10 Terrifying Things Scientists Think Are Lurking Inside the Milky Way

[00:00:00]All right, let's go. Number 10, the Milky Way's missing matter. In 2020, a team of astronomers cross-referencing decades of observational data arrived at a conclusion that should have been impossible. Nearly half of the ordinary matter the Milky Way should contain, according to every accepted cosmological model, simply could not be found. Not hidden in an unusual location, not misidentified, just gone, at least as far as our instruments were concerned.

[00:00:25]According to the standard model of cosmology, ordinary baryonic matter, the stuff that makes up stars, planets, gas clouds, and everything we can see or touch, accounts for roughly 5% of the universe's total mass energy content.

[00:00:38]The Milky Way, with its estimated 100 to 400 billion stars, should contain a calculable quantity of this matter.

[00:00:45]Astronomers had been confident they understood the basic inventory of our own galaxy. That confidence turned out to be premature. The accounting simply did not balance. When researchers totaled the observed stellar mass, the gas, the dust, and all the other detectable components of the Milky Way, they came up significantly short of the predicted figure. This was not a rounding error or an instrumentation quirk. This was a fundamental discrepancy, suggesting that enormous quantities of ordinary matter were somehow evading every detection method available to science. The leading resolution came from an unexpected direction. Astronomer Jean-Pierre Macquart and his colleagues published findings in Nature in May 2020, suggesting that fast radio bursts, those millisecond pulses of radio energy from across the cosmos, could be used as probes to map the diffuse material between galaxies. Their work pointed toward a medium called the warm-hot intergalactic medium, or WHIM, a vast web of filaments existing at temperatures between 100,000 and 10 million Kelvin. Too hot to emit visible light, too cool for standard X-ray detection, the WHIM had been hiding in a thermal gap between our instruments' capabilities. This thermal gap is not a minor technical inconvenience. It represents a blind spot that spans an enormous range of physical conditions, a zone in which matter can exist in enormous quantities while radiating almost nothing that our telescopes are designed to capture. The implication is unsettling. The very instruments we built to understand the universe were, by their design, incapable of seeing a substantial fraction of it. Even with the Whim identified as a candidate reservoir, the precise distribution of this hidden matter within our own galaxy's extended halo remains unresolved. We have mapped the Milky Way in extraordinary detail across decades of observation, and yet nearly half of everything it should contain remains effectively invisible to us, woven through the darkness between everything we know. Number nine, magnetars. On December 27th, 2004, a pulse of energy struck Earth's upper atmosphere, immeasurably compressed our planet's magnetosphere. It had crossed 50,000 light-years of space to reach us. Its source was a dead star roughly the size of a city, and it had released more energy in 0.2 seconds than our sun produces in 250,000 years. The object responsible was SGR 1806-20, a magnetar located near the edge of our galaxy.

[00:02:57]Magnetars are a subclass of neutron stars, the collapsed remnants of massive stars that have ended their lives in supernova explosions. Neutron stars are already extreme objects, packing more mass than our sun into a sphere roughly 20 km across. Magnetars take that extremity further, generating magnetic fields reaching 10 to the power of 15 gauss, roughly a quadrillion times stronger than Earth's own magnetic field. What makes magnetars genuinely terrifying is the scale of energy their behavior can release. The 2004 burst from SGR 1806-20 was detected and studied by multiple space observatories, and the numbers it produced were extraordinary. Astronomers calculated the energy output using data from NASA's Wind spacecraft and ESA's Integral Telescope, and the figures were initially considered errors. They were not errors. The burst was simply that powerful, arriving from across the galaxy, and still carrying enough energy to affect our atmosphere. The Milky Way is estimated to harbor approximately 12 to 30 confirmed magnetars, with theoretical models suggesting thousands more remain undetected. Their surface temperatures reach 1 million degrees Celsius. Their crusts are crystalline and under extraordinary stress, and when they fracture in what astronomers call starquakes, they release energy equivalent to millions of nuclear weapons in milliseconds. Palmer et al.

[00:04:16]published the definitive analysis of the 2004 event in the journal Science in 2005, confirming the burst as the most powerful cosmic event ever recorded affecting Earth directly. If a magnetar were positioned at the distance of the moon, its magnetic field would strip the iron from human blood and erase every magnetic storage device on the planet.

[00:04:35]The nearest confirmed magnetar sits safely distant, but confirmed is a word that depends entirely on the completeness of our catalogs, and our catalogs, by any honest assessment, are far from complete. Number eight, stellar-mass black holes. In October 2022, astronomer Karim Badry and his colleagues published a paper in Monthly Notices of the Royal Astronomical Society announcing the discovery of a stellar-mass black hole in the constellation Ophiuchus, just 1,560 light-years from Earth. It was the closest black hole ever confirmed. It had been there all along, invisible and silent, and we had simply never noticed it. The object, designated Gaia BH1, was identified not by what it emitted, but by the gravitational influence it exerted on a nearby sun-like star, whose unusual orbit betrayed the presence of an invisible companion roughly 10 times the mass of our sun. The European Space Agency's Gaia telescope, originally designed to map stellar positions with extraordinary precision, inadvertently became the tool that revealed our nearest known black hole. A second object, Gaia BH2, was confirmed in 2023 at approximately 3,800 light-years distance using the same astrometric technique. The existence of of objects is not in itself surprising. Stellar mass black holes form when massive stars exhaust their fuel and collapse. What is deeply unsettling is the arithmetic.

[00:05:54]Theoretical models predict the Milky Way contains somewhere between 10 million and 1 billion stellar mass black holes.

[00:06:00]As of the most recent surveys, astronomers have confirmed roughly 20.

[00:06:04]The ratio of predicted to observed is so extreme that it borders on absurdity.

[00:06:08]Those 20 confirmed objects were found primarily because they were actively feeding on companion stars, generating x-ray emissions that betrayed their presence. The overwhelming majority of stellar mass black holes are dormant, drawing in nothing, emitting nothing, detectable by nothing in our current arsenal of instruments. They sit in the darkness of interstellar space, their positions unknown, their nearest approaches to populated regions of the galaxy uncataloged. El Badry's work demonstrated that Gaia's precision astrometry could identify them through stellar motion, but the survey has only scratched the surface of what the galaxy actually contains. There are potentially a billion dark invisible gravitational wells distributed through the Milky Way around us. We have found 20. The other 999 million are out there, unannounced and unmapped. We have no reliable way of knowing how close any of them are.

[00:06:56]Number seven, the galactic center's radio filaments. In September 2022, researchers using the MeerKAT radio telescope array in South Africa's Karoo Desert published images of the galactic center that stopped the astronomy community cold. Stretching through the region surrounding Sagittarius A star, were hundreds of enormous thread-like structures, some extending up to 150 light-years in length, organized in parallel formations unlike anything previously documented in astrophysics.

[00:07:24]The filaments had been partially glimpsed before. Astronomer Farhad Yusef-Zadeh at Northwestern University had identified smaller-scale versions in the 1980s using earlier radio instruments, but MeerKAT, a 64-dish array operating with unprecedented sensitivity, revealed the true scale and complexity of these structures for the first time. Alongside the filaments, a separate radio-emitting bubble, approximately 430 light-years across, sat above the galactic plane. Its origin equally unexplained. Heywood et al. had first described this bubble in a 2019 Nature paper, but the 2022 survey placed it in context with the filaments and deepened the mystery considerably. The filaments appear in two distinct orientations, some running perpendicular to the galactic plane, others parallel to it suggesting two separate formation mechanisms operating in the same region.

[00:08:13]All of them emit synchrotron radiation, the characteristic glow produced when electrons are accelerated to near light speeds along magnetic field lines. What is accelerating those electrons to such extreme velocities, and why the resulting structures are so geometrically organized has not been satisfactorily explained by any current model. The leading hypothesis connects the filaments to Sagittarius A* the supermassive black hole at the galactic center, and to the ancient outburst that produced the Fermi bubbles. The idea is that energetic particles expelled during that event are being channeled along magnetic field lines threading through the region, producing the observed structures as a kind of afterglow of ancient violence. But the precise geometry, the parallelism, the sheer regularity of the formations does not fit neatly into this explanation without significant assumptions. What makes the filaments stranger still is what their regularity implies about the magnetic environment of the galactic center. For charged particles to align so uniformly across structures spanning over a hundred light-years, the magnetic field threading that region must be extraordinarily organized. Turbulent, chaotic magnetic environments produce diffuse, irregular emission. The filaments suggest something more structured, a coherent architecture of magnetic field lines on a scale that has no clear analog elsewhere in the observable galaxy. We do not fully understand what maintains that structure, or how long it has existed.

[00:09:35]We have studied the galactic center for decades across every wavelength available to us and only now with MeerKAT operating at its design sensitivity are we seeing structures of this scale and strangeness. What other features of our own galaxy's core remain invisible to us simply because we have not yet built the instrument capable of revealing them. Number six, the dark matter halo. In 2022, the LUX Zeppelin experiment operating 1.5 km underground at the Sanford Underground Research Facility in South Dakota completed its most sensitive search for dark matter particles to date. The detector filled with 10 tons of liquid xenon and shielded from cosmic rays by a kilometer and a half of solid rock found nothing.

[00:10:14]It was the most precise null result in the history of dark matter research and it made the mystery significantly worse.

[00:10:20]Dark matter is not a fringe concept or a theoretical speculation. It is a load-bearing component of every accepted model of how galaxies form and maintain their structure. The Milky Way is embedded in a dark matter halo estimated to extend up to 1 million light-years from the galactic center containing roughly 1 trillion solar masses of material that interacts with ordinary matter only through gravity. Remove it from the equations and the galaxy does not hold together. The stars in the outer disk orbit far too fast for the visible mass to explain. Dark matter must be there. It simply refuses to be found. The leading candidate particle for decades has been the WIMP, the weakly interacting massive particle, a hypothetical object with a mass somewhere between 35 and 50 times that of a proton that should in theory occasionally interact with ordinary matter in detectable ways. Experiments including XENON1T at Italy's Gran Sasso Laboratory and LUX Zeppelin in South Dakota have pushed the sensitivity of WIMP detection to levels that according to the most popular theoretical models should have produced results by now. The silence from these detectors is not merely a negative result. It is forcing a genuine reckoning with whether WIMPs exist at all. Alternatives have been proposed: axions, sterile neutrinos, primordial black holes formed in the early universe. None have been confirmed. Each successive non-detection narrows the parameter space available to theorists and raises the possibility that dark matter is something more exotic than any current model describes.

[00:11:45]The Planck collaboration's 2018 cosmological data confirm the figure of approximately 27% of the universe's content being dark matter. The substance is real. Its nature is not understood.

[00:11:57]We live inside a structure, the dark matter halo of our own galaxy, that outweighs everything we have ever seen or measured in the Milky Way combined.

[00:12:04]It holds us together, shapes our orbit, and has resisted every attempt at direct detection for decades. The dominant component of our own galaxy remains in the most literal scientific sense completely unknown. Number five, rogue planets. In October 2023, researchers using the James Webb Space Telescope published a survey of the Orion Nebula that forced a quiet but significant recalculation of the galaxy's contents.

[00:12:29]Among the findings were more than 40 free-floating planetary mass objects drifting through the nebula without any parent star. Several of these objects appear to exist in pairs traveling together through open space. No accepted model of planet formation could explain how they got there. The paper, authored by Samuel Pearson and Mark McCaughrean, introduced a new category of object dubbed jumbos or Jupiter-mass binary objects with masses between roughly 1 and 13 times that of Jupiter.

[00:12:55]Free-floating planets, objects ejected from solar systems during the chaotic early stages of planetary formation, had been theorized and occasionally observed before. But objects of this mass existing in gravitationally bound pairs orbiting each other in open space far from any star had never been predicted.

[00:13:12]Their existence implies either a significant gap in our understanding of how planets form or a formation mechanism that operates entirely outside current theory. The broader population of rogue planets in the Milky Way is staggering to contemplate. Conservative estimates place the number at approximately 50 billion free-floating planetary bodies. Some theoretical models incorporating sub-Earth mass objects, too small for current detection, raise that estimate by orders of magnitude, potentially to the trillions. These objects generate no light. They emit minimal heat. They are functionally invisible to most of our detection instruments, detectable only through gravitational microlensing events that require precise alignment and careful monitoring. A rogue planet of sufficient mass transiting within a few light-years of our solar system would be essentially impossible to detect in advance with current technology. We would not see it approaching. We would not know it was nearby. The first indication of its passage might come not from any direct observation, but from subtle statistical anomalies in the orbital behavior of distant objects in the outer solar system, changes accumulating gradually over decades before anyone recognized their cause. The implications for our own solar system are not trivial. A rogue planet passing through the outer reaches of our solar system would not need to approach the inner planets to cause significant disruption. The Oort Cloud, a vast spherical reservoir of comets extending roughly halfway to the nearest star, is sensitive to gravitational perturbations. A sufficiently large rogue planet transiting the Oort Cloud could scatter comets inward toward the inner solar system, triggering an increased impact rate that would persist for millions of years. We would have almost no advance warning of such a transit using current survey capabilities. There may be trillions of invisible planetary bodies drifting silently through the galaxy, some potentially passing through the solar system's outer boundaries right now, and we would have almost no way of knowing until they had already come and gone. Number four, the Fermi bubbles and Sagittarius A's hidden history. In November 2010, Meng Su, Tracy Slatyer, and Douglas Finkbeiner at Harvard published an analysis of data from NASA's Fermi Gamma-Ray Space Telescope that revealed two colossal structures extending above and below the center of the Milky Way. Each one stretched approximately 25,000 light-years from the galactic plane. Together they spanned half the diameter of the galaxy.

[00:15:31]They had been there for millions of years and no one had known. The structures became known as the Fermi bubbles and their discovery was genuinely shocking to the astronomical community. Features of this scale extending far above and below the visible disc of our own galaxy had remained completely undetected for the simple reason that they radiate primarily in gamma rays, a wavelength invisible to human eyes and inaccessible to most conventional telescopes. The Fermi space telescope specifically designed for high-energy observation finally had the sensitivity to resolve them. In 2020, the eROSITA X-ray telescope revealed even larger associated structures, the eROSITA bubbles, extending up to 45,000 light-years in each direction from the galactic center, as reported by Predehl and colleagues in Nature. The energy contained within the Fermi bubbles is almost incomprehensible. Published estimates place it at the equivalent of approximately 100,000 supernova explosions. Their edges are unusually sharp and well-defined, which tells scientists something important about their origin. Gradual continuous processes produce diffuse irregular structures. Sharp boundaries indicate a single dramatic event, an enormous release of energy over a relatively brief period, after which the bubbles expanded outward and cooled into their current configuration. The most widely accepted explanation points to Sagittarius A* the supermassive black hole at the galactic center. Multiple studies, including a 2021 analysis in the Astrophysical Journal, have concluded that Sagittarius A* underwent a massive active phase approximately 2 to 4 million years ago, during which it was somewhere between 10 and 100 billion times more luminous than it is today.

[00:17:05]The black hole we observe now is quiet, almost dormant by galactic standards.

[00:17:09]The Fermi bubbles are what it left behind the last time it was not. For millions of years, two structures each spanning a quarter of the galaxy have been silently expanding outward from our galactic center, the preserved record of a violence that predates our species by millions of years, and whose full implications for the present state of the galaxy we are still working to understand. Number three, Sagittarius A, the sleeping giant. On May 13th, 2019, astronomers monitoring the galactic center detected a burst of near infrared radiation from Sagittarius A* that was 75 times brighter than the black hole's established normal output. It was the most powerful flare ever recorded from our galaxy's central black hole. It peaked and faded over a period of roughly 2 hours. No one had predicted it. No model had anticipated an outburst of that magnitude, and the team led by Tuan Do at UCLA, who published the findings in the Astrophysical Journal Letters, were candid about what it meant. Our understanding of Sagittarius A*'s behavior was less complete than assumed. Sagittarius A* sits 26,000 light-years from Earth at the precise gravitational center of the Milky Way.

[00:18:14]Its mass was established at approximately 4.15 million solar masses through decades of work tracking the orbits of stars in its immediate vicinity, a project that earned astronomers Reinhard Genzel and Andrea Ghez the Nobel Prize in Physics in 2020.

[00:18:28]On May 12th, 2022, the Event Horizon Telescope collaboration published the first direct image of Sagittarius A*, confirming its nature beyond any reasonable doubt. By the standards of supermassive black holes, it is considered unusually quiet, accreting matter at an extremely low rate compared to the active galactic nuclei observed in other galaxies. The 2019 flare complicated this characterization. In the years prior, a dense cloud of gas designated G2 had been tracked approaching Sagittarius A* and was observed to undergo partial disruption as it passed close to the black hole between 2013 and 2014. The passage was expected to trigger some brightening, and modest increases were observed.

[00:19:08]Then, several years later, came the May 2019 event, far exceeding anything the G2 interaction alone should have produced, suggesting either a delayed response or an entirely separate triggering mechanism that remains unidentified. It is worth dwelling on what the 2019 flare actually represents as a data point. Astronomers have been monitoring Sagittarius A* in the near infrared for roughly two decades with any serious consistency. Two decades is not a representative sample of a black hole that has existed for billions of years. The flare may have been a rare anomaly. It may also have been entirely routine by the standards of Sagittarius A*'s longer history, the kind of event that occurs regularly but had simply never been observed before because we had not been watching long enough or carefully enough to catch it. We genuinely do not know which of these interpretations is correct. Sagittarius A* is currently quiet. The operative word is currently. Its behavior over the past few million years, written into the structure of the Fermi bubbles and the eRosita bubbles, demonstrates a capacity for activity that dwarfs anything in the observational record. Material is known to be present in the galactic center region, feeding slowly toward the black hole. The threshold between its present near dormant state and a significantly more active phase is not well constrained by any current model. We observe it in a single moment of its 13.6 billion year existence and draw conclusions about its stability from a data set measured in decades. It sits 26,000 light years away, contains the mass of 4 million suns, and spent millions of years in an active state powerful enough to blast structures across half the galaxy. In 2019, without any warning, it briefly became 75 times brighter than normal. What we understand about Sagittarius A*'s future behavior may be considerably less than we currently believe. Number two, the galactic center gamma-ray excess. In 2009 and 2010, astronomer Dan Hooper at the Fermi National Accelerator Laboratory and his colleague Lisa Goodenough published analyses of data from NASA's Fermi Large Area Telescope revealing something unexpected at the center of the Milky Way. After accounting for all known sources of gamma-ray emission, a persistent smoothly distributed excess remained.

[00:21:19]The signal could not be attributed to any cataloged astrophysical source. It peaked at energies between 1 and 3 giga electron volts and extended outward from the galactic center in a roughly spherical pattern. It matched with uncomfortable precision the theoretical signature of dark matter particles annihilating each other. The galactic center gamma-ray excess, as it became known, has now persisted across more than a decade of continuous Fermi telescope observations. Its spatial morphology, the way it is distributed across the sky, is consistent with a dark matter halo profile. Its energy spectrum, the specific energies at which it peaks, aligns with predictions for dark matter particles with masses of approximately 35 to 50 giga electron volts annihilating into bottom quarks.

[00:22:03]These are not approximate matches or loose correlations. They are precise agreements with specific theoretical predictions that were made before the signal was found. The scientific community has searched extensively for alternative explanations. The most serious candidate is an unresolved population of millisecond pulsars, rapidly spinning neutron stars that emit gamma rays. Individual millisecond pulsars are too faint to detect at galactic center distances, but a sufficiently large population could collectively produce a diffuse excess.

[00:22:33]However, studies examining the signal's detailed morphology have struggled to fully reconcile the pulsar hypothesis with the observed characteristics. In 2022, a paper by Rebecca Leane and Tracy Slatyer in Physical Review Letters raised a more troubling concern, demonstrating that standard analysis methods used to search for the excess could systematically obscure genuine dark matter signals, casting doubt on earlier work that had seemed to favor the pulsar interpretation. The debate has not been resolved. Both the dark matter interpretation and the millisecond pulsar explanation have active credential proponents in the astrophysics community. What is not disputed is the excess itself. The signal is real. It has been measured and confirmed repeatedly. Something at the center of the Milky Way is producing gamma rays at energies and in spatial distributions that current catalogs of known sources cannot fully account for.

[00:23:22]At the heart of our galaxy, something has been producing a decade-long gamma ray signal that matches the predicted signature of annihilating dark matter more closely than any known astrophysical source. And the scientists who study it most carefully are not yet willing to rule out that this is the first indirect detection of the invisible substance that built the universe itself. Number one, the great silence. In 2021, researchers Tom Westby and Christopher Conselice at the University of Nottingham published a study in the Astrophysical Journal applying updated astrophysical and biological assumptions to the question of how many communicating civilizations the Milky Way should currently contain.

[00:24:00]Using conservative estimates for the rate of star formation, the prevalence of habitable planets informed by NASA's Kepler mission data, and the minimum time required for intelligent life to develop, they arrived at a figure.

[00:24:11]Approximately 36 active communicating civilizations should exist in our galaxy right now. The number was presented carefully with full acknowledgement of its uncertainties. What the paper could not address was the aspect of the calculation that has haunted scientists since physicist Enrico Fermi first raised it informally in 1950. If the galaxy should contain communicating civilizations, why is there no evidence that it ever has? The Milky Way is 13.61 billion years old. The physics and chemistry required for life as we understand it have been in place for the majority of that time. Civilizations arising just 1 billion years before our own would have had time, even at sublight speed expansion rates, to colonize every reachable star system in the galaxy many times over. The observable signatures of a galaxy-spanning civilization, engineered stars, structured energy used detectable across light years, deliberate signals, megastructures would be unmistakable and by now unavoidable. We have looked for all of these things. We have found none of them. The galaxy appears by every measure currently available to be empty of intelligence except for us. It is worth being precise about what we mean when we say we have looked. The SETI program and its successor efforts have monitored thousands of star systems for artificial radio signals. The Breakthrough Listen initiative, launched in 2015 with substantial funding and access to some of the world's most sensitive radio telescopes, has surveyed millions of stars across a wide range of frequencies. The results have been, without exception, silence. Not ambiguous signals of uncertain origin, not faint candidates requiring further investigation, silence. In more than 60 years of dedicated search, nothing in the sky has returned the unmistakable signature of another intelligence reaching outward into the dark. The most mathematically rigorous framework for thinking about this silence was proposed by economist Robin Hanson in 1998 and is known as the Great Filter. The argument is straightforward. Something consistently prevents matter from evolving into galaxy-spanning intelligence. That filter could lie behind us, meaning the evolution of complex life or technological civilization is extraordinarily rare and we are among the first to achieve it. Or it could lie ahead of us, meaning the barrier is something that technological civilizations encounter after reaching our current stage of development, something that ends them before they can expand. The Fermi paradox does not on its own tell us which of these is true, but it insists that one of them must be.

[00:26:31]The discovery of simple microbial life elsewhere in the solar system, on Mars, in the oceans of Europa, in the clouds of Venus, would be, counterintuitively, among the most alarming findings in the history of science. Not because life itself is frightening, but because of what its independent emergence would imply statistically. If life arises readily wherever conditions permit, then the Great Filter almost certainly does not lie behind us. The barrier is not the emergence of life. It is something that comes later, something we have not yet encountered, something that for every civilization before us that reached our level of development appears to have been insurmountable. Every item in this countdown has described something hiding inside the Milky Way, invisible matter, dormant black holes, a sleeping giant at the galactic center, unexplained energy signals, the invisible scaffolding of dark matter woven through everything. Each of these is a genuine mystery, scientifically documented and unresolved, but they are mysteries about physics. The great silence is a mystery about fate. If the great filter lies ahead, then everything described in this video, the magnetars, the rogue planets, the gamma-ray excess, even Sagittarius A*s hidden potential for violence, may simply be components of a universe that is not, in the long run, hospitable to beings like us. The silence does not require any of those specific mechanisms. It merely requires that something somewhere in the development of every civilization goes wrong before the galaxy fills up. The most terrifying thing hiding inside the Milky Way may not be a black hole, a magnetar, or an ocean of invisible matter pressing in from every direction.

[00:28:01]It may be the silence itself, a 13.6 billion-year-old galaxy threaded with the chemistry of life, seeded with billions of potentially habitable worlds, old enough to have been transformed by intelligence a hundred times over, and yet conspicuously, persistently, deafeningly empty.

[00:28:17]Whatever the galaxy is hiding from us, it may already be hiding it inside us, too. If you want to see more videos like this, click the video on screen now and make sure to subscribe.