You've probably read or heard about the latest breakthrough in gravitational-wave astronomy--the first detection to two neutron stars merging, with the added bonus of the first follow-on observations of the event across the entire electromagnetic spectrum from gamma rays to radio waves.
Artist's conception of neutron stars merging
Credit: NASA
With three gravitational-wave observatories online (see LIGO and VIRGO), observers were able to accurately triangulate the most recent burst of gravitational waves that rumbled past Earth on August 17. With a much smaller part of the sky to scan, astronomers were able to pin down the source of the event--the merger of two neutron stars in a distant galaxy producing a kilonova--and track its evolution through observations in gamma-rays, x-rays, visible light, infrared and radio waves.
This unprecedented series of observations let astronomers compare the neutron-star merger to theoretical predictions in great detail, including proving that most of the elements heavier than iron--including gold, platinum and uranium-are forged in these collisions. They also provided new information about the accelerating expansion of the universe. In addition, it demonstates that astronomers now have a huge new window into the universe that promises a stream of surprises and new discoveries.
For great pictures, animations and a more in-depth description of this breakthrough and its implications, click here.
Researchers at LIGO, the Laser Interferometry Gravitational-Wave Observatory, announced today their third detection of space-time vibrations from the collision of of a pair of black holes, in this case nearly three billion light-years from Earth.
In terms of mass, this new black hole merger--which created a black hole with a mass 49 times heavier than our Sun--fell neatly between the two earlier detections, in September and December of 2015. Those two cosmic crashes resulted in black holes with 62 and 21 times the Sun's mass respectively, and took place much closer to Earth.
The current crash was between black holes with estimated masses of 31.2 and 19.4 times that of the Sun. That means that a mass equal to two Suns was converted into gravitational waves in a fraction of a second as the two black holes completed their death spiral.
Simulated black-hole merger
Credit: LIGO Lab Caltech
This third detection tells the scientists that the unique new window on the cosmos provided by gravitational-wave detectors is now wide open. With improved sensitivity of LIGO's existing laser interferometers and the addition later this year of a third detector, called Virgo, the researchers hope to be able to detect black hole mergers and other space-time-shaking events on a daily basis.
Aerial view of the Virgo interferometer near Pisa, Italy Credit: The Virgo Consortium
Besides further proof of the existence of black holes in this mass range, the detection allowed researchers to test one of the predictions of Einstein's General Relativity--that gravitational waves travel through space at the same speed regardless of their frequency. Once again, General Relativity passed the test.
“It is remarkable that humans can put together a story, and test it, for such strange and extreme events that took place billions of years ago and billions of light-years distant from us," says MIT's David Shoemaker, LIGO's spokesperson.
The number of black holes in this mass range raises the intriguing possibility that they may at least partly explain dark matter, which is known to exist because of its gravitational effects on galaxies and galaxy clusters, but whose nature remains mysterious.
"There's this intriguing indication that with the size of black holes, 10-100 solar masses, in about the
quantity that we see them or expect to see them, might account for
dark matter," says LIGO researcher Mike Landry. "It's not
impossible."
For the first time, researchers were able to suss out information about how the black holes were spinning before they collided. It's more likely than not that the black holes were not spinning in the same plane as their orbit. That, in turn, implies that they may have formed far apart and only later fell into each other's gravitational thrall.
As gravitational-wave astronomers detect more of these incredibly powerful cosmic events, and gain the ability to match them with observations using visible light, infrared, X-rays and gamma rays, astrophysicists, nuclear physicists and cosmologists all expect exciting new findings that will cast light on black holes, neutron stars, dark matter and the nature of space-time itself.
It
took a century. In 1916, Albert Einstein predicted the existence of
gravitational waves – ripples in the fabric of spacetime. Today, a
worldwide consortium of researchers announced the first detection of this fundamental phenomenon, confirmed through
measurements made by two exquisitely sensitive instruments in
Louisiana and Washington.
"Einstein would be beaming, wouldn't he," said Gabriela Gonzalez, spokesperson for the LIGO consortium.
This epochal discovery not only demonstrates the phenomenal power and reach of Einstein's General Theory of Relativity,
it also opens up a whole new way of studying the universe,
something we'll be hearing much more about -- gravitational astronomy.
"We
have detected gravitational waves. We did it!” said David Reitze,
Executive Director of the LIGO Laboratory. "Four hundred years ago, Galileo turned a telescope to the sky and
opened the era of observational astronomy. We're opening a new window
on the universe, gravitational astronomy.”
The
crucial observation took place on September 14, 2015, when the two
huge detectors of LIGO, the Laser Interferometer Gravitational Wave
Observatory, one in Hanford, Washington, the other in Livingston,
Louisiana
simultaneously recorded ripples in spacetime that increased in frequency and
intensity and then subsided over the course of one-fifth of a second. Those waves precisely matched what
Einstein's equations of general relativity predict for the final moments of the death
spiral and merger of two black holes.
First spacetime "seismogram," tracing the death spiral and merger of two black holes
You can view a simulation of two black holes merging at this URL.
“These waves were
produced by two colliding black holes about 1.3 billion years ago,
and detected by LIGO, the most precise measuring device ever built," said Reitze.
The LIGO interferometer in Hanford, Washington. Each leg is 4 km (2.5 miles) long
Researchers tell us that during the last moments of the black hole merger, the amount of power roiling spacetime was greater than all the light being emitted by all the stars in the observable universe. Even though the energy released by the merger was enormous -- as much as if the mass of three suns were converted into energy in a fraction of a second -- by the time the signal reached Earth, it was incredibly faint, distorting the 4-kilometer long arms of the LIGO detector by just one thousandth the width of an atomic nucleus. It took 40 years of research and engineering to build detectors able to measure such miniscule spacetime distortions.
"Each of these black holes are about
150 km in diameter," said Reitze. "Pack thirty times the mass of the sun in that.
Accelerate it to half the speed of light. Then take another like
that and collide them together. That's what we saw here. It's mind
boggling."
The researchers who announced the discovery said that this was the dawn of a new era in astronomy and our understanding of the cosmos. Since gravitational waves have been roiling space since the Big Bang, Advanced LIGO and its successors may allow scientists to listen in on the earliest moments of the the birth of the cosmos. They will also open a window on the strangest and most violent events in the universe, such as the merger of two neutron stars, and help researchers to home in on the mysterious dark energy that is speeding up the expansion of the universe.
"LIGO is a fantastic beginning," said Kip Thorne, one of LIGO's co-founders. "It has opened a new window on the
universe. Every time a new window
has been opened up there have been surprises. Gravitational waves are so
radically different [from light and other electromagnetic radiation] that we will see big surprises, perhaps even bigger than we've seen through the radio and x-ray windows."
Remarkably, the frequency of the "chirp" produced by the merging black holes lies in the range of human hearing. You can hear it yourself here. If you listen carefully, you can hear the gravitational-wave signal getting both louder and higher, exactly as predicted as two colliding black holes rock the surrounding spacetime just before merging into one.
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