Space gold is even rarer than Earth gold, which makes the precious metal special—on our planet and in the Universe at large.

A team of astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) observed a special gamma-ray burst last month; these powerful phenomena appear to originate in cataclysmic events… and in this case it was likely the collision of two neutron stars.

Neutron stars are the dense remains of imploded stars: they are up to three times the mass of the Sun, condensed into the area of San Francisco.

Deep in their cores, regular stars create elements that are eventually spewed into space when the stars explode. Chris Impey, professor of astronomy at the University of Arizona, explains, “We know that stars make heavy elements, and late in their lives, they eject gas into the medium between stars so it can be part of subsequent stars and planets (and people).” Carbon, oxygen, nitrogen, and a host of other elements—even nickel and iron—all originate within different types of stars.

But it takes a collision between two neutron stars to create rare elements such as gold. The lead author of a recent paper, Edo Berger, describes the phenomenon by paraphrasing one of Carl Sagan’s famous quotes, “We are all star stuff, and our jewelry is colliding-star stuff.” And it makes sense—gold requires 79 protons, 79 electrons and 118 neutrons, a concoction only a dense neutron star would have the atomic supplies to produce.

When two particular neutron stars collided about 3.9 billion light years away from Earth, astronomers named the resulting gamma-ray burst GRB 130603B. Although the burst lasted only two-tenths of a second, a slowly fading infrared glow told the Harvard research team that the burst was particularly valuable.

“We estimate that the amount of gold produced and ejected during the merger of the two neutron stars may be as large as 10 moon masses—quite a lot of bling!” says Berger.

At today’s prices, the explosion would produce the equivalent of  $10,000,000,000,000,000,000,000,000,000 (10 octillion dollars). But don’t get too excited: these types of explosions happen in our galaxy only once every 10,000 years, and you might find it difficult to go and collect the loot.

This is big money, but there are additional implications of the neutron star collision.

“We’ve been looking for a ‘smoking gun’ to link a short gamma-ray burst with a neutron star collision. The radioactive glow from GRB 130603B may be that smoking gun,” explains Wen-fai Fong, a graduate student and a co-author of the paper.

Now that we have better evidence linking gamma-ray bursts and neutron star collisions, perhaps we can gain insight into the mystery radio bursts found outside our galaxy!

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Credit: NASA/Dana Berry

Upon further examination, astronomers realized that Swift had witnessed its brightest x-ray source since beginning operations in 2005 – a sudden flood of radiation that measured 5 times larger than the brightest burst previously observed and 14 times brighter than the brightest-known continuous source of x-rays in the sky.  According to Phil Evans, PhD, who authored parts of Swift’s software, “It was like trying to use a rain gauge and a bucket to measure the flow rate of a tsunami.”

The source, dubbed GRB 100621A, was a gamma ray burst, a sudden eruption of the highest-energy form of radiation known, followed by longer-lasting  “afterglows” of x-rays and other forms of energy. Originally discovered in 1967 by military satellites designed to detect secret nuclear weapons tests, gamma ray bursts originate in far outside the Milky Way Galaxy and are believed to occur as massive stars collapse to form black holes.

How much energy does such an event release?  Well, June’s record-breaking burst occurred nearly halfway across the observable universe!

Currently, astronomers detect gamma ray bursts roughly twice per day somewhere in the sky. Within a galaxy the size of the Milky Way, astronomers estimate that one gamma ray burst may occur about every 100,000 to 1,000,000 years.  Studies suggest that if one took place close enough to Earth – within, say, 3,000 light years – its radiation could have catastrophic effects on the planet’s biosphere.  No evidence suggests that this has happened in the past, but who knows what the future holds?  Of course, we have (smaller, but) bigger things to worry about closer to home…

Image: NASA/Swift/Stefan Immler

Scientists thought that the gamma-rays outside our galaxy were jets emitted from the large black-holes found in the center of other, distant galaxies. But, data gathered with the Fermi telescope has indicated that this is wrong… Well, not entirely wrong, but about 70 percent wrong.

“Active galaxies can explain less than 30 percent of the extragalactic gamma-ray background Fermi sees,” said Marco Ajello, an astrophysicist at the Kavli Institute for Particle Astrophysics and Cosmology at Stanford. “That leaves a lot of room for scientific discovery as we puzzle out what else may be responsible.”

Ajello and the Fermi team analyzed data acquired by Fermi’s Large Area Telescope during the observatory’s initial year in space. The first challenge was eliminating emissions from our own galaxy.

“The extragalactic background is very faint, and it’s easily confused with the bright emission from the Milky Way,” said Markus Ackermann, another member of the Fermi team who led the measurement study. “We have done a very careful job in separating the two components to determine the background’s absolute level.”

These measurements, published online yesterday in the journal Physical Review Letters, demonstrate that active galaxies turn out to be only minor players in the gamma-ray sky.

What else may contribute to the extragalactic gamma-ray background? Particle acceleration in star-forming galaxies and merging galaxies, perhaps. Also, the ever-mysterious dark matter could be a source. According to Ajello, “Dark matter may be a type of as-yet-unknown subatomic particle. If that’s true, dark matter particles may interact with each other in a way that produces gamma rays.”

Improved analysis and continued observations will enable scientists to address these potential contributions. Meanwhile, Fermi will stay on the job, looking for more surprises in the gamma-ray sky.