Most celestial bodies in space have their own magnetic fields. Magnetic fields are also found in individual galaxies, and are estimated to play a fundamental role in the evolution of galaxies. However, it is difficult to observe the magnetic fields of distant celestial bodies, and there are many mysteries about the role of magnetic fields in galaxies. It is also not well understood why the galaxy’s magnetic field is generated.
A research team led by JE Geach of the University of Hertfordshire uses a broadband radio interferometer called…Alma (From Earth through observations made by the large millimeter/submillimeter Atacama interferometer (Atacama Desert, Chile).He succeeded in measuring the intrinsic magnetic field of the “9io9” galaxy, which is about 20 billion light-years awayVerb. This is itObservational record of the farthest intrinsic magnetic field in historyHe is.
(*Editor’s note: The value of approximately 20 billion light-years up to 9io9 is based on the “moving distance,” which takes into account the expansion of the universe. It is the distance that light from a celestial body travels before it is observed on Earth. The value is based on “ The distance of the light path is about 11.3 billion light-years.
■The mysterious galactic magnetic field
The Earth has its own magnetic field called geomagnetism, which can be compared to a magnet. Not only does the Earth have a magnetic field, but almost all celestial bodies in the universe do. Galaxies consisting of many stars are no exception, and the galactic magnetic field is as wellGalactic magnetic field” he is called.
Because magnetic fields affect various materials, they are thought to be involved in the evolution of celestial bodies such as galaxies. However, until now its role has not been well understood. One reason is that it is generally soThe magnetic fields of distant celestial bodies cannot be measured directly.It’s from.
In order to know the structure and strength of the galaxy’s magnetic field, we can observe the object using radio waves.polarization“It must be measured. Radio waves are literally ‘waves’ and vibrate perpendicular to the direction of travel. The directions of vibration are usually different, but for some reason the directions of vibration may be aligned at a certain angle. This is polarized light.”
In addition to stars, galaxies contain large amounts of dust, and dust emits radio waves. Since the galactic magnetic field has the property of aligning dust particles in a certain direction, the directions of vibration of radio waves generated by dust also tend to line up at a certain angle. In other words, if we can observe the polarization of radio waves emitted by dust, we can know the strength and direction of the galactic magnetic field.
However, the more distant a celestial body is, the weaker the power of radio waves reaching Earth. Furthermore, the polarization generated by the magnetic field is very weak, making observation itself technically difficult, so there has been little progress in research on the magnetic fields of distant galaxies. The farther into the universe we look, the closer we are to the early universe. In other words, we lack information about magnetic fields in early galaxies.
■The challenge of observing the unique magnetic field of “9io9”, which is about 20 billion years away
A research team including Geach used ALMA to observe the galaxy 9io9, which is about 20 billion light-years from Earth. One of the reasons for choosing 9io9 is that detailed observations have been made using ALMA and the Hubble Space Telescope in the past. In addition, 9io9 has a gravitational lensing effect (※1) Because it is highlighted, it is bright for a distant celestial body and suitable for detailed observation.
*1…If there is another celestial body between the celestial body and the observer, gravity may bend the light and focus it on a single point, making it possible to obtain information about distant celestial bodies that are normally difficult to observe. This phenomenon is called gravitational lensing because gravity acts like a convex lens.
The research team observed 9io9 for two days in April 2022 and analyzed the data. As a result, we successfully extracted the polarized component of 9io9. The polarization is about 1%, which is similar to that of nearby spiral galaxies. From this result,9io9 has a magnetic field structure of less than 500 micrograms over a range of about 16,000 light-years.It has been concluded that this isObservational record of the farthest intrinsic magnetic field in historyIt will become. The strength of the magnetic field is 1/1000 of the Earth’s magnetism, but this50 times more powerful than ordinary spiral galaxiesThis is a very strong value for the galactic magnetic field.
It is believed that 9io9 is a young galaxy that has been in the universe for 11 billion years, 2.5 billion years after its birth. The formation process of the galactic magnetic field is not well understood, but the very weak magnetic field of individual dust particles is thought to amplify, taking about a billion years to grow to the strength and size of the galactic magnetic field. field. It is estimated that it will take some time. This is consistent with the detection of a galactic magnetic field in a young galaxy called 9io9.
In addition, amplification of the magnetic fields of individual dust particles may lead to star formation. (※2) It is assumed that this is due to the turbulence caused by the supernova explosion in the dust, but star formation in particular is thought to play a key role in maintaining the unique magnetic structure. 9io9 stars are thought to be forming 1,000 times faster than the present-day Milky Way, and the theoretical strength of the magnetic field generated by the turbulence caused by star formation agrees well with this observation.
*2…The dust and gas that fill the galaxy gather together due to gravity, and stars are born.
The 9io9 observational results are the most distant observational record of the unique magnetic field in the history of observation, but it cannot be said that detailed observations have been made, so there is still room for additional observations.
For example, the strength of the galactic magnetic field in 9io9 is so strong, it is present in many stellar galaxies for which the galactic magnetic field has been measured. (※3) higher than . However, the detailed strength of 9io9’s galactic magnetic field at each location is not well understood. Given the intensity of star formation in 9io9, such a strong magnetic field is unlikely to occur throughout the galaxy. Since 9io9 can be explained by taking into account that there are regions of locally strong magnetic force, more detailed measurements of the magnetic force are needed.
*3…A galaxy in which star formation is very intense compared to normal galaxies.
■Observation results related to the secrets of the universe other than galaxies
In addition, the results of this research are:Cosmic infrared background radiation“or”Cosmic microwave background radiation“It may also be affected by other factors. This is the infrared and microwave radiation that fills the entire universe, but its source is supposed to be completely different. While the cosmic infrared background radiation is radiation from dust distributed in galaxies, the cosmic microwave background radiation is.” Universal cleansing. (※4) It is believed that the light of time expands with the expansion of the universe.
*4… For a period of time after its creation, the universe was at a high temperature, and the atoms were in a plasma state in which electrons and nuclei were separated. Light does not travel in a straight line in an electrically charged plasma. About 380,000 years after the birth of the universe, when the temperature of the universe had cooled enough, electrons were captured by atomic nuclei, the plasma disappeared, and light began to travel in a straight line. This is the purification of the universe.
In particular, the cosmic microwave background is actively observed because it contains a lot of information about the very early stages of the universe, including the polarized components of light. However, since the results of this study investigated the polarization component of radio waves emitted by dust, they suggest that infrared radiation emitted by dust may also be polarized. Infrared radiation expands as the universe expands and becomes microwaves depending on the distance it travels, so there is a possibility that the polarized component of the cosmic microwave background radiation is mixed with a small amount of the polarized component of the cosmic infrared background radiation.
Polarization of the cosmic infrared background radiation has never been observed, and even if it did, it is estimated that its intensity would be very weak. Like this time 9io9Research indirectly observing the magnetic fields of distant galaxies may lead to predictions of the polarization of the cosmic microwave background radiation and the removal of noise from the cosmic microwave background radiation..
Written by Riri Aya
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