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Astronomers Devise a New Way to Measure Cosmic Expansion with Lensed Supernovae
Superliminous supernovae are miraculous events. For astronomers, they also provide a vital tool for measuring cosmic distances and the rate at which the Universe is expanding. As part of the Cosmic Distance Ladder, these incredibly bright stellar explosions are the “standard candles” for objects billions of light-years away. In a rare event, researchers from the University of Munich, using the Large Binocular Telescope (LBT) in Arizona, witnessed a superluminous supernova 10 billion light-years away that was far brighter than most explosions of its kind.
What was especially amazing about this supernova was that it appeared five times in the night sky due to gravitational lensing by two foreground galaxies. These galaxies bent the path of the supernova’s light, causing it to take different paths. Because these paths have different lengths, the light appeared in different places around the galaxies at different times. By measuring the time delays between the multiple images, the researchers were able to obtain measurements of how fast the Universe is expanding – aka the Hubble-Lemaitre Constant.
The team consisted of researchers from the Technical University of Munich (TUM), the Max Planck Institute for Astrophysics (MPG), the Harvard & Smithsonian Center for Astrophysics (CfA), the E.O. Lawrence Berkeley National Laboratory, ETH Zurich, the Research Center for the Early Universe (RESCEU), the Cosmic Dawn Center (DAWN), the Ulugh Beg Astronomical Institute, the Chinese Academy of Sciences (CAS), Institute of Space Sciences (ICE, CSIC), the Excellence Cluster ORIGINS, the National Astronomical Observatory of Japan (NAOJ), the European Southern Observatory (ESO), the Space Telescope Science Institute (STScI), and multiple universities.
*Large Binocular Telescope on Mount Graham in Arizona, USA. Credit & ©: Dr. Christoph Saulder/MPE*
The paper describing their observations has been accepted for publication in Astronomy & Astrophysics
Only a few such measurements have been attempted to date because gravitationally lensed supernovae are so rare. It is also a challenging process, where astronomers must determine the masses of the lensing galaxies because this dictates how strongly the light from the background object is bent. To determine the masses of the two galaxies, the team obtained images with the LBT, using its two 8.4-meter (27.5 ft) mirrors and an adaptive optics system. The observations revealed two foreground lens galaxies at the center surrounded by five bluish images of the supernova explosion, making it look like fireworks!
Sherry Suyu, Associate Professor of Observational Cosmology at TUM and Fellow at the Max Planck Institute for Astrophysics, explained in an MPG press release:
We nicknamed this supernova SN Winny, inspired by its official designation SN 2025wny. It is an extremely rare event that could play a key role in improving our understanding of the cosmos. The chance of finding a superluminous supernova perfectly aligned with a suitable gravitational lens is lower than one in a million. We spent six years searching for such an event by compiling a list of promising gravitational lenses, and in August 2025, SN Winny matched exactly with one of them.
The image came as a surprise to the team since galaxy-scale lens systems normally produce only two or four copies. Using the positions of all five, junior researchers Allan Schweinfurth (TUM) and Leon Ecker (LMU) built the first model of the lens mass distribution. Said Allan Schweinfurth:
Until now, most lensed supernovae were magnified by massive galaxy clusters, whose mass distributions are complex and hard to model. SN Winny, however, is lensed by just two individual galaxies. We find overall smooth and regular light and mass distributions for these galaxies, suggesting that they have not yet collided in the past despite their close apparent proximity. The overall simplicity of the system offers an exciting opportunity to measure the Universe’s expansion rate with high accuracy.
This, in turn, could help astronomers and cosmologists relieve the ongoing issue of the Hubble Tension. To date, scientists have relied primarily on two methods to measure cosmic expansion: the Cosmic Distance Ladder and measurements of the Cosmic Microwave Background (CMB). The former is the local method, combining parallax, supernovae, and redshift measurements of bright objects to establish distances one step at a time. Since every step is dependent on the previous one, even small errors can add up and affect the final result.
In contrast, CMB measurements look back to the beginning of cosmic time by examining the “relic radiation” left over from the Big Bang. This approach is highly precise and relies on models of the early Universe to calculate its current rate of expansion. It relies heavily on assumptions about how the Universe evolved, however, which are still subject to debate. This study presents a third possible method in which astronomers use gravitationally lensed supernovae and measure the time delays between the multiple copies of the same image.
By calculating the mass distribution of the lensing galaxy, scientists can directly calculate the Hubble-Lemaitre Constant. “Unlike the cosmic distance ladder, this is a one-step method, with fewer and completely different sources of systematic uncertainties,” said Stefan Taubenberger, a leading member of Professor Suyu’s team and first author on their study.
Meanwhile, astronomers worldwide are observing SN Winny in detail with ground-based and space-based telescopes. Their results will provide new insights into cosmic expansion that could help resolve the Hubble Tension.
Further Reading: MPG
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More Young Men Say Religion Is ‘Very Important’ to Them, Poll Finds
“I wanted something new and something traditional and something that felt holy.”
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What Happens When Light Goes Boom? Part 1: The Scientist Who Stared at a Glow
I want you to imagine a scene. It’s the red carpet. It’s the night of the Oscars, or the Emmys, or the participation trophy ceremony for your kid’s soccer team. That’s not the essential part of the metaphor. What matters is who is there: Brad Bradington’s adoring fans, curious onlookers, and of course the paparazzi, ready to take their shot.
In our analogy, Brad Bradington is a particle. An electron, a proton, even a neutrino if it felt like it. The crowd of onlookers and fans? That’s a material — a substance, like air or water or diamond or the inside of your eyeball (which is mostly water and hopefully very little diamond).
And those paparazzi? They’re the most important part.
I’m talking today about something called Cherenkov radiation, which I prefer to call a “light boom” but as usual nobody listens much to me. We’ll get to Brad Bradington and his red carpet moment. But first we need to talk about the man who stared at a faint blue glow for three years and refused to look away.
It’s 1934. Pavel Alekseyevich Cherenkov is working in Moscow, doing the kind of science that sounds almost embarrassingly simple when you describe it at a party: he’s shining gamma rays into a bottle of water.
That’s it. That’s the whole experiment.
Hey — in the 1930s, a lot of particle physics involved shining or shooting X into target Y, so it’s not as lame as it sounds. But still. A bottle of water.
And when he shoots the gamma rays into the water, it glows. Blue. Faint, barely there. But unmistakably there.
Now here’s the thing. This wasn’t the first time anyone had seen this. Marie Curie’s lab had noticed the same glow years earlier. Other physicists had seen it too. And every single one of them had looked at it, shrugged, and written it off as fluorescence — some impurity in the water absorbing the radiation and re-emitting it as light. Secondary effect. Not interesting. Move along.
Cherenkov looks at it and thinks the great hallmark of most scientific discoveries: huh, that’s weird.
It’s said that good scientists don’t discover new things — they look at old things in a new way. Pavel did that.
He’s not sure why he’s suspicious. But he’s suspicious. So he does what any good experimentalist does when something doesn’t sit right — he starts poking it. He tries purifying the water. The glow stays. Hmm. He tries different liquids. The glow changes. Ooh! He varies the energy of the radiation. The glow responds. Neat! He changes the geometry of the experiment.
The glow has a direction.
Wait, what?
Fluorescence glows in all directions equally — it doesn’t care which way you’re looking at it. But this glow was asymmetric. It was stronger in some directions than others. It was doing something fluorescence absolutely does not do.
He doesn’t know what this is. But this is definitely NOT fluorescence.
So Cherenkov does something that separates the great scientists from the merely good ones: he decides that not knowing what something is is not a reason to stop looking at it. He spends the next three years characterizing this phenomenon with almost obsessive precision. He’s not a theorist — he can’t tell you WHY it’s happening. But he can tell you everything about WHAT it’s doing. He measures its intensity, its direction, its dependence on the speed of the incoming particles, its behavior in different materials. He builds up a complete empirical portrait of something he fundamentally doesn’t understand.
He publishes his results. The physics community is…mildly interested. This is the 1930s. There’s a lot going on. Quantum mechanics is still being sorted out. Nuclear physics is exploding — literally. A faint blue glow in a bottle of water is not exactly front page news.
A few years later, a pair of theorists pick up his careful measurements and figure out what’s actually going on.
It’s Brad Bradington, showing up at the red carpet.
In Part 2, we need to talk about the crowd — and why the speed of light is not actually a universal speed limit.
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Hundreds of affordable housing units funded by new L.A. County agency

For Michael Miller, getting a project off the ground is usually a bureaucratic juggling act.
When building affordable housing like the 200-plus units he’s planning in Harbor Gateway and Stevenson Ranch, the president of Bold Communities said he’d typically be forced to find funding through three to five different local and state agencies.
This time around, he’s going to just one: the newly established L.A. County Affordable Housing Solutions Agency.
The agency, known as LACAHSA, bills itself as a one-stop shop for affordable housing financing with offers of construction loans, permanent loans, rental subsidies and other types of funding products. It’s betting that in doing so developers can build low-income homes quicker and cheaper in a county with a bruising affordability and homelessness crisis.
There’s some evidence this is the case. According to the Terner Center at UC Berkeley, each additional public funding source an affordable developer uses, on average, delays a project four months and increases total cost by $20,460 per unit — more than $2 million for a 100-unit community.
“We want to build housing cheaper and quicker, because that means more units,” LACAHSA interim chief executive Ryan Johnson said.
On Wednesday, the agency gave approval to just over $100 million for ten projects, including the two from Bold Communities.
The Terner Center said going to multiple agencies for needed funding adds costs because developers have to endure higher legal, staffing and compliance costs to manage additional applications and contracts.
Each process, of course, also takes time, during which developers pay additional holding costs on predevelopment loans, all the while inflation pushes up the cost of materials and wages.
Miller estimated by going through only LACAHSA, he could cut down total costs around 5% to 10%.
LACAHSA, founded through state legislation in 2022, receives its funding from the recent voter-approved Measure A half-cent sales tax to fight homelessness and build affordable housing.
Until now, the agency had awarded money only for homeless prevention efforts such as direct rental subsidies to tenants.
It’s first batch of funds to build and preserve affordable housing, approved Wednesday, will pay for 554 below market units. The vast majority will be brand new homes, while a small share will be conversions of existing market rate residential units into affordable units and extending deed-restrictions on some existing below-market units.
LACAHSA pointed to data showing that of the top performing quarter of new construction projects that recently applied for its funding, total development costs came in below the typical cost to build affordable units in the county. Savings rose to nearly 12% when project proposals relied primarily or entirely on LACAHSA funding, rather than mixing state funding with just one or two LACAHSA products.
Terner Center managing director Ben Metcalf said it’s unclear to what extent those savings might reflect that cheaper projects just happened to apply for funding from LACAHSA. But he expects at least some of the savings can be attributed to LACAHSA’s structure.
Not only does the agency offer a plethora of financial products, but LACAHSA said it ranks project proposals by their efforts to reduce costs and considers that as a significant factor when deciding to approve funding.
Metcalf, who previously served as director of the California Dept. of Housing and Community Development, said such a focus on awarding dollars based on the estimated development cost isn’t the norm among public agencies.
In part, he theorized that was because “the rising cost of affordable housing has really only become an issue of visible concern over the last few years.”
In 2022, the Times reported the cost to build just one unit of affordable housing in California routinely cost more than $1 million. Voters have also expressed growing frustration at the lack of progress in reducing homelessness and overall housing costs.
LACAHSA isn’t the only effort to simply a complicated funding process, with Gov. Gavin Newsom proposing to streamline state funding as part of this year’s budget.
Meanwhile, LACAHSA plans to approve another round of affordable housing funds in May.
To apply for that funding and the dollars approved Wednesday, LACAHSA said it required developers to be able to break ground within 12 months. Developers submitted 127 applications, seeking a total of $1.5 billion to build 11,625 units.
Long Beach Mayor Rex Richardson, who serves as chair of the LACAHSA board, argued the high interest shows it’s really a lack of “financing and operational support” holding back the construction of more affordable housing in L.A. County, rather than a lack of “sites or community will.”
“LACAHSA was built to meet this moment,” he said in a statement.
The projects that Bold Communities plans in Harbor Gateway and Stevenson Ranch are conversions of extended stay hotels into low-income senior housing.
Now that funding is secured, Miller said he expects the buildings to be full of new residents by the end of next year.
“I think these will be, honestly, pretty straight forward,” the non profit executive said.
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