In a remarkable turn of events, astronomers have observed a massive, dying star that did not explode in the dramatic fashion typically associated with supernovae; instead, it quietly imploded to form a black hole. This extraordinary finding illustrates the complex life cycles of stars and has been detailed through the efforts of a collaborative team utilizing advanced telescopes to pursue this cosmic mystery.

The initial observations were made possible by an impressive combination of technologies, including the Large Binocular Telescope (LBT) and NASA's Hubble and Spitzer space telescopes. These instruments allowed astronomers to search for remnants of the once-mighty star, only to find that it had completely vanished from sight.

This particular star, known as N6946-BH1, was estimated to be 25 times more massive than our own Sun. Under normal circumstances, such a massive star would be expected to meet its end in a spectacular supernova explosion. However, in this instance, the star did not fulfill that expectation, fading away quietly instead and leaving behind a black hole.

The research team from The Ohio State University, led by Professor Christopher Kochanek, has provided insights into what they refer to as massive fails. These events, which occur in nearby galaxies, could help explain the astronomically low number of observed supernovae stemming from the most massive stars in the universe. Kochanek suggests that as many as 30 percent of these colossal stars may undergo a quiet collapse into black holes without the accompanying explosion that typically marks the end of their life cycle.

The conventional understanding is that a star must go supernova to create a black hole, Kochanek stated. If a star can skip the supernova phase and still transition into a black hole, that could clarify why we observe fewer supernovae in the most massive stars.

The Hubble Space Telescope has provided critical visible-light and near-infrared images of N6946-BH1, illustrating the star's progression. On the left side of the image, taken in 2007, we see the star in its prime. By 2009, it experienced a dramatic increase in brightness, becoming over a million times more luminous than our Sun. However, by 2015, it seemed to have vanished entirely, confirming the hypothesis that it had collapsed into a black hole. A faint amount of infrared light was later detected from the site where the star once shone; researchers believe this radiation emanates from debris spiraling into the newly formed black hole, which is situated 22 million light-years away in the spiral galaxy NGC 6946.

After exhausting all avenues of research and testing, the team concluded that the star must have indeed transformed into a black hole. Scott Adams, a former doctoral student at Ohio State who contributed significantly to this work, provided an early estimate from their findings. N6946-BH1 is the only likely failed supernova we discovered in the first seven years of our survey, during which we noted six regular supernovae in galaxies we were observing. This suggests that between 10 to 30 percent of massive stars may meet their end without a supernova explosion, he noted.

Co-author Krzysztof Stanek, also a professor at Ohio State, emphasized the implications of this discovery for understanding the origins of extremely massive black holes, similar to those detected by the LIGO (Laser Interferometer Gravitational-Wave Observatory) experiment. He pointed out the paradox of a massive star undergoing a supernovawhere it expels much of its outer layersand still having enough mass left over to create a black hole of the size observed by LIGO. I suspect its far more feasible to create a very massive black hole if the star does not experience a supernova, Stanek concluded.

Adams has since taken his expertise to Caltech, while other contributors include Ohio State doctoral student Jill Gerke and astronomer Xinyu Dai from the University of Oklahoma. Their research received support from the National Science Foundation, illustrating the collaborative efforts behind such groundbreaking discoveries.

NASA's Jet Propulsion Laboratory in Pasadena, California, oversees the Spitzer Space Telescope mission, while the Hubble Space Telescope is managed through an international partnership between NASA and the European Space Agency (ESA). The science operations for Hubble are performed at the Space Telescope Science Institute in Baltimore, Maryland, which is operated for NASA by the Association of Universities for Research in Astronomy, Inc. The Large Binocular Telescope represents an international collaboration involving institutions from the United States, Italy, and Germany.