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Primitive black holes could solve major mysteries – if they exist

a black hole
Theories claim that black holes could have formed in the first second of the Big Bang.
(Credit: NASA / ESA and G. Bacon (STScI))

All the black holes that astronomers have seen fall into a
of three categories: stellar black holes, intermediate mass black holes,
and supermassive black holes. Each is bigger than our sun and trained to
less hundreds of thousands of years after the Big Bang, as our universe grew
and evolved.

But there is another type of black hole astronomers not
still seen, but think could exist. These are primordial black holes.

As their name indicates, primordial black holes are born
very early in the life of the universe, just a fraction of a second
Big Bang. It was well before stars or galaxies (and other types of
holes) could exist. But some theories predict that primordial black holes should
have arisen anyway on the stage. It's because in this split second
after the beginning of the universe, the space was not completely homogeneous (the same
at each point). Instead, some areas were denser and warmer than others, and
these dense regions could have collapsed into black holes.

A brief window

It was only a small period of time – about 1 second – following
the Big Bang where primordial black holes could have formed. But in the extreme
the world of our expanding primitive universe, many things can happen in a second. And
later in this window of time that the primordial black holes were formed, the more
they would be massive. According to the exact moment they were formed, the primordial black
the holes could have masses as low as 10-7 ounces (10-5
grams), or 100,000 times less than a paper clip, up to about 100,000 times more
than the sun.

The idea of ​​these tiny black holes intrigued the astrophysicist Stephen Hawking, who explored their properties of quantum mechanics. This work led to his discovery in 1974 that black holes can evaporate over time. And although Hawking realized that a big black hole would evaporate faster than the universe has been up to now, small black holes could be s & # 39; 39, be evaporated or are currently evaporated, depending on their mass. Hawking calculated that any primordial black hole with a mass greater than 1012 pound sterling ([ten[10[dix[1012 kilograms]; it is much less than the mass of a planet, a dwarf planet, and most of the asteroids and comets named in our solar system) could still exist today, while smaller ones would have already disappeared .

And according to their mass (which, remember, depends on
when they formed), the primordial black holes left today could explain
some of the outstanding issues in astronomy.

Galaxies, including the Milky Way (left) and Andromeda, have large dark matter (gray) halos that extend far beyond their visible stars and dust. If primordial black holes are a form of dark matter called MACHO, they could reside in these halos. (Credit: Kavli IPMU)

Candidates for black matter

Such a problem is dark matter. Although this represents about 30% of our universe, astronomers remain perplexed on dark matter is. The primordial black holes could be the solution – or at least a part of it. The primitive black holes could be a type of dark matter called MACHO, which represents huge halo compact objects, because astronomers think they are in the halos, or suburbs, of galaxies. It would be difficult to see such black holes if they simply float in space and stand between them.

One way to spot MACHO is to look for events called microlenses, which occur when a massive object (eg a black hole) passes in front of a farther object, such as a star or a galaxy. The black hole deflects the light from the far source while illuminating and magnifying the image. These events are infrequent and short-lived, but capturing enough of them could allow astronomers to determine which objects are making the microlens and whether they can be primordial black holes.

However, several recent studies have shown that even if primordial black holes of this type existed, they probably could not explain all or even the most observed dark matter effects.

Mergers are another way to search for large, primordial black holes. Gravitational wave observatories such as LIGO and VIRGO have already witnessed several mergers of black holes, and future projects such as LISA will detect mass mergers different from those we can currently identify. Since astronomers can trace the masses of the black holes that merge, they have found that future events are caused by black holes with the appropriate masses, making them primordial black holes.

Alternatively, primordial black holes could be tiny. Some theories argue that although black holes evaporate, there may be a size limit. So when a black hole that evaporates reaches a certain mass, it stopped evaporate and just stay very small. If this is the case, the primordial black holes could still represent the dark matter, albeit in a different way, and their search would be more difficult. Perhaps astronomers could spot black holes evaporating, which would release energetic particles that, in turn, would release gamma rays. If the black holes eventually disappear, they may die under intense energy explosions – equivalent to about a million 1 megaton hydrogen bombs, writes Hawking – that we could also detect in the form of gamma rays .

Supermassive seeds

Even if they do not take into account dark matter, there is a
second problem in astrophysics to which primordial black holes could answer. primary
black holes of different size than needed to explain the darkness
the material might rather explain astronomers supermassive black holes see in
the centers of massive galaxies. These black holes, millions or billions of
times the mass of the sun, can not be created by one or even several exploding
stars. Astronomers do not know how these black holes got there or what created
their; maybe they're built from primordial black holes that have been around
since the first second of our universe, serving as seeds from which
supermassive black holes may develop.

This possibility, however, may also not be likely, as primordial black holes had to form when the universe only had 1 second. Even the primordial black holes that formed at the last possible moment would be, according to physics, only 100,000 times larger than the Sun, which is not really part of the weight class of supermassive black holes. To get even bigger black holes than we see today, they have to extract a lot of material and grow very fast. It's not impossible, but it may explain less the number of supermassive black holes that exist today.

No matter where and how they are, primordial black holes could say a lot about the universe of astronomers. Depending on their mass, they could serve as probes for the evolution of the galaxy, high energy physics and even the very first fractions of a second after the birth of the universe. But although the primordial black holes could exist, they have not been seen yet and remain today one of the big questions of astronomy, rather than a neat answer.

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