If you want to talk about the most mysterious electromagnetic signal in the universe today, it is the fast radio burst (FRB). Since 2001, through radio telescopes, astronomers have received intense radio waves from the depths of the universe that last only a few milliseconds and are essentially disposable, and their origins remain unsolved to this day.
Fast radio storms come from distant universes beyond the Milky Way, and most of their sources are hundreds of millions or even billions of light-years away. FrB 190523 is the farthest known fast radio burst, 8 billion light-years from Earth, and it took 8 billion years for this signal to reach Earth.
Because fast radio bursts mostly appear once and then disappear, it is difficult for astronomers to study them in depth. Until 2012, when astronomers received the first time a repeating rapid radio burst, the FRB 121102, and the Chinese Celestial Eye (FAST) also received the signal several times.
Now, astronomers have received a more specific fast radio burst, FRB 20200120E. According to a new study published in The Astrophysical Journal Letters[1], FRB 20200120E is a repeating radio burst, and it is very close, about 12 million light-years from Earth.
Based on this rapid radio burst, which has been repeatedly detected 3 times, astronomers can locate its source in the M81 galaxy 12 million light-years away. It is currently known to be the closest rapid radio burst to Earth, and the distance is one-fortieth of the previously known closest.
The M81 galaxy, also known as the Boulder Galaxy, is smaller than the Milky Way and is estimated to be 90,000 light-years in diameter. M81 is not part of the local group of galaxies, it belongs to the M81 cluster. This galaxy is easy to see through binoculars, the following figure is the author with a 150mm aperture astronomical telescope to take M81 (left) and the nearby galaxy M82 (right), the cumulative exposure time of 4.6 hours:
The rapid radio bursts discovered this time are not only getting closer and closer, but also the source is in a very special place - the globular cluster in the M81 galaxy. Dr. Bryan Gaensler, an astrologer at the Dunlap Institute for Astronomy and Astrophysics and one of the study's co-authors, said this is by no means where fast radio bursts should be.
Globular clusters are very old structures in galaxies, where hundreds of thousands of stars are usually clustered and tens of thousands of light-years in diameter. Because globular clusters have existed for a very long time, generally reaching more than 10 billion years, most of them are old stars.
Astronomers speculate that one type of origin of fast radio bursts is young magnetars. So, what kind of object is a magnetar? Why don't globular clusters have young magnetars?
When some massive stars consume their core fuel and explode into supernovae, their core regions will collapse violently under the action of gravity, compressing electrons outside the nucleus into the nucleus of atoms, so that they combine with protons to form a dense object composed of neutrons, neutron stars. A neutron star with a mass of twice the Sun is only 40 kilometers in diameter, while the Sun can reach a diameter of 1.4 million kilometers.
Some neutron stars have just formed, will be accompanied by a very strong magnetic field, such objects are called magnetars. It is estimated that the magnetic field strength of magnetars can reach at least 10 trillion times the magnetic field on the Earth's surface. If a person is less than 1,000 kilometers away from a magnetar, then the extreme magnetic field of the magnetar causes the water on the human body to produce strong antimagnetic properties, which is enough to destroy human cells and cause a fatal effect.
Astronomers believe that young magnetars are so active that they can burst out super-strong radio waves, creating fast radio bursts. Magnetars have a short lifespan, generally only remaining active for tens of thousands of years, and the magnetic field strength will drop significantly, and eventually evolve into ordinary neutron stars.
Since the higher the mass of the star, the shorter the "burning" time, those large stars that can collapse into neutron stars can usually only exist for tens of millions of years. Globular clusters are very old, so there will be no young massive stars in them, and there will be no newly formed magnetars. As a result, astronomers are puzzled by the discovery of fast radio bursts in globular clusters.
In addition, different views were raised. These mysterious repetitive radio bursts may not have formed naturally, but were emitted by advanced alien civilizations. If these signals really come from extraterrestrial civilizations, do we have to answer them?
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[1] M. Bhardwaj, B. M. Gaensler, V. M. Kaspi, et al. A Nearby Repeating Fast Radio Burst in the Direction of M81, The Astrophysical Journal Letters, 2021, 910, L18.