For weeks, rumors swirled that scientists had detected gravitational waves - tiny ripples in space and time - of a new type not associated with colliding black holes. And now we have received the final confirmation that we saw similar waves produced by the violent collision of two massive superdense stars 100 million light-years from Earth.
The discovery was made on August 17 by a global network of advanced gravitational-wave interferometers consisting of two LIGO detectors in the United States and their European cousin Virgo in Italy. The discovery is extremely important, not least because it helps solve some of the biggest mysteries in astrophysics - including the cause of the bright flares known as "gamma ray bursts" and perhaps even the origin of heavy elements such as gold.
Next - in the first person: Martin Hendry, professor of gravitational astronomy and cosmology at the University of Glasgow.
As a member of the LIGO research collaboration, I was delighted as soon as I saw the raw data. The next period was definitely the most intense and sleepless, but also exciting, in two months of my career.
The announcement comes a few weeks after three scientists were awarded the Nobel Prize in Physics for their important work that led to the discovery of gravitational waves, first announced in February 2016. Since then, detecting gravitational waves from colliding black holes has been getting closer to us - four more similar events have been recorded. But as far as we know, the collision of black holes only opens a window to the dark side of the universe. We could not capture the light from such events with any instruments.
But GW170817 - the title of the August 17 event - changed everything. Because the source of the waves this time were two "neutron stars" - incredibly dense remnants of stars the size of a city, each weighing more than the sun. These stars rush around one another at gigantic speed, and then merge in a terrible collision, which we saw, stunning the very fabric of space and time.
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That space concert was just the beginning. Astronomers have long suspected that the merger of two neutron stars could be an overture for a short gamma ray burst - a powerful burst of gamma rays that emit more energy in a fraction of a second than the sun does in ten billion years. We've been observing gamma rays for decades, but we didn't know what caused them.
However, just 1.7 seconds after gravitational waves from GW170817 arrived on Earth, NASA's Fermi satellite detected a short burst of gamma rays in the same region of the sky. LIGO and Virgo found a smoking gun, and the link between neutron star collisions and short bursts of gamma rays was finally established.
A combination of gravitational-wave and gamma-ray observations made it possible to determine the position of the cosmic explosion with an accuracy of up to 30 square degrees of the sky - or 100 times larger than the full moon. This, in turn, allowed an entire battery of astronomical telescopes, sensitive to light from the entire electromagnetic spectrum, to search this small area of the sky for the afterglow of the explosion. And they found it - in the back of the rather modest galaxy NGC4993, in the constellation Hydra.
In the following days and weeks, astronomers watched the agony, while the embers from the explosion flashed and went out, beautifully merging into a picture describing the so-called "kilon". It is born when material rich in subatomic particles - neutrons - from the original fusion is ejected at high speed by a gamma ray burst. All this is thrown into the surrounding space and leads to the production of heavy radioactive elements.
The unstable elements then decay to a stable state with radiation emission. This leads to the glow of the kilonova, which we confirmed by drawing up a detailed map. Our observations also supported the theory that the stable end products of these reaction chains include an abundance of precious metals such as gold and platinum. While we suspected that neutron stars played a key role in creating these elements in space, this hypothesis now seems much more compelling. Indeed, the kilonova, which formed from the debris of GW170817, could produce gold as large as the entire Earth - 1000 trillion tons.
By observing the kilonova “intimate” for the first time, and seeing how well it fits into the unfolding astronomical storyboard that began with the merging of a neutron star, astronomers have made a huge leap towards understanding these brutal cosmic events.
The idea that we are all made of stardust is incredibly popular in the cultural consciousness - everywhere, from documentaries to song lyrics. But the mind-boggling concept that the gold in our wedding rings and Rolex watches is made from neutron stardust is even more interesting. Even more exciting is the enormous potential that is opening up in radical new approaches to space exploration.
Working together - using instruments that not only work across the entire spectrum of light, but are also sensitive to gravitational waves and even neutrinos - astronomers are poised to open up a completely new window into the universe. For example, they have already used their observations to make the first joint measurement of the expansion rate of the universe using both gravitational waves and light.
New results will follow shortly. With this explosion, a new and exciting era of multiplayer astronomy is just beginning.
Ilya Khel
