On Nov. 20, 2004, NASA’s Neil Gehrels Swift Observatory took to the skies aboard a Delta 7320 rocket and entered orbit around Earth. The satellite was on the hunt to uncover the mystery of gamma-ray bursts, the universe’s most powerful explosions.
“Fifteen years since its launch, Swift continues to observe some of the most exciting events in the cosmos,” said Paul Hertz, director of the Astrophysics Division at NASA Headquarters in Washington. “Neil Gehrels’ vision for the mission is being realized every day, and I look forward to many more years of exceptional science from this versatile spacecraft.”
Gamma rays, the most energetic form of light, are associated with dynamic events such as merging neutron stars and some types of supernovae — the explosive deaths of stars. The duration of a gamma-ray burst can vary from milliseconds to several hours, but the explosion leaves an afterglow that can be seen for hours to months in different wavelengths, such as radio, infrared, optical, ultraviolet and X-rays.
Swift is equipped with three instruments to study events across the electromagnetic spectrum: the Burst Alert Telescope (BAT), which sees gamma rays, the X-ray Telescope, and the Ultraviolet/Optical Telescope. The BAT scans the sky for gamma-ray bursts, and, when spotted, accurately determines their positions.
When the BAT detects a burst, the spacecraft alerts the worldwide astronomical community to its location so astronomers using other ground- and space-based telescopes can follow up. Swift then autonomously repoints its two other science instruments to study the afterglow in X-rays, ultraviolet and visible light. The satellite’s speedy reaction to these quick, high-energy events is the reason it was named for a type of bird. The spacecraft continues to revisit the burst location in the subsequent hours, days and even weeks to better understand the nature of the explosion and its environment.
Swift’s ability to rapidly repoint and its sensitive X-ray and ultraviolet imaging have led it to observe a wide variety of sources. The spacecraft now receives an average of five “target-of-opportunity” requests from the community each day to respond to objects ranging from comets to distant black holes.
“Swift’s science focus has grown and evolved since its launch,” said Principal Investigator S. Bradley Cenko, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It still conducts gamma-ray burst science by observing light, astronomy’s original cosmic ‘messenger.’ Yet, now a suite of observatories can detect other signals — messengers like cosmic rays, neutrinos and gravitational waves. As a part of this new field of multimessenger astronomy, Swift works in conjunction with these facilities to try and link these signals to changes we see in various wavelengths of light.”
As the Swift mission celebrates its 15th anniversary, here are five times in the past five years it has helped reveal something new about the universe.
1. Star shredder
Analysis of data from Swift and other spacecraft revealed new details of a tidal disruption event — a black hole shredding a star that got too close. The missions detected echoes from flares of high-energy X-rays produced during this catastrophic encounter.
2. Comet slowdown
In May 2017, Swift data showed that comet 41P/Tuttle-Giacobini-Kresák was rotating three times slower than it had been in March. This slowdown was the most significant change in a comet’s rotation ever seen.
3. Core crash
Swift’s follow-up observations of two merging neutron stars indicated an ultraviolet emission from the gravitational wave source. This was a major accomplishment in the field of multimessenger astronomy.
4. The Cow
In 2018, Swift detected a burst of light at least 10 times brighter than a typical supernova. This event, called AT2018cow, was nicknamed “the Cow.” Swift observations, along with data collected by other telescopes, led scientists to two different explanations: a tidal disruption by a monster black hole or a supernova that gave birth to a black hole or neutron star.
5. Ultra gamma-ray burst
As astronomers continue to work toward understanding these quick, powerful bursts, Swift will continue to scan the sky in search of answers.
“Swift’s two-year prime mission is long over, yet Swift is still going strong in its 13th year of extended operations,” said Jamie Kennea, lead of Swift’s science operations team at Penn State in University Park, Pennsylvania. “We are on the cusp of a new era of multimessenger astronomy, and Swift will play a huge role in this emerging chapter.”
Goddard manages the Swift mission in collaboration with Penn State, the Los Alamos National Laboratory in New Mexico and Northrop Grumman Innovation Systems in Dulles, Virginia. Other partners include the University of Leicester and Mullard Space Science Laboratory in the United Kingdom, Brera Observatory and the Italian Space Agency in Italy.