Scientists Watch Black Hole Born in Split-Second Light Flash

Neutron star collision: The Swift spacecraft's Gamma Ray burst observation fits the theory of a collision between some combination of black holes or neutron stars. Neutron stars are dense spheres about 20 miles across. Black holes have no surface and are regions in space of infinite density. Theory predicts that these kinds of collisions would not produce a long afterglow because there isn't much "fuel" -- dust and gas -- from the objects and in the region to sustain an afterglow. Credit: NASA/Dana Berry

After 30 years, they finally caught one. Scientists on Monday have for the first time detected and pinned down the location of a so-called "short" gamma-ray burst, lasting only 50 milliseconds.

The burst marks the birth of a black hole. The astronomy community is buzzing with speculation on what could have caused the burst, perhaps a collision of two older black holes or two neutron stars. A multitude of follow-up observations are planned; the answer might come in a few more days. "Everything about this gamma-ray burst so far supports the merger theory," said Steinn Sigurdsson, associate professor of astronomy and astrophysics at Penn State and a gamma-ray-burst theorist.

Gamma-ray bursts are the most powerful explosions known in the universe. Recently, the longer ones -- lasting more than two seconds -- have become easy prey for NASA satellites such as Swift , built to detect and quickly locate the flashes. Short bursts had remained elusive until Monday, when Swift detected one, autonomously locked onto a location, and focused its onboard telescopes in less than a minute to capture the burst afterglow.

"Seeing the afterglow from a 'short' gamma-ray burst was a major goal for Swift, and we hit it just a few months after launch," said Neil Gehrels, Swift project scientist at NASA Goddard Space Flight Center in Greenbelt, Maryland. "Now, for the first time, we have real data to figure out what these things are."

Like clues left at a crime scene, the afterglow contains information about what caused the burst. Most scientists are convinced short and long bursts arise from two different catastrophic origins. The longer bursts appear to be from massive star explosions in very distant galaxies. The shorter ones -- less than two seconds and often just a few milliseconds -- are the deeper mystery because they have been simply too fast to observe in detail.

Ground based Observation by W.M. Keck Observatory: The location of the gamma-ray burst as determined by the Swift X-Ray Telescope (XRT) is shown by the blue circle on this infra-red image of the sky from the W.M. Keck telescope. The burst went off in the outskirts of this huge galaxy 2.6 billions lights years away. The location outside, but near, the galaxy fits perfectly with the theory that short bursts are due to black hole formation when orbiting neutron stars collide. The gamma ray source has not yet been securely identified and scientists are most interested in the 4 objects within Swift’s X-ray telescopes error circle.

Credit: Cenko, Soifer, Bian, Desai, Kulkarni (Caltech), Berger (Carnegie), Dey and Jannuzi (NOAO)

The Monday burst is called GRB 050509B. Swift's X-ray Telescope detected a weak afterglow that faded away after about five minutes. Swift's Ultraviolet/Optical Telescope did not see an afterglow. Ground-based telescopes have not yet definitely detected an afterglow either. In contrast, afterglows from long bursts linger from days to weeks.

All of this fits the pattern of a collision between some combination of black holes or neutron stars, both of which are created in the death of massive stars. Neutron stars are dense spheres about 20 miles across. Black holes have no surface and are regions in space of infinite density. Theory predicts that these kinds of collisions wouldn't produce a long afterglow because there isn't much "fuel" -- such as dust and gas -- from the objects and in the region to sustain an afterglow.

GRB 050509B appears to have occurred near an unusual galaxy that has old stars and is relatively nearby--about 2.7 billion light years away--which also is consistent with the theory that short bursts come from older, evolved neutron stars and black holes. In contrast, longer gamma-ray bursts tend to be in young, distant galaxies filled with young, massive stars -- remnants of the early universe.

"We are combing the region around the burst with the Keck Telescope for clues about this burst or its host galaxy," said Shri Kulkarni, a gamma-ray burst expert at Caltech. "What we are seeing so far is what proponents of the merger theory have been saying all along." Such an evanescent afterglow has been expected in the most popular model for short hard bursts to date. Additional observations are planned for NASA's Hubble Space Telescope and Chandra X-ray Observatory.

Swift is a NASA mission in partnership with the Italian Space Agency and the Particle Physics and Astronomy Research Council, United Kingdom; and is managed by NASA Goddard. Penn State controls science and flight operations from the Mission Operations Center in University Park, Pennsylvania. The spacecraft was built in collaboration with national laboratories, universities, and international partners, including Penn State University; Los Alamos National Laboratory in New Mexico; Sonoma State University in Rohnert Park, California; Mullard Space Science Laboratory in Dorking, Surrey, England; the University of Leicester in England; Brera Observatory in Milan, Italy; and ASI Science Data Center in Frascati, Italy. For more information about this and other Swift-detected bursts, refer to http://grb.sonoma.edu.

CONTACTS AT PENN STATE:

Steinn Sigurdsson, ssigurdsson@astro.psu.edu, 814-863-6038

John Nousek: 814-863-1937, nousek@astro.psu.edu

Barbara K. Kennedy (PIO), science@psu.edu, 814-863-4682

An artist's impression of merging neutron stars, one of the theoretical progenitors of gamma-ray bursts. Credit: NASA E/PO, Sonoma State University, Aurore Simonnet

Credit: J. Bloom, University of California at Berkeley

GRB 050509B, detected on 9 May 2005, was a *very* short burst, lasting just 30 milliseconds (0.03 seconds)! Swift was able to slew to the burst in well under a minute. Analysis of the X-Ray Telescope shows a very faint detection of X-rays from the burst, and in fact this is the faintest X-ray afterglow Swift has yet detected this early from a burst.

This is potentially a very exciting burst. It appears very near a galaxy at a redshift of 0.226, corresponding to a distance of 2.7 billion light years-- relatively close by, as these things go. The galaxy itself is a member of the cluster NSC J123610+285901. If the burst was from that galaxy, it has a projected distance of about 100,000 light years from the galaxy center-- about the diameter of our own Milky Way Galaxy.

What is even more interesting is that this is an old galaxy; observations show it is not currently forming stars. This gives more support to the hypothesis that short-duration bursts are not from hypernovae, or exploding high-mass stars. Only young stars explode as hypernovae, and this galaxy has no young stars! The current hypothesis is that short bursts are from merging neutron stars, which means this would only happen in older systems (it can take billions of years for the orbits of two neutron stars to decay enough to allow them to merge, but when they finally do, the explosion is very short in length, only a few milliseconds).

The image displayed is from the WIYN 0.9 meter telescope in Arizona. More images can be found athttp://pairitel.org/grb050509b-candidate.gif,http://www.srl.caltech.edu/~cenko/grb050509b/050509.jpg