Dark Matter Dilemma: New Insights from the Bullet Cluster and Beyond

[00:00:00] [SPEAKER_00] This is Space Time, Series 29, Episode 124, for broadcast on the 16th of October, 2026. Coming up on Space Time, is dark matter real? The unique supernova remnant with a corpse in its heart? And yet another clue in the search for life on the red planet Mars? All that and more coming up on Space Time.

[00:00:23] [SPEAKER_03] Welcome to Space Time with Stuart Gary.

[00:00:42] [SPEAKER_00] A new study has raised more questions about the existence of that mysterious substance called dark matter. Scientists have no idea what dark matter actually is. They think it exists because they can see its gravitational effect on galaxies, holding them together as they rotate. In fact, calculations suggest up to 80% of all the mass in the universe is dark matter. The new findings, reported in the journal Physical Review D,

[00:01:08] [SPEAKER_00] focusing on the Bullet Cluster, which has so far been considered one of the strongest pieces of evidence for the existence of dark matter. But according to a new analysis of data from NASA's Webb Space Telescope, the observations of the Bullet Cluster are also consistent with an alternative explanation that doesn't involve dark matter at all, namely, Modified Newtonian Dynamics, or MOND. This alternative hypothesis to dark matter was first proposed by Israeli physicist Mordehai Milgrom back in 1983.

[00:01:37] [SPEAKER_00] It suggests that the laws of gravity and inertia depart from standard Newtonian physics when objects experience very low accelerations, which happens in the outer regions of galaxies, the same places dark matter was first identified. So, what about the Bullet Cluster? Well, around 4 billion years ago, there was a huge collision in space. Two massive galaxy clusters, each containing hundreds of galaxies, crashed into each other at speeds of over 2,500 kilometers per second.

[00:02:06] [SPEAKER_00] Now, galaxy clusters contain billions of stars. The majority of their visible matter, however, consists of interstellar gas and dust. While the two gas clouds were passing through each other, they were significantly slowed down by frictional forces, which also heated them up considerably. Using X-ray telescopes, the hot clouds can be easily seen from Earth as two diffuse patches that lie relatively close to one another. The galaxies in the two clusters, however, were able to pass through each other unhindered.

[00:02:35] [SPEAKER_00] That's because the distance between the individual stars in each of the galaxies is so great, they simply fly by one another. So, the collision resulted in the two galaxy clusters being separated from the interstellar gas they were carrying with them. Cluster 1 is now to the left of the left gas cloud, and cluster 2 is to the right of the right one. Together, these four now separate structures form what's known as the Bullet Cluster. And it's earned a degree of fame among astrophysicists,

[00:03:02] [SPEAKER_00] as it's considered compelling evidence for the existence of dark matter. You see, images from the formation show that galaxies behind the Bullet Cluster appear distorted into crescent shapes due to gravitational lensing. This refers to that phenomenon first predicted by Albert Einstein, in which the mass of a foreground object can literally bend the light from a more distant background object. Incredibly, however, this deflection isn't especially large in the region of the two luminous clouds of matter in the Bullet Cluster, where the greatest mass should be concentrated.

[00:03:32] [SPEAKER_00] Instead, the galaxy clusters to their left and right exert a much stronger lensing effect, despite their lower mass. So, it appears that further mass must be hidden there which we're unable to see. One of this new study's authors, Harvel Krupa from the University of Bonn, says this observation is so far big incident evidence for the existence of dark matter. That's because, according to current theory, dark matter exerts gravitational forces but does not otherwise interact with normal matter.

[00:04:00] [SPEAKER_00] As a result, unlike the gas clouds, it's not slowed down by friction and is also not separated from visible matter in the galaxy clusters. However, technically, that's not evidence that dark matter exists. Modified Newtonian dynamics, or MOND, has been considered a fringe theory for years, largely because previously it had been assumed that it simply can't explain the observations in the Bullet Cluster. However, this new study by Krupa and colleagues shows that, on the contrary,

[00:04:28] [SPEAKER_00] the Bullet Cluster is actually especially consistent with the MOND scenario. That's because the new data from Webb allows astronomers a better, more precise calculation of the number of stars in both of the clusters. It's now also known that the Bullet Cluster contains a large number of heavy elements such as iron and oxygen. These are produced in the fusion processes inside the star's core, but only in very massive stars. It doesn't happen in smaller stars like our Sun.

[00:04:54] [SPEAKER_00] And when these massive stars eventually die, they don't become white dwarfs like our Sun will, they become much more massive objects, neutron stars and black holes. And just like dark matter, both neutron stars and black holes exert huge gravitational forces. Krupa says the remnants of the massive stars are taking on the role of dark matter to a certain extent, at least in the MOND scenario. Now even in the Standard Model, which assumes the existence of dark matter,

[00:05:22] [SPEAKER_00] its postulated quantity would have to be significantly reduced by about half. And so that makes the MOND scenario much more plausible. This is Space Time. Still to come, a unique supernova remnant with a corpse at its heart. And more clues in the search of past life on the red planet Mars. All that and more still to come on Space Time.

[00:05:50] [SPEAKER_00] Astronomers have discovered that the only known supernova remnant of its kind in the Milky Way galaxy has an unexpectedly intricate structure, including chains of gas knots resembling pearls on a string, each wide enough to fit our entire solar system inside at multiple times. The findings reported in the Astrophysical Journal show the ever-expanding structure, the remains of a massive stellar explosion first witnessed by Japanese and Chinese astronomers in the year 1181, is shaped like a giant dandelion.

[00:06:19] [SPEAKER_00] Modern day astronomers using the Gemini North Telescope in Hawaii, have now captured the most detailed observations yet of this supernova remnant, which has been catalogued as PA-30, and is located some 7,500 light years away. It's one of only five known supernovae recorded before the age of modern telescopes, whose remnants are still unidentified. The data on PA-30 is revealing striking new features of the aftermath of the block,

[00:06:46] [SPEAKER_00] which destroyed the progenitor some 850 years ago. The remnant has what appears to be smooth firework-like streaks. Adding to its unusual character is a surviving zombie star at its core, the stellar remnant of an incomplete explosion. The study's lead author, Laria Carraza, from the Institute of Science and Technology in Austria, says PA-30 is the only known object of this kind in the Milky Way. While astronomers have identified a few similar objects in other galaxies,

[00:07:15] [SPEAKER_00] it remains the only one where our telescopes can see the surviving remnant of this incomplete explosion at its core, the zombie star. This type of incomplete explosion is known as a Type 1AX supernova, a rare class of stellar explosion. The authors believe that PA-30 is the result of a collision between two white dwarves, the stellar remains of a pair of sun-like stars, that have lost their outer gaseous envelopes after exhausting their nuclear fuel supplies and exposing their stellar cores.

[00:07:45] [SPEAKER_00] The authors analysed ionised sulphur emission lines in the red part of the visible spectrum and doubly ionised oxygen emissions in the blue-green part. The sulphur observations revealed roughly ten times as many filamentary features as previous images could resolve. The data shows that PA-30's filaments are composed of tight chains of gas knots that appear to have remarkably uniform sizes. The surviving zombie star appears to sit almost perfectly in the nebulous centre.

[00:08:14] [SPEAKER_00] This is space-time. Still to come, another clue in the search for life on the red planet Mars, and later in the science report, a new study warns that night owls are almost twice as likely as early birds to retire early due to poor health. All that and more still to come on Space Time.

[00:08:48] [SPEAKER_00] NASA's Mars Perseverance rover has discovered nickel-rich rocks in Jezero Crater's Nativa Valleys region, providing yet another clue in the ongoing search for past microbial life on the red planet. The Eretra River Valleys is a 400-metre-wide ancient river channel that once carried water and sediments into a lake in the crater. Located on the western edge of Jezero Crater, it's one of four major valleys feeding into the crater. The new findings, reported in the journal Nature Communications,

[00:09:17] [SPEAKER_00] are providing fresh insights into the sorts of chemical reactions that occurred on early Mars. The authors used both a laser infrared spectrometer and an X-ray spectrometer on the Karsai Sixgall Mobile Laboratory to examine 126 sedimentary rocks and 8 rock surfaces in Nativa Valleys that are thought to be more than 3 billion years old. And they detected nickel in 32 rock samples, concentrations up to 1.1% of their weight, which is the highest abundance ever observed in Martian bedrock.

[00:09:46] [SPEAKER_00] And these nickel deposits tended to co-occur with iron sulfide compounds and with sulfate minerals produced from the breakdown of rocks such as gyricide and acogamitite. The authors found similarities between the composition and shape of the nickel-rich iron sulfide Martian deposits and those of pyrite, an iron sulfide mineral in sedimentary rocks found here on Earth. Now, previous researchers suggested that iron sulfides in sedimentary rocks on Earth are primarily formed from microbial anaerobic respiration

[00:10:16] [SPEAKER_00] using sulfides in the presence of iron-containing minerals. And earlier observations at Narativa Valleys also detected iron sulfides in the presence of organic carbon compounds. It's been proposed that these compounds could have been formed by living organisms, although the authors admit they could also be the result of geological chemical reactions. Still, nickel isn't a central component for enzymes in many ancient archaea and bacterial species here on Earth.

[00:10:43] [SPEAKER_00] See, it's required for some chemical pathways used in energy production, carbon fixation, and organic matter decomposition. The authors say the presence of nickel-rich rocks indicates that if living microorganisms had been present on early Mars, the nickel may have been available in a form that they could have used. They speculate the nickel may have originated from the breakdown of igneous rocks or from a nickel-rich meteorite. Of course, this isn't the first clue

[00:11:11] [SPEAKER_00] pointing to at least the possibility of past life on the red planet. The now infamous leopard spots, discovered on the Shower of a Fools formation, are still best explained as products of organic matter, which on Earth at least are usually a by-product of microbial life. But that's Earth. What about the exact same minerals on Mars? This report from NASA TV.

[00:11:33] [SPEAKER_01] A year ago, we thought we found what we believe to be signs of microbial life on the Mars surface. And so we put it out to our scientific friends to pressure test it, to analyze it, and go, did we get this right? Do we think this is signs of ancient life on Mars? And after a year of review, they've come back and they said, listen, we can't find another explanation. So this very well could be the clearest sign of life that we've ever found on Mars,

[00:12:02] [SPEAKER_01] which is incredibly exciting.

[00:12:03] [SPEAKER_02] Today, we are really showing you how we are kind of one step closer to answering humanity's, one of their most profound questions, and that is, are we truly alone in the universe? So last July, NASA's Perseverance rover found a leopard-spotted rock at Mars. And scientists immediately knew it was interesting. We hadn't seen anything like that before on Mars. And we talked about it last summer. The moment we found it, we put out the images for everybody to see and everybody to share.

[00:12:32] [SPEAKER_02] And so they've done the analysis on these leopard spots, and we think they are potentially made by some sort of ancient life. It's a signature. It's a sort of leftover sign. It's not life itself. And it certainly could have been from ancient life, and that would have been something that was there billions of years ago. Nothing that's current there. And, you know, it could certainly, as we say, be made by ancient life. And what that means is we look at everything we know about life on Earth,

[00:13:01] [SPEAKER_02] and this is the kind of signature that we would see that was made by something biological. In this case, it's kind of the equivalent of seeing, like, leftover fossils, you know, leftovers from a meal. And maybe that meal's been excreted by a microbe. And that's what we're seeing in this sample. I'll be providing some overall geologic context for the discovery of these leopard spot features.

[00:13:24] [SPEAKER_05] The Perseverance rover landed in Jezero Crater in 2021. Jezero was selected because it's in a location amongst the most ancient terrains on Mars, exposing some of the oldest rocks anywhere in the solar system. And these really ancient rocks provide us a window into a period of time that's not particularly well represented on our own planet Earth, but it's a time when life was emergent on Earth and could have been on Mars as well.

[00:13:50] [SPEAKER_05] The rover spent several months exploring this area, ultimately pushing to the edge, the northern edge of the channel, where the bright angel formation met the margin unit. And it's here at the contact, this edge of the river valley, that the rover explored a special target called Chiago Falls. In order to really understand what makes this particular outcrop so special, we have to get our noses to the outcrop, or in this case, the rover's arm, up close and personal to take a look at all the details of these rocks.

[00:14:18] [SPEAKER_04] And what we saw in this rock were these layers of very fine-grained, rusty red mudstone. These textural features told us that something really interesting had happened in these rocks. Some set of chemical reactions occurred. The set of spectra that are called Raman spectra. And there's a lot of information on these graphs, but the key thing to take note of is the fact that what we see in these spectra is something called a G band.

[00:14:46] [SPEAKER_04] The G band for us is a smoking gun indicator for the presence of organic matter in this mud. And what's exciting about these finds, this sort of combination of mud and organic matter that has reacted to produce these minerals and these textures,

[00:15:03] [SPEAKER_04] is that when we see features like this in sediment on Earth, these minerals are often the byproduct of microbial metabolisms that are consuming organic matter and making these minerals as a result of those reactions.

[00:15:17] [SPEAKER_04] So what we need to do from here is to continue to do additional research in laboratory settings here on Earth and ultimately bring the sample that we collected from this rock back home to Earth so that we can make the final determination for what process actually gave rise to these fantastic textures.

[00:15:35] [SPEAKER_00] And in that report from NASA TV, we heard from US Transportation Secretary Sean Duffy, NASA Associate Administrator Nicky Fox, Mars Perseverance rover project scientist Katie Stack Morgan and Mars Perseverance pixel instrument principal investigator Joel Horowitz from Stony Brook University. This is Space Time.

[00:15:55] [SPEAKER_00] And time now to take another brief look at some of the other stories making news in science this week with a science report. A new study has warned that night owls are almost twice as likely as early birds to retire early from work due to poor health, regardless of their income or education.

[00:16:25] [SPEAKER_00] The findings reported in the British Medical Journal are based on data from over 5,000 Finnish people aged around 46 about what time of day they felt most awake. Follow ups over the next 12 years showed that night owls were more likely to get a disability pension early. Now, as these are only granted in Finland after severe and long-term health decline, the authors conclude that poorer health of night owls can cause them to lose core years of their careers.

[00:16:52] [SPEAKER_00] Scientists are warning that the barely studied Wook subglacial basin of East Antarctica contains enough ice to cause global sea levels to rise by more than 4 metres. The findings reported in the journal Nature Review's Earth and Environment warn that this area is also the least explored and understood part of the frozen continent, and consequently needs urgent study.

[00:17:13] [SPEAKER_00] This largely unexplored region is situated almost entirely within Australia's Antarctic territory, and it's showing signs of having retreated substantially during past periods of global warming. Researchers are warning that after compiling everything they currently know about the Wook subglacial basin, there are still huge gaps in their knowledge and understanding of the area, and they warn that without further study, they won't know the types of conditions that could trigger large-scale melting in the future.

[00:17:42] [SPEAKER_00] A new study claims magenta-coloured solar panels that are partly transparent could generate renewable electricity while at the same time letting through enough light to grow crops underneath them. The findings, published in the journal Cell Reports Physical Science, shows that unlike normal solar panels, these magenta ones let through some blue and red light, which is what plants need to grow.

[00:18:03] [SPEAKER_00] The authors say broccoli grown under them took 25 days longer to finish growing than those grown in full sunlight, but still retained similar amounts of nutrients like calcium. However, they also found that the same broccoli had lower levels of important micronutrients, like iron and zinc. A new type of clock could push precision timekeeping to a new level.

[00:18:24] [SPEAKER_00] A report in the journal Nature claims teams from Europe and China have independently built the world's first nuclear clocks that could eventually be more accurate and more precise than the best atomic clocks used today. Nuclear clocks use a nuclear transition or energy jump of protons or neutrons inside the atomic nucleus, usually the low-energy isomeric transition in thorium-229.

[00:18:46] [SPEAKER_00] On the other hand, atomic clocks use electron transitions in atoms such as cesium, stratium or uterbium as their frequency reference. Researchers say that the technology could eventually make it possible to measure incredibly small changes, giving scientists a powerful new tool to test fundamental physics, including dark matter. Anti-vaxxers have started a new campaign trying to stop parents from allowing their newborns to be given a vitamin K shot.

[00:19:13] [SPEAKER_00] Vitamin K is usually administered at the same time as hepatitis B vaccinations. Skeptics Tim Mendham says a vitamin K shot is safe and it saves the lives of babies, so it's not even a discussion.

[00:19:25] [SPEAKER_06] Vitamin K shots are given basically as soon as you're born. It's given at the same time as a hep B vaccine or treatment. It stops babies bleeding to death, almost making that hemophiliac. There's two sorts of vitamin K. One comes from plants, especially leafy green vegetables. Another comes from animal-sourced food, especially poultry and eggs, which babies don't eat. And apparently babies don't get vitamin K through the placenta or through mother's milk. So that's why they give a shot of vitamin K to newborn babies.

[00:19:51] [SPEAKER_06] If they don't have that, a lot of babies will have bleeding either internally, externally on the brain and there are babies that die. If you don't give vitamin K shots to babies, a lot more babies will die because of it and they'll bleed to death or they'll bleed into their brain. It's a fairly innocuous treatment for a fairly serious condition. It's something that should be done, but again, the anti-vaxxers are saying that they shouldn't let it happen. That vaccination is inherently bad and that no one ever died of these diseases. Well, they do.

[00:20:19] [SPEAKER_06] So until babies start eating regular foods, which is usually about when they're half a year old, something like that. And until their normal intestinal bacteria begin making vitamin K, they need it as a supplement, as a preventative. Probably the most frustrating thing the skeptics in the world will deal with. I know we had a survey once of what's the most important issues. And worldwide, it was the anti-vaxx movement. Worldwide, you ask any skeptic, what's the biggest issue? It's not Loch Ness Monster or flying saucers or flat earthers or things like that. It's vaccination. Anti-vax. That's the serious end of the skeptical world.

[00:20:48] [SPEAKER_06] Will we ever get rid of anti-vaxxers? Probably not, unfortunately. Wouldn't it be nice?

[00:20:51] [SPEAKER_00] That's the skeptics Tim Mendham. And this is Space Time. And that's the show for now.

[00:21:12] [SPEAKER_00] Space Time is available every Monday, Wednesday and Friday through Bytes.com, SoundCloud, YouTube, your favorite podcast download provider, and from Space Time with Stuart Gary.com. Space Time is also broadcast through the National Science Foundation on Science Zone Radio and on both iHeart Radio and TuneIn Radio. And you can help to support our show by visiting the Space Time store for a range of promotional merchandising goodies.

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[00:21:59] [SPEAKER_03] This has been another quality podcast production from Bytes.com.