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That morning in August 2017, Fermi’s GBM detected a brief but bright flash of gamma rays and alerted astronomers on Earth. Barely 1.7 seconds earlier, detectors called LIGO and Virgo had felt the almost imperceptible tug of gravitational waves pass through. Fermi, LIGO and Virgo alerted astronomers around the world, who then commissioned visible light telescopes, X-ray satellites and radio networks. In concert, they confirmed that the signals were all coming from the same event. After further analysis, the researchers got a solid picture of what happened: The gravitational ripples and the full spectrum of light came from a collision long ago between two ultra-dense stellar remnants called stars at neutrons. By finding this gamma-ray burst, Fermi had connected these gravity signals, a new type of messenger carrying information about celestial objects, to different types of light. If gravitational waves are a new window on the universe, Fermi provided the plans; it showed the context of how this window connects to what we know.
Starting in his 10th year of service, Fermi became “the premier space observatory for multi-messenger science,” says Adam Goldstein, Fermi scientist. In fact, it has become essential. There is no replacement planned at NASA; only smaller, short-lived missions that will assume parts of Fermi’s watch as a crucial counterpart to ground-based gravitational wave detectors.
Shortly after the 2017 discovery, then-Fermi Project scientist Julie McEnery said: “What we’re really seeing is a whole new era for Fermi.” This era could last for years; Fermi runs on solar energy, so as long as its panels keep collecting light and its positioning readers remain healthy, it will continue to reveal the gamma sky.
This is what we must hope, because no other telescope does what Fermi does. It bridges the gap between light (from stars that we have known since childhood) and gravitational waves, this new type of messenger. Fermi has shown us – showed me – so much about our sensational, exciting and ever-changing cosmos. It changed my way of seeing the universe.
Liz kruesi is a freelance science journalist specializing in cosmology and astronomy, with a penchant for the high energy universe.
This essay has been adapted for the June 2021 issue of National Geographic magazine from nationalgeographic.com’s Dear Spacecraft series, in which we ask writers, scientists and astronomy enthusiasts to share why they feel personally connected to robotic space explorers. . Read the original story here.
