supernova in the galaxy M100 approximately 50 million light-years from Earth, was discovered by an amateur astronomer in 1979. The star that exploded that year was just on the edge of the theoretical mass limit for forming black holes, about 20 times the mass of the sun. After the supernova, the leftover matter could either have collapsed into a black hole or an extremely dense neutron star.

New observations from the Chandra X-ray Observatory seem to clinch it in favor of the black hole, astronomers announced today. As material falls in to a black hole, it heats up to millions of degrees and spews X-rays. If the object that was SN 1979c was a neutron star, the brightness of the X-rays it emits would tail off with time. But if it was a black hole, the X-rays would stay nearly as bright as the black hole gobbled new material.

Observations show that SN1979c blasted out X-rays at a constant brightness level between 1995 and 2007, definitely tilting the odds in favor of a black hole -- although the object could still be a rapidly spinning neutron star with a powerful wind of high energy particles.

Image: X-ray: NASA/CXC/SAO/D.Patnaude et al, Optical: ESO/VLT, Infrared: NASA/JPL/Caltech

Authors: Lisa Grossman

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