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Most assessments of global warming use 1850-1900 as a baseline, but researchers have now established a new pre-industrial reference by using Antarctic ice cores to estimate the average temperature before 1700

Experiments show that illuminating the underside of a decoy seal reduces attacks by great white sharks, revealing a possible strategy to protect surfers and swimmers

Voyager 2 flew by Uranus in 1986, giving us our only up-close look at the planet – but unusual space weather just before the craft arrived has given us a misleading idea about the planet’s magnetic field

Extreme weather and a growing population is driving a food security crisis. What can we do to break the vicious cycle of carbon emissions, climate change and soaring food costs – or is it already too late?

Seven major datasets used to train audio-generating AI models are three times more likely to use the words "man" or "men" than "woman" or "women", raising fears of bias

Thanks to some generous readers, we now have about four batches of wildlife photos. But we always need more, you know.

I’m delighted today to welcome back ace bird photographer Colin Franks, who contributed a batch of photos that haven’t been published here. Colin’s website is here, his Facebook page is here (lots of new bird photos), and his Instagram page is here.  His text and IDs are indented below:

It’s been a little over three years since my diagnosis of PLS (a form of ALS).  In spite of major changes in my life due to that, and a steady decline of my balance and walking, I continued with my bird photography as long as I could.  Back in July of this year I made my final post on FB and IG, as I could no longer negotiate the terrain required.  It was a very sad time.  About a week ago I discovered and purchased an “All-Terrain” walker, and this has allowed me to once again visit some of my old haunts.  There is still much in the way of gnarlier terrain that I cannot traverse, but at least I can keep on a little while with this great pastime. Here are some older shots not yet shared on WEIT.

American Kestrel (Falco sparverius):

Common Yellowthroat (Geothlypis trichas):

Spotted Towhee (Pipilo maculatus):

Great Blue Heron (Ardea herodias):

Barred Owl (Strix varia):

Long-billed Curlew (Numenius americanus):

Anna’s Hummingbird (Calypte anna):

Cedar Waxwing (Bombycilla cedrorum):

Marbled Godwit (Limosa fedoa):

Barn Swallow (Hirundo rustica):

Western Sandpiper (Calidris mauri):

Black-bellied Plover (Pluvialis squatarola):

Osprey (Pandion haliaetus):

Climate change is a huge topic and often debated across the world. We continue to burn fossil fuels and ignore our charge toward human driven climate change but while our behaviour never seems to improve, something else does! For the last few decades we have been pumping chlorofluorocarbons into the atmosphere causing a hole in the ozone layer to form. Thanks largely to worldwide regulation changes and a reduction in the use of these chemicals, the hole it seems is finally starting to get smaller. 

The ozone layer is the protective shield in Earth’s stratosphere. It’s about 15 to 35 kilometres above the Earth and its presence helps to protect us by absorbing harmful ultraviolet radiation. The region is mostly ozone composed of three oxygen molecules and it filters out the UV-B and UV-C radiation which can lead to skin cancer, cataracts and can even damage parents crops. The rest of the atmosphere is composed mostly of nitrogen gas (78%), oxygen (21%) and a few other gasses making up the remaining 1%. 

A view of Earth’s atmosphere from space. Credit: NASA

In the late 20th century scientists found that certain chemicals like the well known chlorofluorocarbons (CFC’s) were slowly destroying the layer. This resulted in seasonal holes appearing in the ozone especially over Antarctica. In 1987, the Montreal Protocol international treaty was signed to curb the global release of CFC’s and other ozone harmful gas. 

Just recently, a team of scientists from NASA and the National Oceanic and Atmospheric Administration (NOAA) have confirmed that the hole in the ozone layer over the south pole was relatively small compared to previous years. During the month of September to October, when the ozone depletion process is at its peak, it was the 7th smallest hole since 1992. An average season sees an incredible 20 million square kilometres of ozone depletion. The teams data even suggests the layer could fully recover by 2066. 

To collect the data the team uses a number of systems. A number of satellites (Aura, NOAA-20, NOAA-21 and Suomi NPP) are used to collect data from orbit. In addition they use weather balloons which are launched from the South Pole Baseline Atmospheric Observatory to directly measure ozone concentrations. 

Geostationary orbits are where telecommunication satellites and other monitoring satellites operate. This image shows one of the NOAA’s Geostationary Operational Environmental Satellites. Image Credit: NOAA.

The measurements are captured as Dobson Units. One Dobson Unit is equivalent to the number of ozone molecules that would be needed to create a layer of pure ozone 0.01 millimetres thick. Of course temperature and pressure would effect this so the measurement is based on a layer at 0 degrees Celsius and 1 atmosphere (the average pressure of atmosphere at surface of Earth.) In 2024, the measurement in October 2024 was 109 Dobson Units in comparison to the lowest ever value of 92 Dobson Units in 2006. 

The Montreal Protocol certainly seems to be making a difference seeing a significant and continuous decline in CFCs. This, along with an infusion of ozone from north of Antarctica have combined to reverse the depletion. 

Source : Ozone Hole Continues Healing in 2024

The post Good News, the Ozone Layer Hole is Continuing to Shrink appeared first on Universe Today.

Reaching net-zero emissions is essential for halting climate change - but even after we achieve this goal, parts of the planet will continue to warm. Delaying net zero will worsen these effects

Last week, Donald Trump defeated Kamala Harris and will return to the White House in January. What does this mean for science-based federal health policy? Hint: Nothing good. Just like the rest of the government, the worst people are likely to be in charge of health and science policy.

The post Donald Trump won. Now what for science-based federal health policy? first appeared on Science-Based Medicine.

Here’s Bill Maher’s 7-minute comedy/news bit from Friday’s “Real Time.”  The title of the episode refers, of course, to comedian Tony Hinchcliffe’s statement at a Trump Rally in NYC: “”There’s a lot going on. I don’t know if you know this but there’s literally a floating island of garbage in the middle of the ocean right now. Yeah, I think it’s called Puerto Rico.”  It was not funny, and did not go down well, though of course nothing hurts Trump.

In this bit Maher is calling attention to the human-caused “death of the ocean”.  He avers that un-polluting the ocean will be much harder than curbing global warming.  And what we see on the surface (there’s one “garbage island” the size of France!) is only the tip of the iceberg:  70% of the garbage, much of it plastic, sinks to the bottom.

Curiously, Maher avoids discussing the election results save to say that Harris was part of the only party that even deals with the environment, yet she never mentioned pollution and even reversed her earlier anti-fracking position. Maher clearly sees oceanic pollution—and environmental pollution in general—as critical but ignored issuea.  Recycling, he says, is a crock, since only 9% of plastic gets recycled.

. . . and here’s his 3½-minute monologue about the election itself:

From January 10-12 (Friday through Sunday), there will be a substantial conference at the University of Southern California on censorship in science, and by that they mean all the sciences: STEMM.  You can see details about the conference at the website below (click on screenshot), and view the preliminary program here.  (There was an sketchier announcement of the conference in August, but now things are in their final stages.)

You can register here; the fee is $200 ($100 for students), and that’s not a bad deal given that the registration includes lunches, coffee breaks, and receptions with drinks and food.  And the participants include, beyond a passel of working scientists, people like Jonathan Rauch, Jesse Singal, FIRE President Greg Lukianoff and, mirabile dictu, Marcia McNutt, President of the National Academy of Science.

And of course there’s this by way of self-promotion (end of the meeting):

Yes, I team up again with my partner in crime Dr. Maroja, on a two-person panel moderated by UC Berkeley molecular biologist Julia Schaletzky.

I hear that space is filling up, so if you want to register, and have the time and ability to go to USC (in LA), I recommend registering ASAP.

One of the most difficult challenges when assembling a telescope is aligning it to optical precision. If you don’t do it correctly, all your images will be fuzzy. This is particularly challenging when you assemble your telescope in space, as the James Webb Space Telescope (JWST) demonstrates.

Unlike the Hubble Space Telescope, the JWST doesn’t have a single primary mirror. To fit in the launch rocket, it had to be folded, then assembled after launch. For this reason and others, JWST’s primary reflector is a set of 18 hexagonal mirror segments. Each segment is only 1.3-meters wide, but when aligned properly, they act effectively as a single 6.5-meter mirror. It’s an effective way to build a larger space telescope, but it means the mirror assembly has to be focused in space.

To achieve this, each mirror segment has a set of actuators that can shift the segment along six axes of alignment. They are focused using a wavefront phase technique. Since light behaves as a wave, when two beams of light overlap, the waves create an interference pattern. When the mirrors are aligned properly, the waves of light from each mirror segment also align, creating a sharp focus.

The primary mirrors of Hubble and JWST compared. Credit: Wikipedia user Bobarino

For JWST, its Near Infrared Camera (NIRCam) is equipped with a wavefront camera. To align the mirrors, the JWST team points NIRCam at a star, then intentionally moves the mirrors out of alignment. This gives the star a blurred diffraction look. The team then positions the mirrors to focus the star, which brings them into alignment.

This was done to align the mirrors soon after JWST was launched. But due to vibrations and shifts in temperature, the mirror segments slowly drift out of alignment. Not by much, but enough that they need to be realigned occasionally. To keep things proper, the team typically does a wavefront error check every other day. There is also a small camera aimed at the mirror assembly, so the team can take a “selfie” to monitor the condition of the mirrors.

The JWST was designed to maintain a wavefront error of 150 nanometers, but the team has been able to maintain a 65 nanometer error. It’s an astonishingly tight alignment for a space telescope, which allows JWST to capture astounding images of the most distant galaxies in the observable universe.

You can learn more about this technique on the NASA Blog.

The post How Webb Stays in Focus appeared first on Universe Today.

Despite the calls of both Presidential candidates to “unite America”, the calls of many to “reach across the aisle” and confect bipartisan legislation, and the advice of some that it’s time to discuss America’s differences instead of hating one’s opponents, we are now hearing calls from Democrats and liberals to boot those who voted for Trump out of our lives.

I disagree. I know some of those people, and although I don’t like the way they voted, I don’t think that’s sufficient to avoid them forever, or to give them sharp lectures that they are fascists and tried to ruin America and our livelihood. There are, as I’ve pointed out in the nooz over the last few days, a diversity of reasons why people voted for Trump: wokeism of the Left, their own economic problems due to inflation, immigration, and so on—reasons that can be debated but not dismissed.

Sadly, we have some on the Left becoming haters like this. One such person is discussed in a column on by Jonathan Turley written on his website.  Turley is a professor at George Washington University Law School, an attorney, a legal scholar. and, I believe, a libertarian.  As noted below, Turley wrote a recent column in The Hill about the “liberal rage” that is spreading now that Democrats have started to internalize the election debacle. In that piece Turley made a reasonable point:

It is important to note at the outset that there is no reason Democratic activists should abandon their values just because they lost this election. Our system is strengthened by passionate and active advocacy.

Rather, it is the collective fury and delirium of the post-election protests that was so disconcerting. Pundits lashed out at the majority of voters, insisting that the election established that half of the nation is composed of racists, misogynists or domination addicts who long to submit to tyranny.

No, not everyone who voted for Trump is a fascist racist, or misogynist. (For crying out loud, a huge number of women voted against Harris.( In fact, more than half of all Americans voted for the Orange Man, since Harris apparently lost the popular vote. I am embarrassed before the world that we chose Trump to hold the most important job in the country, but there it is.

Ergo the rage. In his new column, Turley note a particularly striking and offensive (to me) example of that rage: a resident in psychiatry at Yale. Turley’s words:

With women pledging to break up with their boyfriends and divorce their husbands over the Trump victory, Yale University chief psychiatry resident Dr. Amanda Calhoun is advising that it may also be necessary for your mental health to cut off your family and friends who supported Trump. In that way, you can avoid being “triggered” by opposing political views — much like Yale itself.

As academics, we are dealing with the election on campuses across America. After the election, I had some valuable discussions with students who supported Harris and some who supported Trump. I wish there would be more interaction between the two groups. That is why this story stood out for me. I do not believe that further separation or isolation will help this country or these individuals.

Dr. Calhoun went on MSNBC’s Joy Reid to offer the curious take on good mental health. Reid has spent the week condemning the majority of voters (particularly minority voters) in the nation as racists and misogynists for the Trump victory.

Reid joined a rising tide of rage, which I discussed in my column this weekend. Dr. Calhoun added her voice to the madness.

“So, if you are going into a situation where you have family members, where you have close friends who you know have voted in ways that are against you… it’s completely fine to not be around those people and to tell them why…

…You know, to say, ‘I have a problem with the way that you voted because it went against my very livelihood, and I’m not going to be around you this holiday. I need to take some space for me.’ I think you should very much be entitled to do so, and I think it may be essential for your mental health.”

There is another possibility. You can try to resolve those feelings with people who you previously liked or loved. It may actually help to discuss these issues outside of the echo chamber of your political associations.

If you want to hear Calhoun, who is African-American, actually say what she said above, click on the screenshot below, which will take you to the Fox News column showing a video of Calhoun speaking to Joy Reid on MSNBC. Yes, the words she said are indeed the ones above:

Turley adds this and touts his book, which I haven’t read:

Across the country, women have been cutting their hair and joining the Korean 4B movement—bihon (no marriage), bichulsan (no childbirth), biyeonae (no dating), and bisekseu (no sex). One is quoted as saying, “I fear The Handmaid’s Tale will become our reality.”

It is a curious response since figures like Reid blame white women for the loss. Trump won white women voters by eight points at 53 percent. Harris actually fell slightly in the support of women overall. Conversely, roughly 43 percent of men voted for Harris. Yet I watched one deranged voter say that she is thinking of buying a “Glock” and shooting the first man who comes near her. If so, she would have an over 4 out of 10 likelihood of shooting a fellow Harris supporter.

None of this is good for our nation’s mental health and suggesting that people retreat further into their silos does not make for particularly healthy advice.

As discussed in my book, The Indispensable Right, we have become a nation of rage addicts. Taking another hit of rage will do little to break that addiction.

Now I didn’t vote for Trump, of course, but I am not prepared to either lecture people who did, telling them that they were attacking my livelihood, or telling them that I don’t want to associate with them. I suppose it’s okay to say that “I want to take some time for myself right now,” without giving the reason, and then trying to have a discussion later.

Of course people can sever any relationship they want over the election, but that sort of attitude doesn’t seem to me conducive to mental health—even though Calhoun is a shrink—and it’s certainly not good for the Democrats. After all, a common element in post-election analyses is the idea that the elitism of Democrats, combined with their characterizing their enemies as yokels or fascists, are factors that turned off centrists and leftish Republicans.

There will be some lively discussion around the Thanksgiving and Christmas groaning boards, but Calhoun’s table will be emptier than usual.

h/t: Bill

Well, we have one more batch of photos after this, and then the feature goes belly-up.  If you don’t want that to happen, please send in your good wildlife photos.

Today being Sunday, we have a visit by John Avise, who sent photos of some birds near his home. John’s captions and IDs are indented, and you can click the photos to enlarge them.

A Morning at the Beach 

A few days ago, I went to Crystal Cove State Park, which is only a 15-minute drive from my house here in Southern California.  I timed my visit so as to capture the long morning light at low tide.  Here are some of the birds that I photographed on that short but special visit.  All of these species are regulars along our beaches, especially during the autumn and winter months.

Willet (Tringa semipalmata) posing:

Willet standing on one leg

Willet showing the white stripe along its wing (normally visible only during flight):

Whimbrel (Numenius phaeopus) posing:

Whimbrel with small crab:

Another Whimbrel pose. showing its head stripes:

Sanderling (Calidris alba) posing:

Sanderling stretching:

Western Gull (Larus occidentalis) posing:

Black phoebe (Sayornis nigricans) (yes, they inhabit beachfronts as well as many other habitats in S. Cal.):

Black Turnstone (Arenaria melanocephala) posing:

Black Turnstone in flight:

Mass purges and prosecutions of scientists have happened before. We shouldn't pretend they can't happen here.

The post Dr. Vinay Prasad: “I Don’t Believe in Forgiveness Because in My Opinion These Pieces of Shit Are Still Lying.” first appeared on Science-Based Medicine.

Astronauts on the International Space Station generate their share of garbage, filling up cargo ships that then deorbit and burn up in the atmosphere. Now Sierra Space has won a contract to build a trash compactor for the space station. The device will compact space trash by 75% in volume and allow water and other gases to be extracted for reclamation. The resulting garbage blocks are easily stored and could even be used as radiation shielding on long missions.

Called the Trash Compaction and Processing System (TCPS), plans are to test it aboard the International Space Station in late 2026.

Sierra Space said this technology could be critical for the success of future space exploration — such as long-duration crewed missions to the Moon and Mars — to handle waste management, stowage, and water reclamation.

“Long-term space travel requires the efficient use of every ounce of material and every piece of equipment. Every decision made on a spacecraft can have far-reaching consequences, and waste management becomes a matter of survival and mission integrity in the vacuum of space,” said Sierra Space CEO, Tom Vice, in a press release. “We’re addressing this challenge through technological innovation and commitment to sustainability in every facet of space operations. Efficient, sustainable, and innovative waste disposal is essential for the success of crewed space exploration.”

A sample trash tile, compressed to less than one-eighth of the original trash volume, was produced by the Heat Melt Compactor. Credit: NASA.

NASA said that currently aboard the International Space Station (ISS), common trash such as food packaging, clothing, and wipes are separated into wet and dry trash bags; these bags are stored temporarily before being packed into a spent resupply vehicle, such as the Russian Progress ship or Northrup Grumman’s Cygnus vehicle. When full, these ships undock and burn up during atmospheric re-entry, taking all the trash with it.

However, for missions further out into space trash will have to be managed and disposed of by other methods, such as jettisoning the trash into space – which doesn’t sound like a very eco-friendly idea. Additionally, wet trash contains components that may not be storable for long periods between jettisoning events without endangering the crew. 

Plus, there’s currently no way for any water to be reclaimed from the “wet” waste. The TCPS should be able to recover nearly all the water from the trash for future use.

TCPS is a stand-alone system and only requires access to power, data, and air-cooling interfaces. It is being designed as simple to use.

Sierra Space said the device includes an innovative Catalytic Oxidizer (CatOx) “that processes volatile organic compounds (VOCs) and other gaseous byproducts to maintain a safe and sterile environment in space habitats.” Heat and pressure compacts astronaut trash into solid square tiles that compress to less than one-eighth of the original trash volume. The tiles are easy to store, safe to handle, and have the added — and potentially very important — benefit of providing additional radiation protection.

Sierra Space was originally awarded a contract in 2023, and in January 2024 they completed the initial design and review phase, which was presented to NASA for review. Sierra Space is now finalizing the fabrication, integration, and checkout of the TCPS Ground Unit, which will be used for ground testing in ongoing system evaluations. Based on the success of their design, Sierra Space was now awarded a new contract to build a Flight Unit that will be launched and tested in orbit aboard the space station.

NASA said that once tested on the ISS, the TCPS can be used for exploration missions wherever common spacecraft trash is generated and needs to be managed.

The post A Trash Compactor is Going to the Space Station appeared first on Universe Today.

The most amazing thing about light is that it takes time to travel through space. Because of that one simple fact, when we look up at the Universe we see not a snapshot but a history. The photons we capture with our telescopes tell us about their journey. This is particularly true when gravity comes into play, since gravity bends and distorts the path of light. In a recent study, a team shows us how we might use this fact to better study black holes.

Near a black hole, our intuition about the behavior of light breaks down. For example, if we imagine a flash of light in empty space, we understand that the light from that flash expands outward in all directions, like the ripples on a pond. If we observe that flash from far away, we know the light has traveled in a straight line to reach us. This is not true near a black hole.

The gravity of a black hole is so intense that light never travels in a straight line. If there is a flash near a black hole, some of the light will travel directly to us, but some of the light will travel away from us, only to be gravitationally swept around the backside of the black hole to head in our direction. Some light will make a full loop around the black hole before reaching is. Or two loops, or three. With each path, the light travels a different distance to reach us, and therefore reaches us at a different time. Rather than observing a single flash, we wound see echoes of the flash for each journey.

In principle, since each echo is from a different path, the timing of these echoes would allow us to map the region around a black hole more clearly. The echoes would tell us not just the black hole’s mass and rotation; they would also allow us to test the limits of general relativity. The only problem is that with current observations, the echoes wash together in the data. We can’t distinguish different echoes.

This is where this new study comes in. The team propose observing a black hole with two telescopes, one on Earth and one in space. Each telescope would have a slightly different view of the black hole. Through long baseline interferometry the two sets of data could be correlated to distinguish the echoes. In their work the team ran tens of thousands of simulations of light echoes from a supermassive black hole similar to the one in the M87 galaxy. They demonstrated that interferometry could be used to find correlated light echoes.

It would be a challenge to build such an interferometer, but it would be well within our engineering capabilities. Perhaps in the future, we will be able to observe echoes of light to explore black holes and some of the deepest mysteries of gravity.

Reference: Wong, George N., et al. “Measuring Black Hole Light Echoes with Very Long Baseline Interferometry.” The Astrophysical Journal Letters 975.2 (2024): L40.

The post Using Light Echoes to Find Black Holes appeared first on Universe Today.

Placing a mass driver on the Moon has long been a dream of space exploration enthusiasts. It would open up so many possibilities for the exploration of our solar system and the possibility of actually living in space. Gerard O’Neill, in his work on the gigantic cylinders that now bear his name, mentioned using a lunar mass driver as the source of the material to build them. So far, we have yet to see such an engineering wonder in the real world, but as more research is done on the topic, more and more feasible paths seem to be opening up to its potential implementation. 

One recent contribution to that effort is a study by Pekka Janhunen of the Finnish Meteorological Institute and Aurora Propulsion Technologies, a maker of space-based propulsion systems. He details how we can use quirks of lunar gravity to use a mass driver to send passive loads to lunar orbit, where they can then be picked up with active, high-efficiency systems and sent elsewhere in the solar system for processing.

Anomalies in the Moon’s gravitational field have been known for some time. Typically, mission planners view them as a nuisance to be avoided, as they can cause satellite orbits to degrade more quickly than expected by nice, simple models. However, according to Dr. Janhunen, they could also be a help rather than a hindrance.

Mass drivers have been popular in science fiction for some time.
Credit – Isaac Arthur YouTube Channel

Typical models of using lunar mass drivers focus on active or passive payloads sent into lunar orbit. Active payloads require some onboard propulsion system to get them to where they are going. Therefore, these payloads require more active technology and some form of propellant, which diminishes the total amount available for use elsewhere in the solar system.

On the other hand, passive payloads will typically end up in one of two scenarios. Either they make one lunar orbit in about one day and then deorbit back to the lunar surface, or they end up in a highly randomized orbit and essentially end up as lunar space junk. Neither of those solutions would be sustainable for significant mass movement off the lunar surface.

Dr. Janhunen may have found a solution, though. He studied the known lunar gravitational anomalies found by GRAIL. This satellite mapped the Moon’s gravity in great detail and found several places on the lunar surface where a mass driver could potentially launch a passive payload into an orbit that would last up to nine days. These places are along the sides of mountains, and three of them are on the side of the lunar surface facing Earth. Importantly, all of them have their gravitational quirks.

The Artemis missions might be our best chance in the coming decades to build a mass driver on the Moon – Fraser discusses their details here.

More time in orbit would mean more time for an active tug to grab hold of the passive lunar payload and take it to a processing station, such as a space station at the L5 point between Earth and the Moon. This active tug could be reusable, have a highly efficient electrical propulsion system developed and built on Earth, and only need to be launched once.

All that would be required for the system to work would be a mass driver that could accelerate a payload up to a lunar orbital velocity of about 1.7 km/s. That is well within our capabilities to build with existing technologies, but it would require a massive engineering effort far beyond anything we have built-in space so far. However, every study that shows a potential increased benefit or lowered cost to eventually exploiting the resources of our nearest neighbor to expand our reach into the solar system takes us one step closer to making that a reality.

Learn More:
P Janhunen – Launching mass from the Moon helped by lunar gravity anomalies
UT – Moonbase by 2022 For $10 Billion, Says NASA
UT – NASA Wants to Move Heavy Cargo on the Moon
NSS – L5 News: Mass Driver Update

Lead Image:
DALL-E illustration of a lunar electromagnetic launcher

The post Launching Mass From the Moon Helped by Lunar Gravity Anomalies appeared first on Universe Today.

Interview with Brian Cox; Quickie with Bob: Superheavy Element Chemistry; News Items: Biogenome Project, Ancient Solar Magnetic Field, MAHA, Miranda Ocean, Club 27 Myth; Who's That Noisy; Science or Fiction

Massive stars about eight times more massive than the Sun explode as supernovae at the end of their lives. The explosions, which leave behind a black hole or a neutron star, are so energetic they can outshine their host galaxies for months. However, astronomers appear to have spotted a massive star that skipped the explosion and turned directly into a black hole.

Stars are balancing acts between the outward force of fusion and the inward force of their own gravity. When a massive star enters its last evolutionary stages, it begins to run out of hydrogen, and its fusion weakens. The outward force from its fusion can no longer counteract the star’s powerful gravity, and the star collapses in on itself. The result is a supernova explosion, a calamitous event that destroys the star and leaves behind a black hole or a neutron star.

However, it appears that sometimes these stars fail to explode as supernovae and instead turn directly into black holes.

New research shows how one massive, hydrogen-depleted supergiant star in the Andromeda galaxy (M31) failed to detonate as a supernova. The research is “The disappearance of a massive star marking the birth of a black hole in M31.” The lead author is Kishalay De, a postdoctoral scholar at the Kavli Institute for Astrophysics and Space Research at MIT.

These types of supernovae are called core-collapse supernovae, also known as Type II. They’re relatively rare, with one occurring about every one hundred years in the Milky Way. Scientists are interested in supernovae because they are responsible for creating many of the heavy elements, and their shock waves can trigger star formation. They also create cosmic rays that can reach Earth.

This new research shows that we may not understand supernovae as well as we thought.

Artist’s impression of a Type II supernova explosion. These supernovae explode when a massive star nears the end of its life and leaves behind either a black hole or a neutron star. But sometimes, the supernova fails to explode and collapses directly into a black hole. Image Credit: ESO

The star in question is named M31-2014-DS1. Astronomers noticed it brightening in mid-infrared (MIR) in 2014. For one thousand days, its luminosity was constant. Then, for another thousand days between 2016 and 2019, it faded dramatically. It’s a variable star, but that can’t explain these fluctuations. In 2023, it was undetected in deep optical and near-IR (NIR) imaging observations.

The researchers say that the star was born with an initial mass of about 20 stellar masses and reached its terminal nuclear-burning phase with about 6.7 stellar masses. Their observations suggest that the star is surrounded by a recently ejected dust shell, in accordance with a supernova explosion, but there’s no evidence of an optical outburst.

“The dramatic and sustained fading of M31-2014-DS1 is exceptional in the landscape of variability in massive, evolved stars,” the authors write. “The sudden decline of luminosity in M31-2014-DS1 points to the cessation of nuclear burning together with a subsequent shock that fails to overcome the infalling material.” A supernova explosion is so powerful that it completely overcomes infalling material.

“Lacking any evidence for a luminous outburst at such proximity, the observations of M31-2014-DS1 bespeak signatures of a ‘failed’ SN that leads to the collapse of the stellar core,” the authors explain.

What could make a star fail to explode as a supernova, even if it’s the right mass to explode?

Supernovae are complex events. The density inside a collapsing core is so extreme that electrons are forced to combine with protons, creating both neutrons and neutrinos. This process is called neutronization, and it creates a powerful burst of neutrinos that carries about 10% of the star’s rest mass energy. The outburst is called a neutrino shock.

Neutrinos get their name from the fact that they’re electrically neutral and seldom interact with regular matter. Every second, about 400 billion neutrinos from our Sun pass right through every person on Earth. But in a dense stellar core, the neutrino density is so extreme that some of them deposit their energy into the surrounding stellar material. This heats the material, which generates a shock wave.

The neutrino shock always stalls, but sometimes it revives. When it revives, it drives an explosion and expels the outer layer of the supernova. If it’s not revived, the shock wave fails, and the star collapses and forms a black hole.

This image illustrates how the neutrino shock wave can stall, leading to a black hole without a supernova explosion. A shows the initial shock wave with cyan lines representing neutrinos being emitted and the red circle representing the shock wave propagating outward. B shows the neutrino shock stalling, with white arrows representing infalling matter. The outer layers fall inward, and the neutrino heating isn’t powerful enough to revive the shock. C shows the failed shock dissipating as a dotted red line and the stronger white arrows represent the collapse accelerating. The outer layers are falling in rapidly, and the core is becoming more compact. D shows the black hole forming, with the blue circle representing the event horizon and the remaining material forming an accretion disk. (Credit: Original illustration created for this article.)

In M31-2014-DS1, the neutrino shock was not revived. The researchers were able to constrain the amount of material ejected by the star, and it was far below what a supernovae would eject. “These constraints imply that the majority of stellar material (?5 solar masses) collapsed into the core, exceeding the maximum mass of a neutron star (NS) and forming a BH,” they conclude. About 98% of the star’s mass collapsed and created a black hole with about 6.5 solar masses.

M31-2014-DS1 isn’t the only failed supernova, or candidate failed supernova, that astronomers have found. They’re difficult to spot because they’re characterized by what doesn’t happen rather than what does. A supernova is hard to miss because it’s so bright and appears in the sky suddenly. Ancient astronomers recorded several of them.

In 2009, astronomers discovered the only other confirmed failed supernova. It was a supergiant red star in NGC 6946, the “Fireworks Galaxy.” It’s named N6946-BH1 and has about 25 solar masses. After disappearing from view, it left only a faint infrared glow. In 2009, its luminosity increased to a million solar luminosities, but by 2015, it had disappeared in optical light.

A survey with the Large Binocular Telescope monitored 27 nearby galaxies, looking for disappearing massive stars. The results suggest that between 20% and 30% of massive stars can end their lives as failed supernovae. However, M31-2014-DS1 and N6946-BH1 are the only confirmed observations.

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