{"id":100553,"date":"2017-10-23T12:00:48","date_gmt":"2017-10-23T11:00:48","guid":{"rendered":"https:\/\/www.transcend.org\/tms\/?p=100553"},"modified":"2017-10-17T16:15:21","modified_gmt":"2017-10-17T15:15:21","slug":"how-we-discovered-gravitational-waves-from-neutron-stars-and-why-its-such-a-huge-deal","status":"publish","type":"post","link":"https:\/\/www.transcend.org\/tms\/2017\/10\/how-we-discovered-gravitational-waves-from-neutron-stars-and-why-its-such-a-huge-deal\/","title":{"rendered":"How We Discovered Gravitational Waves from \u2018Neutron Stars\u2019 \u2013 And Why It\u2019s Such a Huge Deal"},"content":{"rendered":"
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Artist\u2019s illustration of two merging neutron stars.
National Science Foundation\/LIGO\/Sonoma State University\/A. Simonnet., CC BY-SA<\/p><\/div>\n

16 Oct 2017 – <\/em>Rumours have been swirling for weeks<\/a> that scientists have detected gravitational waves<\/a> \u2013 tiny ripples in space and time \u2013 from a source other than colliding black holes. Now we can finally confirm that we\u2019ve observed such waves produced by the violent collision of two massive, ultra-dense stars more than 100m light years from the Earth.<\/p>\n

The discovery was made on August 17 by the global network of advanced gravitational-wave interferometers<\/a> \u2013 comprising the twin LIGO detectors in the US and their European cousin, Virgo, in Italy. It is hugely important, not least because it helps solve some big mysteries in astrophysics \u2013 including the cause of bright flashes of light known as \u201cgamma ray bursts<\/a>\u201d and perhaps even the origins of heavy elements such as gold.<\/p>\n

As a member of the LIGO scientific collaboration, I was immediately in raptures as soon as I saw the initial data. And the period that followed was definitely the most intense and sleep deprived, but also incredibly exciting, two months of my career.<\/p>\n

The announcement comes just weeks after three scientists were awarded the Nobel Prize in Physics<\/a> for their foundational work leading to the discovery of gravitational waves, first announced in February 2016. Since then, detecting gravitational waves from colliding black holes has started to feel like familiar territory \u2013 with four further such events detected<\/a>. But as far as we know, colliding black holes offer purely a window on the dark side of the universe. We haven\u2019t been able to register light from these events with any other instruments.<\/p>\n

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LIGO Washington. Anthony Bolante<\/p><\/div>\n

But GW170817 \u2013 the catchy title for the event of August 17 \u2014 changes all that. That\u2019s because the source of the waves this time was two \u201cneutron stars<\/a>\u201d \u2013 incredibly dense stellar remnants the size of a city, each weighing more than the sun. These stars whizzed around each other at a sizeable fraction of the speed of light before merging in a cataclysmic collision that we\u2019ve now seen shake the very fabric of space and time.<\/p>\n

Mysteries solved<\/strong><\/p>\n

The cosmic concerto was just beginning, however. Astronomers have long suspected that the merger of two neutron stars could be the overture to a short gamma ray burst<\/a> \u2013 an intense flash of gamma-ray light that releases more energy in a fraction of a second than the sun will pump out in ten billion years. For several decades we have observed these gamma ray bursts, but without knowing for sure what causes them.<\/p>\n

However, just 1.7 seconds after the gravitational waves from GW170817 arrived at the Earth, NASA\u2019s Fermi satellite<\/a> observed a short burst of gamma rays in the same general region of the sky. LIGO and Virgo had found the smoking gun, and the link between neutron star collisions and short gamma ray bursts was finally and clearly established.<\/p>\n

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Many hands make light (and gravity) work. NASA\u2019s Fermi satellite was instrumental in the discovery. NASA<\/p><\/div>\n

The combination of gravitational-wave and gamma-ray observations allowed the position of the cosmic explosion to be pinpointed to less than 30 square degrees on the sky \u2013 or about 100 times the size of the full moon. This, in turn, allowed a whole barrage of astronomical telescopes sensitive to light across the entire electromagnetic spectrum to search this small patch of sky for the aftermath of the explosion. And sure enough this was found \u2013 in an unfashionable backwater towards the edge of a fairly unassuming galaxy called NGC4993<\/a>, in the constellation of Hydra.<\/p>\n

Over the next few days and weeks astronomers watched agog as the embers from the explosion glowed brightly and faded, beautifully matching the pattern expected for a so-called \u201ckilonova\u201d<\/a>. This is produced when material rich in subatomic particles known as neutrons from the initial merger is ejected at great speed by the gamma ray burst. This ploughs into the surrounding region of space, triggering the production of heavy radioactive elements.<\/p>\n

These unstable elements typically split up (decay) to a stable state by emitting radiation. This is what causes the glow of the kilonova, which we have now confirmed by mapping it out in exquisite detail. Our observations also strongly support the theory that the stable end-products of these chains of reactions include copious amounts of precious metals like gold and platinum. While we\u2019ve suspected neutron stars to be key to producing these elements in space<\/a>, that hypothesis now looks a whole lot more convincing. Indeed, the kilonova that formed from the embers of GW170817 could have produced as much gold as the entire mass of the Earth \u2013 that is 1,000 trillion tonnes.<\/p>\n

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What is a binary neutron star? @Martin_astro<\/a> tells us about one of the most bizarre objects in the universe. #GoldenBinary<\/a> pic.twitter.com\/AzHTReV8Z7<\/a><\/p>\n

— University of Glasgow (@UofGlasgow) October 16, 2017<\/a><\/p><\/blockquote>\n