Baffling blowup in distant galaxy

High-energy blast has gone on for 11 days

Astronomers have witnessed a cosmic explosion so strange they don’t even know what to call it. Although the blowup, discovered with NASA’s Swift satellite on March 28, emits high-energy radiation like a gamma-ray burst would, the event has now lasted for 11 days. Gamma-ray bursts last for an average of about 30 seconds.

COSMIC FIREWORKS This view of a puzzling cosmic explosion combines images from the Swift satellite’s ultraviolet/optical telescope (white and purple) and its X-ray telescope (yellow and red), recorded over a 3.4-hour period on March 28, 2011. Stefan Immler/NASA GSFC, NASA, Swift

DISTANT EXPLOSION The Hubble Space Telescope was able to pinpoint the location of a recently observed cosmic explosion, showing that it took place in the center of a galaxy that lies 3.8 billion light-years from Earth. This image may support the idea that the fireworks come from a star that fell into a supermassive black hole at the core of the galaxy. A. Fruchter/STScI, NASA, ESA

Also unlike a gamma-ray burst, the explosion has faded and brightened, emitting staccato pulses of energetic radiation lasting for hundreds of seconds.

“It’s either a phenomenon we’ve never seen before or a familiar event that we’ve never viewed in this way before,” says Andrew Fruchter of the Space Telescope Science Institute in Baltimore. The outburst might have been generated by a star torn to shreds when it ventured too close to a black hole in its host galaxy, he suggests. Gas from the star falling into the black hole could have triggered the gravitational monster to emit a jet of X-rays and gamma rays that by chance happens to point directly at Earth.

A radio-wavelength image taken March 29 along with a Hubble Space Telescope image taken in visible light on April 4 supports that model. The images show that the explosion took place 3.8 billion light-years from Earth, at the center of a galaxy where a supermassive black hole would lie. It’s also possible that the star might have been ripped apart by a smaller black hole, Fruchter notes.

“Tidal disruption of a star by a black hole seems very plausible,” says Andrew MacFadyen of New York University. The blast’s duration “is much longer than anything we’d naturally expect from [explosive] collapse of a single star,” which is the traditional model for producing a gamma-ray burst, he says.

But Stan Woosley of the University of California, Santa Cruz says the event might be explained by the gravitational collapse of a giant star into a black hole, a scaled-up version of the process that usually produces a gamma-ray burst. In Woosley’s scenario, the core of the giant star collapses to form a black hole but it takes days for the outer layers to fall in and emit radiation, accounting for the unusually long duration of the observed explosion.

More Stories from Science News on Space

From the Nature Index

Paid Content