The cosmic radio wave AT2019dsg detected in 2019 is said to be high-energy neutrinos commonly known as “ghost particles” created by black holes tearing apart stars. However, a study published in the Astrophysical Journal at the beginning of the month indicated that after analysis, it was found that AT2019dsg is quite ordinary, at least as far as the black hole tearing apart stars, and the energy it emits is not enough to produce “ghost particles.”
AT2019dsg was first detected on April 9, 2019, from a galaxy 750 million light-years away. X-ray and radio observations confirmed that it came from a supermassive black hole, whose mass is 30 million times the mass of the sun, and once released dazzling flares to form a tidal disruption event (TDE).
To tear a star, first the star is close enough to the black hole to be captured by the black hole’s gravity; the huge tidal force of the black hole first stretches and then pulls the star to tear. TDE refers to the process of the black hole tearing the star. Half of the fragments of the disintegrated star emit light as they rotate into a disk around the black hole, and generate huge heat and light before being pulled out of the event horizon; the other half of the star fragments will be thrown into space.
Tearing a star The star is closer to the black hole
Nearly 6 months after the appearance of AT2019dsg, that is, on October 1, 2019, the IceCube neutrino detector in the South Pole detected a neutrino named IC191001A with an energy level of more than 200 teraelectronvolts.
Neutrino (neutrino) are called “ghost particles” because they have almost zero mass, can fly at a speed close to the speed of light, and do not really interact with normal matter; however, sometimes neutrino will interact, this It is also the working principle of IceCube: neutrinos will produce flashes when they meet Antarctic ice. The detector digs tunnels deep in the ice layer to make the flashes more prominent.
According to the characteristics of light propagation mode and brightness, scientists can calculate the energy level of neutrinos and the direction of their source. Previously, IC191001A was alleged to be from the direction of AT2019dsg, so close that scholars calculated that the probability that neutrinos had nothing to do with the TDE was only 0.2%.
However, the argument raises some major problems. Yvette Cendes, an astronomer at the Harvard Center for Astrophysics who led the study, questioned if this neutrino came from AT2019dsg in some way, but why hasn’t the academia discovered a neutrino related to a supernova at this distance or closer? Because the latter is more common and has the same energy velocity.
Neutrino energy can be calculated from light propagation and brightness
The research team led by Cendes used Chile’s Atacama Large Millimeter/Submillimeter Array (ALMA) to observe AT2019dsg in radio wavelengths for more than 500 days and found that TDE kept brightening in radio wavelengths for about 200 days, and after reaching its peak It started to darken slowly.
The team also calculated the total amount of energy flowing out of the TDE, which is about as much as the energy released by the sun in 30 million years, which falls within the standard range of energy emission of TDE and Type Ib and Ic supernovae.
However, to generate neutrinos with the same high energy as IC191001A, the outflow energy needs to be about 1,000 times larger. In addition, the energy flow needs to have a strange geometric shape, which is not the case with AT2019dsg. In other words, AT2019dsg is quite common, and a new statement may be needed to explain the emergence of IC191001A.
However, humans still have a lot of ignorance about neutrinos and TDE, which means that AT2019dsg will continue to receive attention. Cendes also added that the team may test AT2019dsg again because the black hole is still eating stars.
source:
Science Alert, A Mysterious ‘Ghost Particle’ Probably Didn’t Come From a Black Hole’s Meal After All, 16 October 2021
report:
Cendes, Y., Alexander, K.D., Berger, E. & et al. (2021). Radio Observations of an Ordinary Outflow from the Tidal Disruption Event AT2019dsg. The Astrophysical Journal vol 919 Number 2. doi: 10.3847/1538-4357/ac110a
Sentence / Alan Chiu