Semaglutide, the active ingredient in Ozempic, and other drugs in the same class have revolutionized the treatment of obesity and type 2 diabetes. Now, a clinical trial suggests the medicines can treat type 1 diabetes, as well.
The trial results, published June 23 in the journal NEJM Evidence, suggest semaglutide can improve blood sugar levels and induce weight loss in people with type 1, potentially introducing a new drug that could be used along with insulin to manage the disease.
“For a hundred years, we are fixated on insulin and insulin delivery … and there aren’t really extra medications that are approved for type 1,” lead study author Dr. Viral Shah, a diabetes researcher at Indiana University, told Live Science. There are some add-on drugs approved for use alongside insulin, but Shah envisions Ozempic-like drugs as a potential firstline treatment.
The insulin resistance and impaired release of digestive hormones that fuel type 2 diabetes can also exist in type 1, so it does make sense to explore treatments for those, he said.
Type 1, type 2, and double diabetes
Type 1 and type 2 diabetes are driven by very different mechanisms.
In type 2, cells in the pancreas that make insulin become less sensitive to blood sugar and produce less insulin in response. Insulin normally helps usher sugar from the bloodstream into cells, so this effect causes sugar to build up in the blood. Meanwhile, type 1 diabetes is an autoimmune disorder in which the insulin-secreting cells are destroyed by one’s own immune system.
Related: In a 1st, scientists reversed type 1 diabetes by reprogramming a person’s own fat cells
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There are several drugs for type 2 diabetes that focus on driving cells to secrete more insulin, and there are standard treatments centered around improving blood sugar control, weight loss, high blood pressure and cardiovascular disease risk through lifestyle changes. Drugs like semaglutide, known as GLP-1 agonists, control blood sugar in type 2 by reducing a liver-made hormone that raises blood sugar, as well as slowing down digestion. This makes you feel fuller for longer and allows the pancreas more time to release the right amount of insulin.
The primary way to control blood sugar in type 1 diabetes, however, is insulin replacement. But type 1 diabetics, especially those with obesity, often have insulin resistance and thus many of the same health issues as those with type 2 — for example, nerve damage, foot ulcers and eye damage, all due to uncontrolled blood sugar. This condition has been termed “double diabetes.”
“Type 1 diabetes does not exclude the presence of type 2 diabetes,” Shah said. “People with the double diabetes phenotype may benefit from some of the medications that are currently approved for type 2 diabetes.”That was the idea behind the new trial of semaglutide, the ingredient found in the weight-loss drug Ozempic and type 2 diabetes drug Wegovy.
The researchers recruited 72 patients with type 1 diabetes and obesity, based on their BMIs. Half the participants received a weekly semaglutide injection and the other half a placebo for 26 weeks. All the participants continued using insulin as needed throughout the trial, and their blood sugar was monitored using continuous glucose monitors.
The patients taking semaglutide had better control over their blood sugar levels, staying within an acceptable range of blood sugar levels over 70% of the time while also spending less time with low blood sugar levels. The treated individuals also lost at least 5% of their body weight. But no one in the untreated group met all three of these criteria.
These results support findings from other recent trials, showing that these drugs used for type 2 diabetes are worth exploring in type 1 diabetics, said Ahmad Haidar, a diabetes researcher at McGill University in Canada, who was not involved in the study.
“It’s an important study that adds to the existing evidence toward the safety and efficacy of the use of semaglutide in type 1, but it is not enough,” Haidar told Live Science. “We need more evidence to help these drugs be approved by regulatory agencies.”
Shah and his colleagues hope that with more clinical trials with bigger cohorts of patients, the research community will gather enough evidence to have this use of GLP-1s approved by the Food and Drug Administration and added into the American Diabetes Association standards of care for type 1. If approved, the treatments could then potentially be covered by health insurance.
“And if that happens, I think this would be probably the first drug beyond insulin for people with type 1 diabetes to use,” Shah said. “It’s really exciting that it’s moving forward.”
This article is for informational purposes only and is not meant to offer medical advice.
Biomass refers to the total mass of living plant material in an area, typically measured as dry weight. Forest biomass includes the trunks, branches, leaves, and roots of trees. Biomass is a key indicator of how much carbon is being stored in forests, since trees absorb carbon dioxide from the atmosphere and store it in their tissues. Tracking biomass helps scientists better understand carbon fluxes, assess the impact of deforestation and forest degradation, and improve climate change models. This information also supports international agreements aimed at reducing carbon emissions, such as the Paris Agreement.
“These first images are nothing short of spectacular — and they’re only a mere glimpse of what is still to come,” said Michael Fehringer, ESA’s Biomass Project Manager. “As is routine, we’re still in the commissioning phase, fine-tuning the satellite to ensure it delivers the highest quality data for scientists to accurately determine how much carbon is stored in the world’s forests.”
ESA leaders celebrated the achievement and the collaborative effort behind the mission. “It was extremely emotional because it was the work of hundreds of people,” said Simonetta Cheli, ESA’s Director of Earth Observation Programmes, in an interview with Space.com. “It’s very symbolic of the effort behind the scenes and the potential that this mission has.”
ESA image of the Bolivian landscape at the Beni River in the rainforest. (Image credit: ESA)
One of the first images captures a vibrant region in Bolivia, where rainforest blends into riverine floodplains. This area has experienced extensive deforestation driven largely by agricultural expansion. In the false-color image, green represents rainforest, red indicates forested wetlands and floodplains, and blue-purple highlights grasslands. Cutting through the terrain is the dark, snaking line of the Beni River, one of the last major undammed rivers in the region. “It shows the beauty of our Earth and what we can do to protect it,” Cheli said during a press conference at the Vienna symposium.
A comparison of the same Bolivian region, imaged by both Biomass and Copernicus Sentinel-2, underscores the mission’s unique capabilities. While Sentinel-2 offers natural-color imagery of surface features, Biomass uses P-band radar to penetrate the canopy and reveal the forest’s vertical structure—essential for accurately measuring biomass and carbon content.
A side-by-side comparison of the Bolivian landscape reveals one image captured by the Sentinel-2 satellite and the other by ESA’s Biomass mission. (Image credit: ESA)
Other early images further showcase the satellite’s global reach and scientific potential. Over northern Brazil, Biomass recorded its first image, highlighting diverse Amazonian terrain. Red and pink shades mark wetlands and floodplains, while green depicts denser, higher forests to the north. This level of detail offers new ways to monitor forest health in some of the world’s most ecologically vital and remote regions.
In Indonesia, an image of the mountainous Halmahera rainforest captures the rugged topography shaped by volcanic activity, including the still-active Mount Gamkonora. Despite the dense vegetation, Biomass can reveal subsurface features such as volcanic slopes and forest floor contours, demonstrating its value for both ecological and geological studies.
The first image captured by Biomass. was the Amazon rainforest in northern Brazil (Image credit: ESA)
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Halmahera rainforest in Indonesia showing the mountains and biomass. (Image credit: ESA)
From Africa’s Congo Basin, the satellite offers a view of Gabon, where the Ivindo River winds through pristine rainforest. The radar imagery brings clarity to one of the most carbon-dense forest regions in the world, aiding conservation efforts in a region under increasing pressure.
In a striking contrast, an image of the Sahara Desert in Chad reveals hidden ancient riverbeds and geological features beneath the sand. Biomass’s radar can see up to five meters below the desert surface, opening new frontiers in understanding past climates and identifying groundwater resources in arid environments like the Tibesti Mountains region.
The mission also reaches into polar extremes. A view of Antarctica’s Nimrod Glacier, alongside the Transantarctic Mountains, showcases how Biomass can peer into the ice itself—providing insights into internal glacial structures and movement. This could prove vital for tracking ice sheet stability and predicting future sea-level rise.
The biomass view of the Nimrod Glacier in Antarctica (Image credit: ESA)
While these initial images are still undergoing calibration and are not yet ready for scientific analysis, they confirm that the satellite is functioning as intended—and potentially exceeding expectations. With a planned five-year mission, Biomass will provide regular, global forest coverage, offering vital data for climate research, conservation planning, and international carbon accounting.
As the satellite moves into full operations, scientists anticipate a flood of high-quality data that could reshape how we observe and protect Earth’s ecosystems—especially its forests, which remain among the planet’s most critical carbon sinks.
In his new book ’52 Assignments: Night Photography’, award-winning astrophotographer Josh Dury invites you to raise your lens and embark on a journey through the night sky to capture everything from the moon and Milky Way, to satellite megaconstellations and aurora.
The latest book in Ammonite Press’ popular ’52 Assignments’ series seeks to demystify the technically demanding hobby of astrophotography by offering stargazers a year’s worth of weekly workshops packed with advice and photography techniques for capturing the night sky.
Each assignment will help aspiring astrophotographers gain a better understanding of how their camera performs at night, while arming them with the technical knowledge and tricks of the trade needed to capture spectacular images of the post-sunset realm.
Space.com caught up with Dury to discuss his experience of writing the book, how aspiring astrophotographers can benefit from the assignments, and the importance of capturing unique images of the night sky.
A composite image showing satellite trails criss-crossing the night sky. (Image credit: Josh Dury)
Josh Dury: The whole experience really started off from a very young age, when I was seven years old. Back then, there were children’s programs about the planet Mars, and it was when I purchased my first telescope that [I was] ultimately encouraged me to look up to life on other worlds, at the planets of the solar system. I thought, well, how can I document that?
So it began by taking images with these planetary cameras at the time. But then I pursued an education and then a degree in photography, and now pursuing a career as a landscape astrophotographer. It’s one of those bucket list things I’ve always wished to do to educate others, which is to publish a book. But at the same time, when I was approached by Ammonite Press, [there were] very pressing issues in the astrophotography community.
With the [rising] popularity of taking images of the night sky and the Milky Way, not only are we seeing environmental effects of light pollution and artificial light at night, but we’re also seeing consequences of [so many people] going to dark sky places — hundreds of photographers in one go producing artificial light in dark sky areas. And so this book aims to promote sustainable astrophotography so that we can take further respect and consideration for the night sky and also just the etiquette of being respectful of other photographers in these dark sky areas. I feel it’s a pressing issue at the moment that needs to be addressed.
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You’re a passionate dark sky advocate, yet a number of the assignments that you picked out specifically take aim at light pollution and the satellites that crisscross our sky. Could you tell me a little bit more about your process, your thought process, and including them as targets in the book?
I think it’s very important to take images of light polluted areas, because it demonstrates the state of affairs in which we are living. The majority of the British public and further afield live under light polluted skies. When I was a youngster living on the Mendip Hills, I was one of the lucky ones [who got] to look up at the beautiful dark skies and see the Milky Way glowing on down, but also the pressing issues that have come from that.
“…are we potentially the last generation that will see the night’s sky in its entirety?”
As a delegate of Dark Sky International, I work with a group of like minded people who are producing research on the impacts of light pollution. So not only the effects to astronomers and astrophotographers like myself, but also wildlife conservation, how light at night is affecting nocturnal and marine wildlife as well as ourselves. Human health, how exposure to light at night affects chemical reactions during our sleeping patterns, our circadian rhythm and effectively affecting melatonin cycles. But [there’s] also the next pressing issue, which is satellite megaconstellations. I respect the fact that it’s very much a double edged sword.
We live in the 21st Century. We need internet technology, globally, across the world, for communication. But there’s also the pressing issue of what it’s doing to the night sky?
It is a concerning issue, and it’s going to grow. So it’s my concern as a delegate and an astrophotographer: are we potentially the last generation that will see the night sky in its entirety?
So including satellites as targets in the book was your way of grabbing people and making them look directly at the issue?
“You don’t need the latest photographic technologies to get a good image.”
Exactly, and even just after sundown, Anthony, when you look up, you will see them easily. You’ll just see one after another moving throughout the night. So when an avid or professional photographer takes an image of the sky, and they see one of the trails, they will easily — through the assignments — be able to identify what is a meteor and what is a satellite.
And I think it’s that readdressing issue of: ‘what is it we are looking at, what is it all about?’ I believe the connection between being an astronomer and an astrophotographer is to really know your subjects, because without that prior knowledge, things can easily be mistaken for [one another] in the night sky.
One of the assignments gives advice on how to capture a rare ‘planetary parade.’ (Image credit: Josh Dury)
Astrophotography is an inherently intimidating and technically demanding hobby, especially for beginners. That said, your book does a great job of demystifying the terms and camera settings needed to capture the night sky by breaking it down into individual projects, each of which adds to the user skill set and confidence over time. Could you walk us through your process when it came to creating the assignments?
Really it was putting myself back in my shoes when I was a youngster, but also the experience of being involved with astronomical societies, photographic societies, and years of research. Astrophotography is a technically competent area or niche within photography and so, as opposed to taking an image of, say, a sunset, or architecture, we’re dealing with much longer exposures. And also, we need to let as much light into our cameras as possible — identified as the aperture of our camera lenses — but we also have what’s called ISO (camera sensitivity) and so again, it’s just trying to break down these barriers. You don’t need the latest photographic technologies to get a good image.
I still take a lot of my images on a Sony α7S II, which is considered a more traditional model of the α7 series, but it’s still more than competent [enough] to take these quality images. One pressing issue, I would say, however, is the camera. You need a good quality piece of glass. In the past couple of years I’ve been lucky enough to work with Sigma as a leading purveyor for astrophotography style lenses, dealing with F numbers like f 1.4 that let the light into your camera. That’s where the cutting edge technology comes in, and quite frankly, breaking new boundaries to test this equipment and hopefully the ambition of making it more accessible to everyone.
The assignments tend to provide a structure for the shoot, and then you ask the photographer to go off and put their own personal touches on the composition. What were the challenges when it came to finding the line between handholding and simply providing the necessary structure for newcomers to enjoy the pastime?
“When a viewer or a potential client is looking on their mobile devices at hundreds of submissions all the time, they’re looking for images that are unique and not those same compositions.”
I have taken it upon myself to think deep within what is of interest to me, through my background, through ancient astronomy and stone circles and ancient sites. But I also appreciate that there have been purveyors in astrophotography who were there long before I was and have their own take on the astrophotography landscape. This is my concern when I see locations which have been photographed a hundred times or more, [how can you find] originality?
And so the book is there to speak to the reader, to dive deep into what interests them, and to [help them] apply that knowledge to produce an image that has never been seen before. So it could be one of your hobbies, it could be one of your interests, somewhere where you like walking, your own area of the landscape. Just something new, something refreshing.
When a viewer or a potential client is looking on their mobile devices at hundreds of submissions all the time, they’re looking for images that are unique and not those same compositions. And most importantly, it’s got [to have] an interesting story to tell. So I’ll give you one example, which is one of the assignments titled ‘Meteor Showers.’ So the image [I took as an example] was the Perseid meteors over Stonehenge. Yes, okay, it’s been photographed millions of times before, but it’s somewhere of interest to me. I thought ‘I’m trying out a particular lens here. I want to capture the Milky Way [tumbling] down’. Just being a creative mind, I can picture it in my mind already and [I] executed this image over three and a half hours. It was endorsed by NASA, Apollo 11 astronaut Buzz Aldrin and the European Space Agency. So to have this backing, even by a scientific journal, was huge and it just shows where originality goes a long way.
Perseid meteors captured streaking through the skies over Stonehenge in Wiltshire, UK. (Image credit: Josh Dury)
Do you have a personal favorite assignment that you keep coming back to?
I would say it would have to be one of the final assignments, which is traveling far afield. Not only have I been lucky enough to go to some of the darkest skies in the world, but also to make friendships through the experience. So that particular photograph [Assignment 51] captures the iconic Moai statues of Easter Island from the southern hemisphere skies, and the photograph wouldn’t be possible without the support of the local Islanders and the community. And this is again something which is very easily forgotten in astrophotography today, is that there are people who help you along the way.
Towards the end of the book, you get to the aspirational, bucket list shots that people eventually want to get. But it was really refreshing that throughout, for quite a few of the assignments all you needed was a camera and a tripod, there was no real barrier to entry. If you are already a photographer or have any interest in it, you’ve probably already got most of this gear and then you can just enjoy it and embrace it (and maybe pick up a star tracker).
“With astrophotography, it’s about having fun.”
Well, this is it. So you take yourself on that initial journey. So you start off with the basics, your tripod, your camera, and then as you begin to learn more about your camera and how it operates, is then the realization that if I want to take even cleaner, crisper images, that I will need to deploy the use of a star tracker.
And so it’s just trying to break down what this information means to an audience, and that with one of these devices, you can track the sky for a longer period of time, so that, yes, you can use the longer exposures, you can bring down the ISO levels and produce a cleaner image. But by that point, already, you’re learning. And this is the whole point of the book is to take you for a guided rhythm, really, of the assignments themselves.
A colorful aurora captured above a Norman church situated on the Knowlton Henge earthwork in Dorset, UK. (Image credit: Josh Dury)
So what do you think would be one of the most difficult photography concepts or techniques for a newcomer to pick up that’s included in your book?
There’s a number. So I would say, first of all, image stacking, which is addressed in the assignments. Why is there a need to stack images? So at night we have to remember that, as we have camera settings with a greater sensitivity [and] a longer exposure, when the camera has produced the image you’ll zoom in on it and it almost looks like the surface of sandpaper — it’s very textured. And so the purpose of stacking is so that computer software — Photoshop, being one of them — can read the individual images and, like a cake, stack them together. And so by doing that, it increases what’s known as the signal-to-noise ratio and produces a cleaner image as a result. And then you can produce those minor adjustments to make the Milky Way more representative of what you’ve seen on the night.
Is there anything else you’d like to say to our readers about the book?
“…by remaining true to yourself, you interact with your subjects more.”
With astrophotography, it’s about having fun. That is what I’ve learned throughout the experience. But also not to be put off by numbers and competition, that’s so easily done now, by social media, peer pressure, likes and the modern day following count, none of that at all. Do it for the reason you enjoy doing it and the love of the subject.
Final question — for someone who picks the book up this week to start their journey in astrophotography, what is the one piece of golden advice that you would give them to carry through their entire journey?
Remain true to yourself. It’s something I don’t see very often in astrophotography, but by remaining true to yourself, you interact with your subjects more. It becomes an emotional experience, and through that connection and understanding of a story, [you get] an image that has never been seen before, and ultimately to connect with our open window that is the universe.
This interview has been edited for length. You can buy ’52 Assignments: Night Photography’ at Amazon.com.
There’s good news and bad news: The bad news is that Meta’s continued development of generative AI has led it to add a privacy nightmare setting to its Facebook app. The good news is that, in a big departure from Meta’s status quo, you have control over whether you participate.
It’s all about whether the company and its AI get access to your camera roll and all the pictures there, even the ones you haven’t posted anywhere.
Meta, Facebook’s parent company, has been trying to keep up with AI heavyweights for the past few years in an ultracompetitive race to make the most advanced AI models. Meta distinguished itself by adding its AI to its social media apps, including Instagram, Facebook, WhatsApp and Messenger. Nowadays, most of us who use those apps have to interact with Meta AI, even if we don’t want to.
The company also uses the social media posts that its adult users publicly share to train its AI. There is no way to opt out of training, though European users can object to their data being used thanks to more stringent privacy laws protecting them. For those of us who are concerned about AI systems eating up the content we share online, it’s been a nonstop headache.
So it’s not totally surprising to see this feature on Facebook. It’s called camera roll cloud processing, and Facebook says it’s a way to get more creative help when you share photos and videos. It pulls from your newer pictures, from the last 30 days or so, and recommends the best options, makes AI edits or entirely reimagines your photos with AI. It can also pull from your older photos for themed compilations like travel highlights, monthly recaps and birthday and special event content. You also get more ways to sort your photos and videos by topic and suggestions from Meta about the best photos to share.
Before you opt in, you need to understand the privacy implications.
Meta’s AI terms and how to access camera roll cloud processing
When you allow camera roll cloud processing, Meta can “automatically upload your photos and videos to our cloud so that we can create personalized creative ideas for you.” This is not the same as allowing Meta access to your camera roll so you can post photos and videos you took. If you enable this additional setting, Meta can upload your content to its cloud “on a regular basis to create ideas for you with machine learning and AI models.” Meaning Meta will have continual access to your photos, even if you don’t post them on Facebook or post the newly created suggestions.
A Meta spokesperson said, “We’re exploring ways to make content sharing easier for people on Facebook by testing suggestions of ready-to-share and curated content from a person’s camera roll. These suggestions are opt-in only and only shown to you — unless you decide to share them — and can be turned off at any time. Camera roll media may be used to improve these suggestions, but are not used to improve AI models in this test.”
The mobile app help page says that enabling this feature means you agree to Meta’s AI terms, and it says your photos won’t be used for advertising targeting. The feature is in early stages of testing for US- and- Canada based users, but it won’t be available for folks who live in Illinois or Texas. Your suggested photo won’t be shared automatically unless you choose to.
Here’s how to access the setting:
Open the Facebook app and tap Menu at the bottom right corner.
Tap the gear icon in the upper right corner. You can also scroll down to Settings & privacy and then navigate to Settings.
Tap Camera roll sharingsuggestions.
Scroll to Get creative ideas made for you by allowing camera roll cloud processing.
This feature is currently only available on the iPhone or Android mobile apps. If you have this setting enabled but then change your mind, Meta’s help page says it will remove your content from its cloud after 30 days. There’s no way to confirm its removal, though.
For more, check out how to stay relatively safe while using AI models.
A mandatory update for Google’s mid-range Pixel 6A phones is coming next week that is meant to reduce the risk of the battery overheating on some devices. According to a support page post, Google is issuing the mandatory Android 16 update starting July 8 to all Pixel 6A devices. However, only users with “Impacted Devices” will see any effect on their battery.
Google says affected users will get a notification when the phone has completed 375 cycles, giving them a heads-up that the new battery management features will be activated soon. Once these management tools are in effect, the battery won’t last as long between charges.
According to Google, users may see other changes, “like reduced charging performance or short-term changes to how the battery-level indicator on your phone shows your battery capacity as your phone learns its revised battery capacity.” It’s not clear why some Pixel 6A phones are affected and others aren’t, but if yours is, Google is offering free battery replacement — you can check here to see if you’re eligible.
The company has already dealt with a similar issue on the Pixel 4A, offering owners a free battery replacement or a $100 credit towards a new phone. It currently has an extended repair program for battery swelling issues on the Pixel 7A.
It’s officially summer, and with that comes the first full moon of the season. July’s full moon — known as the Buck Moon or the Thunder Moon — will light up the night sky on July 10 and be at its fullest going into July 11, reaching peak luminosity at around 4:37 a.m. local time, which is a bit late, but it’ll still be bright for the whole night.
According to Stellarium’s sky map, the moon will rise from the southeastern horizon just after sunset in your local time and streak across the sky before setting on the southwestern horizon just before dawn. No matter where you are in the US, you’ll be able to see it virtually all night.
Should you not be able to see the moon due to weather or some other reason, you can also soak up a great view anytime from July 8-12 as the moon will be more than 95% full during those days.
Why is it called the Buck Moon or Thunder Moon?
According to The Farmer’s Almanac, July’s full moon actually has several names, including Buck Moon, Thunder Moon, Feather Moulting Moon, and Salmon Moon. These names typically come from Native American and colonial times and were used to describe the moon for the entire month, not just when it’s full.
White-tailed deer start growing antlers in March or April as the days start to lengthen. July marks the peak of their antler growth season, hence the name Buck Moon. Thunderstorms are also common in July, which is why it’s also called the Thunder Moon.
The other two names are less common, but July marks the time when some species of salmon begin migrating for the mating season, while ducks engage in their annual molting around this time of year as well.
Catch a glimpse of Mars and Venus, too
The moon will be joined in the sky by Mars and Venus during its trip across the sky on July 10. Mars will be visible just after sunset in the western sky before setting. You won’t have long, since it’s scheduled to dip below the horizon before midnight. If you choose to stay up late, Venus will crest the eastern horizon shortly after 2 a.m. local time and be visible until sunrise.
Saturn will also be visible in the eastern sky, not far from the moon, but you’ll likely need binoculars or a telescope to see it with the moon’s glow.
Once the moon finishes its monthly cycle, skygazers can check out the Alpha Capricornids and Southern Delta Aquariids meteor showers, both of which are scheduled to peak during the last few days of July.
In other cases, another member of the system will go on to form a second white dwarf. If gravitational instabilities bring these two objects together, then their collision will create a single object with a much higher mass. This will also restart fusion, leading to an explosion.
We have found evidence for both of these events happening. However, there are some questions about whether they happen often enough to explain the frequency of type Ia supernovae that we see. Both mechanisms require stars of sufficient mass orbiting within a reasonably close distance for either mass transfer or a collision to occur. So, astronomers have been considering other ways of blowing up a white dwarf.
The most promising option appears to be a double detonation. This can also require the transfer of some helium-rich material from another companion, but it can also occur if the white dwarf ends up with some unfused helium left on its surface. Regardless of how it ends up there, the helium can start fusing if enough of it pools up, or simply if its movement causes a sufficiently high local density in one region. However it happens, once fusion starts, the entire surface of the white dwarf will quickly follow, creating detonation number one.
That in turn will create compression in the carbon-oxygen portion of the white dwarf, pushing it past the density needed for that to start fusing. Once again, the initiation of fusion heats and compresses nearby material, creating a chain reaction that triggers widespread fusion in the white dwarf, blowing it to pieces as part of detonation two.
A shell game
The key thing about this is that it allows the explosion of white dwarfs before they reach a mass sufficient enough to trigger the fusion of their carbon and oxygen. Instead, it can potentially happen any time enough helium gathers on their surface. A double-detonation event would also be very difficult to detect, as the explosions would happen in rapid succession, and the environment in the immediate surroundings of a type Ia supernova is going to be complex and difficult to resolve.
