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Why shards obey a hidden rule
by Spektrum der Wissenschaft
Record supernova from the early days of the cosmos
20.12.2025
Translation: machine translated
The James Webb Space Telescope has made another important discovery: a supernova from the epoch of reionisation, around 730 million years after the Big Bang. And it behaves completely differently than would have been expected for such early stellar explosions.
Observations with the James Webb Space Telescope (JWST) made another impressive achievement possible: the discovery of the most distant supernova to date. It exploded when the universe was just 730 million years old and still deep in the phase of reionisation, reports a team led by Andrew Levan from Radboud University in Nijmegen and the University of Warwick in England in the journal «Astronomy and Astrophysics Letters». This means that the record previously held by the JWST has once again been significantly surpassed: The previous leader among supernovae discovered with Webb occurred when the universe was 1.8 billion years old.
However, the discovery was not made entirely without help: the first clues were provided on 14 March 2025 by the French-Chinese mission SVOM (English: Space-based multi-band astronomical Variable Objects Monitor). It reported a long, approximately ten-second gamma-ray burst from a distant source. Around an hour and a half later, the Neil Gehrels Swift Observatory was able to localise the event, which was subsequently named GRB 250314A; subsequent observations with the ESO's Very Large Telescope in Chile, barely 17 hours after the first signal, finally revealed an age of around 730 million years after the Big Bang. This corresponds to a cosmological redshift of z = 7.3.
A long gamma-ray burst is often followed by a supernova - the explosion of a massive star. Its light is normally only visible for a few weeks before it slowly fades. However, due to the expansion of the cosmos, the team expected the supernova following GRB 250314A to brighten over several months. So on 1 July 2025, around three and a half months after the gamma-ray burst was first detected, the JWST was pointed at its point of origin - on the assumption that the supernova would be at its brightest at this time.
The results were astonishing: as expected, Webb revealed the most distant supernova to date; however, to the astronomers' surprise, it turned out to be almost identical to current representatives of its kind. Its brightness is similar to that of the event SN 1998bw in the galaxy ESO 184-G82. This was the first supernova to be associated with a gamma-ray burst and probably followed the collapse of a very massive star. The similarity with the supernova that has now been discovered is remarkable: early stars were expected to produce supernovae with significantly different properties due to their lack of heavy elements and their greater mass.
Source: Rekordfund aus der Frühzeit des Universums | Das James-Webb-Weltraumteleskop hat die Quelle des extrem hellen Gammastrahlenausbruchs GRB 250314A identifiziert: eine Supernova, die explodierte, als das Universum erst 730 Millionen Jahre alt war. In den hochauflösenden Nahinfrarotaufnahmen wurde mit Webb zudem ihre Wirtsgalaxie gefunden.
However, the observations indicate that GRB and supernova properties change only within a relatively narrow range over a large part of cosmic history. The team was able to rule out a significantly brighter or bluer supernova than SN 1998bw, as expected from early stars. The star that produced the violent gamma-ray burst GRB 250314A and the supernova now discovered by Webb was therefore not significantly more massive and possibly resembles the GRB progenitors in the local universe, the team surmises.
The JWST also succeeded in identifying the extremely faint host galaxy of GRB 250314A. It appears in the infrared as a blurred, reddish spot and is similar to other galaxies in this early phase of the universe. The team could not completely rule out the possibility that it also contributed to the observed brightness of the supernova.
In order to better understand the «spectral fingerprint» of such distant galaxies, Levan's group is already planning further investigations, in particular of the inconspicuous afterglow of early gamma-ray bursts. Only very few of these are known from the beginnings of the universe. The team has already secured the coveted observation time with the JWST.
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Original article on Spektrum.de
Header image: NASA, ESA, CSA, STScI, Leah Hustak (STScI) / Image B: Supernova GRB 250314A (Artist's Concept) (detail)
Explosion of a massive star | The illustration shows the expanding gamma-ray burst GRB 250314A after the outburst (left) and the supernova itself (right). It occurred less than a billion years after the Big Bang, when the first stars and galaxies formed.
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