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Cosmic alchemy: Colliding neutron stars show us how the universe creates gold

Cosmic alchemy: Colliding neutron stars show us how the universe creates gold

Illustration of hot, dense, expanding cloud of debris stripped from the neutron stars just before they collided.
NASA’s Goddard Space Flight Center/CI Lab, CC BY

Duncan Brown, Syracuse University and Edo Berger, Harvard University

For thousands of years, humans have searched for a way to turn matter into gold. Ancient alchemists considered this precious metal to be the highest form of matter. As human knowledge advanced, the mystical aspects of alchemy gave way to the sciences we know today. And yet, with all our advances in science and technology, the origin story of gold remained unknown. Until now.

Finally, scientists know how the universe makes gold. Using our most advanced telescopes and detectors, we’ve seen it created in the cosmic fire of the two colliding stars first detected by LIGO via the gravitational wave they emitted.

The electromagnetic radiation captured from GW170817 now confirms that elements heavier than iron are synthesized in the aftermath of neutron star collisions.
Jennifer Johnson/SDSS, CC BY

Origins of our elements

Scientists have been able to piece together where many of the elements of the periodic table come from. The Big Bang created hydrogen, the lightest and most abundant element. As stars shine, they fuse hydrogen into heavier elements like carbon and oxygen, the elements of life. In their dying years, stars create the common metals – aluminum and iron – and blast them out into space in different types of supernova explosions.

For decades, scientists have theorized that these stellar explosions also explained the origin of the heaviest and most rare elements, like gold. But they were missing a piece of the story. It hinges on the object left behind by the death of a massive star: a neutron star. Neutron stars pack one-and-a-half times the mass of the sun into a ball only 10 miles across. A teaspoon of material from their surface would weigh 10 million tons.

Many stars in the universe are in binary systems – two stars bound by gravity and orbiting around each other (think Luke’s home planet’s suns in “Star Wars”). A pair of massive stars might eventually end their lives as a pair of neutron stars. The neutron stars orbit each other for hundreds of millions of years. But Einstein says that their dance cannot last forever. Eventually, they must collide.

Massive collision, detected multiple ways

On the morning of August 17, 2017, a ripple in space passed through our planet. It was detected by the LIGO and Virgo gravitational wave detectors. This cosmic disturbance came from a pair of city-sized neutron stars colliding at one third the speed of light. The energy of this collision surpassed any atom-smashing laboratory on Earth.

Hearing about the collision, astronomers around the world, including us, jumped into action. Telescopes large and small scanned the patch of sky where the gravitational waves came from. Twelve hours later, three telescopes caught sight of a brand new star – called a kilonova – in a galaxy called NGC 4993, about 130 million light years from Earth.

Astronomers had captured the light from the cosmic fire of the colliding neutron stars. It was time to point the world’s biggest and best telescopes toward the new star to see the visible and infrared light from the collision’s aftermath. In Chile, the Gemini telescope swerved its large 26-foot mirror to the kilonova. NASA steered the Hubble to the same location.

Movie of the visible light from the kilonova fading away in the galaxy NGC 4993, 130 million light years away from Earth.

Just like the embers of an intense campfire grow cold and dim, the afterglow of this cosmic fire quickly faded away. Within days the visible light faded away, leaving behind a warm infrared glow, which eventually disappeared as well.

Observing the universe forging gold

But in this fading light was encoded the answer to the age-old question of how gold is made.

Shine sunlight through a prism and you will see our sun’s spectrum – the colors of the rainbow spread from short wavelength blue light to long wavelength red light. This spectrum contains the fingerprints of the elements bound up and forged in the sun. Each element is marked by a unique fingerprint of lines in the spectrum, reflecting the different atomic structure.

The spectrum of the kilonova contained the fingerprints of the heaviest elements in the universe. Its light carried the telltale signature of the neutron-star material decaying into platinum, gold and other so-called “r-process” elements.

Visible and infrared spectrum of the kilonova. The broad peaks and valleys in the spectrum are the fingerprints of heavy element creation.
Matt Nicholl, CC BY

For the first time, humans had seen alchemy in action, the universe turning matter into gold. And not just a small amount: This one collision created at least 10 Earths’ worth of gold. You might be wearing some gold or platinum jewelry right now. Take a look at it. That metal was created in the atomic fire of a neutron star collision in our own galaxy billions of years ago – a collision just like the one seen on August 17.

And what of the gold produced in this collision? It will be blown out into the cosmos and mixed with dust and gas from its host galaxy. Perhaps one day it will form part of a new planet whose inhabitants will embark on a millennia-long quest to understand its origin.The Conversation

Duncan Brown, Professor of Physics, Syracuse University and Edo Berger, Professor of Astronomy, Harvard University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The post Cosmic alchemy: Colliding neutron stars show us how the universe creates gold appeared first on Interalia Magazine.

We’ve discovered the world’s largest drum – and it’s in space

We’ve discovered the world’s largest drum – and it’s in space

The Earth’s magnetosphere bangs like a drum.
E. Masongsong/UCLA, M. Archer/QMUL, H. Hietala/UTU

Martin Archer, Queen Mary University of London

Universities in the US have long wrangled over who owns the world’s largest drum. Unsubstantiated claims to the title have included the “Purdue Big Bass Drum” and “Big Bertha”, which interestingly was named after the German World War I cannon and ended up becoming radioactive during the Manhattan Project.

Unfortunately for the Americans, however, the Guinness Book of World Records says a traditional Korean “CheonGo” drum holds the true title. This is over 5.5 metres in diameter, some six metres tall and weighs over seven tonnes. But my latest scientific results, just published in Nature Communications, have blown all of the contenders away. That’s because the world’s largest drum is actually several tens of times larger than our planet – and it exists in space.

You may think this is nonsense. But the magnetic field (magnetosphere) that surrounds the Earth, protecting us by diverting the solar wind around the planet, is a gigantic and complicated musical instrument. We’ve known for 50 years or so that weak magnetic types of sound waves can bounce around and resonate within this environment, forming well defined notes in exactly the same way wind and stringed instruments do. But these notes form at frequencies tens of thousands of times lower than we can hear with our ears. And this drum-like instrument within our magnetosphere has long eluded us – until now.

Massive magnetic membrane

The key feature of a drum is its surface – technically referred to as a membrane (drums are also known as membranophones). When you hit this surface, ripples can spread across it and get reflected back at the fixed edges. The original and reflected waves can interfere by reinforcing or cancelling each other out. This leads to “standing wave patterns”, in which specific points appear to be standing still while others vibrate back and forth. The specific patterns and their associated frequencies are determined entirely by the shape of the drum’s surface. In fact, the question “Can one hear the shape of a drum?” has intrigued mathematicians from the 1960s until today.

The outer boundary of Earth’s magnetosphere, known as the magnetopause, behaves very much like an elastic membrane. It grows or shrinks depending on the varying strength of the solar wind, and these changes often trigger ripples or surface waves to spread out across the boundary. While scientists have often focused on how these waves travel down the sides of the magnetosphere, they should also travel towards the magnetic poles.

Physicists often take complicated problems and simplify them considerably to gain insight. This approach helped theorists 45 years ago first demonstrate that these surface waves might indeed get reflected back, making the magnetosphere vibrate just like a drum. But it wasn’t clear whether removing some of the simplifications in the theory might stop the drum from being possible.

It also turned out to be very difficult to find compelling observational evidence for this theory from satellite data. In space physics, unlike say astronomy, we’re usually dealing with the completely invisible. We can’t just take a picture of what’s going on everywhere, we have to send satellites out and measure it. But that means we only know what’s happening in the locations where there are satellites. The conundrum is often whether the satellites are in the right place at the right time to find what you’re looking for.

Over the past few years, my colleagues and I have been further developing the theory of this magnetic drum to give us testable signatures to search for in our data. We were able to come up with some strict criteria that we thought could provide evidence for these oscillations. It basically meant that we needed at least four satellites all in a row near the magnetopause.

Thankfully, NASA’s THEMIS mission gave us not four but five satellites to play with. All we had to do was find the right driving event, equivalent to the drum stick hitting the drum, and measure how the surface moved in response and what sounds it created. The event in question was a jet of high speed particles impulsively slamming into the magnetopause. Once we had that, everything fell into place almost perfectly. We have even recreated what the drum actually sounds like (see the video above).

This research really goes to show how tricky science can be in reality. Something which sounds relatively straightforward has taken us 45 years to demonstrate. And this journey is far from over, there’s plenty more work to do in order to find out how often these drum-like vibrations occur (both here at Earth and potentially at other planets, too) and what their consequences on our space environment are.

This will ultimately help us unravel what kind of rhythm the magnetosphere produces over time. As a former DJ, I can’t wait – I love a good beat.The Conversation

Martin Archer, Space Plasma Physicist, Queen Mary University of London

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The post We’ve discovered the world’s largest drum – and it’s in space appeared first on Interalia Magazine.