C&B Notes

Titanic on a Different Scale

Late this summer, astronomers witnessed an incident that happened millions of years ago, but whose evidence just got to Earth.  The event, a “titanic collision” of two neutron stars (the densest things in the universe besides black holes) clarified a lot of open questions.

Progress, as they say, is slow.  In science, this is often true even for major breakthroughs; rarely is an entire field of research remade in a single swoop.  The Human Genome Project took a decade. Finding the first gravitational waves took multiple decades.  So it’s hard to overstate the enormous leap forward that astronomy took on Aug. 17, 2017.  On that day, astronomers bore witness to the titanic collision of two neutron stars, the densest things in the universe besides black holes. In the collision’s wake, astronomers answered multiple major questions that have dominated their field for a generation. They solved the origin of gamma-ray bursts, mysterious jets of hardcore radiation that could potentially roast Earth.  They glimpsed the forging of heavy metals, like gold and platinum.  They measured the rate at which the expansion of the universe is accelerating. They caught light at the same time as gravitational waves, confirmation that waves move at the speed of light.  And there was more, and there is much more yet to come from this discovery.  It all happened so quickly and revealed so much that astronomers are already facing a different type of question: Now what?

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The Aug. 17 gravitational wave gave astronomers a glimpse at an entirely different universe.  For most of history, they’ve studied stars and galaxies, which seem static and unchanging from the vantage point of human timescales.  “You can look at them today and look at them 10 years from now, and they will be the same,” Berger said.  But GW170817 revealed a universe alive, pulsating with creation and destruction on human timescales.  Think about that: GW170817 was a relatively close 130 million light years from Earth, meaning its gravitational waves and light were emitted while the first flowering plants were busy evolving on Earth, around the time stegosauruses roamed the plains.  But the event itself unfolded in less than three human-designated weeks.  This faster timescale is “pushing the way astronomy is done,” Berger said.

When the wave crashed through Earth, it caused a tiny shift in the path of laser beams traveling down long corridors in observatories called the Laser Interferometer Gravitational-Wave Observatory (LIGO), in the U.S., and the Virgo interferometer, in Italy.  On Aug. 17, LIGO’s twin detectors and Virgo each felt the wave, which allowed astronomers to roughly triangulate from which direction it rolled in.  They swung every bit of glass they had, both on Earth and in the heavens, in that general direction.  In space, the Fermi space telescope glimpsed a burst of gamma radiation. Within an hour, astronomers made six independent discoveries of a bright, fast-fading flash: A new phenomenon called a kilonova.  Astronomers saw the telltale sign of gold being forged, a major discovery by itself.  Nine days later, X-rays streamed in, and after 16 days, radio waves arrived, too.  Each type of information tells astronomers something different.  Richard O’Shaughnessy, an astronomer at the Rochester Institute of Technology, describes the discovery as a “Rosetta stone for astronomy.”  “What this has done is provide one event that unites all these different threads of astronomy at once,” he said.  “Like, all our dreams have come true, and they came true now.”



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