This text was initially printed at The Dialog. The publication contributed the article to Area.com’s Knowledgeable Voices: Op-Ed & Insights.
Scientists working with the James Webb Area Telescope found three uncommon astronomical objects in early 2025, which could also be examples of darkish stars. The idea of darkish stars has existed for a while and will alter scientists’ understanding of how strange stars type. Nonetheless, their identify is considerably deceptive.
Nonetheless, the identify captures the essence of this phenomenon. The “darkish” within the identify refers to not how vivid these objects are, however to the method that makes them shine — pushed by a mysterious substance referred to as darkish matter. The sheer dimension of those objects makes it tough to categorise them as stars.
As a physicist, I have been fascinated by darkish matter, and I have been looking for a approach to see its traces utilizing particle accelerators. I am curious whether or not darkish stars might present an alternate technique to seek out darkish matter.
What makes darkish matter darkish?
Darkish matter, which makes up roughly 27% of the universe however can’t be instantly noticed, is a key concept behind the phenomenon of darkish stars. Astrophysicists have studied this mysterious substance for almost a century, but we have not seen any direct proof of it apart from its gravitational results. So, what makes darkish matter darkish?
People primarily observe the universe by detecting electromagnetic waves emitted by or mirrored off varied objects. For example, the moon is seen to the bare eye as a result of it displays daylight. Atoms on the moon’s floor soak up photons – the particles of sunshine – despatched from the solar, inflicting electrons inside atoms to maneuver and ship a few of that mild towards us.
Extra superior telescopes detect electromagnetic waves past the seen spectrum, similar to ultraviolet, infrared or radio waves. They use the identical precept: Electrically charged parts of atoms react to those electromagnetic waves. However how can they detect a substance – darkish matter – that not solely has no electrical cost but additionally has no electrically charged parts?
Though scientists do not know the precise nature of darkish matter, many fashions recommend that it’s made up of electrically impartial particles – these with out an electrical cost. This trait makes it inconceivable to watch darkish matter in the identical method that we observe strange matter.
Darkish matter is regarded as manufactured from particles which might be their very own antiparticles. Antiparticles are the “mirror” variations of particles. They’ve the identical mass however reverse electrical cost and different properties. When a particle encounters its antiparticle, the 2 annihilate one another in a burst of power.
If darkish matter particles are their very own antiparticles, they’d annihilate upon colliding with one another, probably releasing massive quantities of power. Scientists predict that this course of performs a key position within the formation of darkish stars, so long as the density of darkish matter particles inside these stars is sufficiently excessive. The darkish matter density determines how usually darkish matter particles encounter, and annihilate, one another. If the darkish matter density inside darkish stars is excessive, they’d annihilate regularly.
What makes a darkish star shine?
The idea of darkish stars stems from a basic but unresolved query in astrophysics: How do stars type? Within the broadly accepted view, clouds of primordial hydrogen and helium — the chemical components fashioned within the first minutes after the Massive Bang, roughly 13.8 billion years in the past — collapsed beneath gravity. They heated up and initiated nuclear fusion, which fashioned heavier components from the hydrogen and helium. This course of led to the formation of the primary technology of stars.
In the usual view of star formation, darkish matter is seen as a passive aspect that merely exerts a gravitational pull on every little thing round it, together with primordial hydrogen and helium. However what if darkish matter had a extra energetic position within the course of? That’s precisely the query a bunch of astrophysicists raised in 2008.
Within the dense setting of the early universe, darkish matter particles would collide with, and annihilate, one another, releasing power within the course of. This power might warmth the hydrogen and helium gasoline, stopping it from additional collapse and delaying, and even stopping, the standard ignition of nuclear fusion.
The end result could be a starlike object — however one powered by darkish matter heating as an alternative of fusion. Not like common stars, these darkish stars may dwell for much longer as a result of they’d proceed to shine so long as they attracted darkish matter. This trait would make them distinct from strange stars, as their cooler temperature would end in decrease emissions of assorted particles.
Can we observe darkish stars?
A number of distinctive traits assist astronomers determine potential darkish stars. First, these objects have to be very outdated. Because the universe expands, the frequency of sunshine coming from objects far-off from Earth decreases, shifting towards the infrared finish of the electromagnetic spectrum, which means it will get “redshifted.” The oldest objects seem essentially the most redshifted to observers.
Since darkish stars type from primordial hydrogen and helium, they’re anticipated to include little to no heavier components, similar to oxygen. They might be very massive and cooler on the floor, but extremely luminous as a result of their dimension — and the floor space emitting mild — compensates for his or her decrease floor brightness.
They’re additionally anticipated to be monumental, with radii of about tens of astronomical items — a cosmic distance measurement equal to the typical distance between Earth and the solar. Some supermassive darkish stars are theorized to succeed in plenty of roughly 10,000 to 10 million instances that of the solar, relying on how a lot darkish matter and hydrogen or helium gasoline they’ll accumulate throughout their development.
So, have astronomers noticed darkish stars? Probably. Knowledge from the James Webb Area Telescope has revealed some very high-redshift objects that appear brighter — and presumably extra large — than what scientists count on of typical early galaxies or stars. These outcomes have led some researchers to suggest that darkish stars may clarify these objects.
Darkish stars could clarify early black holes
What occurs when a darkish star runs out of darkish matter? It relies on the dimensions of the darkish star. For the lightest darkish stars, the depletion of darkish matter would imply gravity compresses the remaining hydrogen, igniting nuclear fusion. On this case, the darkish star would finally change into an strange star, so some stars could have begun as darkish stars.
Supermassive darkish stars are much more intriguing. On the finish of their lifespan, a useless supermassive darkish star would collapse instantly right into a black gap. This black gap might begin the formation of a supermassive black gap, like the sort astronomers observe on the facilities of galaxies, together with our personal Milky Approach.
Darkish stars may also clarify how supermassive black holes fashioned within the early universe. They might make clear some distinctive black holes noticed by astronomers. For instance, a black gap within the galaxy UHZ-1 has a mass approaching 10 million photo voltaic plenty, and could be very outdated – it fashioned simply 500 million years after the Massive Bang. Conventional fashions wrestle to clarify how such large black holes might type so rapidly.
The concept of darkish stars just isn’t universally accepted. These darkish star candidates may nonetheless prove simply to be uncommon galaxies. Some astrophysicists argue that matter accretion — a course of through which large objects pull in surrounding matter — alone can produce large stars, and that research utilizing observations from the James Webb telescope can’t distinguish between large strange stars and fewer dense, cooler darkish stars.
Researchers emphasize that they may want extra observational information and theoretical developments to unravel this thriller.
