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A New Study into Dark Matter in the Bullet Cluster Could Disprove its Existence
Dark Matter (DM), that mysterious matter that accounts for 85% of the Universe’s mass, continues to fascinate and puzzle scientists. While we are unable to resolve it in visible light, its influence can be seen in the rotational curves of galaxies, Dark Matter halos, and the gravitational lenses they cause. The Bullet Cluster, consisting of two colliding galaxy clusters located about 3.7 billion light-years from Earth, is of particular interest to astronomers searching for DM. The reason being that gravitational lensing studies are claimed to provide strong evidence for its existence.
When examining the Bullet Cluster, scientists noted that galaxies located beyond it appeared distorted, the result of the cluster’s gravity warping spacetime around it.
Using the James Webb Space Telescope (JWST), an international team of researchers analyzed new data and existing images to gain new insight into this cluster. According to their analysis, there is an alternative explanation for the observed effects of the cluster that does not involve DM at all. Their findings could force astronomers to reevaluate what was considered to be some of the most compelling evidence for DM.
The collision that created the Bullet Cluster occurred around 4 billion years ago, when two clusters containing hundreds of galaxies collided at speeds of over 2,500 km/s (1,550 mps). While galaxy clusters contain stars in the trillions, the majority of their visible matter consists of gas located between star systems – aka. the interstellar medium (ISM). During the collision, the two gas clouds experienced frictional forces as they passed through each other, causing them to both heat up and slow down. These gas clouds are visible today as diffuse patches that glow brightly in the X-ray spectrum.
*Image from the James Webb Space Telescope of the inner region of the Bullet Cluster. © Image: NASA/ESA/CSA/STScI/CXC/Caltech/IPAC*
However, the galaxies in the two clusters passed through each other without incident, since the distance between individuals stars was so great that they were able to fly past each other. As a result, the two clusters were separated from the interstellar gas they carried with them. In the Webb image (shown above), the hot gas clouds appear in pink, while the distribution of dark matter appears in blue. Cluster 1 is visible to the left of the left-most gas cloud, while Cluster 2 is just to the right of the right one. These four structures form the entirety of the Bullet Cluster.
Another thing that is clear from the image is how galaxies beyond the cluster appear distorted and crescent-shaped. Strangely, the galaxy clusters show the strongest lensing effect, despite their relatively low mass. Meanwhile, the two luminous clouds, where the greatest mass should be concentrated, show a comparatively weak effect. This suggests that there is additional matter hidden in these galaxies that astronomers cannot detect.
According to current theories, DM interacts with normal matter only through gravity, and not through the other fundamental forces (electromagnetism, the weak and strong nuclear forces). Because of this, it is not slowed down by friction and would not be separated from the galaxy clusters. The data also supports another interpretation: Modified Newtonian Dynamics (MOND), the cosmological model that does away with DM entirely. To this day, MOND has been considered something of a fringe theory because it cannot explain phenomena such as the Bullet Cluster.
“However, we show in our study that, on the contrary, the Bullet Cluster is actually particularly consistent with the MOND scenario,” said HISKP researcher Dong Zhang, the lead author and the one who carried out a large proportion of the calculations. “If massive stars eventually burn up, they become neutron stars or black holes. Like dark matter, both are invisible and can only be detected by the huge gravitational forces that they exert.”
Artist’s impression of “ghost galaxies” within the Milky Way’s Dark Matter Halo. Credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI)
As HISKP Professor Pavel Kroupa, a co-author on the study, added:
This observation has so far been considered evidence of the existence of dark matter. The remnants of massive stars take on the role of dark matter to a certain extent in the MOND scenario. Even in the standard model, which assumes the existence of dark matter, its postulated quantity would have to be significantly reduced – by around half.
Additionally, new data from Webb have enabled more precise calculations of the number of stars and heavy elements in both clusters. Dr. Indranil Banik of the Institute of Cosmology and Gravitation at the University of Portsmouth (another co-author) showed that the newly calculated numbers of stars and other objects can account for the observed gravitational lensing effect. This new data and insight into the Bullet Cluster have cast doubt on a key piece of evidence for DM and made for a more compelling case for MOND.
Further Reading: Universität Bonn, Physics Review D
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Boyle Heights warehouse cleanup halted by solar operator, Lineage says

Cleanup efforts at a fire-ravaged cold storage warehouse in Boyle Heights just got messier.
In a letter sent Friday, Greg Lehmkuhl — chief executive of Lineage, which manages the facility — accused Altus Power, the solar panel subcontractor whose rooftop equipment is suspected of potentially sparking the June 17 blaze, of obstructing demolition efforts.
According to the letter, which was addressed to Los Angeles Mayor Karen Bass and county Supervisor Hilda Solis, Lineage was prepared and had the necessary permits to begin demolition work at the site Friday, as required under emergency executive orders and a Los Angeles County public health directive issued June 29.
“Unlike Altus and other involved parties, Lineage has been on the front lines since day one, and we are committed to doing everything in our power to execute a safe and swift remediation effort,” Lehmkuhl wrote.
An Altus spokesperson said Friday that the company’s primary concern is the well-being of the community affected by the fire, and added that the company is cooperating with local officials as the investigation continues.
Lehmkuhl wrote that crews were ready to begin removing debris when they received a notice Thursday ordering them to halt demolition. The letter did not explain the pause, but suggested it may have been intended to preserve evidence.
“The work we planned does not affect the suspected area of origin or materials potentially relevant to evidence preservation or further investigation,” Lehmkuhl wrote. “This is unacceptable. Public safety is our number one priority.”
However, the Altus Power spokesperson said because an official cause of the fire has not yet been determined, concerns about the investigation stand.
“In the last 24 hours multiple parties joined in asking Lineage to appropriately preserve and not destroy relevant evidence during its site remediations,” the Altus spokesperson told The Times. “It is unfortunate that Lineage appears to be focused on pointing fingers rather than getting this community the swift clean-up and answers it deserves.”
Lineage previously said the fire started days after Altus Power conducted performance tests on the warehouse rooftop June 17.
Lehmkuhl said there is an urgent need to prevent additional flareups, clear debris and address the persistent odor of millions of pounds of rotting food at the site.
Many residents living near the warehouse have expressed concerns for their health and loved ones, with some calling for the warehouse to shut down entirely.
Councilmember Ysabel Jurado, who represents Boyle Heights, said in a written statement that “no private party should be allowed to use process, finger-pointing, or liability disputes as an excuse to slow down cleanup that the community urgently needs.”
“I am calling on Lineage, Altus, the property owner, and every involved party to cooperate immediately with the City, County, LAFD, Public Health, and regulatory agencies,” Jurado said in the statement to The Times. “If there are legitimate evidence-preservation concerns, they must be addressed through a clear, written protocol that allows investigators to do their work without delaying urgent remediation.”
Crews battled the Boyle Heights warehouse fire for about a week before they got it under control. Questions remain about how long the cleanup process will take, and what long-term repercussions there may be from the resulting air pollution.
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Blistering Heat Puts Damper on Some Fourth of July Events
While relief could come to the Great Lakes and parts of the Northeast over the weekend, the Mid-Atlantic and Southeast will stay hot.
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This Giant Planet Survived the Death of its Star
All stars die eventually, including our Sun. Depending on the star, that can spell doom for planets. Massive stars die in cataclysmic explosions called supernovae, and their powerful blast waves can destroy any planets within range. If our Sun were massive enough to explode like this, it would mean an instantaneous end for Earth. But the Sun isn’t big enough.
Instead, the Sun’s end is more prosaic. As it runs out of fuel for fusion, it will gradually swell and cool, becoming a red giant. As it swells, it will engulf Mercury and Venus, but maybe not Earth. Astronomers aren’t certain, but Earth may survive the Sun’s swelling. If it does, it’ll face much different prospects. Earth will then orbit a white dwarf, for a time surrounded by a glorious nebula created by the Sun as it shed layers of gas. But that fate is uncertain, too.
Astronomers have found intact planets orbiting white dwarfs, showing that planets can survive the evolutionary shift of their stars. One of them is named WD 1856 b, where WD stands for white dwarf. It’s about 80 light years away, and TESS discovered it in 2019. The star it orbits is about 5.8 billion years old and half the mass of the Sun.
The planet is a giant with a radius about 10 times larger than Earth’s. It’s extremely close to its star, orbiting at about 0.02 astronomical units. It whips around the star rapidly, with an orbital period 60 times shorter than Mercury’s around the Sun.
Since its discovery, astronomers have wondered about it. To be in this orbit, the planet could have migrated inward after the star became a white dwarf. Otherwise, it would’ve been destroyed by engulfment when the star became a red giant.
This planet has led to questions about habitability. If planets can survive a star’s red giant phase, can they somehow be habitable? White dwarfs don’t generate heat by fusion, but they have remnant heat that can take trillions of years to dissipate, enough to power life on a nearby planet.
Scientists want to know how the planet survived in the first place, and new research in Nature examined its atmosphere for clues. It’s titled “Aerosols and hydrocarbons in the atmosphere of a white dwarf planet.” The lead author is Ryan MacDonald, a lecturer in extrasolar planets at the University of St. Andrews in Scotland.
“The planet is quite the oddball,” said lead author MacDonald in a press release. “It’s about the size of Jupiter, but the white dwarf it orbits is the size of Earth, so the planet is seven times larger than its star.”
Since it’s the size of Jupiter, this system could be a glimpse into the future of our Solar System. When the Sun becomes a red giant, it will engulf planets that are too close. But the fate of the more massive planets further from the Sun is unclear.
“We’re used to looking back in time when we use telescopes, but this is the first time we have been able to look forward to what might happen to the outer planets around the remnant of a Sun-like star. It’s like using a time machine to peer into the distant future of our Solar System,” added MacDonald.
“Several planet candidates have recently been identified orbiting white dwarfs, demonstrating that planets can survive the stellar post-main-sequence stage intact,” the authors write. “Little is known about the atmospheric composition of post-main-sequence planets, with the most evolved transiting planets with atmospheric detections so far orbiting subgiants.”
Some white dwarfs have debris disks made of material from the planets they destroyed when they were red giants. Astronomers think that planets can form in them, but have dismissed that possibility in this case. Image Credit: NASA/JPL-Caltech.
When a red giant star engulfs its closest planets, it can create a debris disk. Astronomers think it’s possible that explanets could form in this disk, but that’s not possible in this situation. The debris disks aren’t massive enough for a planet this massive to form.
That leaves only two explanations for WD 1856 b: it may have been engulfed by the star and somehow survived, coming out of the harrowing experience intact. Or it migrated inward without being engulfed. That inward migration didn’t have to be driven solely by the star itself. WD 1856 is actually a triple star system with two red dwarfs.
“The big question is how WD1856b ended up where it is today, and there are two theories,” said study co-author Christopher O’Connor of Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics. “One is that the planet was swallowed by its host star as it was dying and managed to survive on the other side. The other is that the migration took place due to the gravitational effect of other objects in the system. The white dwarf is part of a triple star system, and the outer companion stars could have influenced WD1856b’s orbit.”
This work is based on observations of the planet’s atmosphere with the JWST. The researchers used the telescope to obtain transmission spectroscopy with the telescope’s NIRSpec instrument. They also determined the planet’s temperature. The results are vital clues to the planet’s history.
This is the atmospheric retrieval of the transmission spectrum of WD 1856 b from the JWST. It shows multiple CH4 absorption features and one tentative ethane feature. Image Credit: MacDonald et al. 2026 Nature.
The temperature is much higher than expected. While the expected planetary equilibrium temperature is about 160 Kelvin, the temperature as measured is between 390 and 412 K. So the planet is much hotter than it should be if it were heated only by starlight. These observations show that the planet survived the red giant phase, migrated inward and experienced heating. This can also explain the exoplanet’s tight orbit.
“On the basis of cooling models, these results indicate that WD 1856 b underwent a migration-related reheating event 3.0–5.5 Gyr into the white dwarf phase, consistent with post-main-sequence tidal evolution to the present-day 0.02-au circular orbit,” the authors write.
The JWST detected an abundance of methane in the giant planet’s atmosphere. This strongly suggests that it formed further away from the star and migrated inward. Image Credit: NASA, ESA, CSA, Joseph Olmsted (STScI)
The observations found hydrocarbons in the atmosphere, specifically methane (CH4), at about 7%. This is also evidence of the planet migrating inward after the star’s red giant phase. A 7% CH4 atmosphere is a carbon-rich atmosphere. For this much methane to be present, the planet’s H2 atmosphere had to be enriched by carbon. This strongly suggests that the planet formed beyond its system’s water and carbon monoxide ice lines, then migrated inward.
“Our findings have bearing on the long-term fate of our solar system,” O’Connor said. “In roughly five billion years, our Sun will die, and we don’t know precisely what will happen to the planets at that time. The fact that planets can survive into that final stage of the stellar life cycle really widens the range of possibilities for where and when habitable planets might exist in the universe.”
There’s much to learn about exoplanets and their fates as their stars age and leave the main sequence. While the JWST is known for examining the red-shifted light from ancient objects like the first galaxies, one of its science themes is planetary systems. It’s powerful spectrometry capabilities let it examine exoplanet atmspheres in detail, providing clues to their origins, and their fates.
“Our results provide a window into the ultimate fate of giant planets orbiting stars with masses similar to our Sun,” the authors write. “As WD 1856 b demonstrates, spectroscopy of planets orbiting white dwarfs offers a new opportunity to determine the fate of planetary systems after the death of their star,” they conclude.
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