ann1108 — Announcement
Hubble pinpoints source of mysterious outbursts
7 April 2011
The NASA/ESA Hubble Space Telescope has joined forces with other telescopes to study the source of one of the most puzzling bursts of high-energy gamma rays and X-rays ever observed. More than a week after the burst was first spotted, high-energy radiation continues to brighten and fade.
“We know of objects in our own galaxy that can produce repeated bursts, but they are thousands to millions of times less powerful than the bursts we are seeing now. This is truly extraordinary,” said Andrew Fruchter at the Space Telescope Science Institute in Baltimore, USA.
Astronomers say they have never seen anything this bright, long lasting and variable before. Usually, gamma ray bursts mark the destruction of a massive star, but X-ray emission from these events never lasts more than a few hours.
Although research is ongoing, scientists say that the unusual blast likely arose when a star wandered too close to the black hole at the centre of its galaxy. Intense tidal forces tore the star apart forming a stream of gas that continues to fall towards the black hole. The black hole may have formed a jet and this jet may by chance be pointed towards us, giving us a powerful blast of X-rays and gamma rays. If confirmed, this would be the first time this phenomenon has been observed.
The gamma ray burst was spotted on 28 March by the NASA/ASI/STFC Swift satellite, which looks for transient X-rays and gamma rays.
As dozens of telescopes turned to the spot, astronomers quickly noticed that a small, distant galaxy appeared very near the position identified by Swift. A deep image taken by Hubble on 4 April pinpoints the source of the explosion at the centre of this galaxy. The galaxy, which lies 3.8 billion light-years away, appears as a bright blob at the centre of the Hubble picture.
Further observations with NASA’s Chandra X-Ray Observatory confirmed that the explosion occurred at the centre of the galaxy imaged by Hubble.
“We have been eagerly awaiting the Hubble observation,” says Neil Gehrels of the Goddard Space Flight Center in Greenbelt, USA, who is the lead scientist for the Swift mission. “The fact that it was found in the centre of a galaxy tells us it is most likely associated with a massive black hole. This solves a key question about the mysterious event.”
Most galaxies, including our own, contain central black holes with millions of times the Sun’s mass; those in the largest galaxies can be even larger. The disrupted star probably succumbed to a black hole less massive than the Milky Way’s, which has a mass four million times that of our Sun.
Astronomers previously have detected stars disrupted by supermassive black holes, but none have shown the X-ray brightness and variability seen here.
Scientists think that the X-rays may be coming from matter moving near the speed of light in a particle jet that forms as the star’s gas falls toward the black hole.
“The best explanation at the moment is that we happen to be looking down the barrel of this jet,” said Andrew Levan of the University of Warwick in the United Kingdom. “When we look straight down these jets, a brightness boost lets us view details we might otherwise miss.”
Astronomers are now planning additional Hubble observations.
Credit: NASA, ESA, and A. Fruchter (STScI)
Hubble/ESA, Garching, Germany
NASA Headquarters, Washington DC
NASA Goddard Space Flight Center, Greenbelt, USA
Space Telescope Science Institute, Baltimore, USA
Chandra X-ray Center, Cambridge, Mass.
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