Mission accomplished for Integral, ESA's gamma-ray telescope

Mission accomplished for Integral, ESA's gamma-ray telescope
by ESA Staff Writers
Paris (ESA) Feb 27, 2025

The European Space Agency's gamma-ray telescope ends its observations next 28th February. During its 22 years in space, Integral has reshaped our view of the most dramatic events in the Universe. The high-energy observatory played a pivotal role in revealing the nature of the cosmic explosions known as gamma-ray bursts and in uncovering the origin of gravitational wave events. Recently, it delivered unique insights into how thermonuclear blasts drive jets in neutron stars and captured the giant flare from an extragalactic magnetar.

ESA's Integral was launched on 17 October 2002, from the Baikonur Cosmodrome in Kazakhstan, on a mission to observe the ever-changing, powerful, and extreme cosmos.

"For over two decades, Integral has shown us time and time again how important it is to look at the sky in gamma-ray light," notes Jan-Uwe Ness, ESA's Integral Project Scientist. "Some of the bursts of light associated with extreme physical events in our Universe can only be fully understood if we catch the light rays that come from the very core of the blasts: the gamma rays."

Unlike visible and radio light coming from space, which we can observe from the ground, cosmic gamma-rays can only be captured in space. This is because Earth's atmosphere acts as a shield to protect us from these harmful rays.

"Integral has transformed our understanding of the dynamic high-energy Universe and physics in extreme conditions," adds Prof. Carole Mundell, ESA Director of Science.

"That Integral's spacecraft and instrumentation have performed so exquisitely well for so many years is testament to the quality of the technology developed by the European scientific community and space industry at the turn of the millennium, and the science and engineering teams at ESA who have operated this mission ever since. Congratulations to all our communities for their dedication and achievements."

Solving mysteries and breaking new ground

Integral's observations have been key to solving the mysteries of gamma-ray bursts (GRBs), the powerful flashes of energetic light that flare up somewhere in the sky about once per day. These flashes often shine brighter than all other gamma-ray sources together.

Nowadays, scientists trace the origin of 'longer' GRB events lasting several seconds to the runaway collapse of massive stars that go supernova, while shorter bursts are due to black holes and neutron stars smashing into each other.

"What I find impressive about Integral are its unexpected discoveries," remarks Jan-Uwe. "It turned out that Integral was ideal for tasks not at all foreseen when the mission was conceived. An example is its ability to track down the sources in the sky that generated some of the gravitational waves and ultrahigh-energy neutrinos caught by specialised instruments on the ground."

At the time of Integral's launch, scientists were not even sure whether gravitational waves could ever be directly detected; the first observation of these elusive ripples in spacetime was made 13 years after Integral's launch by the LIGO gravitational wave detectors in the US, in 2015.

Breakthroughs kept coming.

"Just in the last two years or so, I was stunned by exciting new results. Integral captured the most powerful gamma-ray flash ever observed, and the blast impacted the atmosphere's protective ozone layer," continues Jan-Uwe. "This GRB took place in a galaxy almost two billion light-years away - it is mind-boggling to think that Earth can be affected by an event that took place in a remote corner of the Universe, two billion years ago."

Two more recent findings focus on an extremely rare 0.1-second magnetar outburst that emitted as much energy as our Sun produces in half a million years, and the discovery that thermonuclear explosions drive jets in a neutron star.

Sharp gamma-ray eyes

At the time of launch, Integral was the most advanced gamma-ray observatory and the first space observatory able to see celestial objects simultaneously in gamma rays, X-rays, and visible light.

Three features of Integral's instrumentation have made these many discoveries possible: a very large field-of-view covering about 900 square degrees of the sky in the most energetic X- and gamma rays; the ability to obtain, simultaneously, detailed images and spectra at the highest energies; the monitoring capability of the X-ray and optical cameras to help pinpoint the gamma-ray sources.

Ramping down

"After more than 2886 orbits and 22 years gazing into the depths of our cosmos, today Integral's sensitive instruments will stop collecting scientific data. But the legacy of ESA's gamma-ray observatory will serve scientists for many more years to come," concludes Matthias Ehle, Integral's Mission Manager at ESA.

"The wealth of data collected over two decades will be stored at the Integral Science Legacy Archive. It will be essential for future research and to inspire a new generation of astronomers and engineers to develop exciting new missions."

Following the end of its science observations, the spacecraft will continue to orbit Earth for four more years. ESA engineers will monitor the satellite until it re-enters Earth's atmosphere in early 2029. Thanks toa special four-thruster burn executed back in 2015, the satellite's entry into the atmosphere will meet ESA's pledge to minimise space debris.