational waves
are not part
of the electromagnetic spectrum
Second, LIGO is the opposite of
round. Since LIGO
doesn’t need to collect light from stars or other objects in the Universe, it
doesn't need to be dish-shaped like telescope mirrors or radio dishes, which
collect and focus electromagnetic radiation to produce images
Third,
LIGO cannot function alone. While an
astronomical observatory can function and collect data just fine on its own
(some do not, by choice), gravitational wave observatories like LIGO cannot operate solo. The only
way to definitively detect a gravitational wave is by operating in unison with
a distant twin so that local vibrations are not mistaken for signals from
gravitational waves.
How LIGO Works:
LIGO
is the world's largest gravitational wave observatory. It consists of two
detectors situated 1,865 miles (3,002 kilometers) apart in isolated regions in
the states of Washington and Louisiana. Each L-shaped facility has two arms
positioned at right angles to each other and running 2.5 miles (4 kilometers)
from a central building. Lasers are beamed down each arm and bounced back by
mirrors, essentially acting as a ruler for the arm. Sensitive detectors can
tell if the length of the arms of a LIGO detector varies by as little as
1/10,000 the width of a proton, representing the incredibly small scale of the
effects imparted by passing gravitational waves. LIGO has two observatories to
act as a check on the other to rule out that potential gravitational-wave
signal detection is not due to a local, terrestrial disturbance; both
facilities will detect a true gravitational wave moving at the speed of light
nearly simultaneously. Although the twin LIGO facilities act as a single
observatory, they are not designed for "observing" in the
conventional sense. Instead of eyes, the facilities can be thought more of as
"ears" listening for gravitational waves, or even as a skin trying to
"feel" the slightest of movements.
Advanced LIGO (aLIGO):
The
initial technology deployed for LIGO was sensitive to movement of 1/1000 the
diameter of a proton, but with an upgrade begun in the 2010s, LIGO's
sensitivity was boosted 10-fold. The many enhancements included increasing the
power of the lasers from 10 watts to 200 watts and mirror seismic isolation
technology improvements. Overall, aLIGO will be able to detect possible
gravitational wave-producing events three times farther away than the initial
LIGO setup. Accordingly, a far larger volume of space will now be within
"earshot" of the LIGO project, with the opportunity to catch far more
potential sources of space-time ripple.
The
overall performance of Advanced LIGO is dominated at most frequencies by the
quantum noise of sensing the position of the test masses, with a contribution
at mid-frequencies from the internal thermal noise of the test masses. This
design, with modest enhancements after it enters scientific use, should take
this interferometer architecture to its technical endpoint; it is as sensitive
as one can make an interferometer based on familiar technology: a Fabry-Perot
Michelson configuration with external optical readout using room temperature
transmissive optics. Further advances will come from R&D that is just
beginning, such as the exploration of cryogenic optics and suspensions, purely
reflective optics, and a change in the readout to one which fully exploits our
understanding of the quantum nature of the measurement (e.g., quantum
non-demolition speed meters). These later developments will be timely for
instruments to be developed in the second decade of this century.
Collected By:
Prajna
Preethi Salyan K S
Rachana K
Rashmitha H
Source:
Internet
