Scientists glimpse first direct proof of Einstein’s gravitational waves
In a landmark discovery for physics and astronomy,
international scientists said on Thursday they have glimpsed the first direct
evidence of gravitational waves, or ripples in space-time, which Albert
Einstein predicted a century ago. When two black holes collided some 1.3 billion years ago,
the joining of those two great masses sent forth a wobble that hurtled through
space and arrived at Earth on September 14, 2015, when it was picked up by
sophisticated instruments, researchers announced.
“Like Galileo first pointing his telescope upward, this new
view of the sky will deepen our understanding of the cosmos, and lead to
unexpected discoveries,” said France Cordova, director of the US National
Science Foundation, which funded the work. The phenomenon was observed by two US-based underground
detectors, designed to spot tiny vibrations from passing gravitational waves, a
project known as the Laser Interferometer Gravitational-wave Observatory, or
LIGO.
It took scientists months to verify their data and put it
through a process of peer-review before announcing it on Thursday, marking the
culmination of decades of efforts by teams around the world. “LIGO has ushered in the birth of an entirely new field of
astrophysics,” said Cordova. Gravitational waves are a measure of strain in space, an
effect of the motion of large masses that stretches the fabric of space-time --
a way of viewing space and time as a single, interweaved continuum. They travel at the speed of light and cannot be stopped or
blocked by anything.
Einstein said space-time could be compared to a net, bowing
under the weight of an object. Gravitational waves would be like ripples that
emanate from a pebble thrown in a pond. While scientists have previously been able to calculate
gravitational waves, they had never before seen one directly.
Wobbling like jelly
According to the Massachusetts Institute of Technology’s
(MIT) David Shoemaker, the leader of the LIGO team, it looked just like
physicists thought it would. “The waveform that we can calculate based on Einstein’s
theory of 1916 matches exactly what we observed in 2015,” David Shoemaker, the
leader of the LIGO team, told AFP. “It looked like a chirp, it looked at something that started
at low frequencies -- for us low frequencies means 20 or 30 hertz, that’s like
the lowest note on a bass guitar, sweeping very rapidly up over just a fraction
of a second... up to 150 hertz or so, sort of near middle C on a piano.”
The chirp “corresponded to the orbit of these two black
holes getting smaller and smaller, and the speed of the two objects going
faster and faster until the two became a single object,” he explained. “And then right at the end of this waveform, we see the
wobbling of the final black hole as if it were made of jelly as it settled into
a static state.”
Underground detectors
The L-shaped LIGO detectors -- each about 1.5 kilometers
(four kilometers) long -- were conceived and built by researchers at MIT and
Caltech. One is located in Hanford, Washington, and the other is in
Livingston, Louisiana. A third detector, called VIRGO, is scheduled to open in
Italy later this year. Tuck Stebbins, head of the gravitational astrophysics
laboratory at NASA’s Goddard Spaceflight Center, described the detectors as the
“most complex machines humans have ever built.”
Both LIGO and VIRGO have undergone major upgrades in recent
years. Physicist Benoit Mours of France’s National Center for
Scientific Research (CNRS), which is leading the VIRGO team along with Italian
colleagues, described the discovery as “historic” because it “allows us to
directly verify one of the predictions of the theory of general relativity.”
Physicists said the gravitational wave detected at 1651GMT
on September 14 originated in the last fraction of a second before the fusion
of two black holes somewhere in the southern sky, though they can’t say
precisely where. Einstein had predicted such a phenomenon would occur when
two black holes collided, but it had never before been observed.
An analysis by the MIT and Caltech found that the two black
holes joined about 1.3 billion years ago, and their mass was 29-36 times
greater than the Sun. The wave arrived first at the Louisiana detector, then at
the Washington instrument 7.1 milliseconds later. The two instruments are 1,800 miles (3,000 kilometers)
apart, and since both made the same reading, scientists consider their
discovery confirmed.
‘New era ‘
“Black holes are interesting because they do not give off
any light and that is why these particular objects had never been seen before
-- because all of the astrophysical instruments to date use light,” said
Shoemaker. “So this is one of the ways in which this tool is special
and unique in the astronomical toolkit.” He said the new data “can really help to explain the
formation of galaxies and overall large scale structures of the material in the
universe.”
Details of the discovery are being published in the journal
Physical Review Letters. Indirect proof of gravitational waves was found in 1974
through the study of a pulsar and a neutron star. Scientists Russell Hulse and
Joseph Taylor won the Nobel Prize for physics for that work in 1993. “Humanity has now another tool for exploring the universe,”
Stebbins told AFP. “This is like the perfect outcome. The door is open to new
discoveries,” he added. “This is a new era in astrophysics.”
