Stars are normally considered to be immensely bright balls of nuclear fury.
At least until they go into a post-normal star state, such as collapsing into a black
hole, or becoming a neutron star, or cooling white dwarf.
But in the early universe, things were a little different as far as star formation, and recent
thinking has envisioned another type of star that’s not at all like a normal main sequence
star we see today.
About 80 to 100 million years after the big bang the universe’s clouds of hydrogen and
helium began to cool.
This unusual situation may have allowed for a rather odd first generation of early stars
that were dependent on dark matter to form at all.
These extremely early stars would have been enormous, they had a lot of material to work
with at the time, meaning they could have been 500 to 1000 times more massive than the
sun, and physically much, much larger in diameter.
If these stars indeed existed, they operated very differently from the normal fusion energy
of stars as we know them.
Known as Dark stars, by nature they would be cool and ill-defined, and not radiate in
visible light, hence the term dark.
But they would do so at other wavelengths.
Instead of nuclear fusion, they would instead have been powered by dark matter heating.
This might have allowed for two types of early star, dark matter dependent stars, but also
the first generation of normal stars producing heavier elements.
Detecting these stars is a problem however, even for the James Webb space telescope which
is designed to try to detect the earliest, most distant normal stars.
The reason is dark stars should emit in gamma rays, neutrinos and even anti-matter, but
not in the visual spectrum making them very difficult to search for.
They would probably congregate at the centers of early galaxies due to those being the densest
areas of dark matter concentration.
It goes both ways however, in that if dark matter can fuel types of stars there should
be other evidence of its effect in neutron stars and white dwarfs at the centers of galaxies,
yet this has not been seen.
Yet again, this is a problem for the existence of dark matter, but without it, it’s an
equal problem because our ideas of gravitation at long distances are flat wrong, and the
evidence we do see of dark matter would still need to be accounted for with something else.
What might be possible however is to use instruments like LIGO in gravitational waves to look into
dark star mergers, which may well be the easiest method of detecting them.
But there is an oddity here.
In 2011 observations by the Hubble Space Telescope of one of the most distant galaxies ever detected
showed an odd signature drop off in infrared.
The problem is that it’s difficult to prove the observation with the capabilities of Hubble,
so no one is sure just what that detection represents other than a tantalizing hint that
this odd class of star may actually exist or have existed early on.
If Dark Stars could be detected unambiguously however it would provide strong evidence for
the existence of dark matter as a whole, a major question in cosmology.
The James Webb Telescope offers an advantage because dark stars should radiate at longer
infrared wavelengths that it can detect that might better show the signature of a supermassive
dark star.
There is strong hope here, because Webb has already detected similar signatures from very
young stars within stellar nurseries that were not detectable before with any other
telescope.
But even if you could prove the existence of dark matter above and beyond its overall
effect on galaxies and dark stars, it still doesn’t tell you what it is.
And that may be key in answering a new mystery that’s cropped up recently.
It’s an issue with antimatter.
The question of anti-matter has always been murky.
We know it can exist because we can create it under lab conditions.
It doesn’t last long, antimatter famously annihilates with normal matter if they come
into contact.
But we live in a large universe full of mostly empty space where particles of anti-matter
can go a long while without running into any normal matter.
This raised a question, if that’s the case, then where is all the antimatter that should
have been produced in about equal amounts to normal matter during the big bang?
Originally the answer was that it might still be around, and you could never tell the difference
between a star made of normal matter and an antistar, because both forms of matter behave
much the same otherwise.
They shine the same and operate the same.
In the intervening years however, ways to possibly detect the presence of large amounts
of antimatter in the universe have been devised.
But no one really expected to see it, defaulting on the appearance the universe presents of
there being no large amounts of antimatter out there, other than in rare positron fountains,
a mystery in their own right.
At least that was until an experiment unexpectedly and out of nowhere showed large amounts of
it.
In 2018 an experiment mounted on the exterior of the international space station known as
the Alpha Magnetic Spectrometer detected something unusual.
The scientists involved found what appeared to be two anti helium nuclei, in addition
to six more of another isotope previously.
If that detection was real, which is still an open question, it’s based on one instrument,
then it’s far too much antimatter for us to easily run across with an experiment like
this, and it’s in a form far too complex than it should be.
That said, the numbers aren’t huge, the detector sees many millions of times more
regular helium nuclei than it does antihelium, but the effect is still there in that it shouldn’t
see any antihelium at all.
There are several ways that these particles could be created, but one possibility is that
they are being created in antistars lurking out in the universe somewhere.
And evidence for that seems to be mounting.
Another group of researchers linked the antihelium finding to yet another mystery, strange gamma
ray sources discovered by the Fermi Large Area Telescope that also remain unexplained.
Antistars would normally look just like regular stars, emitting photons at the identical wavelengths
as their normal matter counterparts.
But space isn’t completely empty, so you should have particles and gas falling into
the antistars and annihilating, which should produce bursts of gamma rays, but at very
specific wavelengths.
That was seen.
But other astronomical sources of known origin can also do this, so any known sources like
that were eliminated from the study leaving 14 candidates for antistars.
The team notes that they probably aren’t antistars, and other more mundane means should
be considered first, but if the observations continue to line up with that of experiments
detecting antihelium, the prospect of antistars will have to be carefully examined.
One problem is that there are 14 candidates, which is a lot, and it would suggest that
antistars are relatively common, which seems a bit hard to swallow.
They should be rare.
But then there’s the antihelium detections.
We know antiparticles can be created in two known natural ways, one more hypothetical
than the other.
One is through cosmic rays and the other through the interactions of dark matter.
The problem is, the odds for either one of these options being the culprit seem really
slim, which then points in the direction of antistars being more plausible.
This is because of how hard it is to form a large antiparticle.
Forming an antiproton is straightforward, it’s something that can be done in the lab.
It gets harder though when you start to mess with things like anti deuterium, it’s more
complex.
Antihelium is even worse, to the point that the heavier the atomic nucleus, the more difficult
it gets for it to form outside of an antistar.
So in nature, the possible avenues to create these antiparticles works like this.
The first is from high energy cosmic rays, emitted by supernovae.
This process is called spallation, so a high energy particle comes cooking along through
the interstellar medium until it hits some gas or something and in that energetic collision
an antiparticle can result.
The problem with the antihelium detections is that six were antihelium 3, and two antihelium
4.
That level of complexity is almost statistically impossible to happen enough through spallation
for it to be readily detectable, this stuff was seen the earliest moment we could detect
it, if it even happens much at all in the universe.
It’s not impossible, but it’s a step too far for nature except under very rare conditions
so far as we know.
The other is the elusive dark matter.
This one is more ambiguous, and honestly almost on level with the idea of an antistar kicking
out particles.
It’s that some ideas about dark matter are that particles of it, if it is indeed a particle,
might annihilate with one another under certain conditions, and that might too create antiparticles.
Other than the issue of potentially not existing, this process would also have a huge problem
producing enough antihelium, especially antihelium-4, in enough of a number for us to be able to
simply turn a detector on and see right off the bat.
So the antistar option sits on the table as the best fit.
The achilles heel here however may be in errors in the detection, that hasn’t been eliminated
yet, and the analysis is ongoing along with further experiments to try to verify the antihelium
detections.
In other words, it could all have been a fluke of the detector, and if it’s never verified,
then the idea of antistars goes back to the purely hypothetical.
But say for a moment it turns out that antistars do exist.
They would require at least a modification to just how we think the evolution of the
early universe occurred, which is starting to happen anyway due to other somewhat odd
results from the James Webb Space Telescope that are for another video.
But if you play with the idea of antistars, and assume they exist, they would be true
relics dating from the earliest times of the universe, a phenomena that are no longer currently
forming.
The clouds they formed out of would have likely long ago annihilated on contact with normal
matter.
And another mystery would await, exactly how did the anti-stars manage to survive so long?
That would be a difficult question as well, since they probably should not have in large
numbers assuming we are not in some special circumstance like a jet of them pointed in
our direction or one located unusually close by.
Or they’re created by some other process we aren’t aware of yet.
But another question would be what are the rules for antistars.
If they behave like normal stars, do they follow the same classifications of mass and
temperature than normal stars do?
The answer seems a likely yes, so was it ever possible to form massive antistars that went
supernova and sprayed antimatter into the early universe in huge fits of annihilation?
Is there any evidence left of that?
Would it have been a cataclysm far greater than an already cataclysmic normal supernova?
The questions are many.
But antimatter is a mysterious substance, not in itself, it’s just an anti counterpart
to normal matter that we know exists and can create, but rather in how nature generates
it both in the big bang, but also now.
And there’s still the matter of the Antimatter positron fountains found in the Milky Way,
that probably exist in a large number of galaxies in the universe.
We still haven’t the slightest idea of what’s causing these gigantic streams of 15 billion
tons of positrons per second, only that we see them annihilating.
You can play around with ideas of neutron stars or supermassive black holes creating
the circumstances of that, but why don’t they more commonly do that?
You could also question antistars here, though it’s hard to see how one would survive in
the densest parts of the galaxy.
But the reality is that with antimatter, it seems the mysteries of how it comes to be
in the universe have only just begun.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently introducing a new
term into the channel lexicon: Garden hubris.
Oh yes, it’s spring here, and as a long time gardening and plant enthusiast currently
having gone overboard with urban square foot gardening and putting containers everywhere,
the amount of growth is particularly good this year with all manner of lettuce and spinach
harvesting going on.
But perhaps it’s too strong, and the plants seem to have struck a machiavellian deal with
the rabbits and the squirrels this year as nothing is getting eaten … it’s quiet.
Too quiet.
Keep a watchful eye on the greenery and be sure to do the same with my books at your
favorite online book retailer and subscribe to my channels for regular, in-depth explorations
into the interesting, weird and unknown aspects of this amazing universe in which we live.