BERLIN — It took six years. Six years of scanning the same patch of sky, waiting for a light that might never come. The odds were less than one in a million. But the team from TUM, LMU and the Max Planck Institutes finally got their payoff: a supernova named SN Winny, visible not once, but five times.
The trick is gravitational lensing. Two massive foreground galaxies sit between Earth and the explosion, which detonated about 10 billion light-years away. Their gravity bends spacetime. Light from the supernova follows several different paths around them, each one a different length. So the same flash reaches us at five different moments. Cosmic echoes.
That five-image alignment is what makes this rare. Superluminous supernovas are uncommon. Perfectly aligned ones, with a foreground galaxy cluster acting as a cosmic magnifying glass, are vanishingly rare. The researchers knew it. They kept looking anyway.
Now the real work begins. The time delays between the five images — the gaps between those echoes — can be measured. Those gaps encode a number. The Hubble constant. The rate at which the universe expands.
This matters because the Hubble constant is currently a problem. Two established ways of measuring it give different answers. One method, based on the cosmic microwave background, yields one number. Another, using standard candles like Type Ia supernovas, gives a higher number. Astronomers call this the Hubble tension. It has not been resolved.
SN Winny offers a third route. Gravitational lensing time delays let scientists calculate the expansion rate independently. No reliance on the early universe. No reliance on a separate ladder of distance measurements. Just geometry and gravity.
The math is straightforward in principle. Light travels at a fixed speed. If you know how much longer one path is than another, you know how much later that image should arrive. The delay itself tells you the distance. And the distance, combined with the redshift of the supernova’s host galaxy, gives the Hubble constant.
In practice, it is painstaking. The delays must be measured precisely. The mass distribution of the lensing galaxies must be modeled accurately. A small error in either step throws the whole calculation off.
But the payoff is a direct measurement. No assumptions about the nature of dark energy. No calibration of Cepheid variables. Just the geometry of bent light.
The discovery was announced June 3. The paper is out. The data is public. Other teams will now try to replicate the measurement, refine it, test it.
If the lensing result matches one of the two existing methods, that method gains credibility. If it matches neither, the tension deepens. Both outcomes would be useful. Both would tell astronomers something about where their models are wrong.
SN Winny itself is long dead. The star exploded 10 billion years ago, when the universe was a quarter of its current age. The light has been traveling ever since. It passed through the gravitational field of those two foreground galaxies, got split into five beams, and kept going. It reached Earth in 2024, 2025, and will arrive again in the years ahead as the last of the five images finally completes its journey.
Six years of searching. A one-in-a-million alignment. Five images of a single dead star. One number that might settle a cosmological dispute. That is the bet the researchers made. They found their supernova. Now they have to read what it says.
