Brussels, 05 Sep 2005
New observations from the NASA-run Swift mission reveal for the first time that the birth of black holes can involve more than one massive explosion, suggesting that baby black holes may begin devouring nearby material within minutes of their birth.
Swift is a NASA medium-class explorer mission with participation of the Italian Space Agency and the Particle Physics and Astronomy Research Council (PPARC) in the United Kingdom.
When a massive star runs out of fuel, it no longer has the energy needed to support its mass. The core collapses and forms a black hole. Shockwaves bounce out and obliterate the outer shells of the star creating a gamma-ray burst - the most powerful explosive event in the Universe. Swift has detected several huge bursts of high-energy light associated with newborn black holes. Until now, it was assumed that stars died in a single massive explosion creating a baby black hole and an even afterglow of dying embers.
The new scenario of a blast followed by a series of powerful 'hiccups' was particularly evident during a gamma-ray burst on May 2, 2005, named GRB 050502B. This burst lasted seventeen seconds and occurred in the early morning hours in the constellation Leo. About 500 seconds later, Swift detected a spike in X-ray light about a hundred times brighter than anything seen before. There had been previous hints of an 'X-ray bump' between the burst and afterglow in previous gamma-ray bursts, coming a minute or so after the burst, but until now, scientists couldn't get to the scene of the explosion fast enough. Swift has the unique ability to detect bursts and turn its X-ray and ultraviolet-optical telescopes to the explosion's embers within minutes.
Now Swift has seen over a dozen clear cases of multiple explosions. There are several theories to describe this newly discovered phenomenon and most point to the presence of a sloppy, newborn black hole.
Professor Peter Meszaros of Penn State, US, head of the Swift theory team explains: 'The newly formed black hole immediately gets to work. We aren't clear on the details yet, but it appears to be messy.'
The material shooting away from the dead star could start to fall back on to itself heating up enough in the process as to produce X-ray light. Professor Andrew King of the University of Leicester, lead author on a paper in the Astrophysical Journal which tries to explain the observations says: 'This [multiple explosion] could be due to dense clumps of matter falling on to the newly formed black hole.'
His co-author, Dr. Paul O'Brien, also from the University of Leicester, suggest another explanation: 'The black hole is unable to eat all of the available fuel in one go, so instead it digests it over a few minutes. It's a bit like feeding a baby - sometimes it takes big mouthfuls and sometimes little ones.' To download the Astrophysical Journal Letters paper, please visit: http:///xxx.soton.ac.uk/PS_cache/astro-ph /pdf/0508/0508126.pdf Remarks: Reference document: Gamma-ray bursts: Restarting the Engine. Andrew King, Paul T. O'Brien, Michael R. Goad, Julian Osborne, Emma Olsson, Kim Page (University of Leicester). Astrophysical Journal Letters, Volume 630, September 2005