What goes on at the edge of a black hole? NASA launches NuSTAR to find out. (+video)

The broad outlines of supernovae explosions for massive stars are fairly well established, notes Robert Kirshner, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

For stars like the one involved in Supernova 1987A, in essence, the star runs out of fuel. When the star burns its initial stock of hydrogen, it begins fusing helium. That process continues until the star progressively burns its way through increasingly heavy elements up to iron. By then, however, the star lacks the energy needed to fuse iron. This slams the brakes on fusion reactions, and the forces vanish that allow the star to remain a large gas ball.

What remains of the star begins a runaway collapse that continues until the core is nothing but compressed neutrons, which can collapse no farther. Temperatures and pressures are so high at this point that fusion briefly resumes, forming even heavier elements, including silver, gold, and titanium. The collapse comes to a sudden halt; all the gravitational energy gathered in the collapse is released, hurling the layers into interstellar space.

A second broad category of supernovae results from overfeeding. A white dwarf in a binary system can attract material from its companion if the companion is close enough. Once the white dwarf's mass grows beyond about 1.38 times the sun's mass, pressures and temperatures grow so high at the core that they trigger a runaway nuclear blast.

But the details of these explosive processes are poorly understood, says Steven Boggs, an astrophysicist from the University of California at Berkeley on the NuSTAR science team. For instance: Where does the process begin? How do the runaway reactions proceed through the core of some supernovae? How does the explosion disrupt the star?

Researchers will tease out these details by looking at a product of that final fit of fusion as the star gets set to shed its shells – titanium-44.

By mapping the distribution of titanium-44 across the expanding debris cloud – and then comparing that map with different models of supernovae explosions – researchers can in effect reverse the process and see how the titanium would have been distributed in the progenitor stars during the blasts. And by measuring the speed at which individual clumps of titanium are traveling, researchers can glean information about other details of the explosion.

"Between those two, we have a lot of information about the nuclear physics" involved in the initial blasts, he says.

NuSTAR also will be a powerful tool for studying black holes of all sizes – from the black holes that supernovae produce to the supermassive black holes that lurk in the cores of massive galaxies like the Milky Way and can be billions of times the mass of the sun.

The craft will hunt both for the X-rays emitted as black holes compress and heat matter, as well as high-energy X-rays emanating from black holes' "poles" in beams of charged particles accelerated nearly to the speed of light by intense magnetic fields.

In one experiment, NuSTAR will team up with NASA's orbiting Fermi Gamma-ray telescope to measure the rotation speed of supermassive black holes in galactic cores.

Launch is scheduled for 11:30 a.m. Eastern Daylight Time from the US Army's facilities at Kwajalein Atoll in the Pacific. NuSTAR is tucked into a package about 4 feet wide and 7 feet long, allowing it to be lofted using a rocket from Orbital Sciences Corp. that is launched from underneath a Lockheed L-1011 jumbo jet.

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