Science

Where do the magnetic fields that shape the universe come from?

The power that shapes our universe is not solely gravity. The magnetic field that has long been forgotten may have played an important role in it. Image Source: “New Scientist”

(Compilation / Shea) Whenever it comes to the universe, gravity does its part. It allows our feet to stand firmly on the ground, and it shapes our universe. It causes the cloud of gas to collapse, forming stars and planets. It gave birth to hundreds of billions of stars in galaxies. It is also under its influence that galaxies converge into galaxy clusters and further form super-galaxy clusters. However, in this game, gravity is not the only player – there is a force between the universe, it is magnetic.

In the near vacuum universe, the magnetic field can be extended to a very long distance, even if billions of light-years of vast space between galaxts goes without saying. Of course, these fields are extremely weak. Magnets attached to the refrigerator magnetic field, filled with the Milky Way inside and outside the magnetic field, the intensity should be higher than 1 million times. This may be why magnetic fields are often overlooked in cosmology. After all, how can such trivial things affect the entire galaxy?

However, the times and perspectives are changing. True, gravity keeps the celestial bodies together, but the most crucial physical processes in cosmology and the high-energy jets emerging from stars to black holes require the participation of a magnetic field. “As a result, many of the unsolved mysteries in previous astronomy were suddenly enlightened as long as the interstellar magnetic fields were added,” said Bryan Gaensler of the University of Sydney in Australia.

The same is true for the larger-scale universe? The magnetism of galaxies and larger scales is so appealing because they may be the remains of some of the physical processes that took place shortly after the Big Bang. In addition, most of the visible matter in the universe consists of charged particles, whose motion follows the domination of magnetic fields and gravitation. This gave rise to a tempting possibility – from the very beginning of time, the magnetic field played a key role in shaping the universe.

However, before deciding on this, we also need to answer some important questions: When and how the magnetic field was formed?

We already know that magnetic fields play an important role around our planet. In 1835, the German physicist Carl Friedrich Gauss measured the Earth’s magnetic field for the first time with a magnet attached to a line. We now have a good understanding of how the Sun and the Earth produce their own magnetic fields. When the molten iron in the extragalactic core (or the plasma inside the sun) does the cutting of the magnetic field, it induces an electric current. These currents in turn create a magnetic field that complements the existing magnetic field. Thanks to this generator action, a weak “seed” magnetic field can grow into a much stronger magnetic field.

Things do not stop there. Earth’s magnetic field protects the ozone layer from damage by energetic particles so our planet will not be exposed to harmful UV rays. The magnetic field of the sun also protects us, deflecting harmful particles from outside the solar system. On a larger scale, magnetic fields can even contribute to the origins of life.

However, few people in the past expected a magnetic field in interstellar space. The first evidence came in 1949 when American astronomers John Hall and William Hiltner discovered that there was “something” that polarized the stars in their flight to us . The results show that such things are actually cosmic magnetic fields, which make the interstellar dust particles neatly arranged like tiny compass pointers. Geisler said that this is an amazing discovery.

Since then, a series of techniques have been developed to measure the magnetic fields in the Milky Way galaxy and its neighbors. In 2011, Niels Oppermann and his colleagues at the German Max Planck Institute for Astrophysics mapped the best Milky Way magnetic field distribution to date, revealing the distribution of the magnetic lines along the spiral arm of the Milky Way, It has also been confirmed that the total magnetic field strength of the Milky Way is only a few micro-gauss (1 micro-Gauss = 10-6 Gauss) – only one hundredth of a million of the Earth’s surface magnetic field.

Astronomers believe that in spiral galaxies like the Milky Way galaxy, the magnetic field will be amplified and maintained by a “generator.” With the rotation of the galaxy, the charged particles will cut the existing magnetic field, making it further enhanced. “The theory is that the galaxy was born with a much weaker magnetic field,” said astrophysicist Larry Widrow of Queen’s University in Canada. “But these weak primary magnetic fields, which are seeds for generators, are again Where did you come from?

The first magnetic field

For decades, scientists have been trying to solve the puzzle, but their instruments and equipment are not yet sufficiently sensitive to test any theory.

So, the model is endless.

One theory is that the initial magnetic field was generated by very early stars and then diffused into the interstellar medium through the onset of the wind or supernova.

Another theory is that about 100 million years after the big bang, when the first generation of galaxies was formed, the supermassive black hole at its center produced a very strong magnetic field and was then transported by its powerful jet into the intergalactic space.

A recent view is that the cosmic magnetic field may be caused by plasma fluctuations in young galaxies. As long as you have a weak magnetic field, it can be amplified by the generator effect. Therefore, the rotation and turbulence of interstellar media (gas and dust between stars) enhance the initial weak magnetic field. These processes can double the intensity of a magnetic field during a single rotation of a star or a central black hole. These time spans are insignificant compared to the age of the universe, so newborn magnetic fields can quickly reach considerable intensity.

The problem, however, is that if so, the magnetic field of distant young galaxies should be much weaker than the magnetic field of the next-generation galaxy. However, a great deal of evidence discovered by astronomy indicates that there are also micro-Gaussian intensity magnetic fields in these early galaxies. Thus, either the generator effect is stronger, or the seeds of the magnetic field formed earlier, it formed in the big bang.

Australia’s Square Kilometer Antenna Array Pathfinder (ASKAP) is used to find radio waves emitted by the electrons in a cosmic ray that move around a magnetic field line. Picture source: csironewsblog.com

The beginning of time

Widlow and his colleague at the University of Chicago in the United States, Michael Turner, put forward this idea in 1988. They argue that the original magnetic field was formed shortly after the Big Bang and later amplified by the inflationary phase of the expansion of the universe’s superluminal velocity. The large-scale galaxy structure we observed today is formed by the quantum fluctuations of energy in that period. Weidero and Turner proved that inflation can also amplify fluctuations in the electromagnetic field, so that the entire universe is filled with magnetic fields.

To make this idea work, they had to transform the Maxwell equations that describe the electromagnetic field, introducing a special kind of particle called the axion. Wedero admits: “The idea is peculiar and theoretically troublesome particle physicists.” Their calculated seed magnetic field, with a strength of 10-50 gauss – means that there must be a strong “power generation Machine “in order to amplify the magnetic field strength to what we observe today.

However, Widero and Turner’s ideas still inspire many others. “Their theory for the first time raised the idea that a magnetic field can be generated in inflation,” said Dominik Schleicher of the University of Göttingen in Germany. “It marks a cornerstone of our understanding.”

In early 2013, Leonardo Campanelli, a physicist at the University of Bari in Italy, explained how these fluctuations can form the original magnetic field without modifying the standard physics. He used mathematical techniques called renormalization. Particle physicists have long used this method to eliminate the infinity that would invalidate an equation. Campanelli said: “Nobody ever thought of using reformatting to deal with the original magnetic field.”

He got a much stronger initial magnetic field, reaching 10-12 Gauss, still less than 10-6 Gauss observed in the intergalactic space. But he said that with the formation of the first generation of stars and galaxies, this background magnetic field was enough to be magnified to today’s value.

Weidero left a deep impression on Campanelli’s essay. “If the calculations in this paper are correct, then a large-scale magnetic field will be a natural and unexpected product of inflation, without the need to make any special changes to the laws of physics.”

Others question the magnetic field that produced cosmic scales shortly after inflation or shortly thereafter. This is because the magnetic field is likely to be almost completely erased in what is called the “dark age.”

During the first 378,000 years, the temperature of the universe was too high to form atoms, only electrons, nucleons, and photons. This pot of charged particles is a great place to amplify the seed magnetic field formed during the inflationary period.

As the universe expands, it gradually cools, allowing protons to trap electrons to form neutral hydrogen atoms. With their combination, these particles release a wave of radiation to the universe – the CMB.

After that, the universe entered the dark age, because no celestial body would emit light during this period. At that time, the only source of radiation was a hydrogen atom, which emitted radio waves at a wavelength of 21 cm.

For the cosmic magnetic field, the main problem it faces is the steep drop in the number of charged particles. In the Dark Ages, there was only one free electron or proton for every 10,000 hydrogen atoms. Because the magnetic field depends on the movement of electrons or protons, some scientists believe that the seed magnetic field may be erased at this time.

The Dark Ages continued until the first light sources in the universe appeared. With the formation of stars and galaxies, they release a huge amount of radiation, stripping electrons from hydrogen atoms. This re-ionization period will last about 1 billion years, also means that the universe will then be full of magnetic and magnetic fields of electrons and protons.

We are not sure yet how the cosmic magnetic field coped with these chaotic years. However, perhaps decades after the different theories have been removed, there may soon be the answer.

Astronomers will be able to track the evolution of the magnetic field by synthesizing observations from multiple telescopes over different periods of the universe’s history. Knowing the strength of the magnetic field in the early Universe and their evolution will help us to model the origin of the magnetic field.

According to Richard Davis, an astronomer at the University of Manchester in the UK, the study of CMB’s Planck satellite may give an analysis of the universe’s magnetic field. If the primary magnetic field does exist at 378,000 years at the age of the universe, then they should leave a footprint on the CMB.

Integrated telescope

Also working with Planck scientists are the radio astronomers of the Low Frequency Array (LOFAR). LOFAR antennas are available in 5 European countries. Plus two astronomers in Australia with two instruments, Australia’s Square Kilometer Array Pathfinder (ASKAP) and Murchison Large Field of View Antenna Array. They are all looking for radio-frequency synchrotron radiation: the radio waves emitted by the electrons in cosmic rays by the movement of magnetic lines.

LOFAR is specifically designed to measure long-wave radiation so it can detect weaker magnetic fields (such as the magnetic field between galaxies) and investigate how far the magnetic field can extend from the galactic disk. It can also detect magnetic fields in galaxies in the early universe.

As one of the leaders of the ASKAP Cosmic Magnetic Field project, Geisler is confident about what theories are correct. He said, “We will know the answer in two years.”

Rainer Beck of the German Max Planck Institute for Radio Astronomy said that if they found evidence of strong magnetic fields in the original galaxy, it would corroborate that the magnetic field started in the shockwave or plasma in young galaxies drop. However, if the original magnetic field was found near the galactic nucleus, then it would support the generator effect of early stars or early galaxies.

With the construction of one square kilometer aerial array (SKA) in Australia and South Africa, stronger observational capabilities are also on the way. The SKA, which consists of thousands of antennas, will allow scientists to study the magnetic field at 10 times today’s resolution. SKA will make its first observations in the early 1920s. It will probe the re-ionization period of the universe and search for the first generation of objects that appear in the universe. It will also be used to search the universe’s early magnetic field. “SKA will allow us to measure the intensity and polarization of radio waves with unprecedented sensitivity,” said Ethan Vishniac, an astrophysicist at the University of Saskatchewan in Canada.

Baker said that if SKA finds a strong magnetic field around the first generation of celestial bodies, the original theory of the field will be supported. This will show that the magnetic field precedes galaxy formation and may have an impact on galactic evolution. In this case, “Planck” or the next generation of CMB satellites will help its research.

A large number of telescopes are observing the long past magnetic fields in the universe in order to understand the origins of magnetic fields and their impact on the evolution of the universe. Image Source: “New Scientist”

In about 10 years, the observations of all these telescopes and satellites will redraw our universe picture. “Most of the aerodynamic numerical simulations for the evolution of galaxies ignore the magnetic field,” said Avi Loeb, an astronomer at Harvard University in the United States. “The next frontier is the inclusion of magnetic fields and cosmic rays Take a look at the effects on the galaxy. ”

Only by understanding how gravitation and magnetic fields manipulate the universe can we really understand how the universe works.

Faint magnetic field urging life

You need 10 million galaxies to draw a shopping list to the fridge door, and the magnetic field in our galaxy is so weak. But it can still affect the movement of charged particles called cosmic rays, bend their trajectories, and even bind them to the Milky Way for millions of years.

Arvind Lobs, an astronomer at Harvard University in the United States, pointed out that if there is no magnetic field, cosmic rays will fly out of the Milky Way soon after their formation. Its impact is far-reaching. “Cosmic rays are an important part of the Milky Way and they ionize the gas in the depths of the original planets, and they are also very important to the variation of organisms on Earth, and in short, they are elements of life,” he said.

Indeed, the appearance of life may be a masterpiece of magnetic field deflection of high-energy cosmic rays. These energetic particles seem to turn on chemical reactions that form sugars, amino acids, and other substances needed for life in dense gas clouds. Nevertheless, we are still not sure where the cosmic rays originated, because the magnetic fields have changed their trajectories. Lobo said that by studying the magnetic field, we will find clues about the origin of the cosmic rays and unlock the extremely important puzzle.