The Big Bang was a black hole factory

According to Priyamvada Natarajan, the universe is teeming with black holes. Invisible orbs with great gravity from which not even light could escape. Their number may be in the trillions. And they all arose when the age of the universe was a fraction of the second age.

Well, the Indian astronomer, affiliated with the American University of Yale, is not sure, of course. There is no real convincing evidence yet. “But it’s a reasonable idea,” says Natarajan. Together with two of her colleagues, she will soon publish a major article on the topic in the trade magazine Astrophysical Journal†

The beauty of the meditative idea: to kill three birds with one stone. Three pressing problems in astronomy would disappear like snow in the sun if the Big Bang, which heralded the birth of the universe 13.8 billion years ago, was really a black hole factory. No wonder those “primordial black holes” (primordial black holes) has gained popularity in recent years.

strong men

Astronomers know of two types of black holes: heavy and heavy. Relativistic concepts, because light samples already weigh 2.5 to 25 times the weight of our Sun. They are the remains of giant stars that have exploded. Class II black holes can be a few million or even a few billion times more massive than the Sun. These supermassive black holes are found in the cores of galaxies such as our Milky Way.

But in recent years, astronomers have measured gravitational waves — tiny ripples in empty space — emanating from colliding black holes in the depths of the universe. Measurements show that it is sometimes tens of times as heavy as the sun. It is difficult to explain with current theories. Unless they were not created by star explosions, but much earlier, during the Big Bang. Problem 1 has been resolved.

There is also something strange about supermassive galaxies at the core of galaxies. They must have fattened themselves over time by consuming huge amounts of gas and stars from their surroundings. This takes time, of course. But at gigantic distances in the universe, as you look billions of years back, all these strong men are found. Ra ra, how could such giant black holes exist so soon after the Big Bang? Perhaps because the first “germs” have already been around since the birth of the universe. Exit problem 2.

The third and perhaps the most important problem that primordial black holes offer a solution to is the mystery of dark matter. Gravitational measurements show that there must be six times more matter in the universe than astronomers can see with telescopes. The composition of the universe tells you that dark matter cannot consist of ordinary atomic nuclei. Searches for unknown elementary particles have yielded nothing so far. Nor can they be “ordinary” black holes: they are by no means numerous enough. But if trillions of ancient wormholes form shortly after the Big Bang, the dark matter problem also goes away.

Bernard Carr of Queen Mary University of London doesn’t think it’s a far-fetched idea. “It is usually assumed that dark matter is made up of some mysterious particles, but this is mainly because there are more particle physicists than astronomers,” he says. Now that this “completely hypothetical” particle hasn’t been found, people are starting to scratch their heads, says Carr. “We know black holes exist – I don’t need a whole new concept of them.”

Stephen Hawking

It should come as no surprise that Carr is excited about primordial black holes. In 1974, when he was a doctoral student at Cambridge University, he published a groundbreaking article on the subject primordial black holesWith his mentor at the time Stephen Hawking. Although they were already speculated about in the 1960s, including by Russian Igor Novikov, their publication really put the idea on the map for the first time.

A split second after the Big Bang, the expanding universe was not only extremely hot, but also extremely dense. But it wasn’t quite the same everywhere: there were probably small areas where the density was well above average, Carr and Hawking suggested. Under the influence of their own gravity, these regions can collapse into microscopic black holes: as small as the nucleus of an atom, but as massive as Mount Everest.

For a moment it seemed as if this theory could solve a completely different puzzle in astronomy. Astronomers have detected mysterious high-energy gamma-ray bursts in the universe, and Carr and Hawking primordial holes have provided a fascinating explanation. Hawking calculated that black holes evaporate slowly but surely over time by emitting what is now called Hawking radiation – an inevitable effect of quantum physics. This evaporation accelerates as the black hole becomes lighter and ends with a violent explosion. For an “ordinary” black hole, this process takes an unimaginably long time, but the lifespan of microscopic holes of the origin of the universe will be from about ten to twenty billion years. So you should be able to see it explode by now.

However, cosmic gamma-ray bursts appear to arise in a different way. The primordial black holes By Carr and Hawking their number cannot be enough to explain the dark matter in the universe. The whole idea did not gain traction gradually, not least because many counterarguments came to light over time.

So you’d expect there would be some sort of normal distribution in the masses of those old holes: an improbable number of very small holes, but also a myriad of medium-weight samples and a large number of really heavy boys. Those larger and heavier primordial holes must have betrayed their existence in all sorts of other ways, and nothing turned out.

Moreover, accurate measurements of the cosmic microwave background radiation – a type of ‘afterglow’ of the Big Bang – show that density changes in the newborn universe were extremely small: a tiny fraction of one percent, which is well below production. black holes. Admittedly, these measurements only relate to relatively large areas, but it seems wishful thinking to assume that on a small scale this would suddenly be very different. So there have always been many theorists who resolutely refer the idea of ​​primordial black holes to the realm of superstition.

Old holes under the radar

But the tide is turning, notes Carr, who is now 73. I’ve been wearing it for over 45 years primordial black holes It worked, he says, and in recent years other researchers have gotten excited again. Like Yale astronomer Priamvada Natarajan, who is now involved with Nico Cappellotti of the University of Miami and Gunter Hasinger, scientific director of the European Space Agency (ESA).

Shortly after birth, the universe underwent some separate phase transitions, somewhat similar to the transitions from water vapor to liquid water and from water to ice. During those phase transitions, primordial black holes with somewhat definite masses may have formed, as Natarajan explains via Zoom call from India, where she is visiting her parents. Then there is no normal distribution of mass. For example, ancient wormholes may have remained under astronomical radar until now.

But this may not last long. According to Capelloti, Hasinger and Natarajan, the existence of primordial black holes may soon be confirmed by the new James Webb Space Telescope, launched in late December, or by the LISA gravitational-wave detector, launched by the European Space Agency in the mid-1930s.

Webb looks back a few hundred million years after the Big Bang. If the nascent universe was inhabited by primordial black holes, they would have exerted additional gravity on their surroundings. Then stars and galaxies formed much earlier than current theories suggest, Natarajan explains, and Webb should be able to see that. You might also expect that black holes collided a lot in the youth of the universe – after all, this is how the first supermassive holes formed in the cores of galaxies. LISA can detect gravitational waves from those early collisions.

Trillions of black holes are as old as the universe itself, which despite their mysterious nature sheds new light on the mystery of dark matter – Bernard Carr can’t wait to prove their existence. “The clues are getting stronger, maybe we’ll have the answer in ten years,” he says.