Radio “Awakens” – Dr. Assaf Harash from the Hebrew University revealed a new and surprising phenomenon concerning the destruction of stars by black holes * The researcher and his team managed to reveal the release of radio flashes months and years after the star was first torn to pieces by the black hole. Even a researcher proves that such radio flashes exist, relatively long after the destruction of the star.The study also proves the intensity of the event and the partial understanding of the world of science on the subject.The study was published in nature astronomy
Note: On the same day, another article by Dr. Harash was published, which we reported on yesterday: For the first time, a neutrino particle was detected that came to us from the vicinity of a super-massive black hole.
In recent years, more and more bright (optically) flashes of visible light have been detected in galaxy centers. The flashes of light last for several weeks to months. The prevailing opinion is that these flashes of light result from a particularly violent event, during which a star moves too close to a super-massive black hole located in the center of the same galaxy, and is torn to shreds by the tidal forces exerted on it by the black hole. The star ceases to exist as the gas that has made up the star so far becomes a stream of matter (gas) some of which remains in a circle around the black hole, and some of which flies at a tremendous speed away from the black hole. Events of this type are called tidal disruption events (TDEs).
Such events are of great importance in the field of black hole exploration. First, we now know that most galaxy centers today have a supermassive black hole (for example, our Milky Way galaxy has a black hole with a mass of about four million solar masses, a discovery for which the Nobel Prize was awarded this year). In some galaxies the black hole is defined as active – there is a large gas reservoir in the center of the galaxy in the form of a disk, called an adsorption disk, around the black hole and material from the disk is attached to the black hole. In this process strong radiation is released and as a result from the vicinity of the black hole (but not directly from it) powerful jets are emitted which are visible at different wavelengths and especially in radio radiation. There are also “dormant” black holes that do not have such a disk around them and do not emit unusually strong radiation from this area.
Incidents of star destruction with tidal forces of a black hole can also occur following the passage of a star in the vicinity of these black holes (so-called dormant), and in fact the temporary flash of radiation as a result of the star tearing at the dormant black hole indicates the existence of the same black hole in the center of the galaxy. This event, then, is another way to expose black holes. It also allows us to learn about the structure of matter in the very close vicinity of the black hole, even in distant galaxies, which is not possible in any other way today. Beyond that these events allow us to explore processes of adsorption of matter to the black hole. For example, it is not clear to us how adsorption discs are formed. Even when the star is torn to shreds by the black hole there is an open question what leads to the flash of light we see – was it caused as a result of rapid adsorption of the star’s material into the black hole? Some argue that adsorption of material from a star that has ceased to exist cannot occur immediately, and the flow of material torn from the star continues to circle around the black hole, and shock waves created by impact of one part of the current in another part of it cause the light we see.
The research group, led by Dr. Assaf Harash, the Rakach Institute of Physics at the Hebrew University, in collaboration with the director of the Swift Space Telescope, Prof. Brad Senko, and Dr. Yair Harkabi of the Department of Astrophysics at Tel Aviv University, has recently been investigating such events. Reach the Earth and announce the activity of the Black Hole. A new study by the group was published this week in the prestigious scientific journal nature astronomy. The researchers were able to detect radio radiation detected in only a few incidents of this type, and usually indicate the presence of a flying material immediately after a high-speed starburst event (or a powerful jet ejected from the black hole as a result of adsorption, if any) of star-destroyed material. Black). However, in all the few cases where radio radiation has been detected so far, in events of this type, it has been detected almost immediately after the destruction of the star, indicating material flying at high speed from the vicinity of the black hole immediately at the event. This time, however, the researchers were surprised to discover radio flashes from the event that were emitted months (and then also years later) after the time the star was destroyed.
The sensitive radio observations were made as part of a study on an event (known as ASASSN-15oi) of star destruction by tidal forces of a black hole, revealing for the first time late radio flashes (delayed) emitted at such events. The star destruction event was revealed as a visible flash of light in the ASASSN project. Immediately after the incident was discovered, Dr. Deaf and his colleagues conducted a radio observation of the incident with the radio telescope known as the “Very Large Array” in New Mexico in the United States (a telescope consisting of 27 radio antennas 25 meters in diameter each ).
No radio radiation was detected in the first observation despite the high sensitivity of the observation. The researchers repeated the observation twice more in the three months after the first observation, and even in these observations no radio radiation was detected. Surprisingly, the insistence of the researchers, led by Dr. Harash, to continue testing was worthwhile. “The prevailing theory at this stage is that if no radio radiation is detected, then it is not expected that radiation will be detected later,” says Dr. Harash. “However, we decided to go beyond the predictions of the known theories, and make another observation about six months after the time the incident was first discovered in visible light, and to our great surprise we discovered bright radio radiation. Immediately after the discovery we collected more detailed data through a radio telescope over a year. In addition, we analyzed data collected as part of a large celestial survey (conducted by the U.S. National Radio Astronomy Observatory using the same radio telescope) in 2019 for another (second) radio flash from the same point in the sky, about four years after the first light event. “This is the first time that radio flashes that occur in a delay of months and years after the initial event in which a star was destroyed by a black hole are detected.”
Analysis of the findings drew three key conclusions. The first is that none of the standard models of star destruction by a black hole can explain the radio flashes that appear so long after star destruction (including the behavior of radio radiation that evolved differently from the way radio radiation evolved in similar events in which radio radiation was detected Previously close to the time of star destruction). The second is that there is a possibility that eruptions of late radio radiation in these events are common phenomena and it will be possible to detect more of these, and to investigate the new phenomenon that was discovered if radio observations were made at later times than has been the case so far. Third, it is possible that some of the material left over from the destroyed star was attached to the black hole with high efficiency but not immediately, several months late.
“What caused this delay and what ultimately led to the adsorption of the substance to the black hole, these are questions that remain open. If such late material adsorption did occur, a jet may be ejected very quickly after adsorption, with the jet responsible for the late radio flash we discovered in the present study.” , Explains Dr. Deaf who even believes that his discovery is important to understand how black holes grow (gain mass) in the universe, and how they evolve and become super-massive. Adsorption of a substance is one way of growing the black holes and detecting periods in which growth of the black hole occurs by delayed adsorption (if this hypothesis is proven later) is another important step in understanding the whole process.
Also, Dr. Deaf and his research team believe that detecting late (delayed) radio eruptions will not only allow for the study of the physics behind these events, but they can reveal and attest to the existence of additional black holes in galaxy centers. For example, a flash of visible light will not always be detected when a star is destroyed by a black hole, but if a number of late radio flashes are created as a result, the latter will reveal the existence of the black hole involved in the event and allow it to be investigated. “In light of these discoveries, we are preparing to make additional radio observations of such events using radio telescopes around the world, in order to try and discover more radio flashes of this type and get to the bottom of the phenomenon,” notes Dr. Deaf.
To the scientific paper
More on the subject on the Yadan website: