Ghost stars: The radical theory that could solve the mystery of dark matter (2022)

Look up at the sky after sunset and the familiar quilt of night is punctured with bright stars. These blazing furnaces are so vivid that we can see their light, despite the fact that even the nearest are quadrillions of kilometres away.


It’s a sight most of us have seen on countless occasions, so you’d be forgiven for thinking that all stars must behave this way. After all, isn’t shining just what a star does?

Yet if a flurry of recent findings is to be believed, there’s an entirely different class of stars lurking out there – stellar ghosts cloaked under a veil of darkness. These transparent, invisible stars give out no light whatsoever, meaning they skulk unseen in the celestial shadows.

Astronomers already suspect that, unlike ordinary stars, most of the Universe is hidden from view. When they look at galaxies, such as our own Milky Way, they find stars on the outer edges moving far too fast. So fast, in fact, that they should fly off into space.

For them to be kept in tow, there has to be something reining them in. The most popular explanation is that there’s a lot of hidden material in the Galaxy providing a significant amount of extra gravity. Scientists call this material ‘dark matter’ and it’s thought to outnumber the ordinary matter that you and I are made of by a ratio of more than five to one.

The majority verdict over the last couple of decades has been that this celestial glue is made of Weakly Interacting Massive Particles (WIMPs). This had led physicists on an unprecedentedly intense hunt to snare them. They’ve built detectors under the ice in Antarctica, in abandoned gold mines and even aboard the International Space Station.

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So far all their searches have come up empty. It’s somewhat ironic, then, that one of our WIMP detectors may have just found evidence in favour of a rival theory of dark matter – one that opens the door to the possibility of invisible stars.

Read more about dark matter:

  • What is dark matter?
  • Desperately seeking dark matter: the search for 95 per cent of the Universe
  • Could ‘dark matter’ just be dead stars and planets floating in the depths of space?

Dark bosons

The XENON1T experiment is tucked away 3,600 metres beneath the Gran Sasso mountain in Italy and is the largest underground research facility in the world. A huge tank containing over three tonnes of liquid xenon was designed to act as a WIMP trap – if a WIMP hits an atom in the tank, then the atom will recoil and spit out electrons and photons (particles of light).

Yet in the summer of 2020, the XENON1T researchers announced that they’d seen something unexpected: an excess of electrons that didn’t fit with an influx of WIMPs. According to Dr Tongyan Lin, from the University of California, San Diego, there are three possible explanations.

The first two explanations are particles from the Sun, or radioactive contaminants in the experiment. The third, and by far the most interesting, is the arrival of another proposed form of dark matter: dark bosons.

A boson is a subatomic particle that carries a force. The photon, for example, is a boson that carries the electromagnetic force. A dark boson, so the theory goes, could either be dark matter itself or at the very least be responsible for the way dark matter interacts with ordinary matter. If the XENON1T signal stands up to further scrutiny – and the other more mundane explanations can be excluded – it could be the first sign that dark bosons are indeed out there.

Ghost stars: The radical theory that could solve the mystery of dark matter (1)

A further tantalising hint followed in September 2020, a few months after the XENON1T announcement. Two teams of physicists – one in Europe and the other in the USA – used lasers to confine atoms in a table-top trap. Like all atoms, they contained electrons whizzing around a central nucleus in orbits known as energy levels.

Dr Michael Drewsen, from Aarhus University in Denmark, is part of the European team. He says that the presence of a dark boson would create a force that disturbs the atom. “We’d see a small shift in the electron’s energy level,” he says.

While his team didn’t find such a shift, his colleagues in the USA did. As always, scientists are a cautious bunch and aren’t able to immediately leap to the conclusion that a dark boson really is to blame.

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“It could be because they were using a heavier atom,” Drewsen says. The European team trapped calcium, whereas the American team used ytterbium. Still, their findings, coupled with those from XENON1T, are a shot in the arm for those arguing dark bosons are real. The circumstantial evidence is certainly mounting.

Astronomers are bolstering the case yet further. If dark bosons are affected by gravity, then they should also clump together in the same way that ordinary matter does. “They would self-gravitate into boson stars,” says Hector Olivares, from Radboud University in the Netherlands.

Ghost stars: The radical theory that could solve the mystery of dark matter (2)

These stars would be very different from those strung out in constellations across the night sky. For starters, with no nuclear fusion taking place in their cores, they wouldn’t produce any light. They would also be transparent. “Anything that approached them would pass straight through,” says Olivares.

The lack of any non-gravitational interaction between ordinary matter and dark matter means it would be like a ghost drifting through a wall. After all, the only reason you don’t fall through a chair is the repulsive electromagnetic force between the electrons in your bottom and those in the seat.

According to Olivares, a boson star could potentially grow as big as the supermassive black holes (SMBHs) thought to reside at the heart of every major galaxy. In fact, he suspects it may be possible for a giant boson star to initially fool us into thinking it’s a SMBH. “Both of them lack a solid surface,” he says, referring to the fact that a black hole is a cosmic trapdoor with a point of no return known as the event horizon.

Black holes and dark boson stars

Olivares recently conducted the first simulations of material falling towards a black-hole-like boson star. “We discovered that they are distinguishable from black holes,” he says. That’s because they lack a shadow.

In 2019 astronomers released the first-ever image of a black hole, including a dark region – a shadow – rendered by the missing light that the black hole swallowed. While a boson star doesn’t have a shadow – material passes straight through instead of being swallowed – it does sometimes have a feature that does a good job of impersonating one. Olivares calls it a pseudo-shadow.

“In most cases we don’t see a pseudo-shadow and when we do it’s smaller than a black hole’s shadow,” he says. We could soon use this as a test to see if the SMBH at the centre of the Milky Way is actually a giant boson star. “It’s something that can be distinguished using the Event Horizon Telescope [which was the same instrument used to capture the first black hole photograph],” Olivares says. That work is currently ongoing.

Ghost stars: The radical theory that could solve the mystery of dark matter (3)
(Video) Hunt for Dark Matter | How the Universe Works

While we patiently wait for that result, Dr Juan Calderón Bustillo from the University of Santiago de Compostela in Spain may have already found two boson stars masquerading as black holes. Calamitous celestial collisions create ripples – gravitational waves – which trundle out through the Universe and reach Earth.

They were picked up for the first time back in 2015 using the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the USA. The majority of the events we’ve seen so far have been binary black holes – two gravitational monsters orbiting each other before spiralling into oblivion.

Usually, there are three distinct stages to such a collision – the in-spiral, the merger and then the new mega black hole it creates. But, according to Bustillo, one particular event sticks out as odd: GW190521. “We don’t see that first in-spiral stage,” he says. “It could be a head-on collision instead.”

The rest of the black hole mergers we’ve seen so far come from two black holes already orbiting each other. However, if two previously unconnected black holes smashed together, that could explain the lack of an in-spiral stage before collision. So Bustillo did the maths, but that explanation didn’t fly.

“The gravitational wave signal lasts longer than you would expect,” he says. The resulting black hole also spins faster than it should – a head-on collision wouldn’t provide the same rotational boost as a pair of black holes already pirouetting around one another. “So the gate is open for other explanations,” he adds.

Bustillo wondered if a head-on collision between two boson stars could fit the bill instead. It turns out they can. According to his research, there’s an extra stage in the process for colliding boson stars, compared to colliding black holes. The big boson star created from the two colliding ones oscillates for a bit before becoming a black hole.

This extra oscillation stage could explain why the signal lasted longer than you’d expect for two colliding black holes. Bustillo was also able to use the collision data to calculate the mass of the bosons making up the stars. “The value is around the current constraints from other measurements,” he says. In other words, it fits with our existing ideas about dark matter.

The real clincher will come as we see more gravitational waves from collisions without an initial in-spiral stage. “I do expect the detectors to see more signals like this,” Bustillo says. If they can also be explained by colliding boson stars, and each independent event consistently gives the same mass for the dark bosons, then it’ll get harder to ignore the possibility that see-through stars are out there.

(Video) Dark Matter, an Astrophysical Mystery – Physics Documentary

Ghost stars: The radical theory that could solve the mystery of dark matter (5)

Two upcoming experiments could soon join the fray and help us to shore up the case further, according to Dr Costantino Pacilio from Sapienza University of Rome. The first is the Einstein Telescope, a proposed European ground-based gravitational wave detector. The second is the Laser Interferometer Space Antenna (LISA), a trio of spacecraft that will fly in formation separated from each other by 2.5 million kilometres.

“They will both have a higher sensitivity than LIGO, meaning we will get a more accurate and detailed look at the shape of the gravitational waves,” says Pacilio. That’s crucial, because every colliding object imprints its features into the shape of the waves.

In particular, the way the two colliding objects deform each other with their gravity provides a unique signature. “Boson stars are exotic objects,” Pacilio says. “They only interact gravitationally with the Universe, so this is the only way they can show themselves.”

When we invented the telescope, it was to get a better view of the things we could already see. But now, centuries later, it’s becoming increasingly apparent that there’s a lot more to the Universe than meets the eye. Perhaps it’s time to turn our ideas about stars upside-down and accept the fact that there could be just as many invisible stars creeping through the Universe largely unseen.

  • This article first appeared in issue 360 of BBC Science Focus Magazinefind out how to subscribe here


What is cosmic ghost theory? ›

Cosmic ghost

It can produce repulsive gravity to drive cosmic inflation in the big bang, while later on it could generate the more sedate acceleration that is ascribed to dark energy. Moreover, if this slippery substance clumps together, it could form dark matter.

What are ghost stars? ›

: a faint image often seen accompanying the main image of brighter stars and planets due usually to reflection from lenses of an eyepiece or of a camera.

Does dark matter create stars? ›

Dark matter doesn't really do much of anything in the present-day universe. But in the early days of the cosmos, there may have been pockets of dark matter with high enough density that they provided a source of heat for newly forming stars.

Is darkness a matter? ›

Unlike normal matter, dark matter does not interact with the electromagnetic force. This means it does not absorb, reflect or emit light, making it extremely hard to spot. In fact, researchers have been able to infer the existence of dark matter only from the gravitational effect it seems to have on visible matter.

What is the theory of dark matter? ›

The existence of dark matter can be traced back to the pioneering discoveries of Fritz Zwicky and Jan Oort that the motion of galaxies in the Coma cluster, and of nearby stars in our own Galaxy, do not follow the expected motion based on Newton's law of gravity and the observed visible masses.

What is a quantum ghost? ›

In the terminology of quantum field theory, a ghost, ghost field, ghost particle, or gauge ghost is an unphysical state in a gauge theory. Ghosts are necessary to keep gauge invariance in theories where the local fields exceed a number of physical degrees of freedom.

What is known as the Demon Star? ›

Algol /ˈælɡɒl/, designated Beta Persei (β Persei, abbreviated Beta Per, β Per), known colloquially as the Demon Star, is a bright multiple star in the constellation of Perseus and one of the first non-nova variable stars to be discovered.

What is the most mysterious star in the universe? ›

Story highlights. More than 1,000 light-years away, there is a star that has been baffling astronomers since it was first observed in data collected by the Kepler mission. KIC 8462852 is 50% bigger than our sun, and 1,000 degrees hotter.

Do zombie stars exist? ›

A zombie star is a hypothetical result of a Type Iax supernova which leaves behind a remnant star, rather than completely dispersing the stellar mass. Type Iax supernovae are similar to Type Ia, but have a lower ejection velocity and lower luminosity.

Can dark matter be manipulated? ›

In fact, recent estimates put dark matter as five times more common than regular matter in our universe. But because dark matter does not interact electromagnetically, we can't touch it, see it, or manipulate it using conventional means.

Can dark matter be broken? ›

“One possibility is that there's some kind of charge in nature, and dark matter is the lightest thing that carries that charge,” Toro says. In particle physics, charge must be conserved—meaning it cannot be created or destroyed.

Can dark matter pass through you? ›

Even though, at any given instant, there's only around 10-22 kilograms of dark matter inside you, much larger amounts are constantly passing through you. Every second, you'll experience about 2.5 × 10-16 kilograms of dark matter passing through your body.

Are there 7 states of matter? ›

There are four natural states of matter: Solids, liquids, gases and plasma. The fifth state is the man-made Bose-Einstein condensates.

Does dark matter exist on Earth? ›

Despite the almost overwhelming evidence that dark matter does indeed exist, we still don't know what it's made of. Detectors scattered around the world have been operating for decades, trying to catch the faint trace of a passing dark matter particle, but to no avail.

Is dark matter just energy? ›

dark matter, a component of the universe whose presence is discerned from its gravitational attraction rather than its luminosity. Dark matter makes up 30.1 percent of the matter-energy composition of the universe; the rest is dark energy (69.4 percent) and “ordinary” visible matter (0.5 percent).

Is dark matter a theory or a fact? ›

Dark matter is still a hypothesis, albeit a rather well-supported one. Any scientific theory has to make predictions, and if it's right, then the measurements you do should line up with the predictions. The same goes for dark matter.

How can you prove that dark matter exists? ›

Chandra X-ray Center, Cambridge, Mass. Dark matter and normal matter have been wrenched apart by the tremendous collision of two large clusters of galaxies. The discovery, using NASA's Chandra X-ray Observatory and other telescopes, gives direct evidence for the existence of dark matter.

What is the evidence for the existence of the mysterious dark matter? ›

What is the evidence for the existence of the mysterious "Dark Matter"? The outer parts of galaxies rotate about their centers at unexpected velocities. These velocities indicate that there are massive halos around each galaxy made of matter invisible to astronomers.

What is quantum Zen? ›

Quantum Zen. Quantum Zen is the being of Zen, in indivisible form. It is neither from the Buddhist view nor the view of Quantum Mysticism. It is to Zen what Quantum Mechanics is to theoretical physics and cosmology. It is a moment of satori, revealed within a single shared truth.

Is the quantum Zeno effect real? ›

As strange as this may seem, the quantum Zeno effect has been experimentally proven in the real world. Researchers from Cornell found ways to use the quantum Zeno effect to freeze the tunneling of atoms—a phenomenon that usually occurs when atoms are exposed to extremely cold temperatures.

What can quantum powers do? ›

By using quantum manipulation, users can manipulate matter and energy to their essential components: molecules, atoms, and subatomic particles; commanding them leads to the fabrication and transmutation of matter into any material the user desires, manipulating nuclear reactions, commanding both nuclear fusion and ...

What is the demon world called? ›

Dominion. The Demon World is controlled and presided over by the most powerful demon present at the time. Before and during Sparda's time, this was Mundus, until he was sealed away by Sparda.

What is a rogue star called? ›

A rogue star, primarily known as an intergalactic star, is a star that has escaped the gravitational pull of its home galaxy and is moving independently in or towards the intergalactic void. More loosely, any star in an unusual location or state of motion may be termed a rogue star.

Where is the Demon Star? ›

What is the strongest star ever? ›

Meet the Magnetar

The Magnetar is a widely accepted variation on a neutron star, and a common explanation for certain phenomena (like soft gamma repeaters and anomalous X-ray pulsars). The magnetar is, at the moment, the most powerful magnetic object known to exist.

What is the rarest kind of star? ›

Each is classified as an O-type star — and O-type stars are the rarest main sequence stars in the universe, comprising just 0.00003% of known stars. They're extremely prone to going supernova and collapsing into black holes or neutron stars.

Who was the 1st zombie? ›

Night was the first of six films in Romero's Living Dead series. Its first sequel, Dawn of the Dead, was released in 1978.
George A. Romero (1968–1985)
First appearanceNight of the Living Dead (1968)
Created byGeorge Romero
In-universe information
Alias"Romero zombie"
2 more rows

What are the 3 types of zombies? ›

Types Of Zombies
  • Biological zombies. Parasites modify the host creature's behavior. ...
  • Supernatural zombies. These are zombies that are created in a supernatural way. ...
  • Chemical zombies. Strange chemicals are discovered and are meant to bring back the dead to life. ...
  • Technological zombies. ...
  • Constructed zombie. ...
  • Magic zombie.

What causes a Hypernova? ›

A hypernova (alternatively called a collapsar) is a very energetic supernova thought to result from an extreme core-collapse scenario. In this case a massive star (>30 solar masses) collapses to form a rotating black hole emitting twin energetic jets and surrounded by an accretion disk.

Can dark matter give us superpowers? ›

Dark matter is the collective term given to subatomic particles which are capable of altering a human's biological structure to turn them into meta-humans and allow them to develop superpowers.

Can dark matter be weaponized? ›

Weaponized dark matter was dark matter that had been made into a weapon by converting it into a small sphere that could rip molecules at a subatomic level, thus killing an individual.

What happens if you manipulate dark matter? ›

If you can collect two dark matter particles and make them interact with one another, there's a finite probability that they'll annihilate. When an annihilation occurs, they'll produce pure energy in a 100% efficient fashion: via Einstein's E = mc2.

What happens if dark matter touches earth? ›

Dark matter particles can penetrate all other forms of matter, which means that they may even be able to traverse right through our planet without losing any energy whatsoever. On the other hand, their impact with ordinary matter that Earth is comprised of may hamper them slightly, resulting in a loss of energy.

Can dark matter freeze? ›

The universe has evolved through several phases as its various constituents dominated its energy content. Candidate dark matter particles may have undergone freeze-out during any such phase.

What happens if dark matter touches antimatter? ›

So dark matter particles will only annihilate with anti-dark matter particles of the same type. If you were, for example, to place positrons or anti-protons and dark matter together nothing would happen.

Is dark matter antimatter? ›

Third, dark matter is not antimatter, because we do not see the unique gamma rays that are produced when antimatter annihilates with matter. Finally, we can rule out large galaxy-sized black holes on the basis of how many gravitational lenses we see.

What's inside dark matter? ›

Most scientists think that dark matter is composed of non-baryonic matter. The lead candidate, WIMPS (weakly interacting massive particles), are believed to have ten to a hundred times the mass of a proton, but their weak interactions with "normal" matter make them difficult to detect.

What is the theory of cosmic evolution? ›

Cosmic evolution is an inclusive working hypothesis that strives to integrate the big and the small, the near and the far, the past and the present, into a unified whole.

What is Cosmic Ghost Rider's Penance Stare? ›

The Penance Stare is the most powerful tool in Ghost Rider's arsenal, and it's one of the strongest attacks in the Marvel Universe. With an extensive array of demonic abilities, Ghost Rider is one of the strongest superheroes in the Marvel Universe.

What is theory of cosmic origin? ›

Solution : Cosmic origin or extraterrestrial theories states that life came from outer space. The unit of life called spores (panspermia) were transferred to different planets including Earth.

Is Cosmic Ghost Rider father of Thanos? ›

Cosmic Ghost Rider Becomes a Dad, Adopting Baby Thanos.

What is the most powerful cosmic event? ›

Gamma-ray bursts (GRBs) are the brightest, most energetic blasts of light in the universe. Released by an immense cosmic explosion, a single GRB is capable of shining about a million trillion times brighter than Earth's sun, according to NASA — and, for the most part, scientists can't explain why they happen.

What are the 3 cosmic phenomenon? ›

There are 3 cosmic phases:


When did the multiverse theory start? ›

The term multiverse was coined by American philosopher William James in 1895 to refer to the confusing moral meaning of natural phenomena and not to other possible universes.

Can Venom beat Ghost Rider? ›

Ghost Rider recently ascended to the role of All-Rider, with fantastic new powers that he uses to beat Venom down in the most unreal way. Warning: spoilers ahead for Avengers Forever #3!

Who can beat Cosmic Ghost Rider? ›

In Guardians of the Galaxy # 6 of Cates and Shaw's 2019 series run, Hela is shown to easily be able to subdue the Cosmic Ghost Rider. Since, at his core, the Rider is the deceased corpse of Frank Castle, and Hela holds dominion over the dead, she beats him without even breaking a sweat.

What is Ghost Rider's most powerful form? ›

1 Cosmic Ghost Rider

This made him the most powerful Ghost Rider of all time. In fact, he was so powerful that he had to hold back so he didn't destroy the planets he walked on. He has defeated Thanos, survived a cosmic blast from Galactus, and performed many other unbelievable feats.

What is meant by Red Shift? ›

'Red shift' is a key concept for astronomers. The term can be understood literally - the wavelength of the light is stretched, so the light is seen as 'shifted' towards the red part of the spectrum. Something similar happens to sound waves when a source of sound moves relative to an observer.

Is cosmic expansion a theory or law? ›

In order to numerically represent the momentum of the movement of galaxies, Hubble proposed Hubble's Law of Cosmic Expansion (Hubble's Law), which reads: velocity = H0 × distance.

How did the universe begin from nothing? ›

The Big Bang theory says that the universe came into being from a single, unimaginably hot and dense point (aka, a singularity) more than 13 billion years ago. It didn't occur in an already existing space. Rather, it initiated the expansion—and cooling—of space itself.

Who would win Ghost Rider or Scarlet Witch? ›

It would be a very close fight that could go either way, but in a fight to the death, Ghost Rider would win over Scarlet Witch. The Spirit of Vengeance is practically immortal and can't be harmed without a weapon forged in heaven.

Can immortal Hulk beat Cosmic Ghost Rider? ›

The Hulk simply can't hurt the Ghost Rider despite the unlimited strength. And, although the Hulk is immortal (even if he's in Banner form), the spirit of Vengeance doesn't need to kill the Hulk to beat him. He just needs to find a way to return Hulk into Banner.

Is Thanos a descendant of an Eternal? ›

Thanos' Eternals lineage

In the comics, Thanos is an Eternal, and one from a very important bloodline: His father, Al'ars, was the son of Kronos, who ruled the Eternals of Earth following a civil war that divided the original colony. Following his father's death, Al'ars traveled the universe as the Mentor.


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