Astronomers discover a supermassive star that destroys the black hole

    Abdulaziz Sobh


    For the first time, astronomers have directly photographed the formation and expansion of a jet of rapidly moving material when a supermassive black hole shatters a star that wanders too close to the cosmic monster.
    The scientists tracked the event with radio and infrared telescopes, including the Very Long Baseline Array (VLBA) of the National Science Foundation, in a pair of colliding galaxies called Arp 299, nearly 150 million light years from Earth.
    In the center of one of the galaxies, a black hole 20 million times more massive than the Sun destroyed a star more than twice the mass of the Sun, unleashing a chain of events that revealed important details of the violent encounter.
    Only a small number of stellar deaths called macular disruption events (TDEs) have been detected, although scientists have hypothesized that they may be a more common occurrence.
    Theorists suggested that the material extracted from the doomed star forms a rotating disk around the black hole, emitting intense X-rays and visible light, and also throws jets of material outward from the poles of the disk at almost the speed of light.
    "We have never been able to directly observe the formation and evolution of a set of one of these events," said Miguel Pérez-Torres, of the Astrophysics Institute of Andalusia in Spain.
    The first indication came on January 30, 2005, when astronomers using the William Herschel Telescope in the Canary Islands discovered a bright burst of infrared emission from the nucleus of one of the colliding galaxies in Arp 299.
    On July 17, 2005, the VLBA revealed a new source other than radio broadcast from the same location.
    "With the passage of time, the new object remained bright at infrared and radio wavelengths, but not at visible light and X-rays," said Seppo Mattila, of the University of Turku in Finland.
    "The most likely explanation is that the thick interstellar gas and dust near the center of the galaxy absorbed X-rays and visible light, and then re-irradiated it as infrared," Mattila added.
    The measured expansion indicated that the material in the jet was moving at an average of one-quarter of the speed of light. Fortunately, radio waves are not absorbed in the core of the galaxy, but they make their way through them to reach Earth.
    These observations used multiple radio telescope antennas, separated by thousands of miles, to obtain the resolution power, or the ability to see fine details, necessary to detect the expansion of such a distant object.
    The patient, collecting data for years, rewarded scientists with the evidence of a jet.
    Most galaxies have supermassive black holes, which contain millions of billions of times the mass of the Sun in their nuclei. In a black hole, the mass is so concentrated that its gravitational attraction is so strong that even light can not escape.
    When these supermassive black holes actively attract material from their surroundings, that material forms a spinning disc around the black hole and super-fast streams of particles are thrown outward. This is the phenomenon seen in radio galaxies and quasars.
    "Much of the time, however, supermassive black holes do not actively devour anything, so they are in a quiet state," explained Pérez-Torres.
    "Tidal interruption events can provide us with a unique opportunity to advance our understanding of the formation and evolution of jets in the vicinity of these powerful objects," he added.
    "Due to the dust that absorbed any visible light, this particular event of tidal interruption may be just the tip of the iceberg of what has been a hidden population up to now," said Mattila.


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