The explosion, known as a gamma-ray burst, was photographed by the Seeing in the Dark Internet Telescope (SIDINT) in New Mexico on March 30. The SIDINT digital photos show the burst flaring up briefly and then fading from view within 4 hours.

Funded by the National Science Foundation, SIDINT is part of the public outreach effort associated with science writer Timothy Ferris’s documentary film Seeing in the Dark. The telescope has taken thousands of images for students and teachers who visit the show’s web site. The film, which premiered last year, is scheduled for rebroadcast on PBS at 8 P.M. Wednesday, June 11, 2008 (check local listings).

Astronomers studying the gamma-ray burst determined that its light traveled 8.4 billion light-years &#8212 more than half way across the radius of the observable universe &#8212 before reaching Earth. The light therefore was older than the Sun and Earth, which formed some 4.5 billion years ago.

“This detection of ancient light demonstrates that amateur astronomers with backyard telescopes can make real contributions to science, observing celestial events that were beyond the reach of even the largest professional telescopes within living memory,” says Ferris, whose film celebrates amateur astronomy. One of the stargazers appearing in the film, the rock musician Michael Koppelman, photographed an even more remote gamma-ray burst from his homemade observatory in rural Minnesota in 2006.

Gamma-ray bursts are the most energetic events in the known universe. Astronomers remain uncertain about just how they are created, but one mechanism may be the collapse of a giant star to form a black hole, resulting in a titanic explosion that can spit out intense jets of gamma rays, X-rays, and visible light.

When NASA’s orbiting SWIFT satellite detected the March 30 gamma-ray burst, it automatically emails the celestial coordinates to professional and amateur astronomers around the world. In Tucson, Arizona, SIDINT telescope manager Adam Block responded quickly to the news, activating the telescope over the internet and obtaining a sequence of images within minutes of the SWIFT alert. The resulting light curve data can be employed by astrophysicists to help understand how the bursts are produced. See a video of Block’s SIDINT images here.

The March 30 gamma-ray burst was also imaged by professional astronomers at observatories in France, Chile, Sweden, England, Arizona, Texas, and by the orbiting Japanese Hinode X-Ray Telescope. But the SIDINT images are the sole amateur contributions posted to date.

Viewers of the film Seeing in the Dark see SIDINT being installed by a team of four specialists in under 3 hours. The telescope consists entirely of commercially available, off-the-shelf components, but its computer-controlled mount and sensitive digital camera give it a range exceeding that of the famous Hale reflector at Palomar a half century ago, then the world’s largest telescope. Students using SIDINT are able to photograph galaxies more than 100 million light-years from Earth.

“This black hole is really pushing the limits. For many years astronomers have wanted to know the smallest possible size of a black hole, and this little guy is a big step toward answering that question,” says lead author Nikolai Shaposhnikov of NASA’s Goddard Space Flight Center.

The tiny black hole resides in a Milky Way Galaxy binary system known as XTE J1650-500, named for its sky coordinates in the southern constellation Ara. NASA’s Rossi X-ray Timing Explorer (RXTE) satellite discovered the system in 2001. Astronomers realized soon after J1650’s discovery that it harbors a normal star and a relatively lightweight black hole. But the black hole’s mass had never been measured to high precision.

Shaposhnikov and his Goddard colleague Lev Titarchuk presented their results on Monday, March 31, at the American Astronomical Society High-Energy Astrophysics Division meeting in Los Angeles.

Astronomers have long suspected that a QPO’s frequency depends on the black hole’s mass. In 1998, Titarchuk realized that the congestion zone lies close in for small black holes, so the QPO clock ticks quickly. As black holes increase in mass, the congestion zone is pushed farther out, so the QPO clock ticks slower and slower. To measure the black hole masses, Shaposhnikov and Titarchuk use archival data from RXTE, which has made exquisitely precise measurements of QPO frequencies in at least 15 black holes.

Last year, Shaposhnikov and Titarchuk applied their QPO method to three black holes whose masses had been measured by other techniques. In their new paper, they extend their result to seven other black holes, three of which have well-determined masses. “In every case, our measurement agrees with the other methods,” says Titarchuk. “We know our technique works because it has passed every test with flying colors.”

Below some unknown critical threshold, a dying star should produce a neutron star instead of a black hole. Astronomers think the boundary between black holes and neutron stars lies somewhere between 1.7 and 2.7 solar masses. Knowing this dividing line is important for fundamental physics, because it will tell scientists about the behavior of matter when it is scrunched into conditions of extraordinarily high density.

Despite the diminutive size of this new record holder, future space travelers had better beware. Smaller black holes like the one in J1650 exert stronger tidal forces than the much larger black holes found in the centers of galaxies, which make the little guys more dangerous to approach. “If you ventured too close to J1650’s black hole, its gravity would tidally stretch your body into a strand of spaghetti,” says Shaposhnikov.

Shaposhnikov adds that RXTE is the only instrument that can make the high-precision timing observations necessary for this line of research. “RXTE is absolutely crucial for these black hole mass measurements,” he says.