They watch the cataclysmic death of the oldest stars in the Universe, tracking gamma rays

At 625 km altitude, 30° inclination relative to the equator, Svom revolves around the Earth, offering its instruments the deep black of the Universe. Watching, silent, for the inevitable death, formidable and luminous, of a massive star lurking at the confines of space and time, betrayed by an emission of energy such that it will shine brighter than any other source in the cosmos. In a few moments, measured in seconds, in minutes, at most, “the equivalent of what the Sun will radiate during its entire life”says Frédéric Piron, his life of ten billion years…

Svom is a watchman on the lookout. The Franco-Chinese outpost of ten French laboratories, the National Center for Space Studies, Cnes, and dozens of cosmologists and astrophysicists from around the world, dedicated, fascinated, to understanding what the mysterious gamma bursts are, revealed in 1973 by an American publication. The LUPM, the Universe and Particles laboratory at Montpellier University, is one of ten, Frédéric Piron, astrophysics researcher at the CNRS, the head of the small group involved, for a decade, in the genesis of Svom and which, antennas VHF and sharp algorithms, listening since June 22, the day of flight in Xichang, in Chinese Sichuan.

Blastoff! A #LongMarch2C rocket carrying the Space Variable Objects Monitor ???(#SVOM)Satellite, has been launched from the # Xichang Satellite Launch Center in Sichuan Province.@CNES @esa @NMK_ZeroG @IRAP_France @CNRS @iafastro @jamesdcarpenter @aarti_holla
(Video: Xu Lihao) pic.twitter.com/vC1cuIi2So

— Wu Lei (@wulei2020)

The story dates back to 1967. Americans, Russians and British “signed an agreement in 1963 banning nuclear tests in the atmosphere and space”fails the Hérault researcher. And to monitor compliance, the United States sends satellites into orbit capable of detecting particles emitted by an atomic explosion. Gamma rays, therefore: photons, particles of light.

Short bursts or long bursts

“In 1967, the Americans detected a gamma emission, then others. They did not come from the Earth, the Moon, nor the Sun, but, therefore, from deep space. They said nothing about it until “to the publication, in 1973, by researchers from Los Alamos, where the atomic bomb was born, of a paper on these emissions.”

The mission ???? SVOM aims to detect gamma-ray bursts, the most luminous phenomena observed since the Big Bang. Colossal energy!

Here is a video to better understand the @SVOM_mission. pic.twitter.com/9g9JCLpPH1

— CNES (@CNES)

They are called gamma ray bursts (GRB). And they are becoming a major subject of astrophysics, with the research community observing over the years that they are “very intense, very variable”that there are short ones, less than two seconds, and longer ones, questioning their source and origin, their distance from the Earth.

For the source, two hypotheses dominate: the long bursts, the most numerous, would be the product of a star explosion. “A very massive object, at the end of its life, which will create a super nova and a black hole. The burst is the ejection of a phenomenal quantity of matter from this black hole.” Ejection of what, what is the engine? A thousand questions also arise.

We look at the dawn of time

And the short bursts? “See two neutron stars, which come together until they merge, then create a black hole”emit this famous jet. But where in the immensity of space, how far from us?

“In 1997, it was fixed for the first timeresumes Frédéric Piron: several billion light years, outside our galaxy, in a galaxy far, far away.” In space, looking far away is looking at the past: the light that comes from far away comes from ancient times, from the history of the Universe. These bursts, therefore, can sign the death of stars born 500, 600 million years after the Big Bang, “different from those born afterwards” and there is much to learn from a story still full of unknowns.

“I have been working on this subject for twenty yearssays Frédéric Piron. I started with Fermi.” Enrico Fermi, one of the fathers of the bomb, gave his name to a NASA space observatory launched in 2008 to study gamma sources. One of the tools that made it possible to count some “10,000 bursts in fifty years. But the fraction whose distance we know is small.” Svom will help to do better, by speeding up the process implemented.

“We don't locate objects very, very well with gamma raysexplains Frédéric Pironthe source of the jet.” However, this is a prerequisite for measuring its distance and the quality of its observation, from the visible to “hard” gamma rays via “X” and “soft” gamma rays.

? #MissionSVOM ?️ Meeting with Florent Robinet who equipped the MXT telescope with the satellite #SVOM on-board real-time image analysis software to locate gamma bursts with very high precision.

He is a researcher @CNRS at the@IJCLab d’Orsay@CNRSIdFSud pic.twitter.com/LkmQfkpj7l

— CNRS Nuclear & Particles (@CNRS_IN2P3)

X-rays “Hard” gamma and “soft” gamma

For around twenty years, once the emission has been detected, “the game consists of re-pointing the telescopes as quickly as possible” on the area in question. “By covering 1/6th of the sky on the night side with its ECLAIRs instrument”Svom will improve the distance measurement of bursts and its alert to terrestrial observatories will allow them to quickly (automatically) orient their telescopes.

D-10 before the launch of SVOM?

This week, presentation of the ECLAIRs instrument. Designed by French laboratories, it will be responsible for detecting gamma-ray bursts so that the satellite re-orients itself very quickly to observe these phenomena. pic.twitter.com/xtNr9Jo9ko

— CNES (@CNES)

Secondly, the identification by ECLAIRs of a burst will rotate the satellite itself, in order to direct its own MXT and VT telescopes, operating in the X-ray and visible bands, towards the emission source.

“We want to catch the “thing”, refine its location as quickly as possible, to ultimately have a distance measurement and good spectral coverage of the object and to do modeling”comments the Montpellier astrophysicist, who is waiting for January and the start “routine scientific operations”.

“Svom is still in a testing and calibration phasespecifies Frédéric Piron. Automatic repointing of the entire satellite is no small feat.” However, to capture a point of light in unfathomable space, the word precision is… understatement.